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The aim of this study was to evaluate the relationship among age, parasitemia status, spleen size, hematocrit, and antibody levels to Plasmodium vivax merozoite surface protein 1 (MSP1) in individuals chronically exposed to P. vivax. Subjects were recruited from the population of three adjacent villages on the Island of Flores in Indonesia where malaria transmission is hyperendemic and tropical splenomegaly syndrome is highly prevalent. Subjects were evaluated for spleen size, hematocrit, presence of parasitemia, and presence of antibodies to a recombinant peptide consisting of 90 amino acids from the carboxy terminus of MSP1. Fifty-seven percent of 2-4 year olds, 45% of 5-9 years old, and 7% of > or = 15 years old were parasitemic; 99% of the > or = 15 years old had splenomegaly, and 31% of them had Hackett 4 or 5 spleens. The frequency of antibody positivity to MSP1 antigen in ELISA increased with age reaching a maximum of 89% in > or = 20 years old. The frequency of antibody positivity to MSPI also increased with spleen size, and with a decline in the prevalence of parasitemia.

Wild and domestic animals trapped from forests, villages, and rice fields in South Kalimantan (3 degrees 20' S, 115 degrees 02' E, 25 m) were examined for blood parasites using Giemsa stained thick and thin blood films and Nuclepore filter preparations of peripheral vein and heart puncture blood. Presbytis cristatus (silvered leaf monkey) (25%) and Felis catus (domestic cat) (7%) were infected with Brugia malayi and B. pahangi. In addition, P. cristatus was infected with Wuchereria kalimantani (35%); Cardiofilaria sp. (1%) and Dirofilaria sp. (1%). Microfilariae of Cardiofilaria were also recovered from Callosciurus notatus (squirrel), Pitta sordida (bird), Pycnonotus goiavier (bird) and Gallus gallus (bird). Paradoxurus hermaphroditus (civet) and Muntiacus muncak (barking deer), were positive for Dirofilaria sp. Bos indicus (cow) for Onchocerca sp. and Nectarinia jugularis (bird) for Splendidofilaria sp. Plasmodium coatneyi was found in 22% of the P. cristatus examined. Plasmodium sp. was also recovered from Zaocys fuscus and Ahaetulla prasina (reptile); Muscicapa sp. Lonchura malacca, Orthotomus sericeus, Rhipidura javanica, Treron vernans, Pycnonotus melanoleucus and G. gallus (bird). In addition 39% of the Cynopterus brachyotis and 29% of C. horsfieldi (fruit bats) were infected with Hepatocystis pteropi. A single G. gallus was infected with Leucocytozoon sabrazesi and another with Trypanosoma sp.