Parasitic flies of domestic animals

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Many species of flies of the two-winged type, Order Diptera, such as mosquitoes, horse-flies, blow-flies and warble-flies, cause direct parasitic disease to domestic animals, and transmit organisms that cause diseases. These infestations and infections cause distress to companion animals, and in livestock industry the financial costs of these diseases are high. [1] [2] [3] [4] These problems occur wherever domestic animals are reared. This article provides an overview of parasitic flies from a veterinary perspective, with emphasis on the disease-causing relationships between these flies and their host animals. The article is organized following the taxonomic hierarchy of these flies in the phylum Arthropoda, order Insecta. [5] Families and genera of dipteran flies are emphasized rather than many individual species. Disease caused by the feeding activity of the flies is described here under parasitic disease. Disease caused by small pathogenic organisms that pass from the flies to domestic animals is described here under transmitted organisms; prominent examples are provided from the many species.

Contents

Adult Chrysomya megacephala blowfly, known as bazaar fly, feeding by sponging at organic waste from where it may transmit harmful bacteria Ch.megacephala wiki.jpg
Adult Chrysomya megacephala blowfly, known as bazaar fly, feeding by sponging at organic waste from where it may transmit harmful bacteria

Summary of types of disease associated with types of dipteran flies

Disease caused by the feeding activity of dipteran flies is described here under parasitic disease. Disease caused by small pathogenic organisms that pass from the flies to domestic animals is described here under transmitted organisms; these organisms are often of numerous species thus only prominent examples are provided. Feeding by adult flies may cause irritation through acute stress from painful bites, resulting in loss of grazing time and reduced gain in weight. [6] Feeding by adult flies on the blood of their hosts exposes the hosts to pathogenic organisms that are infecting the fly, this can lead to acute disease of the host's blood and other organs. [7] [8] Feeding by adult flies using their sponging mouthparts can also expose the hosts to pathogenic organisms that have contaminated the mouthparts. Larvae of some flies are adapted to feed on the tissues of their host, causing direct pathological damage to organs; this is known as myiasis. [9] [10]

Outline classification (families of main veterinary importance)

1-Complex mouthparts, 2-Paired antennae, 3-Head, 4-Compound eye, 5-Thorax, 6-Open tube heart, 7-Salivary gland, 8-One pair of wings, 9-Halter, 10-Excretory (Malpighian) tube, 11-Gut, 12-Ovary (or testis), 13-Abdomen, 14-Legs (3 pairs), 15-Thoracic ganglion of nervous system, 16-Spiracle opening to respiratory tube (trachea) Dipteran-fly-structure.jpg
1-Complex mouthparts, 2-Paired antennae, 3-Head, 4-Compound eye, 5-Thorax, 6-Open tube heart, 7-Salivary gland, 8-One pair of wings, 9-Halter, 10-Excretory (Malpighian) tube, 11-Gut, 12-Ovary (or testis), 13-Abdomen, 14-Legs (3 pairs), 15-Thoracic ganglion of nervous system, 16-Spiracle opening to respiratory tube (trachea)
Class Insecta
Order Diptera (two-winged flies)
suborder Nematocera
Family Culicidae (Mosquitoes)
Family Ceratopogonidae (Biting midges)
Family Psychodidae (Sandflies)
Family Simuliidae (Black-flies)
suborder Brachycera
Family Tabanidae (Horse-flies)
Family Muscidae (House-flies and others)
Family Glossinidae (Tsetse-flies)
Family Calliphoridae (Blow-flies)
Family Oestridae (Bot-flies and others)
Family Hippoboscidae (Louse-flies)

(Note that the former suborder Cyclorrhapha is now usually classified as part of the Brachycera.)

Nematocera (suborder)

General characteristics

Antennae are usually long, with many similar and symmetric segments. These are small to very small flies, usually of delicate morphology with relatively long legs and wings. Body and wings are often covered in fine scales. Thorax is distinctly humped, abdomen is elongated. All species of veterinary and medical importance are blood feeders, with various types of mouthparts (these variations do not relate clearly to dipteran taxonomy). [11]

Aedes aegypti female mosquito engorging with blood. Aedes aegypti biting human.jpg
Aedes aegypti female mosquito engorging with blood.

Lifecycle is a complete metamorphosis with larvae that are nonparasitic, living in environments such as pools of water, soil, and streams. A complete metamorphosis is illustrated by the photograph of Stomoxys eggs, larvae, and adult (Stomoxys are in suborder Brachycera). Only females feed on blood, taking a large meal to support production of several hundred eggs, followed by several more cycles of blood meal followed by egg laying. [12] [13] Males feed on plant nectar and similar sources of sugars.

