Parasites are organisms that live in or on other living organisms and derive its nutriment from the host partly or wholly from it, and somehow exhibits a particular form of adaptation. Microorganisms are known to inhabit in human bodies, in the intestines, in orifices, and sometimes in blood and human organs like liver, brain, and lungs.

Blood parasites are worth studying for their prevalence and the fatalities they caused. Almost all blood parasites need vectors to carry their life cycle.

One particular blood parasite is caused by a nematode, and one wonders how a nematode becomes a blood parasite. A certain type of nematode under genus Wuchereria is known to caused an illness since they become blood parasites in man.

In tropical and subtropical countries, there is a group of diseases caused by Filarioidea. Two species are known: Wuchereria bancrofti and Brugia malayi. Wuchereria bancrofti is found only in humans, while Brugia malayi is often spread to man from animal hosts. The adult filarioidea live in the human lymphatic system. The microfilariae released by the gravid females are found in the peripheral blood, usually at night. Infection is spread by many species of mosquitoes. The vectors for Wuchereria bancrofti are aedes, culex and anopheles mosquitoes, while for Brugia malayi, the vectors are anopheles and mansonia. The microfilariae are ingested by the mosquitoes and undergo development in the insect’s thoracic muscles, and, when mature, migrate to its mouth parts. When the infected mosquitoes bite new hosts, the microfilariae penetrate the bite puncture and eventually reach the lymphatics, where they develop into an adult stage.

There will be an inflammation and fibrosis in the vicinity of the adult worms producing progressive lymphatic obstructions. Probably, the microfilariae do not contribute directly to this reaction of the host.

The incubation period may be as short as two months. The prepatent period, from the time of the infection to the appearance of the microfilariae in the blood is at least eight months. Clinical manifestations depend on the severity of the infection, and they may include: lymphangitis, lymphadenitis, orchitis, funiculitis, epididymitis, lymph varices, and chyluria. Chills, fever, headache, and malaise may also be present. Elephantiasis and other late severe sequelae may occur with long-time residence in endemic areas and when there are repeated infections.

An aberrant form of filariasis has been identified, and this is called tropical eosinophilia, which is characterized by hypereosinophilia, with presence of microfilariae in the tissues but not in the blood, and high titers of antifilarial antibodies. Clinically, the patient may present with lymhadenosplenomegaly or with cough, bronchospasms, and chest infiltrates. Microfilariae may be found in the blood or lymph fluids.

Treatment consists of mosquito control and drugs: diethylcarbamazine 2 mg/kg orally three times a day, after meals, for three to four weeks. This eliminates the microfilariae in the blood stream. In many patients, the drugs may also kill adult worms or impair their reproductive capacity, resulting in permanent clearing of blood from microfilariae. Severe allergic reactions and abscess formations may follow its use, but may be controlled by antihistamines and steroids.

Surgical interventions may be indicated only to alleviate certain types of elephantiasis, especially of the scrotum. Elephantiasis of the legs could be treated by elevation of the legs and with the use of elastic bandages.

Dirofilariasis also called Heartworms is caused by Dirofilaria immitis, a large filaria, which lives in the right heart of dogs. Microfilariae are released into the peripheral blood, where they are taken up by several species of mosquitoes. However, if they are transmitted to man, which is a rare event, they will find their way to the lungs producing, a well-defined, pulmonary nodules. The patient may experience chest pains, cough, and occasionally, hemoptysis. Diagnosis is made by histologic examination of the pulmonary nodules. No treatment is indicated, aside from the symptomatic remedies.