Periods Of Low Transmission Research Articles

Overlap in the clinical features of pneumonia and malaria in African children

Pneumonia and malaria are common causes of childhood morbidity and mortality in many developing countries and simple guidelines have been proposed to facilitate their diagnosis by relatively unskilled health workers. We have studied children in The Gambia attending out-patient and under-five clinics with clinically suspected pneumonia (cough or difficulty in breathing and a raised respiratory rate) during periods of high or low malaria transmission. During a period of high malaria transmission, 33% of these children had radiological evidence of pneumonia (with or without malaria parasitaemia) compared to 38% who had malaria parasitaemia, no radiological evidence of pneumonia and no other obvious cause of fever. Corresponding figures during a period of low malaria transmission were 48% and 6% respectively. The clinical overlap between pneumonia and malaria has important implications for case management strategies and evaluation of disease-specific interventions in regions in which both pneumonia and malaria are prevalent.

Studies on Plasmodium atheruri

Plasmodium atheruri, a parasite of the African porcupine Atherurus africanus, is infective to splenectomised laboratory Rats and Mice, to Hamsters and to 2 exotic rodents which are easily bred in captivity: Calomys callosus and Meriones unguiculatus. Sporogony develops in Anopheles stephensi fed on Atherurus and on laboratory rodents; it is similar to that of the Rodent Plasmodia. Exoerythrocytic schizogony usually lasts 4 to 6 days but schizonts have been found in the liver of a porcupine at day 8. Schizogony in the blood (induced by inoculation of infected blood or by injections of sporozoites) follows two stages which are morphologically distinct: a) acute infections developing in clean Atherurus, following splenectomy of infected Atherurus or in laboratory rodents; it is characterized by large trophozoïtes, schizonts with 8 to 16 merozoites, gametocytes and infectivity to Anopheles. b) chronic infection which only occurs in the blood of Atherurus and follows the acute stage 15 to 21 days after its onset; it is characterized by small trophozoites and schizonts producing 4 merozoites. Thus it is thought that the chronic stage only occurs in the natural host when it is immunized. We think that, in nature, chronic schizogony maintains the parasitaemia through periods of low transmission and is followed by "recrudescences". The mechanisms that trigger the "recrudescences" are unknown but are probably connected with a decrease in the immune status of the host.

Detection of arboviruses by sentinel hamsters during the low period of transmission.

SummarySixteen arbovirus isolates were obtained from 21 golden hamsters exposed in five different locations in an area of tropical rain forest of Panamá during February and March 1966. This animal proved to be a successful sentinel for the detection of Venezuelan equine encephalitis, Ossa, Madrid, Patois, and Guamá viruses during the low transmission period of 1966. Mosquito collections on the exposed hamsters seemed to point to Culex mosquitoes of the subgenus Melanoconion, and to C. vomerifer in particular, as the vectors of the bulk of the viruses isolated from hamsters. Solutions are suggested for problems, such as feed-back of virus from the sentinel hamsters to wild mosquitoes, which may develop from the use of this method.

Results of exposing mice to Schistosomiasis by immersion in natural water

1. 1) By immersing groups of mice, placed in suitable cages in naturally-infected water in a highly endemic schistosomiasis area in the Eastern Transvaal and later recovering the schistosomes, it was found that there was a well-defined transmission period for S. mansoni during midsummer, preceded and followed by periods of low transmission, and with practically no transmission during the winter. There was no similar transmission period for S. mattheei. The practical advantages of this transmission period for S. mansoni are mentioned in relation to a control programme with molluscicides. 2. 2) It is also suggested that a pre-transmission period of low intensity might afford some protection to the subsequent heavy cercarial onslaught later in the summer. 3. 3) Other findings, such as mice mortality, snail catches in relation to schistosomes recovered, rainfall and temperature, schistosome sex, and the influence of the state of the canal on transmission, are briefly mentioned.