Lifecycle of Stomoxys showing a typical complete metamorphosis from eggs at top left, to three larval stages, followed by transformation as the pupal stage into an adult female or male Stomoxys-stable-fly-life-cycle-2.jpg
Lifecycle of Stomoxys showing a typical complete metamorphosis from eggs at top left, to three larval stages, followed by transformation as the pupal stage into an adult female or male

Disease relations

Nematocerans are very important as transmitters of viruses, protozoa, and nematode worms. Also, they are often important for biting stress when in large numbers, and may cause allergic reactions at their feeding sites. A typical pathway of transmission of organisms by blood-feeding flies is shown below as a virus transmitted by an adult fly that feeds repeatedly on several hosts (see diagram for Biological transmission, and photograph of Culicoides). Insects that transmit pathogenic organisms are commonly known as vectors. The diagram shows what is known as biological transmission (= developmental transmission) because it is necessary for the transmitted organism to develop in the fly to the state where the organism is at an infective stage of its lifecycle. [14] The repeated cycles of egg laying and feeding of the female fly (= gonotrophic cycle) provides the opportunity for the transmitted organisms to develop, multiply, and be exposed to further vertebrate hosts where they can complete their lifecycle. Only the adult flies are involved in this biological transmission, in contrast to biological transmission by other arthropods such as lice or ticks in which all active stages of the lifecycle feed on blood.

Mosquitoes (family Culicidae)

Typical genera are Culex , Aedes , and Anopheles

Morphology, lifecycle, hosts, and feeding

The basic structure of dipteran flies is illustrated in the diagram. Veterinary parasitology also covers arthropods in the class Acari, the ticks of domestic animals, and mites of livestock, which have distinctly different structure from arthropods in the class Insecta. However, flies in the order Diptera show clear division of the body into head, thorax, and abdomen with distinct segmentation of the thorax and abdomen. The thorax contains large blocks of muscle that power the single pair of wings. Digestive and reproductive organs fill the abdomen. Also unique to the Diptera is a pair of halteres (derived from wings during evolution) that aid agile flight by these flies. [15] [16] Mosquitoes have veined and scaled wings, long legs, and long hypodermic mouthparts sheathed in a protective labium (see photograph of Aedes female engorged with blood). Adult females lay eggs in batches on surfaces of stagnant water. Larvae feed on microorganisms and organic detritus in water. Pupation occurs at the surface of the water. Feeding by females is on a wide variety of mammals and birds, whilst males feed on plant sugars.

Transmission pathways of biological transmission of bluetongue virus by Culicoides female midge feeding first on a reservoir cow, then on three susceptible sheep Bluetongue-virus-transmission-by-culicoides.png
Transmission pathways of biological transmission of bluetongue virus by Culicoides female midge feeding first on a reservoir cow, then on three susceptible sheep

Parasitic diseases and transmitted organisms

Culicoides imicola stages of gonotrophic and transmission cycle: top left = unfed female, unable to transmit; bottom left = first blood-meal, may become infected; top right = female after laying an egg batch, ready to feed again; bottom right = a further blood meal that could have involved transmission of pathogenic organism. Culicoides-imicola-bloodfeeding.jpg
Culicoides imicola stages of gonotrophic and transmission cycle: top left = unfed female, unable to transmit; bottom left = first blood-meal, may become infected; top right = female after laying an egg batch, ready to feed again; bottom right = a further blood meal that could have involved transmission of pathogenic organism.
Microfilaria stage of Dirofilaria immitis, heartworm, in blood of a dog (for scale the grey discs are stained red blood cells) Dirofilaria-immitis-microfilaria-dog-blood-film-Giemsa-stain-2.jpg
Microfilaria stage of Dirofilaria immitis, heartworm, in blood of a dog (for scale the grey discs are stained red blood cells)

Biting stress can be severe in varied climatic regions (cold northern or tropics) or conditions of much surface water available for breeding where populations of mosquitoes can become dense. [17] Species of genera Aedes, Anopheles and Psorophora transmit equine encephalitis viruses to horses. Culex, Aedes, and Anopheles species of mosquitoes transmit Plasmodium protozoa that cause types of malaria in birds. Culex mosquitoes transmit West Nile virus between birds and horses; they transmit Rift Valley fever virus to livestock species and humans. [8] The nematode worm Dirofilaria immitis that causes heartworm disease in dogs is transmitted by species of Culex and Aedes. [18] See photograph of microfilaria stage of Dirofilaria immitus in blood of dog; adult worms in dog's heart grow to several centimeters long. (Mosquitoes are of major importance as transmitters of many types of pathogenic microorganisms to humans causing diseases such as malaria and yellow fever. Plasmodium species causing malaria in humans are exclusively transmitted by Anopheles mosquitoes.)

Phlebotomus pappatasi sandfly engorged with blood Phlebotomus pappatasi bloodmeal finished.jpg
Phlebotomus pappatasi sandfly engorged with blood

Biting midges (family Ceratopogonidae)

Typical genera are Culicoides and Leptoconops (the term "midge" is also used for dipteran flies that are harmless to domestic animals such as those also known as lake-flies (Chironomidae).

Morphology, lifecycle, hosts and feeding

These are small to minute flies (a typical vernacular name is "no-see-ums"). Wings are veined, short, and rounded, usually with distinctive patterns of dark brown on clear backgrounds. Mouthparts are relatively short and complex with three pairs of cutting or slashing elements that create a superficial wound from which blood is imbibed. Lifecycle is similar to that of mosquitoes: female feeds on blood, matures, and lays batch of eggs repeatedly. Males are not blood feeders. The site for larval development is within wet soil and bogs. Hosts of biting midges are wide variety of mammals and birds.

