The microfilaria (plural microfilariae, sometimes abbreviated mf) is an early stage in the life cycle of certain parasitic nematodes in the family Onchocercidae. [1] In these species, the adults live in a tissue or the circulatory system of vertebrates (the "definitive hosts"). They release microfilariae into the bloodstream of the vertebrate host. The microfilariae are taken up by blood-feeding arthropod vectors (the "intermediate hosts"). In the intermediate host the microfilariae develop into infective larvae that can be transmitted to a new vertebrate host.
The presence of microfilariae in the host bloodstream is called "microfilaraemia". The success of filariasis eradication programs is typically gauged by the reduction in numbers of circulating microfilariae in infested individuals within a geographic area. [2]
Microfilaria may also refer to an informal "collective group" genus name, proposed by Cobbold in 1882. While a convenient category for newly discovered microfilariae which can not be assigned to a known species because the adults are unknown, [3] it is seldom used today.
All parasites need a mechanism for spreading to new individual hosts. Parasites in the lower gastrointestinal tract usually shed eggs in the host feces. Tissue-dwelling parasites, such as Trichinella spiralis (cause of trichinosis), rely on new hosts eating the tissues of their current host. For members of the family Onchocercidae whose adults live in the "closed" vertebrate circulatory system, transmission to a new host is achieved by the microfilaria stage, with the help of blood-feeding arthropod vectors.
This system is seen in the life cycle of Elaeophora schneideri . [4] The adults of E. schneideri typically reside in the carotid artery of its parasitic life cycle's definitive host, the mule deer. The female may be up to 12 cm (almost 5 inches) long, and releases microfilariae which measure 207 by 13 μm (or 0.008 by 0.00051 inches) into the bloodstream of the host. The blood flow carries the microfilariae away from the female in the carotid artery, and directly into the branching arteries of the head and face. Because of their size, the microfilariae pass easily through successively smaller vessels, becoming physically lodged in the small capillaries near the skin surface of the face and head.
Attracted by the carbon dioxide exhaled by the mule deer, [5] the blood-feeding female horse fly often lands on the head or face to feed. The horse fly uses its scissor-like mouthparts to cut the surface of the skin, creating a pool of blood which it takes in through its sucking mouthparts. The microfilariae, which were just under the surface of the skin, are small enough to be ingested whole by the horse fly. Once inside the horse fly, the microfilariae bore through the stomach wall, and mature into infective larvae about two weeks later. These larvae migrate to the head and mouthparts of the horse fly, and enter the bloodstream of another vertebrate host when the horse fly feeds again.
Most recent parasitology textbooks consider the microfilariae to be "pre-larvae or advanced embryos" which will develop into the first stage larvae (L1) in the arthropod vector (p. 364 [6] ). Some consider them to be the first larval stage, such as "microfilariae; i.e. first larva (= L1)" (p. 361 [7] ).
In either case, the microfilaria is the stage which develops from the egg. In most tissue-dwelling species the eggs hatch in the uterus of the female, and the unsheathed microfilariae are released. In most blood-dwelling species, embryonated eggs (or, microfilariae which are said to be sheathed in the envelope of the egg) are released; and they will only exsheath ("hatch") after being ingested by the arthropod intermediate host. All microfilariae burrow through the stomach wall after being eaten by the arthropod host, and develop into infective third stage (L3) larvae.
