Biology of the Simian Malarias of Southeast Asia. III. Sporogony of the Cambodian Strain of Plasmodium cynomolgi

Abstract

The sporogony of the Cambodian strain of Plasmodium cynomolgi in six species of mosquitoes (Anopheles maculatus, A. kochi, A. philippinensis, A. vagus, A. letifer, and Mansonia uniformis) has been studied in detail. Sporozoites appeared in anopheline hosts as early as 7.5 days after infection. Evidence is presented to suggest that sporozoites undergo morphological changes with time after they reach the salivary glands. It is concluded that the minimum time required for maturation of oocysts, their size, and the time required for sporozoites to reach the salivary glands are factors controlled by the species and/or strain of the malaria parasite. The success of the oocysts in maturing and of the sporozoites reaching the salivary glands is apparently controlled by the species of mosquito. The number of recognized species of malaria parasites in Asian monkeys has greatly increased since 1958 (Eyles, 1963), making identification based on the morphology of the asexual stages of the parasites more and more difficult. Recently Bray (1963) employed such factors as the morphology of the exoerythrocytic stages and/or the effect of the parasite on Macaca mulatta Zimmerman to elevate Plasmodium cynomolgi bastianelli Garnham and P. cynomolgi cyclopis Inoki to specific rank. The taxonomy of simian malarias has largely depended on the morphology of the asexual stages in the blood of the vertebrate host but relatively little attention has been given to the study of sporogony in the invertebrate host. The staff of the Far East Research Project in Kuala Lumpur, Malaysia maintained several strains of Plasmodium cynomolgi Mayer and some of their experimental vectors. This situation provided the opportunity to make a comparative study of the sporogony of different strains of P. cynomolgi and to evaluate the differences found as to their possible taxonomic value. In this paper we will describe the Received for publication 28 January 1966. * Contribution from Far East Research Project, LPC, NIAID, National Institutes of Health, Kuala Lumpur, Malaysia. t Present address: Ontario Research Foundation, 43 Queen's Park Crescent East, Toronto 5, Canada. I Institute for Medical Research, Kuala Lumpur, Malaysia. 632 sporogony of the Cambodian strain of P. cynomolgi in five anopheline and one culicine host, giving particular attention to the pattern and rate of development of the parasite in the different species of mosquitoes. MATERIALS AND METHODS Rhesus monkeys (Macaca mulatta) imported from New Delhi, India, were used throughout the study. None of the large number of this species used in our laboratory has been found naturally infected with malaria parasites on their arrival from northwestern India. Confirmation of their uninfected status was obtained by the examination of one or more blood films prior to their use. Monkeys previously infected with parasites of malaria were also used. Such animals were treated with chloroquine and/or primaquine before their reuse. Sporogony was studied in six species of mosquitoes, Anopheles maculatus Theobald, A. kochi Donitz, A. philippinensis Ludlow, A. vagus Donitz, A. letifer Sandosham, and Mansonia uniformis Theobald. All of the mosquitoes used in the experimental feedings were reared in the laboratory with the exception of Mansonia uniformis. They were obtained as wild-caught adults from areas where no natural infections with malaria had been found. The infected monkeys were tranquilized and then exposed to the bites of uninfected mosquitoes. The fed mosquitoes were maintained in an insectary at 27 C and 80 to 90% relative humidity. Mosquito feedings were done at night; dissections were done in the morning. Thus the sporogonic development of the parasite was recorded on the half day, i.e., 8.5, 9.5, 10.5, etc. The Cambodian strain of P. cynomolgi was obtained from a naturally infected Macaca irus in Cambodia (Bennett and Warren, 1965) and maintained in Macaca mulatta by both sporozoite and This content downloaded from 207.46.13.111 on Sat, 21 May 2016 06:17:38 UTC All use subject to http://about.jstor.org/terms BENNETT ET AL.-SPOROGONY OF CAMBODIAN STRAIN OF PLASM. CYNOMOLGI 633