Parasitic diseases and transmitted organisms

Severe biting stress to cattle, sheep and horses is caused. Horses suffer from a cutaneous hypersensitivity reaction called sweet-itch, or Queensland-itch that is caused by antigenic components of saliva of biting midges. [19] [20] Poultry may be severely afflicted with biting stress. Species such as Culicoides imicola and Culicoides variipennis transmit bluetongue virus between sheep and cattle (see diagram and photograph above), and they transmit African horse sickness virus between horses and other equids. Culicoides midges transmit Leucocytozoon protozoa to poultry birds. [21]

Sandflies (family Psychodidae)

The important genera are Phlebotomus (distributed in Africa and Eurasia) and Lutzomyia (distributed in the Americas). [22] The term "sandfly" is often used to refer to various other types of flies.

Morphology, lifecycle, hosts, and feeding

Sandflies are like small versions of mosquitoes, but also with overall furry appearance from many long setae (like hairs) on body and wings (see photograph of Phlebotomus pappatasi). Mouthparts are medium length. Lifecycle is similar to midges: site for egg laying and larval development is surface of relatively dry soil. Many species of mammals and birds are used as hosts. Females suck blood using medium length complex mouthparts, whilst males feed on plant sugars.

Transmitted organisms

Species of Phlebotomus and Lutzomyia sandflies are notorious as transmitters of species of Leishmania protozoa that cause visceral and cutaneous leishmaniasis in domestic animals and also humans. [23] Dogs become infected with Leishmania infantum and L.tropica; the infection can slowly develop into a multi-organ stage with fatal consequences.

Black-flies (family Simuliidae)

The typical genus is Simulium, but also Cnephia and Austrosimulium are locally important.

Morphology, lifecycle, hosts, and feeding

These are medium nematocerans, halfway in size between mosquitoes and midges. [7] The body is compact, wings are clear except for veins close to leading edge, and antennae are short with compact segments appearing like rings. Thorax is dorsally humped and dark brown or black (see photograph of Simulium). Lifecycle is similar to mosquitoes: females lay eggs on plants at surface of streams and rivers; larvae settle onto solid substrate in water and feed on suspended organic detritus; pupation occurs at water surface. Hosts are most livestock species, horses and poultry and many wild animals. Humans also may be severely distressed by blackflies. Feeding is through skin with short complex slashing mouthparts.

Parasitic diseases and transmitted organisms

Severe biting stress when they seasonally swarm near running water. Severe anaphylaxis may develop rapidly in previously sensitized hosts, potentially leading to death of cattle. Simulium black-flies transmit to Leucocytozoon protozoa poultry. They also transmit Onchocerca nematode worms to cattle causing bovine onchocerciasis. [24]

Brachycera (suborder)

The former suborder Cyclorrhapha is now usually classified as part of the Brachycera.

General characteristics.

Mouthparts of Tabanus horse-fly: sensory palp at left, sponging labella at center, skin-piercing elements at right. Tabanus-horsefly-mouthparts-2.jpg
Mouthparts of Tabanus horse-fly: sensory palp at left, sponging labella at center, skin-piercing elements at right.
Haematopota pluvialis tabanid fly showing distinct patterns on eyes and wings. Haematopota-pluvialis-06-VII-2007-03.jpg
Haematopota pluvialis tabanid fly showing distinct patterns on eyes and wings.

Antennae consist of three relatively short segments with asymmetric shapes. Brachyceran flies are of medium to large size and compact shape. They have large compound eyes, well developed wings, and generally fly during daytime seeking food and mates. Life-cycle is a complete metamorphosis, as for Nematocera. [7] However, in contrast to nematoceran flies which have larvae always non-parasitic and living in the general habitat, some species of brachyceran flies are parasitic in their larval stage whilst the adults that develop from these larvae are non-parasitic. This parasitism by brachyceran larvae causes the disease myiasis.

Some of the brachyceran flies are important transmitters of pathogenic organisms through a route known as mechanical (or contaminative) transmission. [25] [26] These flies have complex cutting mouthparts that make a superficial wound in skin. Blood flowing into the wound is sponged up by the labella organ of the mouthparts (see photograph of Tabanus mouthparts). The flies tend to take small meals from many hosts at short intervals, to avoid the defensive actions of their hosts. Fresh blood on the labella may contaminate other hosts with pathogenic organisms. Many species of brachyceran flies such as the house-flies and blow-flies that do not feed on blood are also mechanical transmitters of pathogenic organisms by a contaminative route on their mouthparts used for sponging up wet nutritious secretions on skin of vertebrate animals. Usually the mechanical transmission of microbes by flies does not involve any developmental stage of the microorganism in the fly. However, some brachyceran flies, such as a group of species of genus Glossina , are important biological transmitters, not mechanical.

Horse-flies (Family Tabanidae).

Typical genera are Tabanus , Haematopota , Chrysops and Hybromitra, also many other genera of importance to domestic animals in some regions of world, tropical and subtropical South America especially. [27] [28]

Morphology, life-cycle, hosts and feeding.

These are large robust flies with massive eyes that often show colored patterns. Antennae are characteristic with three dissimilar segments projecting forward from head. Wings are large and strong with complex venation, and often with complex patterns of brown on clear background. [29] [30] These flies are adapted to hunt widely for their hosts during daytime. Females take repeated small blood meals from their hosts to support development of a large batch of eggs. Eggs are laid on wet soil where larvae develop, sometimes over one or two years by feeding on soil organisms. Males do not feed on blood. Hosts of females include all species of mammalian livestock animals and horses. Tabanid flies have large mouthparts comprising three pairs of cutting / slashing elements that pierce skin in a superficial wound. Blood flowing from this is imbibed through a sponge-like element of the mouthparts, the labella (similar to that shown in photograph of Calliphora). [31]

Parasitic diseases and transmitted organisms.

