Studies on sporozoite-induced and chronic infections with Plasmodium fragile in Macaca mulatta and New World monkeys.

Plasmodium fragile continues to be investigated because of its biologic similarities to the human malaria parasite, Plasmodium falciparum. Two strains of P. fragile are available for study; one strain is able to infect mosquitoes, whereas the other strain is transmissible only by blood inoculation. The Sri Lanka strain of P. fragile was transmitted to Macaca mulatta, Macaca fascicularis, Aotus lemurinus griseimembra, Aotus nancymaae, Aotus vociferans, and Saimiri boliviensis monkeys via sporozoites that developed to maturity only in Anopheles dirus mosquitoes. The prepatent periods ranged from 12 to 35 days for macaques and from 15 to 30 days for New World monkeys after intravenous injection of sporozoites. Eight rhesus monkeys were infected with the Nilgiri strain and followed for 482 days. Parasitemia in 6 animals persisted at relatively high density through the period of observation. Erythrocyte, hematocrit, and hemoglobin values reached their lowest levels 3 wk after infection and slowly recovered; however, the values did not approach preinfection levels as long as parasitemia persisted in the monkeys. The mean corpuscular volume and corpuscular hemoglobin concentration reached their peak and lowest values, respectively, at day 38 and then returned to the preinfection level. The mean corpuscular hemoglobin value decreased to its lowest level at day 87 and then returned to preinfection level.

Studies on two strains of Plasmodium cynomolgi in New World and Old World monkeys and mosquitoes.

Infections that cause the Gombak and Smithsonian strains of Plasmodium cynomolgi were induced in Macaca mulatta, Aotus lemurinus griseimembra, Aotus nancymai, and Saimiri boliviensis monkeys. Transmission of the Gombak strain to Aotus spp. monkeys was obtained by the injection of sporozoites dissected from the salivary glands of experimentally infected Anopheles dirus and by the bites of infected An. dirus and Anopheles farauti mosquitoes. Two S. boliviensis monkeys were infected via the injection of sporozoites dissected from An. dirus. Prepatent periods in New World monkeys ranged from 14 to 44 days, with a median of 18 days. The Smithsonian strain was transmitted via sporozoites to 1 A. lemurinus griseimembra and 9 A. nancymai monkeys. Prepatent periods ranged from 12 to 31 days.

Malaria transmission in urban sub-Saharan Africa.

The rapid increase in the world's urban population has major implications for the epidemiology of malaria. A review of malaria transmission in sub-Saharan African cities shows the strong likelihood of transmission occurring within these sprawling cities, whatever the size or characteristics of their bioecologic environment. A meta-analysis of results from studies of malaria transmission in sub-Saharan Africa shows a loose linear negative relationship between mean annual entomologic inoculation rates (EIR) and the level of urbanicity. Few studies have failed to find entomologic evidence of some transmission. Our results show mean annual EIRs of 7.1 in the city centers, 45.8 in periurban areas, and 167.7 in rural areas. The impact of urbanization in reducing transmission is more marked in areas where the mean rainfall is low and seasonal. Considerable variation in the level of transmission exists among cities and within different districts in the same city. This article presents evidence from past literature to build a conceptual framework to begin to explain this heterogeneity. The potential for malaria epidemics owing to decreasing levels of natural immunity may be offset by negative impacts of urbanization on the larval ecology of anopheline mosquitoes. Malaria control in urban environments may be simpler as a result of urbanization; however, much of what we know about malaria transmission in rural environments might not hold in the urban context.

Plasmodium inui shortii: studies in old world and new world monkeys.

Plasmodium inui shortti was studied in monkeys (66 Macaca mulatta, 2 M. fascicularis, 12 Saimiri boliviensis, 4 Aotus lemurinus griseimembra, and 1 A. nancymaae). Prepatent periods for 30 sporozoite transmissions by Anopheles stephensi, An. dirus, and An. maculatus mosquitoes ranged from 10 to 48 days with a median of 15.5 days. In rhesus monkeys, mean maximum parasite counts for intact animals were 181,970/muL; for splenectomized animals, the mean maximum parasite count was 1,167,890/muL.

Plasmodium fieldi: observations on the Hackeri and ABI strains in Macaca mulatta monkeys and mosquitoes.

Macaca mulatta monkeys infected with the Hackeri strain of Plasmodium fieldi had maximum parasite counts ranging from 1,300 to 301,320/microL. In 43 intact animals infected with the ABI strain, the maximum parasite counts ranged from 672 to 57,189/microL (median = 15,100/microL); in 46 splenectomized monkeys, the maximum parasite count ranged from 660 to 350,000/microL (median = 52,245/microL). Transmission through Anopheles dirus mosquitoes was obtained on 11 occasions with pre-patent periods of 9-14 days. Relapses occurred between two and eight times during a 1-year period. P. fieldi has potential for testing prophylactic and radical curative drugs.