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Biomedical subjects

R G Andre

Publications and source records attributed to R G Andre.

28 records · Page 2Linked to original sources
PubMed1985

Identification of Plasmodium vivax sporozoites in mosquitoes using an enzyme-linked immunosorbent assay.

A sandwich enzyme-linked immunosorbent assay (ELISA) for identifying Plasmodium vivax sporozoites in mosquitoes is described. Monoclonal antibodies produced against Thailand P. vivax sporozoites were used in an ELISA to detect and identify homologous sporozoites of Southeast Asian, Mexican and North Korean origin in extracts of frozen or dried infected mosquitoes. The assay was sensitive enough to detect 1 infected mosquito in a pool of 20 insects or 125-250 sporozoites per 30 microliter of mosquito extract. The use of a nonionic detergent and a single freeze-thaw to disrupt the circumsporozoite antigen significantly increased the sensitivity of the method.

Animals↗
PubMed1984

Cytogenetic studies of some species complexes of Anopheles in Thailand and Southeast Asia.

Recent studies on cytogenetics, behavioral, geographical and distinct morphological characters on adult, pupal and larval stages have revealed that "balabacensis" is a species complex. Anopheles dirus the mainland species, is distributed widely in Thailand and is renowned for its role as primary vector of human malarial parasites. Further, evidence from cytogenetic and taxonomic studies suggests that "An. dirus" is a species complex comprising at least four distinct species provisionally designated: dirus A, B, C and D. These cryptic species are distinguishable only partially morphologically, but can be separated on the basis of metaphase chromosomes using the Giemsa and Hoechst 33258 staining techniques. Apparently, these siblings show distinct patterns of geographic distribution in Thailand and Peninsular Malaysia. The recognition of dirus as a complex of species in Thailand and Peninsular Malaysia requires a re-evaluation of the role that the individual members of this complex have in the transmission of malaria parasites in this region. Cytological analysis of gene rearrangements in ovarian polytene chromosomes has shown that An. maculatus is a sibling-species complex consisting of at least four species in Thailand provisionally designated: maculatus A, B, C and G. These siblings are sympatric in some populations. Furthermore, species B is so highly polymorphic for chromosome rearrangements that four geographic forms can be recognized. It is not known whether these four forms are subspecies or yet further species within the species B complex. These sibling-species must be differentiated in order to understand any differential capabilities in their transmission of human malaria parasites. Anopheles nivipes was elevated from synonymy under An. philippinensis to full species status by Reid, a decision recently confirmed by cross mating experiments. The Thailand Malaria Division does not differentiate these two species and only identifies An. philippinensis, yet, An. nivipes is by far the most common of the two species in Thailand. Furthermore, preliminary surveys of the ovarian polytene chromosomes of several widely separated populations of An. nivipes in Thailand have revealed at least two distinct chromosomal types of nivipes based on fixed inversions on the X chromosomes.

Animals↗
PubMed1984

Sporozoite-induced Plasmodium cynomolgi infections in captive born Macaca fascicularis.

Capability of captive born cynomolgus monkeys to substitute for rhesus in the Plasmodium cynomolgi radical curative antimalarial drug development model was examined. Eighteen monkeys divided into 3 groups were given standard or high doses of sporozoites intravenously. One group of 4 received 0.8 - 1.6 X 10(6) and a second group of 8 received 0.3 - 1.0 X 10(7) sporozoites. The third group of 6 was splenectomized and then received 3.0 - 4.0 X 10(6). The 2 groups of intact monkeys developed a persistent low level parasitemia; however, gametocyte production was poor. The splenectomized group developed a persistent parasitemia with a higher mean, which more closely resembled rhesus parasitemias. A high, post-patent leukocytosis consisting primarily of lymphocytes was observed in this group. Good gametocyte production resulted in the splenectomized group and oocysts were produced from all lots of Anopheles dirus which fed on them. Following clearance of blood forms, relapse potential was demonstrated in the 2 splenectomized monkeys tested. In this study the splenectomized captive born cynomolgus appeared to be capable of supplementing rhesus as an antimalarial drug testing model.

Animals↗
PubMed1981

Rickettsia tsutsugamushi strains found in chiggers collected in Thailand.

R. tsutsugamushi strains found in chiggers collected from 3 different sites throughout Thailand were antigenically characterized. Monotypic infections were observed in 76.7% of the chiggers. Karp was the most predominant strain, followed by TA716, TA763, TA686 and Kato. This study represents the first confirmed report of R. tsutsugamushi infection in 8 different chigger species in Thailand.

Animals↗
PubMed1979

Treatment of vivax malaria with sulfadoxine-pyrimethamine and with pyrimethamine alone.