Bites of tabanid flies are painful. Dense populations of these flies cause severe biting stress to livestock and horses leading to reduction of gain in liveweight. These hosts may additionally suffer loss of grazing time by clustering in tight defensive packs, a situation known as fly-syndrome. Many genera of tabanid flies transmit the protozoan Trypanosoma evansi that causes in camels and horses the disease called surra. [32] These flies also transmit the protozoan T.vivax that causes in cattle the disease called nagana. Tabanid flies are also transmitters the bacteria Anaplasma marginale and A.centrale to cattle, sheep and goats, causing anaplasmosis. [2]

House-flies, Stable-flies and similar (Family Muscidae).

Typical genera are Musca , Hydrotaea , Stomoxys and Haematobia .

Mouthparts of Calliphora blowfly showing sponge structure of labella at lower right. Calliphora-sponging-mouth-parts.jpg
Mouthparts of Calliphora blowfly showing sponge structure of labella at lower right.

Morphology, life-cycle, hosts and feeding.

These are medium to large flies of compact structure, with clear wings of complex venation. Antennae are highly characteristic with antennae consisting of several compact segments that lie in a deep groove between the eyes; the outermost segment of each antenna bears a feather like structure, the arista, which projects forwards. Species within Musca, Hydrotaea, and similar genera have mouthparts adapted for sponging nutritious liquids with their labellar lobes (see photograph of Calliphora mouthparts which also have this sponge structure). [7] Some species of this type, such as Musca vestustissima (Australian bush-fly) also have, as part of this sponge structure, small teeth that can scrape at host's skin down to superficial capillaries to feed on blood. [33] Cattle are a typical host for Musca and similar species of house-flies that are attracted to protein containing liquids at the eyes and nostrils of their hosts.

Species within the genera Stomoxys stable-flies, and Haematobia horn-flies are highly adapted for blood feeding, having mouthparts consisting of a strong projecting labium with cutting elements at its point. [34] This is used to pierce deeply into skin of host to access blood (see photograph of Stomoxys in the Gallery below. Females of these flies typically take repeated small meals from their hosts to support production of their batches of eggs. Both females and males feed only on blood. Cattle and domestic buffalo are also the main hosts of Stomoxys and Haematobia flies. [35]

Parasitic diseases and transmitted organisms.

Irritation is caused by large numbers of Musca house-flies, through to severe biting stress from dense populations of Stomoxys or Haematobia flies. Musca house-flies, face-flies, and similar types transmit a variety of bacteria involved in mastitis of cattle. [36] The conjunctivitis of cattle known as pink-eye is caused by Moraxella bovis bacteria transmitted by Musca autumnalis face-flies. [37] The feeding of various Musca species of fly permits the contaminative transmission of nematode worms, for example Parafilaria bovicola , causing a nodular filariasis in cattle. Stomoxys species transmit several species of Trypanosoma protozoa to cattle, sheep and goats causing various types of trypanosomiasis. Haematobia horn-flies transmit nematode worms in the genus Stephanofilaria to the skin of cattle, causing stephanofilariasis, a suppurating dermatitis known as hump sore. Stomoxys flies transmit the bacterium Eperythrozoon ovis to sheep and this infection may lead to fever and anemia.

Tsetse-flies (Family Glossinidae).

Glossina adult tsetse fly; piercing mouthparts conspicuous. Tsetse-BKF-2.jpg
Glossina adult tsetse fly; piercing mouthparts conspicuous.

There is one genus in this Family: Glossina , known as tsetse-flies or simply tsetse. [38] Flies of this family are similar to Stomoxys flies within the Muscidae, but have a life cycle and veterinary and medical importance justifying a separate Family designation. Tsetse-flies are found only in sub-Saharan Africa.

Morphology, life-cycle, hosts and feeding.

These flies are closely similar to Stomoxys and Haematobia, but are larger and of a paler brown color. Tsetse-flies of both sexes are robust fliers adapted for hunting their hosts during daytime. Male adults support their mating activity with repeated meals of blood from cattle and similar wild bovid hosts, also wild pigs and warthogs are favored. Life-cycle of tsetse-fly is highly specialized. Females take repeated small meals of blood to support the development within their abdomen of a single larvae over one period. This will be repeated for as many times as the female is able to survive, depending mostly on availability of hosts. The single larva emerges fully grown from the female, weighing more than the female. Then the larva immediately burrows into dry sandy soil to pupate within a protective puparium. A new adult emerges from the puparium after a complete metamorphosis. This is known as larviparous reproduction, with the advantage of high survival rate of offspring, but few offspring are produced by each female. [39]

Parasitic diseases and transmitted organisms.

