Cochliomyia | |
---|---|
C. hominivorax larva | |
C. hominivorax adult | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Class: | Insecta |
Order: | Diptera |
Family: | Calliphoridae |
Subfamily: | Chrysomyinae |
Genus: | Cochliomyia Townsend, 1915 [1] |
Type species | |
Musca macellaria Fabricius, 1775 |
Cochliomyia is a genus in the family Calliphoridae, known as blowflies, in the order Diptera. Cochliomyia is commonly referred to as the New World screwworm flies, as distinct from Old World screwworm flies. Four species are in this genus: C. macellaria , C. hominivorax , C. aldrichi, and C. minima. [2] [3] C. hominivorax is known as the primary screwworm because its larvae produce myiasis and feed on living tissue. This feeding causes deep, pocket-like lesions in the skin, which can be very damaging to the animal host. C. macellaria is known as the secondary screwworm because its larvae produce myiasis, but feed only on necrotic tissue. Both C. hominivorax and C. macellaria thrive in warm, tropical areas.
In general, all Diptera have three body regions (head, thorax, and abdomen), three pairs of legs, one pair of forewings used for flight, one pair of halteres which are modified hindwings, and one pair of antennae.
New World screwworm flies share many characteristics of the common house fly. When keying out a dipteran specimen, it is important to first note whether bristles on the meron are present or absent. All species in the family Calliphoridae have bristles on their merones, plumose arista, and well-developed calypters. Both C. macellaria and C. hominivorax are metallic green to bluish green in major coloration, with setae on the dorsal surface of the stem vein, orange gena, pale white anterior spiracles, filiform palps, and three black longitudinal stripes (vittae) on the notum of the thorax. The species C. macellaria has pale setulae on the fronto-orbital plate outside the row of frontal bristles, while C. hominivorax has dark setulae on the fronto-orbital plate outside the row of frontal bristles. The female C. macellaria has a yellowish basicosta while the female C. hominivorax has a brown basicosta. C. macellaria is 6–9 millimetres (1⁄4–11⁄32 inch) in length. C. hominivorax is 8–10 mm (5⁄16–13⁄32 in) in length. [2] [3]
The larvae of both C. macellaria and C. hominivorax have cylindrical bodies tapering anteriorly with 10 or more robust spines around the spiracular area, incomplete peritremes, an indistinct or absent button, and bands of small spines on each segment. The C. hominivorax larvae have distinctly pigmented tracheal trunks. C. macellaria larvae do not have pigmented tracheal trunks; they have spines in a V shape on the anal protuberance and no oral sclerite. The mature third instars of both species' larvae can reach a length of 17 mm (21⁄32 in). [2] [4]
The general life cycle of Cochliomyia is similar to any other Diptera in that they are holometabolous. The four stages are egg, larva, pupa, and adult. This entire life cycle lasts an average of 21 days at prime conditions (preferably a warm, moist environment), and can last as long as three months in colder climates. Females only lay eggs once in a lifetime and can lay 100 to 400 in a clutch. Females usually lay their eggs on the edge of an open wound. Warm and moist conditions are the perfect combination of home and food source. The nasal, oral, or anal areas of a host are especially prone to Cochliomyia oviposition.
