Experimental and field studies on the viability of eggs, and the infectivity of third-stage larvae of the human hookworm Necator americanus recovered from the creek waters of the Niger Delta, Nigeria, and their epidemiological significance

Abstract

SUMMARYIn a combined field and laboratory study, the eggs and 3rd-stage infective larvae of the human hookworm Necator americanus were recovered from the creek waters of the Niger Delta, Nigeria. They were tested for viability and infectivity. Eggs recovered from fresh water creeks showed a viability or hatching index of between 17·5 and 23·7%. Eggs recovered from brackish water showed a viability index of 18·8–21·4% in ‘normal’ cultures, and a maximum index of 6·3% when cultured in brackish water. The differences in the viability indices of these eggs were not significant (P > 0·05). Infective 3rd-stage larvae were recovered from both fresh creek water (205–258 L3/litre of water), and brackish water (45 L3/litre of water). Larvae hatched from brackish water eggs that were cultured in the brackish water were 20% infective by 3 days, but lost all infective potential by 7 days posthatching. Larvae from fresh water eggs, cultured in fresh water and ‘normal’ laboratory cultures reached 50% infectivity in 3–5 days, losing potential infectivity in 11–15 days posthatching. The infectivity patterns of larvae recovered directly from fresh and brackish waters did not differ significantly (P > 0·05) from the infectivity patterns of larvae recovered from laboratory cultures of eggs from all the experimental sources. Although larvae recovered directly from fresh and brackish waters survived in these respective media under laboratory conditions, there was a significant difference (P < 0·05) in their survival patterns. The survival and infectivity rates of field larvae were considerably reduced over time relative to control larvae. These results indicate that both contaminated fresh and brackish water creeks and their banks may form additional hookworm infection foci in areas where various water contact activities are carried out by the human host population.