Associations of peak shifts in age-prevalence for human malarias with bednet coverage

Effects of bednet coverage (C) on prevalence of malaria were analysed using data from 1990-92 from 9 Papua New Guinean villages. Effects of coverage v aried by age, resulting in a shift in age of peak prevalence from 4.7 (C = 0%) to 11.6 (C = 100%) years for Plasmodium falciparum, from 3.4 to 4.9 yea rs for P. vivax and from 11.0 to 16.8 years for P. malariae. In small areas with no bednets the age distribution of P. falciparum parasitaemia was lik e that of a holoendemic area. Where coverage was complete the pattern corre sponded to mesoendemicity. Thus, protracted use of bednets can result in pr ofound changes in the endemicity of malaria even when coverage is incomplet e and without insecticide treatment. Average entomological inoculation rate s (EIRs) estimated from indoor landing rates on individuals without bednets were 35, 12 and 10 infectious bites per person per annum for P. faliparum, P vivax and P. malariae, respectively. Logistic regression analyses indica ted that the EIR estimate for P. falciparum was related to prevalence of th is species independently of effects of bednet coverage. However, the recent EIR still accounted for much less variation than did the bednets. A simila r pattern was seen for P. malariae while there were no significant relation ships between the recent EIR and the parasite positivity for P. vivax. It i s concluded that short-term variations in inoculation rate are not importan t determinants of parasite prevalence in this population.