September / 2006

ANSWER 15=D

DISCUSSION:

It is estimated that more than 120 million people worldwide are infected with one of these three species that cause filariasis. More than 90 percent of these infections are due to Wuchereria bancrofti and the remainder are mostly due to Brugia malayi. Estimates suggest that more than 40 million infected individuals are seriously incapacitated and disfigured by the disease. Adult worms are gradually acquired over years, slowly accumulating and producing microfilariae in infected individuals.

New sensitive diagnostic tests reveal that lymphatic filariasis is first acquired in childhood, often with as many as one-third of children asymptomatically infected before age five. The risk of infection in childhood may be related to the maternal immune response during pregnancy. In one study of mother-newborn pairs, there was a 13-fold increased risk of developing childhood Wuchereria infection, compared to uninfected controls, if the mother had active infection and there were absent filarial-specific T cell responses in cord blood at birth. However, the risk of childhood filariasis was only five-fold higher if there was evidence of T-cell specific immunity in cord blood lymphocytes.

Filiariasis is transmitted by mosquitoes. Unlike other mosquito-borne infections, several different mosquito species, including Anopheles, Culex, Aedes, and Mansonia species can serve as vectors for transmitting filariasis.