The Filarioidea

The Filarioidea or Filaria belong to Nematodes. They are worms that live in the lymphatic system, subcutaneously or some in the human eye. They occur in the tropics and subtropics. Filaria cause filariasis. The main representatives include: Wuchereria bancrofti, Brugia malayi, Brugia timori, Loa loa, Onchocerca volvulus.

After fertilization, females give birth to live larvae - microfilariae, which circulate in the bloodstream of the host and are then sucked from there by an insect carrier, in which they complete their cycle. In insects, they develop into an invasive stage and during the next suckling they are transferred to another host, where they mature. The vector of the disease is therefore a stinging insect, which injects into the host an infectious larva - microfilariae. Human is the definitive host.

Wuchereria bancrofti
 Wuchereria bancrofti is a worm found in the tropics and subtropics of the southern hemisphere. Its intermediate host and at the same time the vector of infection is the mosquito. The definitive host is human. Transmission to humans is due to mosquito bites. It causes wuchereriosis, which in severe cases can lead to elephantiasis, a disease accompanied by severe lymphedema.

A mosquito stings a person and the parasite is transmitted. Microfilariae burrow into the capillaries and migrate to the lymphatic system, where they mature and copulate. The females then give birth to live larvae - microfilariae (most of them are at night). The larvae then travel through the blood and can be sucked by another mosquito.

Adult worms most often parasitize the lymphatic system and can clog lymphatic vessels, for several years, which in turn leads to lymph stagnation and lymphatic varices and can even rupture the lymphatic vessel.

The main manifestations of wuchereriosis include abdominal pain, swelling, vomiting, anemia and in the more severe stages when the lymphatic vessels rupture, chyluria (the presence of lymph in the urine) can occur.

A more serious form is elephantiasis, when the lymph flow is closed and the given part of the body increases in size due to this - the lower limbs, scrotum and vulva. are most often affected.

Direct microscopic detection of microfilariae from the patient's blood or puncture from the patient's lymphatic nodes used in the diagnosis.

The disease is treated with diethylcarbamazine or ivermectin. Prevention - liquidation of mosquitoes is especially important.

Brugia malayi
Brugia malayi is very similar to W. bancrofti - life cycle, transmission, disease and therapy. It occurs mainly in Southeast Asia. The main vector is the mosquito. It causes the disease brugiosis, which mainly affects the upper and lower limbs and can manifest itself in elephantiasis. The only source of infection is man. Direct microscopic evidence is used in diagnostics - larvae are detected in blood taken at night using the thick smear method.

Loa loa
Loa loa is a parasite,that occurs mainly in Central Africa. Its intermediate host is the bug and the final host is the human. Infection occurs when a person is stung. Larvae get through the blood to the subcutaneous tissue or conjunctiva, where they mature and multiply. Females then give birth to larvae (microfilariae), which then circulate in the blood stream and can be sucked by a stinging fly.

The disease caused is called loiasis and is divided into subcutaneous and ocular types. Subcutaneous loiasis is manifested by parasites forming bumps in the subcutaneous tissue. Edema develops around these bumps as a result of an allergic reaction to parasite irritation. If the infection is located only in the subcutaneous tissue, then the disease is not very dangerous. However, if it gets into the eye, an eye loiasis develops -it is more serious but also rarer. In this case, the adult worm is in the conjunctival sac. The patient usually suffers from severe conjunctivitis and may experience visual disturbances and, in the worst case, this leads to blindness.

Direct microscopic detection of microfilariae in the patient's blood is used in the diagnosis. The most important thing in therapy is the surgical removal of the parasite from the eye, and diethylcarbamazine is used as a drug .

Onchocerca volvulus
Onchocerca volvulus is a parasite that occurs mainly around large rivers in Africa and South and Central America. Its final host is a human and the intermediate host is a flycatcher. Transmission is by fly bite. After infiltration, the infectious larvae mature in the host's body and multiply in the subcutaneous nodules. Females give birth to microfilariae that burrow around the bump and from there they can be sucked in again by the fly. The hair follicle causes the disease onchocerciasis, which is manifested by bumps in the subcutaneous tissue, where the parasite adults live. Dermatitis around the nodule leads to depigmentation of the skin, which is then referred to as leopard skin. Less often, the disease manifests as lymphadenitis or elephantiasis. If the skin penetrates the eye, there is a risk of inflammation and damage to the cornea, conjunctiva and retina.

Diagnosis uses direct microscopic identification of larvae in the nodule. Therapy is based on the administration of diethylcarbamazine or ivermectin and surgical removal of the nodule may also occur.

Related articles

 * parasite
 * parasitism

Literature

 * BEDNÁŘ, Marek, Andrej SOUČEK a Věra FRAŇKOVÁ, et al. Lékařská mikrobiologie : Bakteriologie, virologie, parazitologie. 1. edition. Praha : Marvil, 1996. 558 s.  ISBN 8023802976.