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Biomedical subjects

M S Ramasamy

Publications and source records attributed to M S Ramasamy.

13 recordsLinked to original sources
PubMed1995

Antibody and clinical responses in volunteers to immunization with malaria peptide-diptheria toxoid conjugates.

Twenty residue peptides from the 185-200-kD and 45-kD merozoite surface antigens of the malaria parasite Plasmodium falciparum were covalently linked to diphtheria toxoid as a carrier and used to immunize human volunteers with aluminium hydroxide as an adjuvant. Significant antibody levels were elicited by two boosting injections. The antibodies reacted with acetone-methanol fixed merozoite membranes in an immunofluorescence assay, but no inhibition of merozoite reinvasion could be detected in in vitro cultures containing the antibodies. Antibody levels against the immunizing peptides declined markedly within 77 days after the third injection. No hypersensitivity was observed against the peptides. However, the volunteers developed hypersensitivity against diphteria toxoid, and in particular a pronounced type III (Arthus) hypersensitivity after three injections with the toxoid. This effect might appear to limit the use of peptide-diphtheria toxoid conjugates for human immunization. Several biochemical, haematological and immunological tests done on the volunteers showed no other adverse effects from the immunizations.

Adolescent↗
PubMed1995

Dynamics of natural antibody responses to malaria parasite surface proteins in the intermediate rainfall zone of Sri Lanka.

Antibodies against repetitive epitopes on Plasmodium falciparum and P. vivax circumsporozoite (CS) proteins and epitopes on the 45 kDa and 185-200 kDa P. falciparum merozoite surface proteins were measured by radioimmunoassay in a two year longitudinal study in Nikawehera village located in the intermediate rainfall zone of Sri Lanka. The prevalence and concentrations of specific antibodies were in many, but not all instances, greater in adults than in children who were aged 7-15 yr at the beginning of the study. The concentrations and prevalence of antibodies were associated with malaria transmission levels previously determined from entomological and hospital admission data in the area. Antibody responses to epitopes on different P. falciparum antigens, two different epitopes within the 185-200 kDa merozoite surface protein and between the P. falciparum and P. vivax CS repeats were significantly correlated. Antibody concentrations against a conserved epitope in the 185-200 kDa protein were significantly higher in P. falciparum infected individuals than in non-parasitaemic subjects. Antibody concentration and prevalences in Nikawehera were lower than at Weheragala, a site located 70 km away in the dry zone of Sri Lanka. It is postulated that lower levels of immunity in the population in areas such as Nikawehera, that are adjacent to more highly malaria endemic areas, may promote epidemics when conditions favour transmission.

Adolescent↗
PubMed1994

Population dynamics of anthropophilic mosquitoes during the northeast monsoon season in the malaria epidemic zone of Sri Lanka.

Mosquito-borne diseases are a major health problem in Sri Lanka. Human biting mosquitoes were collected during the night (18.00-06.00 hours) at Nikawehera village, in the malaria endemic intermediate rainfall zone of the country. Collections were made at monthly intervals in the period October 1991 to April 1992, which included the main rainy season due to the northeast monsoon (October-January). Thirteen Anopheles, eleven Culex, three Aedes, three Mansonia and one Armigeres species were identified, including known vectors of malaria, Bancroftian filariasis, Japanese encephalitis and dengue fever. Mosquito human-biting rates were highest in December. The main malaria vector Anopheles culicifacies showed peak biting between 18.00 and 23.00 hours whereas the predominant culicines Culex fuscocephala and Cx quinquefasciatus preferred to bite after midnight. In 1991-92 the prevalence of some species of anophelines at Nikawehera differed markedly from that observed in 1990-91 and the possible reasons are discussed.

Animals↗
PubMed1994

Antibodies to epitopes on merozoite and sporozoite surface antigens as serologic markers of malaria transmission: studies at a site in the dry zone of Sri Lanka.

Antibodies against repetitive epitopes on Plasmodium falciparum and P. vivax circumsporozoite (CS) proteins and epitopes on the 45-kD and 185-200-kD P. falciparum merozoite surface antigens were measured by radioimmunoassay in Weheragala, a malaria-endemic site in the dry zone of Sri Lanka. Antibodies were measured in sera collected in February at the end of the main malaria transmission season and three months later in May during the low transmission period. Ninety-seven percent of the sample population had antibodies to the P. falciparum CS repeat in February and a significant proportion possessed antibodies directed against all epitopes tested. Concentrations and prevalence of antibodies to the CS repeats decreased with time after the end of malaria transmission in adults and children. Similar temporal changes were observed with antibodies to the epitopes on merozoite surface antigens. Children 7-15 years of age had lower antibody concentrations against most epitopes than adults. Antibody concentrations to two different epitopes within the same merozoite surface antigen showed significant association as did antibody levels against the P. falciparum CS repeat and the predominant P. vivax CS repeat. However, antibody concentrations did not correlate with the presence of blood-stage malaria infections.

Adolescent↗
PubMed1992

High seasonal malaria transmission rates in the intermediate rainfall zone of Sri Lanka.