Many of the organs of microfilariae are in a very early stage of development. For some species, the developmental fates of individual cells have been followed from the microfilaria stage to the adult worm. The microfilariae of many species undergo a development phase called the "sausage stage", becoming temporarily shorter and thicker, while the first-stage (L1) larval organs develop.[ citation needed ]
In some species of Onchocercidae, the release of microfilariae by the adult female is periodic—occurring daily at a particular time of the day or night. This timing increases the chance that they will be picked up by a blood-feeding arthropod vector, which are often more active at certain times of the day.[ citation needed ]
Loa loa filariasis, (Loiasis) is a skin and eye disease caused by the nematode worm Loa loa. Humans contract this disease through the bite of a deer fly or mango fly, the vectors for Loa loa. The adult Loa loa filarial worm can reach from three to seven centimetres long and migrates throughout the subcutaneous tissues of humans, occasionally crossing into subconjunctival tissues of the eye where it can be easily observed. Loa loa does not normally affect vision but can be painful when moving about the eyeball or across the bridge of the nose. Loiasis can cause red itchy swellings below the skin called "Calabar swellings". The disease is treated with the drug diethylcarbamazine (DEC), and when appropriate, surgical methods may be employed to remove adult worms from the conjunctiva. Loiasis belongs to the group of neglected tropical diseases, and there is a call for it to be included in the high priority listing.
Loa loa is a filarial (arthropod-borne) nematode (roundworm) that causes Loa loa filariasis. Loa loa actually means "worm worm", but is commonly known as the "eye worm", as it localizes to the conjunctiva of the eye. Loa loa is commonly found in Africa. It mainly inhabits rain forests in West Africa and has native origins in Ethiopia. The disease caused by Loa loa is called loiasis and is one of the neglected tropical diseases.
Filariasis, is a filarial infection caused by parasitic nematodes (roundworms) spread by different vectors. They are included in the list of neglected tropical diseases.
Wuchereria bancrofti is a filarial (arthropod-borne) nematode (roundworm) that is the major cause of lymphatic filariasis. It is one of the three parasitic worms, together with Brugia malayi and B. timori, that infect the lymphatic system to cause lymphatic filariasis. These filarial worms are spread by a variety of mosquito vector species. W. bancrofti is the most prevalent of the three and affects over 120 million people, primarily in Central Africa and the Nile delta, South and Central America, the tropical regions of Asia including southern China, and the Pacific islands. If left untreated, the infection can develop into lymphatic filariasis. In rare conditions, it also causes tropical pulmonary eosinophilia. No vaccine is commercially available, but high rates of cure have been achieved with various antifilarial regimens, and lymphatic filariasis is the target of the World Health Organization Global Program to Eliminate Lymphatic Filariasis with the aim to eradicate the disease as a public-health problem by 2020. However, this goal was not met by 2020.
Dirofilaria immitis, also known as heartworm or dog heartworm, is a parasitic roundworm that is a type of filarial worm, a small thread-like worm, and which causes dirofilariasis. It is spread from host to host through the bites of mosquitoes. Four genera of mosquitoes transmit dirofilariasis, Aedes, Culex, Anopheles, and Mansonia. The definitive host is the dog, but it can also infect cats, wolves, coyotes, jackals, foxes, ferrets, bears, seals, sea lions and, under rare circumstances, humans.
Hepatozoon is a genus of Apicomplexa alveolates which incorporates over 300 species of obligate intraerythrocytic parasites. Species have been described from all groups of tetrapod vertebrates, as well as a wide range of haematophagous arthropods, which serve as both the vectors and definitive hosts of the parasite. By far the most biodiverse and prevalent of all haemogregarines, the genus is distinguished by its unique reciprocal trophic lifecycle which lacks the salivary transmission between hosts commonly associated with other apicomplexans. While particularly prevalent in amphibians and reptiles, the genus is more well known in veterinary circles for causing a tick-borne disease called hepatozoonosis in some mammals.
Acanthocheilonema is a genus within the family Onchocercidae which comprises mainly tropical parasitic worms. Cobbold created the genus Acanthocheilonema with only one species, Acanthocheilonema dracunculoides, which was collected from aardwolf in the region of South Africa in the nineteenth century. These parasites have a wide range of mammalian species as hosts, including members of Carnivora, Macroscelidea, Rodentia, Pholidota, Edentata, and Marsupialia. Many species among several genera of filarioids exhibit a high degree of endemicity in studies done on mammalian species in Japan. However, no concrete evidence has confirmed any endemic species in the genus Acanthocheilonema.
