Strongyloides cf. fuelleborni and other intestinal helminths in Papua New Guinea: distribution according to environmental factors.

Age graded prevalence rates for Strongyloides cf. fuelleborni, hookworm, Ascaris and Trichuris from various regions of Papua New Guinea were standardised using the standardised mortality technique. Using regression analyses on the resultant Standardised Prevalence Ratios (SPRs) of the four intestinal helminths and rainfall, altitude, slope and relief values, and population density for the various regions no environmental preference was shown which would account for their distribution. However, an examination of parasite distribution in relation to landform and rock type showed that Strongyloides was rare or absent from areas of limestone and polygonal karst although these substrates were quite suitable for other helminths. When the prevalence rates for each of the parasites were separated for high and low altitude (greater than 1,000 and less than 1,000 m a.s.l.) and then age standardised it was shown that there was no difference in hookworm prevalence rates for different altitudes. Both Ascaris and Trichuris had higher prevalences at the higher altitudes, whereas the reverse was true for Strongyloides. The data were also examined to determine whether there was any degree of association between the prevalence of one parasite and another. No association was established between hookworm and Ascaris, hookworm and Trichuris or Ascaris and Trichuris. A positive correlation was demonstrated between hookworm and Strongyloides, although this appears to be a statistical rather than a real association.