Larvae hatch about 12–21 hours after the eggs have been laid. Larvae are cream colored. C. hominivorax larvae dive head-first into whatever food source is nearest, and burrow deeper, eating into live flesh if available. This results in a pocket-like lesion that causes severe pain to the host. C. macellaria larvae only feed on the necrotic tissue of a wound. After five to seven days, the larvae drop and move away from the food source to pupate. The larvae burrow into the first layer of topsoil, beneath leaves or garbage, and begin their pupation. The pupa is a dark brown color. This stage can last from seven days at a warm temperature to as long as two months if the weather is much colder. Adults emerge and spend a day or two finishing maturity. Adults of C. hominivorax breed only once in their lifetimes. Sexually mature adults breed 3–4 days after emerging from the pupa. Males mature rapidly, and spend their time waiting and eating nearby vegetation and the nectar of flowers. Females, however, are predatory, and feed on the fluids from live wounds. Females can fly long distances to find a mate. Adult flies of this species live around two to three weeks. [5] [6]
The primary screwworm, C. hominivorax , is a parasitic species, whose larvae are renowned for eating and infesting the flesh of living organisms, primarily warm-blooded animals such as cattle and other livestock. Their larvae cause myiasis ("flystrike"), an infestation of maggots in lesions or other wounds and injuries that the host animal may have. Flystrike may occur due to such farming processes as branding, castrating, dehorning, and tailing of the host animals. These processes, along with barbed-wire cuts and flea bites, lead to myiasis in the host animal. Navels of newborns also can be the sites of infestation. [7] C. hominivorax tends to reproduce only on the flesh of a living host. Unlike most other maggots, these maggots attack and consume healthy living tissue along with decaying tissue (hominivorax literally translates to "man-eating"). The larvae are responsible for their common name, the screwworm, because they possess small spines on each body segment that resemble a screw's threads. After the larvae hatch, they dive into the wound and burrow deeper, perpendicular to the skin surface, eating into live flesh, again resembling a screw being driven into an object. The larvae then continue to feed on the wound fluids and the animal's tissue. [5]
The sterile insect technique was proposed by scientists Edward F. Knipling and Raymond C. Bushland, and was rapidly adopted by the United States Department of Agriculture in 1958. The technique centers on a unique reproductive handicap that prevents female C. hominivorax flies from mating more than once. The scientists reasoned that if it were possible to clinically sterilize and release huge numbers of males as breeding time approached, fertile males might be outcompeted and the majority of female flies would lay sterile eggs. Irradiating the males was used for sterilization.
Because the agricultural industry was losing millions of dollars annually due to treatment and loss of fly-struck animals, this solution was quickly approved for testing. It was first applied on a large scale in Florida in the 1950s, due both to the severity of the problem there and to the state's unique island-mimicking geography, which allowed for relative isolation of the Florida C. hominivorax population. The eradication of Florida's primary screwworm population was completed in 1959. The program was then applied throughout the southern United States, and eventually adopted through much of Mexico in 1972 and parts of Central and South America. The primary screwworm was completely eradicated from the southern United States in 1966 and from Mexico in 1991. Livestock there continue to be vulnerable, however, and strict laws regarding animal inspection and reporting of suspected infestations remain in place. [8] [9]
A new screwworm infestation in the Florida Keys was first reported in October, 2016, which was mostly in the Key deer population, along with five confirmed infestations in domestic animals. In response, the USDA released over 80 million sterile flies from 25 ground release sites on twelve islands and the city of Marathon. [10] [9]
There is an ongoing program between the USDA and Panama, the Comisión Panamá–Estados Unidos para la Erradicación y Prevención del Gusano Barrenador del Ganado (COPEG) [11] to prevent the return of screwworm to countries where it has been eliminated and further extend prevention efforts into Colombia. [9]
The first, and to-date largest, documented infestation of C. hominivorax myiasis outside of the Americas occurred in North Africa from 1989 to 1991. The outbreak was traced to a herd of sheep in Libya's Tripoli region, which began suffering screwworm attacks in July 1989; over the following months, the myiasis spread rapidly, infecting numerous herds across a 25,000 km2 area. Eventually, the infested region spanned from the Mediterranean coast to the Sahara Desert, threatening the more than 2.7 million animals susceptible to C. hominivorax that inhabited the area. More than 14,000 cases of large-scale myiasis due to the C. hominivorax species were documented. Traditional control methods using veterinary assessment and treatment of individual animals were insufficient to contain the widely dispersed outbreak, so the United Nations Food and Agriculture Organization launched a program based on the sterile insect technique. [12] About 1.26 billion sterile flies were produced in Mexico, shipped to the infested area, and released to mate with their wild counterparts. Within months, the C. hominivorax population collapsed; by April 1991, the program had succeeded in eradicating C. hominivorax in the Eastern Hemisphere. This effort, which cost under US$100 million, was among the most efficient and successful international animal health programs in UN history. [5] [13]
