Experimental transmission of Brugia Malayi and B. Pahangi to man

Abstract

An attempt was made to transmit back to man a strain of Brugia malayi originally obtained from man and transmitted through a macaque monkey and thence to a cat. Two volunteers were inoculated with infective larvae of this strain which had developed in Mansonia longipalpis. Neither of these volunteers subsequently developed microfilariae. An attempt was also made to transmit to man a strain of B. pahangi, a species hitherto only known as an infection of animals. Two volunteers were inoculated with infective larvae from Armigeres obturbans which had fed on a cat carrying a strain of B. pahangi originally obtained from a naturally infected civet cat. One of the volunteers inoculated with B. pahangi developed microfilariae 84 days later, and these persisted in small numbers for a further 56 days. The microfilariae resembled B. pahangi morphologically, and the identification was confirmed by mosquito-feeding experiments and by experimental transmission to a cat from which an adult male B. pahangi was later recovered. The other volunteer did not develop microfilariae. All four volunteers suffered from episodes of lymphangitis, lymphadenitis, and oedema in the inoculated limb, starting in each instance about one month after the inoculation. Although there was no true leucocytosis, all four volunteers developed a relative increase in eosinophils with maxima ranging from 18 to 32 per cent. occurring 12 to 13 weeks after the inoculation. All volunteers showed positive complement-fixation tests and skin tests (to Dirofilaria antigen) about 12 weeks after the inoculation. One volunteer from each pair developed subcutaneous nodules in the inoculated arm about 4 months afterwards. The significance of these findings is discussed. B. pahangi must now be regarded as potentially infective to man. The clinical episodes are considered to be reactions to the immature developing worms, whereas the eosinophilia is more probably a response to some product of the adult worms. Subcutaneous nodules do not seem to have been described previously in association with filarial infection.