Recovery of adult stages and microfilaraemia after low dose inoculation of third stage larvae of Litomosoides carinii in Sigmodon hispidus.

Because of the negative binomial distribution of filarial third stage larvae (L3) in their vectors, under natural conditions only a few are usually transferred per bite. After an inoculation of 5 L3 per animal into eight host animals at least one developed a long lasting patency based on one reproductive female only. After an inoculation of 15 L3, three of eight animals developed long lasting patency, harbouring between two and five fertile females. The rates of adult stages recovered were 0.43 and 0.30 respectively. The parasitaemias of the six patent animals in both experimental groups increased with the number of reproductive females present (r = 0.89, p = less than 0.005). All non-patent animals which were mf-negative in the pleural fluid and lung blood as well had a single sex or no worm load. In only one animal was there an apparently normal but non-reproductive pair of worms without any pathological alterations of the host animal. Encapsulated adult worms were found rarely, but independent of the final worm load or inoculation dose and always beside normal adults. In three of the 16 animals inoculated with 5 or 15 L3 patency passed after 10-12 weeks p.i., in two others it seemed to pass soon. After inoculation of 30, 40 or 60 L3 per animal patency passed early in about one half of 105 animals, when they were observed up to 24-36 weeks p.i. In conclusion all types of host defensive reactions are already visible after inoculation with such small doses.(ABSTRACT TRUNCATED AT 250 WORDS)