The North African outbreak both provided proof of the sterile male technique's efficacy and led to numerous enhancements in its implementation; after 1991, it entered into use across parts of Central and South America. However, the inaccessibility of some areas that the fly inhabits, language differences, and the need of constant vigilance have slowed the eradication of this species.[ citation needed ]
Research is currently being performed to develop a synthetic odor bait to replace the use of wounded animals as bait for the females of C. hominivorax. This previously used method has fallen out of favor. The synthetic bait is formulated to mimic natural wound fluid from animals. The female flies are attracted to animal wounds to obtain a protein meal and to oviposit. The synthetic bait could be used at research stations that monitor for flies in regions where they are eradicated and to help decrease the screwworm populations in infested regions. [14]
The secondary screwworm, C. macellaria , is a flesh-eating fly whose larvae consume only necrotic tissue, either that of carrion or of an animal or human host (myiasis). This important distinction between C. macellaria and C. hominivorax was not understood for much of medical history; myiasis of humans and animals was viewed as universally disastrous. However, as medical understanding of the process of tissue breakdown and infection progressed, it began to be observed that wounds with specific types of maggot infestation actually had a decreased severity and duration of infection. This progressed to the point where C. macellaria larvae were being applied in some cases as surgical maggots. However, the negative connotation surrounding the word “screwworm” has persisted, and the largely harmless secondary screwworms are often blamed for myiasitic attacks for which primary screwworms are actually responsible. This should not be interpreted to mean that C. macellaria is not an avid consumer of flesh; it is routinely among the first colonisers of carrion, and in forensic cases has long had a habit of literally consuming evidence. Secondary screwworms are especially abundant on corpses and carrion in warm, direct sunlit areas. Fortunately, with the recent advent of molecular evidence, C. macellaria maggots removed from a body and boiled to sterility can now provide vital information regarding a victim and determining a post mortem interval. Forensic entomologists can use various extraction methods to test the composition of the alimentary canal of the larvae to determine if victims had any drugs or mind-altering substances in their systems before they were killed. It is important, though, for forensic entomologists to determine whether the Old World screwworm, Chrysomya rufifacies , is present in the maggot masses on the body, because C. rufifacies is usually after C. macellaria in the succession of colonising a body and C. rufifacies second- and third-instar larvae are facultatively predatory. This could result in a post mortem interval being off by a few days at the most if the C. rufifacies were to prey upon all of the C. macellaria larvae. [6] [15] [16]
Secondary screwworms have the stereotypical metallic green body of the genus, and the larvae are extremely similar to those of C. hominivorax. The most effective way to differentiate the two is to note the absence on C. macellaria of the distinctive pigmented tracheal tubes, as well as the presence of a V-shaped pattern of spines on the anal protuberance, and the lack of an oral sclerite. [2]
Interaction between humans and C. macellaria outside of accidental secondary myiasis has been largely unremarkable, with the notable exception of their early use in surgical maggot therapy. However, given the medical stigma surrounding the screwworm fly, and the slight potential for even C. macellaria to secondarily infest tissue beyond the desired extent of medical use, it has currently fallen out of favor with the medical community, which prefers the predictable Lucilia sericata . [17] [18]
Primary screwworms are primary, obligate parasites in the larval stage, and as a result are capable, unlike secondary screwworms, of initialising the penetration of the skin barrier to create an entry wound. Despite this, they are most commonly seen as colonisers of previously existing wounds, and frequently are hatched from eggs laid at the perimeter of a wound. Once the infestation commences, a dark brown or reddish-brown discharge begins leaking from the wound, sometimes accompanied by an unpleasant smell as the flesh begins to decay. This is often the first sign in both livestock and human victims that something is amiss, and often initiates consultation with a professional. As the infestation increases, the victim begins to experience escalating tissue irritation, and in the case of domesticated animals, may be observed to become withdrawn, listless, and anorexic. [5] [19]
Once the process of clinical diagnosis begins and myiasis is recognised, the larvae are fairly easy to identify. Their overall body structure resembles the spiraled screw shape on which their common name is based, a shape fairly unusual within parasitic larvae. The cranial end of the larvae has two sharply curved hooks, generally dark in color, and distinctive spiracle patterns are observed at the caudal end. The most identifying features, and the easiest way to differentiate between C. hominivorax and C. macellaria, are the prominent darkened tracheal tubes which are visible in the final third of the larval body of the former, and are often visible both with a microscope and to the naked eye. [5] [19]
Treatment of the victim can be time-consuming and, due to the high incidence of secondary infection, frustrating, but with decisive treatment, a surprisingly positive result is often achieved in all but the worst cases. The obvious first step is the manual removal of the maggots, generally using tweezers or forceps to seize the larva at the posterior end as the spiracles emerge to allow respiration. Once all larvae have been removed, a topical antibiotic smear is applied, often with an oral antibiotic accompaniment. Necrotic tissue may need to be debrided, which can be a painful process. A loose dressing is essential to allow continued fluid drainage from the wound. [5] [19]
