Pathological Study of Blood Parasites in Rice Field Frogs, Hoplobatrachus rugulosus (Wiegmann, 1834).

One hundred and forty adult rice field frogs, Hoplobatrachus rugulosus (Wiegmann, 1834), were collected in Srakaew province, Thailand. For blood parasite examination, thin blood smears were made and routinely stained with Giemsa. The results showed that 70% of the frogs (98/140) were infected with 5 species of blood parasites, including a Trypanosoma rotatorium-like organism, Trypanosoma chattoni, Hepatozoon sp.

The variation of Pf155/RESA gene in field isolates of Plasmodium falciparum from Thailand.

Pf155/RESA, an antigen found on the surface of Plasmodium falciparum red blood cell membrane was once a proposed malarial vaccine candidate. The complete sequence of Pf155/RESA gene from one strain and partial sequence from two other isolates revealed that the gene is well conserved. But polymorphism of other antigenic encoded regions occurs with high frequency among isolates especially those collected from the field.

Trials to infect Anopheles stephensi with Plasmodium yoelii nigeriensis by the membrane feeding technique.

The aim of this study was to find optimal conditions for the membrane feeding technique to obtain maximum infection rates of mosquitoes with Plasmodium yoelii nigeriensis. The results show that the malaria parasite Plasmodium yoelii nigeriensis is most infective to Anopheles stephensi mosquitoes on day 3 of the infection in the mice, 1 day before the peak of parasitaemia. The mortality rate of the mosquitoes fed on mice on day 3 after infection was the highest as compared to mosquitoes fed on other days after infection.

A new model for testing gametocytocidal effects of some antimalarial drugs on Plasmodium falciparum in vitro.

A technique is described for obtaining pure gametocyte cultures of Plasmodium falciparum, using pyrimethamine at the minimum concentration for inhibition of asexual parasites. Routine cultures producing sexual stages were exposed to pyrimethamine on days 5 and 6. These cultures grew synchronously and contained gametocytes of stages II, III and V on day 7, 9 and 15 of the cultures respectively.

Plasmodium falciparum: effect of chloroquine, halofantrine and pyrimethamine on the infectivity of gametocytes for Anopheles stephensi mosquitoes.

The activity of chloroquine, halofantrine and pyrimethamine against the gametocytes and sporogonic stages of Plasmodium falciparum (strain NF54) was tested. Five-day-old gametocytes (stages I and II) from in vitro cultures were exposed to the drugs for 48 hours. The effect of the drugs on gametocyte development was assessed by counting gametocytes on days nine and 15 of culture and determining the infectivity of the drug-treated gametocytes to mosquitoes.

Variability in drug susceptibility amongst clones and isolates of Plasmodium falciparum.

Heterogeneity within isolates of Plasmodium falciparum in regard to drug susceptibility is described from studies with three Thai isolates and some clones derived from them. One isolate (T9), which before cloning was resistant in vitro to chloroquine and pyrimethamine, contained a diverse assortment of clones, some of which were sensitive to one or other, or both, of these drugs. Another isolate (CH150) was initially sensitive to mefloquine in vitro, but, on recrudescence of infection in the patient, developed a number of clones all of which had diminished susceptibility to mefloquine.

Susceptibility of Plasmodium falciparum to five drugs: an in vitro study of isolates mainly from Thailand.

This paper describes the results of testing the susceptibility of 60 isolates of the human malaria parasite Plasmodium falciparum from Thailand, and single isolates from five other countries, to five drugs: chloroquine, pyrimethamine, quinine, mefloquine and amodiaquine. The Thai isolates were obtained from patients in three different regions of the country (Chantaburi, Songkhla and Mae Sod), and were first grown in culture by the Trager-Jensen candle-jar technique. Samples were then exposed to a range of concentrations of the five drugs, in Falcon microtest culture wells, for 72 hours, with daily changes of medium (with or without added drug solutions).