Research

Infectious reservoir of Plasmodium infection in Mae Hong Son Province, north-west Thailand

Aree Pethleart^1,2 , Somsak Prajakwong³ , Wannapa Suwonkerd³ , Boontawee Corthong⁴ , Roger Webber¹ and Christopher Curtis¹

¹  London School of Hygiene and Tropical Medicine, London, WC1E 7HT, UK

²  Faculty of Medicine, Thammasat University, Pathumtani 12120, Thailand

³  Vector Borne Disease Section, Office of Disease Prevention and Control No.10, Chiang Mai, 52000, Thailand

⁴  Vector-borne Disease Control Unit No.8, Mae Hong Son Province, Thailand

author email corresponding author email

Malaria Journal 2004, 3:34doi:10.1186/1475-2875-3-34

Published:	22 September 2004

Abstract

Background

It was unknown whether the main reservoir of Plasmodium falciparum and Plasmodium vivax, which infects mosquitoes in Thailand, was (a) in people feeling sufficiently ill with malaria to come to a clinic or (b) in people who had remained in their home villages with some fever symptoms or with none.

Methods

Mass surveys were carried out in Thai villages to identify people with Plasmodium infections and with fever. Malaria patients were also located at a clinic which served these villages. Adults from both sources whose blood slides registered positive for Plasmodium spp. were requested to allow laboratory-bred Anopheles minimus to feed on them. Seven to nine days after the blood feeds the mosquitoes were dissected and checked for presence of oocysts.

Results and Discussion

There were higher rates of Plasmodium infection among people in the villages with fever than without fever and much higher rates of infection among clinic patients than among people who had remained in the villages. People with malarial infections identified via the clinic and the village surveys could infect mosquitoes, especially, but not only, if their blood slides showed visible gametocytes. Because only a very small minority of the village populations were visiting the clinic on any one day, assessment indicated that the main reservoir of infection was not primarily among clinic patients but among those in the villages, especially those feeling feverish.

Conclusions

Efficient use of an anti-gametocyte drug to suppress the parasite reservoir in a population requires that it be given, not just to clinic patients, but to infected people located by mass surveys of the villages, especially those feeling feverish.