Malaria transmission was studied at Nikawehera, a long-established farming village, located in the intermediate rainfall zone of Sri Lanka. Observations were made over a 12-month period (October-September) that included the main rainy season which occurred during the north-east monsoon in November-January. Anolpheles culicifacies, the recognized vector of malaria in Sri Lanka, was the predominant anopheline mosquito collected by human night baiting at Nikawehera. High entomological inoculation rates with An. culcifacies (0.12/hour for Plasmodium vivax) were observed during the height of the transmission season which occurs during, and immediately after, the north-east monsoon. Anolpheles subpictus was identified as a possible additional vector at Nikawehera. Anopheles annularis, a major vector at Weheragala, a site in a new irrigation development (the Mahaweli Scheme) located 70 km away in the dry zone, was not collected by human baiting at Nikawehera. Clinical, entomological and parasitological data suggest that malaria is hyperendemic at Nikawehera, with high seasonal transmission rates.

Adolescent↗
PubMed1992

Host immunity to mosquitoes: effect of antimosquito antibodies on Anopheles tessellatus and Culex quinquefasciatus (Diptera: Culicidae).

Rabbit antibodies to antigens derived from the tissues of sugar-fed Anopheles tessellatus Theobald were fed to An. tessellatus and Culex quinquefasciatus Say in blood meals. These antibodies tended to reduce the number of eggs produced by An. tessellatus, but had no effect on the fecundity of Cx. quinquefasciatus. Ingestion of the rabbit antibodies did not detectably affect the mortality of An. tessellatus but increased the mortality of Cx. quinquefasciatus. The results provide preliminary evidence for the potential of antimosquito antibodies to disrupt the physiology of mosquito vectors and indicate the need for further studies with high-titer, monospecific antibodies against the relevant target antigens.

Animals↗
PubMed1992

Malaria transmission at a new irrigation project in Sri Lanka: the emergence of Anopheles annularis as a major vector.

Malaria transmission was studied in a newly irrigated area of the Mahaweli project in the dry zone of Sri Lanka. Observations were performed for a three-month period following the northeast monsoon. Parasitemia in the population varied from 20.2% in February to 7% in May, and infection was due to both Plasmodium falciparum and P. vivax. Night catches of mosquitoes collected with human bait included a high proportion of Anopheles annularis. Mosquitoes containing sporozoites in the salivary glands were identified by an enzyme-linked immunosorbent assay. Anopheles culicifacies, An. annularis, and An. aconitus were all implicated as vectors in the area. The highest entomologic inoculation rate, 0.12 infected bites/hr, was observed with An. annularis and P. vivax in March. We suggest that a change in the ecosystem from dry zone forest to irrigated cultivated land is the cause of the increased prevalence of An. annularis in this area and its emergence as a major vector of malaria.

Adolescent↗
PubMed1992

Observations on malaria patients seeking treatment in hospitals in a rural and an urban area of Sri Lanka.

Malaria in Sri Lanka is endemic in the dry zone and occurs during epidemics in the wet zone. A survey was carried out on malaria patients presenting at a hospital located in a predominantly rural area in the dry zone (Polonnaruwa) and an urban area in the wet zone (Ragama). Higher incidence of Plasmodium falciparum infections than reported nationally were observed in both locations. Of particular interest is the rapidity with which patients gained access to hospital treatment after the onset of malaria symptoms. The observed mode is 3-6 days. It is postulated that early treatment may impair the development of clinical immunity to malaria in the Sri Lankan population.

Adolescent↗
PubMed1991

Antigenic similarity between the mosquito vectors of malaria and filariasis.

Rabbit antisera were raised to the malaria vector Anopheles tessellatus, head-thorax, abdomen, and midgut preparations. Reactivity of the antisera with An. tessellatus and the filariasis vector, Culex quinquefasciatus, were examined by enzyme-linked immunosorbent assay (ELISA) and Western blots. Although many antigens were shared between the two species of mosquitoes, tissue- and species-specific antigens also were identified.

Animals↗
PubMed1990

Anti-mosquito antibodies reduce the susceptibility of Aedes aegypti to arbovirus infection.

Aedes aegypti (L.) mosquitoes showed a significant reduction in susceptibility to infection with Ross River virus and Murray Valley encephalitis virus when they were fed on a blood-virus mixture containing rabbit antibodies to mosquito midgut components. Presence of the antibodies did not demonstrably affect virus titres in infected mosquitoes, nor the transmission of virus from infected mosquitoes to vertebrates.

Aedes↗
PubMed1990

Effect of anti-mosquito antibodies on the infectivity of the rodent malaria parasite Plasmodium berghei to Anopheles farauti.

The effect of mouse anti-mosquito antibodies, present in the bloodmeal, on the infectivity of Plasmodium berghei Vincke to Anopheles farauti Laveran was investigated. Significantly fewer oocysts developed in mosquitoes feeding on mice immunized with sugar-fed mosquito midgut antigens than in mosquitoes feeding on control mice. Mosquitoes feeding on mice immunized with the midgut antigens derived from sugar-fed mosquitoes also showed reduced mortality and had lower infection rates than those fed on unimmunized mice. Blood-fed midgut antigen was less effective in producing these effects than sugar-fed midgut antigen.

Animals↗
PubMed1988

Anti-mosquito antibodies decrease the reproductive capacity of Aedes aegypti.

Aedes aegypti (L.) fed on rabbits immunized with mosquito antigens showed a reduction in fecundity in the first oviposition and decreased viability of the progeny. Feeding behaviour of mosquitoes was not affected and no significant mortality was observed due to the presence of anti-mosquito antibodies in the bloodmeal. Antibodies were detected in the oocytes of mosquitoes 48 h after the bloodmeal. The role of specific antibodies in influencing fecundity is discussed.

Aedes↗