Bites from tsetse flies are painful but these flies are not generally associated with direct causes of lost production in cattle. Glossina morsitans and G.pallidipes tsetse-flies are transmitters of various species of Trypanosoma protozoa causing animal trypanosomiasis (= nagana) in cattle, and other forms of trypanosomiasis in sheep, goats, pigs, camels and horses. [40] [41] Tsetse-flies are also notorious as transmitters of the Trypanosoma species causing African trypanosomiasis (= sleeping sickness) in humans.

Blow-flies (Family Calliphoridae).

Important genera include Calliphora , Lucilia , Chrysomya , Cochliomyia and Wohlfahrtia.

Chrysomia bezziana, Old World screw-worm, adult fly and third stage larva of type causing myiasis (see header photograph of C.megacephala for colors of live fly). Chrysomya adult larva.jpg
Chrysomia bezziana, Old World screw-worm, adult fly and third stage larva of type causing myiasis (see header photograph of C.megacephala for colors of live fly).

Morphology, life-cycle, hosts and feeding.

All calliphorid flies are all large, robust, strong day-time fliers. Their antennae are as described above for house-flies and others in the Family Muscidae. Adult flies in family Calliphoridae feed as adults of both sexes mostly on proteinaceous liquids found on surface of decaying animal carcasses and similar material. These liquids are taken in using sponging mouthparts (see photograph of Calliphora). In genera such as Calliphora and Lucilia the females lay their eggs on the same dead animal material and the larvae feed their by rasping at the muscle and other tissues with their mouthparts. However, species of Lucilia and some other genera may opportunistically invade the tissues of live hosts, such as sheep or cattle and feed there parasitically. Other genera such as Chrysomya, Cochliomyia and Wohlfahrtia are specifically adapted for this type of feeding by the larvae. [42]

Parasitic diseases and transmitted organisms.

When larvae of Lucilia feed parasitically they cause the disease facultative myiasis (facultative = opportunistic or optional). When this occurs on sheep it is often known as blow-fly strike. This causes severe distress to the host and may be fatal due to toxemia from ammonia excreted by masses of infesting larvae. [43] [44] Females of Chrysomya, Cochliomyia and Wohlfahrtia and similar genera always seek out their host such as cattle, sheep, dogs, to lay their eggs at vulnerable sites such as a small wound. The larvae hatch and rapidly invade the superficial layers of skin to continue feeding there until ready to pupate. This form of parasitism is essential for these types of fly, and causes obligate myiasis (obligate = necessary or essential). This infestation develops into severe disease and can be fatal if the infestation is at a vulnerable site such as ear or navel of the host. [45] Adult blow-flies such as those in the genus Calliphora can be significant as transmitters of various bacteria involved in mastitis of cattle. The conjunctivitis of cattle known as pink-eye is caused by Moraxella bovis bacteria and may be transmitted by blow-flies. [2]

Bot-flies and warble-flies (Family Oestridae).

Larvae of Dermatobia hominis, Torsalo bot-fly; third stage larva top, first stage larva bottom. Dermatobia larvae.jpg
Larvae of Dermatobia hominis, Torsalo bot-fly; third stage larva top, first stage larva bottom.
Furuncular myiasis at shoulder and neck of cow caused by infestation of Dermatobia hominis larvae. Dermatobia-hominis-infestation-cattle-2.jpg
Furuncular myiasis at shoulder and neck of cow caused by infestation of Dermatobia hominis larvae.

Typical genera are Hypoderma , Gasterophilus , Dermatobia and Oestrus (fly) . Oestrid flies at their larval stage tend to be adapted to feed on a few closely related species of host animal and the adult females fly actively to seek out only these hosts on which to lay their eggs.

Adult warble fly, Hypoderma iparece, showing furry appearance and lack of mouthparts. Warble Fly. Oestridae. Hypoderma iparece - Flickr - gailhampshire.jpg
Adult warble fly, Hypoderma iparece, showing furry appearance and lack of mouthparts.

Morphology, life-cycle, hosts and feeding.

Adults are large flies, and unusual amongst brachyceran flies because they have a dense covering of fine setae (like hairs) and colored patterns that make them appear like bumble-bees (Hymenoptera). All species of the Oestridae are so highly adapted to the myiasis type of parasitism that the adults do not feed and have only residual mouthparts (see photograph of Hypoderma iparece). [46] All these flies have an obligate myiasis life-cycle, with a complete metamorphosis. [1] [47] The females lay eggs with high selectivity on their special hosts and at specific sites there. For example, eggs laid on the legs of horses in the case of species of Gasterophilus. [48] The horse licks at the irritated skin and the larvae transfer to the mouth of horse. The larvae penetrate tissues in the oral cavity, feed parasitically whilst migrating through tissue of the esophagus to finally reach the stomach. The final larval stage is completed with the larvae attached to the mucosa of the horse's stomach. When ready to pupate the larvae detach and are voided in the horse's feces. Another example is Dermatobia hominis , torsalo-fly, which is an important parasite of cattle, and sometimes humans, in tropical regions of South America. [49] [50] The larvae cause a localized, furuncular (= like a boil) myiasis in the skin of their hosts. The larvae infest these sites when transported there accidentally by blood feeding mosquitoes; the adult female Dermatobia flies lay their eggs on the legs of mosquitoes, a dispersal mechanism called phoresy.

Parasitic diseases and transmitted organisms.