As with many things, prevention is the best cure. Any open wound, even one so small as a blister, is a potential infestation site, and should be treated accordingly with approved pesticides. At times of the year when livestock are most vulnerable (castration, birthing, etc.), daily inspections should be conducted when possible. Infestations detected early are quite treatable, but fatalities can and do result from advanced infestation, particularly in sheep and newborn calves. [5] [19]
Secondary screwworms appear only around an existing wound (wound in this case being defined as including the opened cord area of newborn livestock), so practice facultative myiasis. They are attracted most strongly to infected wounds due to the strong odor of the wound's discharge, but even a small blister or abrasion can serve as an infestation site. Flies can also be induced to lay their eggs in hair or wool that is matted thickly and stained with any bodily fluid. [6] [19]
As with C. hominivorax, the first sign of an infestation is often the irritated surface of the wound, producing many of the same symptoms. The larvae can be diagnosed and identified by a trained professional based on larval size, shape (again following the spiraled screw-shape), and ultimately on spiracle pattern. These larvae lack the distinctive pigmented tracheal tubes that mark C. hominivorax. [6] [19]
As the secondary screwworm does not have the biological characteristic of single lifetime breeding as does C. hominivorax, no widespread control methods are currently in place beyond the usual pesticide spraying done for general fly control. However, due to its being associated with facultative myiasis, its impact on livestock in the United States is not nearly as severe. It can also be associated with human infestation in poorly run medical facilities and areas stricken by poverty, so vigilance is essential. [19]
Both species thrive in tropical areas which are warm and humid. C. macellaria is the most common species of the two in North America, distributed throughout northern South America, Central America, Caribbean Islands, the United States, and southern Canada.
C. hominivorax was distributed throughout the northern South America, Central America, Caribbean Islands, and the United States prior to the use of the sterile insect technique, after which it was eliminated from the U.S. and Mexico. However, the bordering Central American countries serve a challenge to keep the species eliminated since these countries still have populations of this fly. Many of these countries continue to implement elimination programs. [2] [3]
A maggot is the larva of a fly ; it is applied in particular to the larvae of Brachycera flies, such as houseflies, cheese flies, and blowflies, rather than larvae of the Nematocera, such as mosquitoes and crane flies.
The Calliphoridae are a family of insects in the order Diptera, with almost 1,900 known species. The maggot larvae, often used as fishing bait, are known as gentles. The family is known to be polyphyletic, but much remains disputed regarding proper treatment of the constituent taxa, some of which are occasionally accorded family status.
Botflies, also known as warble flies, heel flies, and gadflies, are flies of the family 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.
The sterile insect technique (SIT) is a method of biological insect control, whereby overwhelming numbers of sterile insects are released into the wild. The released insects are preferably male, as this is more cost-effective and the females may in some situations cause damage by laying eggs in the crop, or, in the case of mosquitoes, taking blood from humans. The sterile males compete with fertile males to mate with the females. Females that mate with a sterile male produce no offspring, thus reducing the next generation's population. Sterile insects are not self-replicating and, therefore, cannot become established in the environment. Repeated release of sterile males over low population densities can further reduce and in cases of isolation eliminate pest populations, although cost-effective control with dense target populations is subjected to population suppression prior to the release of the sterile males.
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. Non-myiatic flies can be responsible for accidental myiasis.
Cochliomyia hominivorax, the New World screwworm fly, or simply screwworm or screw-worm, is a species of parasitic fly that is well known for the way in which its larvae (maggots) eat the living tissue of warm-blooded animals. It is present in the New World tropics. There are five species of Cochliomyia but only one species of screwworm fly in the genus is parasitic; there is also a single Old World species in a different genus. Infestation of a live vertebrate animal by a maggot is technically called myiasis. While the maggots of many fly species eat dead flesh, and may occasionally infest an old and putrid wound, screwworm maggots are unusual because they attack healthy tissue.
Chrysomya is an Old World blow fly genus of the family Calliphoridae. The genus Chrysomya contains a number of species including Chrysomya rufifacies and Chrysomya megacephala. The term “Old World blow fly” is a derivative of both the associated family, Calliphoridae, and the belief that the genus Chrysomya originated in Asia and migrated to North America only relatively recently. Chrysomya’s primary importance to the field of medico-criminal forensic entomology is due to the genus’ reliable life cycle, allowing investigators to accurately develop a postmortem interval. Chrysomya adults are typically metallic colored with thick setae on the meron and plumose arista. The name comes from the word chrysos, meaning “golden” in reference to the metallic sheen of the genus’ species, and -mya, a derivation from the word myia, meaning “fly”.
