Endemicity, focality and seasonality of transmission of human schistosomiasis in Amagunze Village, eastern Nigeria.

The pattern of transmission of human schistosomiasis was studied in Amagunze Village, eastern Nigeria, during 1986-1987. The prevalence of Schistosoma haematobium in 119 schoolboys aged 5-12 years was 79%. The geometric mean of intensity of infection was 49 eggs/10 ml urine and the frequency of visible haematuria was 25.2%. No S. mansoni infections were demonstrated. A marked seasonality in population density of Bulinus truncatus, B. forskalii and Biomphalaria pfeifferi was demonstrated with reduced densities during the late rainy and early dry seasons. Schistosoma sp. infected B. truncatus were found in the late dry and early rainy seasons in 2 out of 7 major human water contact sites studied. Seasonality and focality of transmission of S. haematobium and its high endemicity in the area were thus demonstrated.

Human neonatal infections with hookworms in an endemic area of Southern Nigeria. A possible transmammary route.

Examination of faecal smears of 316 neonates (4-5 weeks old) in a human hookworm endemic area of southern Nigeria showed that 33 (10%) of them were hookworm infected. The majority of the neonatal infections (88%) were due to Ancylostoma duodenale although Necator americanus was the more prevalent hookworm species in the area. The incidence of neonatal infections was pronounced (64%) for mothers who were A. duodenale-positive 5-6 weeks postpartum. A thorough screening of 12.4 litres of colostral milk from all the 316 nursing mothers failed to show the presence of infective hookworm larvae. These results indicate a possibility of a transmammary infection route for the human hookworm A. duodenale.

Experimental Ancylostoma tubaeforme infection of cats: changes in blood values and worm burden in relation to single infections of varying size.

Worm-free cats about 12 weeks old were infected with 100, 500, 1,000 and 2,000 third-stage larvae (L3) of Ancylostoma tubaeforme. The changes in packed cell volume (PCV) and haemoglobin content were monitored, and the worm populations developing in each infection recorded. Cats receiving infection doses of 1,000 L3 and above showed morbidity symptoms by the third week and a rapid decline especially in the PCV value. The low dose rates (500 L3 and below) produced an apparently symptomless condition without pronounced changes in the blood values. Adult hookworm populations were linearly related to the logarithm of the dose of infective larvae administered, but there was a lower female to male ratio (FMR) at high dose levels. No significant size differences were observed in the adult hookworm populations.

Seasonality in human hookworm infection in an endemic area of Nigeria, and its relationship to rainfall.

Detailed parasitological and climatological examination of two rural communities in a hookworm endemic area of Anambra State Nigeria, has shown that infection with the parasite follows a clearly defined pattern. The results suggested a break in the transmission cycle of the parasite during the dry season December--February when only a few larvae (< 500 L3S) could be recovered from contaminated soils for not more than 4 days. Transmission of the parasite and the manifestation of the disease in infected individuals appeared to be a rainy season phenomenon. The implications of these findings are discussed in relation to possible control of the disease.

Necator americanus: population structure, distribution, and fluctuations in population densities of infective larvae in contaminated farmlands.

Observations have been made over a 15-month period on the frequency distribution of human faecal deposits and infective larvae of Necator americanus in a hookworm endemic area. The agestructure of infective larvae in a field population and their vertical distribution in soils were determined. These studies were undertaken to examine the hypothesis that hookworm transmission in the tropics is discontinuous and limited mainly to the rainy season. The distribution of larvae was found to be overdispersed statistically and in general much greater numbers of L3s were recovered during the rainy season. The degree of overdispersion was also reduced during this season, and there was a tendency for larvae to be confined to the surface/topsoil. The implications of these findings have been discussed in relation to human hookworm parasitism in endemic areas of the tropics.

Determinants of the longevity of third-stage infective larvae of Ancylostoma tubaeforme.

The effects of some extrinsic factors on the lipid (energy) reserves and longevity of third-stage larvae of the cat hookworm Ancylostoma tubaeforme, were investigated under controlled laboratory conditions. In nonstressful microenvironmental conditions, larval longevity was directly related to the rate of utilisation of the lipid reserves. The effects of the various environmental stresses on longevity could also be explained largely on the basis of their deleterious effects on the lipid metabolism of the larvae.

Investigations into the free-living phase of the cat hookworm life cycle.

Laboratory studies were undertaken to evaluate the role of environmental factors on the development of free-living stages of the cat hookworm Ancylostoma tubaeforme. An index of development calculated from the proportion of eggs that developed to the infective stage and the reciprocal of the development period, has suggested that the absence of 'high' temperatures (26 degrees - 30 degrees C) would significantly affect the L3 population in contaminated soils. There were, however, no significant differences in the size and lipid content of L3 that had developed at the different temperatures.