Obligate myiasis of various forms are typical of the oestrid genera. Larval Dermatobia torsalo-flies infest the skin and underlying tissues of cattle causing distress, reduced gain in weight and damage to skins used for leather. Larval Gasterophilus stomach-bots infest the upper gastric tract and stomach of horses and other equids. [51] Larval Hypoderma warble-flies infest the skin and muscles of cattle. Larval Oestrus nasal-bots infest the nasal cavities of sheep and goats. [52] In the case of stomach-bots it is often uncertain how much clinical disease or loss of production small levels of infestation causes the host. With infestations of warble-flies and nasal-bots severe distress to the hosts may be caused and there are production losses from reduction of value of cattle hides, and reduced grazing time by sheep. Harm to cattle may be caused through panic (known as gadding) at the approach of the flies if that leads to traumatic injury. There are no organisms of known importance transmitted by oestrid flies.

Louse-flies (Family Hippoboscidae).

Melophagus ovinus sheep-ked: male at left, female center, puparium right. Melophagus-male-female-puparium.jpg
Melophagus ovinus sheep-ked: male at left, female center, puparium right.

Genera of importance are Melophagus and Hippobosca . This is a Family of specialized blood feeding flies with a reproductive cycle similar that described for tsetse-flies. They are often known as louse-flies because some species either shed their wings when as adults they find a host after active flying (in genus Lipoptena ). Alternatively flies of genus Melophagus are so adapted to parasitism that the adults never develop wings. Louse-flies without wings may appear like ticks, but the only stage of tick seen with three pairs of legs will be larvae these are much smaller than louse-flies.

Morphology, life-cycle, hosts and feeding.

Adults of the genus Hippobosca are large, robust flies that retain their wings to fly for repeated blood meals, between hosts such as cattle, camels or horses in a herd. Stout piercing mouthparts project downward from the head (see Hippobosca in Gallery). The abdomen bulges largely, especially when containing a developing larva. The life-cycle is the larviparous type, similar to that of tsetse-flies, few offspring are produced per female but their survival rate is high. [53] In species that never develop wings as adults, such as Melophagus ovinus, the sheep-ked, the fully developed larvae are deposited by the female on the hair coat of the host. There pupation occurs rapidly followed by complete metamorphosis into an adult (see photograph of Melophagus). [54]

Parasitic diseases and transmitted organisms.

Irritation and biting-stress is caused. Damage to skin results in poor quality of leather when hides are processed, a condition known as cockle. Sheep-keds transmit the bacterium Eperythrozoon ovis to sheep and this infection may cause fever and anemia. They also transmit Trypanosoma melophagium, but this protozoan seems non-pathogenic.

Prevention of infestation and infection

Physical barriers and hygiene

These usually consist of netting made of synthetic fibers or fine metal mesh that is fitted to the ventilation slats or windows of housing for livestock animals. The fiber netting can be impregnated with insecticides such as the synthetic pyrethroid deltamethrin that acts rapidly when flies such as Stomoxys or Glossina species land on it. [55] Valuable horses in areas infested with Culicoides midges or Simulium black-flies can be protected with commercially available shields made of cloth that fit over head, neck and back. Flies such as the Musca, Stomoxys, and Haematobia species have larval habitats amongst livestock dung and soiled bedding found around livestock farms. There is scope for reducing fly infestation by clearing these wastes to composting containers or areas. However, for many types of dipteran flies, the larvae inhabit areas such as bogs (Culicoides), swamps (mosquitoes), or rivers (Simulium) that are impractical to treat under typical commercial constraints within agriculture.

Chemical repellents and insecticides, and botanical preparations

Target to control Glossina tsetse-flies; colors of cloth attract flies and cloth is treated with insecticide, brown bottle at top right of target contains an odor attractant. TsetseTrap.jpg
Target to control Glossina tsetse-flies; colors of cloth attract flies and cloth is treated with insecticide, brown bottle at top right of target contains an odor attractant.

Synthetic chemicals such as diethyltoluamide (often called DEET) dissolved in an oily carrier are sometimes used. [17] Also there are various organic, botanical repellents such as citronella oil and neem oil. Typically various types of synthetic pyrethroids such as deltamethrin, cypermethrin, and permethrin are formulated in an oil or watery suspension suitable for application direct to the skin of animals at risk. [56] This is usually done with a pour-on applicator along the back line of the host from where the insecticide spreads downwards through the hair coat. [57] In addition, to protect against flies such as Stomoxys and Glossina species that feed on legs and belly the insecticide can be sprayed selectively to those regions. Also, cattle can be treated using self-applicators such as back-rubbers made of large bundles of fiber impregnated with the insecticide, or in automatic walk-through sprayers. The same types of insecticides are also formulated into the plastic sheet of ear tags for protecting cattle against Musca and similar flies feeding around the head of cattle. [58] Insect growth regulators (juvenile hormones, chitin synthesis inhibitors, etc.) are available. For example, the insect growth regulator cyromazine is effective for the prevention or treatment of infestations with blowfly larvae. Botanical extracts such as azadirachtin from the neem tree can be formulated as repellents and insecticides, with the potential advantage of more rapid degradation to harmless forms in the environment, lower toxicity and potentially lower cost. [59]

Traps and targets

These can contribute to control of blowflies and tsetse-flies for example. [38] The blowfly traps contain a liquid that smells like the rotting flesh of a carcass and the structure of the trap is designed to prevent the flies from escaping once attracted in. [1] [60] Horse-flies can be controlled by traps that attract the flies to a suspended black ball that mimics a potential host; flies attracted become trapped in a cone above. For area-wide control of tsetse-flies targets (these do not trap the flies) that combine a rectangle of dark blue or black cloth and often an attractant chemical act as simple mimics of the fly's host. [61] When the flies land on the cloth they contact the synthetic pyrethroid that is impregnated into the cloth.