Chrysomya rufifacies is a species belonging to the blow fly family, Calliphoridae, and is most significant in the field of forensic entomology due to its use in establishing or altering post mortem intervals. The common name for the species is the hairy maggot blow fly, and it belongs to the genus Chrysomya, which is commonly referred to as the Old World screwworms. This genus includes other species such as Chrysomya putoria and Chrysomya bezziana, which are agents of myiasis. C. rufifacies prefers very warm weather and has a relatively short lifecycle. It is widely distributed geographically and prefers to colonize large carcasses over small ones. The species commonly has a greenish metallic appearance and is important medically, economically, and forensically.
Lucilia illustris is a member of the fly family Calliphoridae, commonly known as a blow fly. Along with several other species, L. illustris is commonly referred to as a green bottle fly. Lucilia illustris is typically 6–9 mm in length and has a metallic blue-green thorax. The larvae develop in three instars, each with unique developmental properties. The adult fly typically will feed on flowers, but the females need some sort of carrion protein in order to breed and lay eggs.
Chrysomya albiceps is a species belonging to the blow fly family, Calliphoridae.
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.
Sarcophaga pernix, also known as the red-tailed flesh fly, is a fly in the Sarcophagidae family. This fly often breeds in carrion and feces, making it a possible vector for disease. The larvae of this species can cause myiasis, as well as accidental myiasis. It is potentially useful in forensic entomology.
Lucilia cuprina, formerly named Phaenicia cuprina, the Australian sheep blowfly is a blow fly in the family Calliphoridae. It causes the condition known as "sheep strike"'. The female fly locates a sheep with ideal conditions, such as an open wound or a build-up of faeces or urine in the wool, in which she lays her eggs. The emerging larvae cause large lesions on the sheep, which may prove to be fatal.
Cynomya cadaverina, also known as the shiny blue bottle fly, is a member of the family Calliphoridae, which includes blow flies as well as bottle flies. In recent years, this family has become a forensically important facet in many medicocriminal investigations in the growing field of forensic entomology. C. cadaverina is specifically important in determining a post-mortem interval, as well as other important factors.
Calliphora livida is a member of the family Calliphoridae, the blow flies. This large family includes the genus Calliphora, the "blue bottle flies". This genus is important in the field of forensic entomology because of its value in post-mortem interval estimation.
Lucilia coeruleiviridis, formerly Phaenecia coeruleiviridis, is commonly known as a green bottle fly, because of its metallic blue-green thorax and abdomen. L. coeruleiviridis was first discovered by French entomologist Pierre-Justin-Marie Macquart in 1855. It belongs to the family Calliphoridae and is one of many forensically important Diptera, as it is often found on decaying substances. L. coeruleiviridis is one of the most ubiquitous blow fly species in the southeastern United States, particularly in the spring and fall months.
Protophormia terraenovae is commonly called northern blowfly, blue-bottle fly or blue-assed fly. It is distinguished by its deep blue coloration and large size and is an important species throughout the Northern Hemisphere. This fly is notable for its economic effect as a myiasis pest of livestock and its antibiotic benefits in maggot therapy. Also of interest is P. terraenovae’s importance in forensic investigations: because of their temperature-dependent development and their prominent presence on corpses, the larvae of this species are useful in minimum post-mortem interval (mPMI) determination.
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. 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. 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.
Cochliomyia macellaria, also known as the secondary screwworm, is a species of blow fly in the family Calliphoridae. These screwworms are referred to as "secondary" because they typically infest wounds after invasion by primary myiasis-causing flies. While blow flies may be found in every terrestrial habitat, C. macellaria is primarily found in the United States, American tropics, and sometimes southern Canada. They are most common in the southeastern United States in states like Florida. C. macellaria have a metallic greenish-blue thorax and a red-orange head and eyes. These adult blowflies range from 5–8 mm in size.
Raymond C. Bushland was an American entomologist. He was awarded the 1992 World Food Prize with his colleague Edward F. Knipling for their combined efforts in the development of the sterile insect technique (SIT).