Prevalence of malaria in Afghan refugees in Pakistan is higher than in the local population. Malaria control officials in Pakistan hypothesized that Afghan refugees have brought a heavy load of malaria infections with them from Afghanistan, causing a serious setback to the malaria control programme in Pakistan. The purpose of this study was to test this hypothesis, because it is important regarding the selection of appropriate strategy for malaria control. The proposed hypothesis is rejected because of the following evidence against it: (i) a comparison of age-specific parasite rates of malaria in Afghan refugees and a nearby local population at Karachi indicated that Afghan refugees were susceptible to malaria even in later age-groups, while infections in the local population were limited to younger age-groups; (ii) a comparison of epidemiological trends of malaria in Afghan refugees and the local population in the North-West Frontier Province from 1979 to 1986 demonstrated that the rate of increase in the prevalence of malaria over the years was much higher in Afghan refugees than in the local population, a manifestation of low herd immunity in Afghan refugees. The most plausible alternate hypothesis is that Afghan refugees, being more susceptible, were at high risk of malaria infection in Pakistan rather than that they brought a high infection load with them from Afghanistan. Therefore, malaria control in Afghan refugee camps in Pakistan should be primarily based on preventive, rather than curative, measures.
Intraspecific variation in the reproductive capacity of Anopheles stephensi Liston females was studied under constant laboratory conditions. Of 421 engorged females examined individually throughout their lifetimes, 260 laid a total of 479 egg batches with a maximum of nine ovipositions per female. The number of eggs per oviposition varied from 5 to 247 (average 96.8). The number of ovipositions per female were correlated positively with the average number of eggs per batch and exhibited a negative binomial distribution among females, indicating that a small portion of the population exhibited a particularly high fecundity. Among the ovipositing females, the total fecundity and fertility ranged, respectively, from 5 to 1,084 eggs and from 0 to 1,036 larvae per female. The estimated maximal number of female progeny produced by a female in her lifetime was 317, and the estimates of net reproductive rate (Ro) and capacity for increase (rc) were 25.7 and 0.17, respectively. The number of eggs in the first oviposition was predictive of the total fecundity of a female. The wide range of individual variation in the reproductive capacity of An. stephensi emphasized the requirement for a large sample size for reliable estimation.
Although the recent distribution of yellowfever mosquito, Aedes aegypti (L.), in Pakistan has been restricted to the port city of Karachi, adult and immature mosquitoes breeding in imported tires in warehouses at Landi Kotal (North-West Frontier Province) were identified as Ae. aegypti. The patterns of tire trade and the current disjunct distribution of Ae. aegypti indicated that the introduction into Landi Kotal may have been either from Karachi or India. Thermal fog application of pirimiphos-methyl and residual spray of malathion during 1993 reduced abundance in October-November. Living larvae or adults were not found during January 1994, apparently because of cold weather. However, Ae. aegypti reappeared during May-June 1994, most probably from eggs that overwintered. Population increased during late August when another round of spray using the same insecticides and fenthion as an additional larvicide again reduced abundance. Although this mosquito apparently has not spread into neighboring areas, its survival at Landi Kotal through all seasons despite control measures indicates its potential of becoming established in other areas of Pakistan.
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