Sterile insect technique

This technique was used to eradicate Cochliomyia hominivorax screw-worm fly from the USA where the flies were endemic, and from Libya where there had been an accidental importation from South America. Although this species of blowfly under natural conditions has larvae of the obligate myiasis type, it is possible to colonize the entire lifecycle in large factory conditions. Massive numbers of pupae are sterilized by irradiation. When released, these flies mate with the wild flies and the matings produce no offspring. The reproductive rate of the wild flies can be reduced to the level of eradication. Eradication schemes are being extended in the Americas. [62] [63]

Pharmaceutical drugs and vaccines

Infections with Trypanosoma species are treated, either prophylactically or to treat acute cases with synthetic chemical drugs such as diminazine. [64] Infections with nematode worms causing filariosis may be treated with the avermectin class of biologically derived drugs (macrocyclic lactones) such as ivermectin, doramectin, moxidectin. [65] There are commercially available vaccines to protect animals against bluetongue, and African horse sickness [66]

Further reading

Related Research Articles

<span class="mw-page-title-main">Tsetse fly</span> Genus of disease-spreading insects

Tsetse are large, biting flies that inhabit much of tropical Africa. Tsetse flies include all the species in the genus Glossina, which are placed in their own family, Glossinidae. The tsetse is an obligate parasite, which lives by feeding on the blood of vertebrate animals. Tsetse has been extensively studied because of their role in transmitting disease. They have a pronounced economic impact in sub-Saharan Africa as the biological vectors of trypanosomes, causing human and animal trypanosomiasis.

<span class="mw-page-title-main">Botfly</span> Parasitic insect

Botflies, also known as warble flies, heel flies, and gadflies, are a family of flies known as the Oestridae. Their larvae are internal parasites of mammals, some species growing in the host's flesh and others within the gut. Dermatobia hominis is the only species of botfly known to parasitize humans routinely, though other species of flies cause myiasis in humans.

<i>Gasterophilus</i> Genus of flies

Gasterophilus, commonly known as botfly, is a genus of parasitic fly from the family Oestridae that affects different types of animals, especially horses, but it can also act on cows, sheep, and goats. A case has also been recorded in a human baby.

<span class="mw-page-title-main">Tabanidae</span> Family of insects

Horse-flies and deer flies are true flies in the family Tabanidae in the insect order Diptera. The adults are often large and agile in flight. Only female horseflies bite land vertebrates, including humans, to obtain blood. They prefer to fly in sunlight, avoiding dark and shady areas, and are inactive at night. They are found all over the world except for some islands and the polar regions. Both horse-flies and botflies (Oestridae) are sometimes referred to as gadflies.

<span class="mw-page-title-main">Myiasis</span> Infestation of parasitic maggots

Myiasis, also known as flystrike or fly strike, is the parasitic infestation of the body of a live animal by fly larvae (maggots) that grow inside the host while feeding on its tissue. Although flies are most commonly attracted to open wounds and urine- or feces-soaked fur, some species can create an infestation even on unbroken skin and have been known to use moist soil and non-myiatic flies as vector agents for their parasitic larvae.

<span class="mw-page-title-main">Warble fly</span> Genus of flies

Warble fly is a name given to the genus Hypoderma: large flies which are parasitic on cattle and deer. Other names include "heel flies", "bomb flies" and "gadflies", while their larvae are often called "cattle grubs" or "wolves." Common species of warble fly include Hypoderma bovis and Hypoderma lineatum and Hypoderma tarandi. Larvae of Hypoderma species also have been reported in horses, sheep, goats and humans. They have also been found on smaller mammals such as dogs, cats, squirrels, voles and rabbits.

<span class="mw-page-title-main">Ceratopogonidae</span> Family of flies commonly known as no see ums, or biting midges

Ceratopogonidae is a family of flies commonly known as no-see-ums, or biting midges, generally 1–3 millimetres in length. The family includes more than 5,000 species, distributed worldwide, apart from the Antarctic and the Arctic.

<span class="mw-page-title-main">Stable fly</span> Species of fly

Stomoxys calcitrans is commonly called the stable fly, barn fly, biting house fly, dog fly, or power mower fly. Unlike most members of the family Muscidae, Stomoxys calcitrans and others of its genus suck blood from mammals. Now found worldwide, the species is considered to be of Eurasian origin.

<span class="mw-page-title-main">Medical entomology</span> Study of insect impacts on human health

The discipline of medical entomology, or public health entomology, and also veterinary entomology is focused upon insects and arthropods that impact human health. Veterinary entomology is included in this category, because many animal diseases can "jump species" and become a human health threat, for example, bovine encephalitis. Medical entomology also includes scientific research on the behavior, ecology, and epidemiology of arthropod disease vectors, and involves a tremendous outreach to the public, including local and state officials and other stake holders in the interest of public safety.

