Studies on Human Malaria in Aotus Monkeys. I. Sporozoite Transmission of Plasmodium vivax from El Salvador

Abstract

Monkey-to-monkey transmission of a strain of Plasmodium vivax from El Salvador was obtained on 12 occasions via the bites or intrahepatic and/or intravenous inoculation of infected salivary glands from Anopheles freeborni, A. albimanus, A. maculatus, and A. balabacensis balabacensis mosquitoes. The prepatent periods ranged from 14 to 48 days. The mean prepatent period was 34 days in intact monkeys and 29 days in splenectomized animals. The transmission rate was approximately the same in intact (57%) and splenectomized (53%) monkeys. Since Porter and Young (1966) reported the successful infection of Aotus trivirgatus monkeys with Plasmodium vivax from Panama, there has been a great deal of interest in the use of these animals as biological models for many different malarial studies. Young et al. (1966) and Porter and Young (1966) reported the successful transmission of P. vivax from the owl monkey to man via the bites of Anopheles albimanus mosquitoes. Subsequently, Baerg et al. (1969) reported transmission of P. vivax from A. trivirgatus and Ateles fusiceps to A. fusiceps, A. trivirgatus, and Saguinus geoffroyi via the bites of A. albimanus mosquitoes. Ward et al. (1969) showed that the Chesson strain of P. vivax could be transmitted with relative ease to A. trivirgatus monkeys via the bites of A. balabacensis balabacensis, A. stephensi, and A. quadrimaculatus mosquitoes. Since 1966, we have studied a number of different isolates of the human malarias in Aotus monkeys. This paper, the first of a series, reports the results of attempts to transmit a strain of P. vivax from El Salvador from monkey to monkey by sporozoite inoculation. MATERIALS AND METHODS The Sal II strain of P. vivax was isolated from a natural infection in the area of Las Guarumas, in the state of La Paz, El Salvador. Blood was inoculated into an A. trivirgatus monkey (AO-219) which was then provided to us by the staff of the Central America Malaria Research Station, CDC, San Salvador. The strain has been maintained by Received for publication 9 March 1973. * Center for Disease Control, Malaria Program, 1600 Clifton Road, Atlanta, Georgia 30333. serial blood or sporozoite passage in A. trivirgatus monkeys. The A. trivirgatus monkeys were obtained commercially, their origin being Colombia, South America. Prior parasitologic and serologic examinations indicated that they were free of natural malarial infection. Some of the animals were splenectomized prior to infection according to the technique of Sodeman et al. (1970). The A. freeborni mosquitoes were originally from Marysville, California, and have been maintained in the laboratory since 1944. The A. maculatts were obtained from the Institute for Medical Research, Kuala Lumpur, Malaysia, in 1964 and have been maintained in our laboratory since then. The A. balabacensis balabacensis colony was originally from Thailand and was obtained from the Walter Reed Army Institute of Research. The A. albimanus were the Apastepeque strain from El Salvador and obtained from CAMRS, San Salvador, in 1971. For the transmission attempts, sporozoites were introduced either by the bites of infected mosquitoes or by the intrahepatic and/or intravenous inoculation of sporozoites from dissected salivary glands. The technique for the intrahepatic inoculation has been reported previously (Held et al., 1967; Sodeman et al., 1969). For the transmission attempts by mosquito bite, mosquitoes were individually caged and allowed to feed on the restrained monkey. After biting, the mosquitoes were dissected and the salivary glands examined for the presence of sporozoites. The gland infections were graded 1+ (1 to 10 sporozoites), 2+ (11 to 100 porozoites), 3+ (101 to 1,000 sporozoites), or 4+ (greater than 1,000 sporozoites). Daily blood smears were made beginning 7 days after sporozoite inoculation to determine the prepatent period. Blood smears were stained with Giemsa.