The effect of pyrimethamine and the combination of pyrimethamine-sulfadoxine (Fansidar) upon the termination of the acute attack of vivax malaria was studied in Thailand. Pyrimethamine was found to be ineffective, providing clearance of parasitaemia in only two of six patients by the end of seven days following treatment. The combination, administered in a two-tablet single dose (sulfadoxine 1 gm, pyrimethamine 50 mg) eliminated parasitaemia in only six of ten patients within seven days. Three tablets (sulfadoxine 1 . 5 gm, pyrimethamine 75 mg) given to 11 patients, provided clearance of parasitaemia in all within seven days; however, mean parasite and fever clearance times in this group were prolonged at 90 and 50 hours respectively. Chloroquine remains the drug of choice for the termination of the acute attack of vivax malaria. Subsequent primaquine is necessary for the prevention of relapse.

Acute Disease↗
PubMedDate not supplied

A stable, oligosymptomatic malaria focus in Thailand.

Blood from most of the 250 residents of a non-migratory farming village in south-eastern Thailand was visually examined for malaria parasites monthly for 2 years. Nearly 97% of the population had at least one (median = 5) patent Plasmodium falciparum infection per year; 72% had one due to P. vivax (median = 1). This contrasted with a slide positivity rate of 17% calculated from 12 months of passive case detection before the study began. Children 1-9 years old had the highest mean monthly prevalence (51%) and highest geometric mean density (10/500 white blood cells) of P. falciparum. Fewer than half the expected number of mixed infections were found but these were more common at high densities of P. falciparum. Individuals over 19 years old comprised 52% of the population but accounted for only 18% of P. vivax and 32% of P. falciparum gametocytaemias. Fever rates were marginally higher in those below 10 years old (8%) but occurred with equal frequency in those with patent infections or negative. The spleen rate (89% stage 1) was 24% in those under 15 years old and 7% in those older. No malaria mortality was seen P. falciparum cases treated for 10 d with quinine+tetracycline (QT) cleared the infection as often as those given one dose of mefloquine+sulfadoxine+pyrimethamine (MSP); both treatments reduced densities in cases not cured. Apparently unsupervised compliance was no better with MSP than with QT. The role played by hyperendemic, cryptic foci in Asian epidemics of malaria may have been underestimated.

Age Factors↗
PubMedDate not supplied

Highly efficient dry season transmission of malaria in Thailand.

Man-biting collections were made for 7 consecutive nights per month for 24 months at 2 sites in a Thai village regularly treated with DDT and fenitrothion yet hyperendemic for Plasmodium falciparum and P. vivax. Only Anopheles dirus was incriminated as a vector: 1.6% were infective and 2.4% were infected (median numbers of oocysts = 3.5). Transmission occurred within the village, which was located in groves of rubber and fruit trees, during the dry months of November to May only, when rates of parity (64%) and biting (2/man-night) were higher than during the monsoon (38% and 0.8%/man-night). Vectorial capacity and inoculation rates surged and then fell during 30 d at the end of the monsoon, quickly reinitiating transmission. Sporozoite species were identified using indirect fluorescent antibody tests or enzyme-linked immunosorbent assays: 76% were P. falciparum, compared to 78% of gametocytes; one mosquito was infected with both species. Vector survival and inoculation rates differed between similar sites 800 m apart. Dry season breeding occurred at the bottom of a deep, concrete-lined well. Much of the natural forest habitat of An. dirus in south-eastern Thailand that was once destroyed for farming is now being replaced with orchards; this ecological change may reintroduce malaria to a wide area.

Animals↗
PubMedDate not supplied

Seasonal fluctuation of Plasmodium falciparum gametocytaemia.

Two numerically minor components of Plasmodium falciparum prevalence--gametocytaemia and trophozoite densities greater than 99/500 white blood cells--displayed an annual cycle that reflected the seasonal abundance of infective Anopheles dirus at a hyperendemic focus in Thailand, even though the gross monthly prevalence for combined ages remained stable. Gametocyte prevalence rose more than 300% within 30 d after the capture of the dry season's first infective mosquito, remained at about 8% until the beginning of the monsoon 7 months later, then fell within 60 d to about 2%. The number of cases with a high density of trophozoites behaved similarly. These periodic fluctuations represented changes in incidence, at least half of which appeared to be due to superinfection. Almost 49% of all gametocyte carriers were older than 14 years, but nearly all gametocyte densities greater than 20/500 white blood cells were in children. These observations, as well as the calculated efficiency of human infectivity, imply that superinfection of adults may contribute significantly to transmission in semi-immune populations.

Animals↗