<i>Haematobia irritans</i> Species of fly

Haematobia irritans, the horn fly, is a small fly. It was first described by Carl Linnaeus in his 1758 10th edition of Systema Naturae. It is of the genus Haematobia which is the European genus of bloodsucking flies. Haematobia irritans is a native of Europe but has been introduced to North America and is considered a potentially dangerous livestock pest.

<i>Cordylobia anthropophaga</i> Species of fly

Cordylobia anthropophaga, the mango fly, tumbu fly, tumba fly, putzi fly, or skin maggot fly, is a species of blow-fly common in East and Central Africa. It is a parasite of large mammals during its larval stage. C. anthropophaga is found in the tropics of Africa and is a common cause of myiasis in humans in the region.

<span class="mw-page-title-main">Housefly</span> Species of insect

The housefly is a fly of the suborder Cyclorrhapha. It possibly originated in the Middle East, and spread around the world as a commensal of humans. It is the most common fly species found in houses. Adults are gray to black, with four dark, longitudinal lines on the thorax, slightly hairy bodies, and a single pair of membranous wings. They have red eyes, set farther apart in the slightly larger female.

<i>Chrysomya bezziana</i> Species of fly

Chrysomya bezziana, also known as the Old World screwworm fly or screwworm, is an obligate parasite of mammals. Obligate parasitic flies require a host to complete their development. Named to honor the Italian entomologist Mario Bezzi, this fly is widely distributed in Asia, tropical Africa, India, and Papua New Guinea. The adult can be identified as metallic green or blue with a yellow face and the larvae are smooth, lacking any obvious body processes except on the last segment.

<i>Lucilia silvarum</i> Species of fly

The common toad fly, Lucilia silvarum, is a member of the fly family Calliphoridae. This fly was first discovered by Johann Wilhelm Meigen in 1826 and is found most notably in European and Western Countries.

<i>Fannia scalaris</i> Species of fly

Fannia scalaris, also known as the latrine fly, is a fly species in the Fanniidae family. This species is smaller and more slender than the house fly, Musca domestica, and is similar in appearance to the lesser house fly, Fannia canicularis. The life cycle of this species can be as long as one month. These flies are globally distributed in urban areas as they are drawn to unsanitary environments. F. scalaris is a major cause of myiasis, the infestation of a body cavity by fly maggots. The adults infest bodies that have decomposed, making the species an important part of forensic entomology. The larvae of this fly have adapted protuberances, or feathered appendages, that allow them to survive in such a moist environment. Entomologists continue to research the effects that F. scalaris may have medically, forensically, and on the environment around them.

<i>Hydrotaea</i> Genus of flies

Hydrotaea is a genus of insects in the housefly family, Muscidae. They occur in most regions of the world but are more populous in warmer climates. They are often found on feces in summer months, and are therefore generally found in close proximity to livestock. Among the 130 known species in this genus, one of the most commonly recognized is the dump fly.

<span class="mw-page-title-main">Ticks of domestic animals</span>

Ticks of domestic animals directly cause poor health and loss of production to their hosts. Ticks also transmit numerous kinds of viruses, bacteria, and protozoa between domestic animals. These microbes cause diseases which can be severely debilitating or fatal to domestic animals, and may also affect humans. Ticks are especially important to domestic animals in tropical and subtropical countries, where the warm climate enables many species to flourish. Also, the large populations of wild animals in warm countries provide a reservoir of ticks and infective microbes that spread to domestic animals. Farmers of livestock animals use many methods to control ticks, and related treatments are used to reduce infestation of companion animals.

<span class="mw-page-title-main">Mites of domestic animals</span> Type of parasite of domestic animals

Mites that infest and parasitize domestic animals cause disease and loss of production. Mites are small invertebrates, most of which are free living but some are parasitic. Mites are similar to ticks and both comprise the order Acari in the phylum Arthropoda. Mites are highly varied and their classification is complex; a simple grouping is used in this introductory article. Vernacular terms to describe diseases caused by mites include scab, mange, and scabies. Mites and ticks have substantially different biology from, and are classed separately from, insects. Mites of domestic animals cause important types of skin disease, and some mites infest other organs. Diagnosis of mite infestations can be difficult because of the small size of most mites, but understanding how mites are adapted to feed within the structure of the skin is useful.

<span class="mw-page-title-main">Mites of livestock</span> Small crawling animals related to ticks and spiders

Mites are small crawling animals related to ticks and spiders. Most mites are free-living and harmless. Other mites are parasitic, and those that infest livestock animals cause many diseases that are widespread, reduce production and profit for farmers, and are expensive to control.

<span class="mw-page-title-main">Chloropidae</span> Family of insects

The Chloropidae are a family of flies commonly known as frit flies or grass flies. About 2000 described species are in over 160 genera distributed worldwide. These are usually very small flies, yellow or black and appearing shiny due to the virtual absence of any hairs. The majority of the larvae are phytophagous, mainly on grasses, and can be major pests of cereals. However, parasitic and predatory species are known. A few species are kleptoparasites. Some species in the genera Hippelates and Siphunculina are called eye gnats or eye flies for their habit of being attracted to eyes. They feed on lachrymal secretions and other body fluids of various animals, including humans, and are of medical significance.

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