Nematode Zoonoses - FILARIASIS

(Brugiasis)

AGENT:

The commonest causative agent is Wuchereria bancrofti, which is not zoonotic. Brugia malayi is zoonotic. Dirofilaria immitis may occasionally infect humans.

RESERVOIR AND INCIDENCE:

B. malayi has been identified in Malaya and the Philippines. D. immitis occurs in dogs in North and South America, Australia, India, the Far East and Europe. Wild monkeys and felines are the reservoir for B. malayi.

TRANSMISSION:

Transmission to humans is via the bite of a mosquito vector (Mansonia and Anopheles). These, on biting humans, release microfilariae on to skin which enter the body through the puncture wound and pass via the lymphatics to lymph nodes. The worms are viviparous, producing microfilaria. These appear in the blood and reinfect the biting insect.

DISEASE IN ANIMALS:

D. immitis is found in the right ventricle of dogs and in the pulmonary artery. Mild infection causes no signs, but long continued infection leads to cardiac insufficiency with ascites and passive congestion.

DISEASE IN MAN:

B. malayi: Repeated bouts of fever, lymphadenopathy, lymphangitis and abscesses occur. This leads to lymphatic obstruction and massive lymphedema followed by fibrosis (so-called elephantiasis) especially in the legs.
D. immitis: Initial symptoms include cough, chest pain, or hemoptysis. However, the filariae die in the human pulmonary vasculature and consequently nodules have been found in the skin or as solitary 1-2 cm "coin" lesions in the periphery of the lungs.

DIAGNOSIS:

Diagnosis is established by finding microfilariae in the blood. Serologic testing is available but false-positive and false-negative reactions occur.

TREATMENT:

Diethylcarbamazine

PREVENTION/CONTROL:

Diethylcarbamazine or Ivermectin can be given as a prophylaxis. Control vectors and avoid their bites. Prophylactic treatment of dogs.