Elaeophora is a genus of parasitic nematodes which live attached to the interior surfaces of major arteries, veins and/or heart chambers in various large mammal hosts. Infestation with Elaeophora species is referred to as elaeophorosis. The species of Elaeophora have been found in Africa, Asia, Europe, and North America. Despite the fact that they produce aneurysms in the arteries and heart of their hosts which measure up to 2 cm in diameter, overt clinical symptoms of infestation are seldom reported, with the notable exception of E. schneideri infestation in sheep, elk, and moose.
Elaeophora schneideri is a nematode which infests several mammalian hosts in North America. It is transmitted by horse-flies. Infection in the normal definitive hosts, mule deer or black-tailed deer, seldom produces clinical symptoms. In other hosts, such as sheep, elk, moose, and goats, infection with E. schneideri leads to elaeophorosis. Symptoms of elaeophorosis include necrosis of the muzzle, ears, and optic nerves; lack of coordination (ataxia); facial or lower limb dermatitis; horn deformities; blindness; and death.
Brugia timori is a filarial (arthropod-borne) nematode (roundworm) which causes the disease "Timor filariasis", or "Timorian filariasis". While this disease was first described in 1965, the identity of Brugia timori as the causative agent was not known until 1977. In that same year, Anopheles barbirostris was shown to be its primary vector. There is no known animal reservoir host.
Thelazia callipaeda is a parasitic nematode, and the most common cause of thelaziasis in humans, dogs and cats. It was first discovered in the eyes of a dog in China in 1910. By 2000, over 250 human cases had been reported in the medical literature.
Thelaziasis is the term for infestation with parasitic nematodes of the genus Thelazia. The adults of all Thelazia species discovered so far inhabit the eyes and associated tissues of various mammal and bird hosts, including humans. Thelazia nematodes are often referred to as "eyeworms".
Mansonella ozzardi is a filarial (arthropod-borne) nematode (roundworm). This filarial nematode is one of two that causes serous cavity filariasis in humans. The other filarial nematode that causes it in humans is Mansonella perstans. M. ozzardi is an endoparasite that inhabits the serous cavity of the abdomen in the human host. It lives within the mesenteries, peritoneum, and in the subcutaneous tissue.
Dirofilaria repens is a filarial nematode that affects dogs and other carnivores such as cats, wolves, coyotes, foxes, and sea lions, as well as muskrats. It is transmitted by mosquitoes. Although humans may become infected as aberrant hosts, the worms fail to reach adulthood while infecting a human body.
The Filarioidea are a superfamily of highly specialised parasitic nematodes. Species within this superfamily are known as filarial worms or filariae. Infections with parasitic filarial worms cause disease conditions generically known as filariasis. Drugs against these worms are known as filaricides.
Gnathostoma hispidum is a nematode (roundworm) that infects many vertebrate animals including humans. Infection of Gnathostoma hispidum, like many species of Gnathostoma causes the disease gnathostomiasis due to the migration of immature worms in the tissues.
Dirofilaria tenuis is a species of nematode, a parasitic roundworm that infects the subcutaneous tissue of vertebrates. D. tenuis most commonly infects raccoons, but some human cases have been reported. They are vectored by mosquitoes and follow similar development and transmission patterns as other Dirofilaria.
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.
Brugia is a genus for a group of small roundworms. They are among roundworms that cause the parasitic disease filariasis. Specifically, of the three species known, Brugia malayi and Brugia timori cause lymphatic filariasis in humans; and Brugia pahangi and Brugia patei infect domestic cats, dogs and other animals. They are transmitted by the bite of mosquitos.
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.
Kolte SS, Satarkar RN, Mane PM. Microfilaria concomitant with metastatic deposits of adenocarcinoma in lymph node fine needle aspiration cytology: A chance finding. J Cytol [serial online] 2010 [cited 2010 Nov 22];27:78-80. Available from: http://www.jcytol.org/text.asp?2010/27/2/78/70759