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Biomedical subjects

K N Mendis

Publications and source records attributed to K N Mendis.

At least 73 records · Page 4Linked to original sources
PubMed1988

Immunoelectron microscopy of Schüffner's dots in Plasmodium vivax-infected human erythrocytes.

Plasmodium vivax induces morphologic alterations in infected host erythrocytes that are visible by light microscopy in Romanovsky-stained blood smears as multiple brick-red dots. These morphologic changes, referred to as Schüffner's dots, are important in the identification of this species of malarial parasite and have been associated by electron microscopy with caveolavesicle complexes along the erythrocyte plasmalemma. We have produced a monoclonal antibody (MAb A 20) that identifies an antigen in Plasmodium vivax-infected erythrocytes that is associated with the caveola-vesicle complexes of the parasitized host cell. This monoclonal antibody reacts with air-dried P vivax-infected erythrocytes to produce a pattern by the indirect immunofluorescence test (IFT) that is evocative of Schüffner's dots. Immunoelectron microscopy of P vivax-infected human erythrocytes using MAb A 20 confirmed the location of this antigen within vesicles of caveola-vesicle complexes. On Western blots MAb A 20 recognized four polypeptides of 54, 64, 72, and 86 kd. MAb A 20 reacted by IFT with 90% of Sri Lankan isolates and with a Brazilian P vivax isolate, which indicates that the epitope identified by this monoclonal is conserved.

Animals↗
PubMed1987

Antigenic variation of cloned Plasmodium fragile in its natural host Macaca sinica. Sequential appearance of successive variant antigenic types.

The course of infection of Plasmodium fragile in its natural host, the toque monkey Macaca sinica, consists of a primary peak of parasitemia followed by several distinct, successive peaks of lower parasitemia. In the S+ host, the late intraerythrocytic asexual developmental stages of P. fragile induce the expression of antigens on the surface of infected erythrocytes, which could be detected using the technique of surface immunofluorescence. Immunofluorescence using unfixed erythrocytes in suspension has shown that antigens are recognized by immune serum on the surface of the erythrocytes infected with more mature stages of the parasite. These antigens undergo variation, each successive peak of parasitemia being characterized by a different variant antigenic type (VAT). The appearance of the successive VATs occurs in a sequential manner, following the same order in different sets of animals. This constitutes the first example of a sequential expression of antigens in a malaria parasite; it indicates that, in P. fragile, antigenic variation is not the result of random mutations selected by antibody. Parasite-induced antigens on the surface of infected erythrocytes could not be detected in the S- host. However, when nonexpressing parasites from the S- host were transferred by blood passage into a naive S+ animal, they began to express antigens on the surface of infected erythrocytes within two erythrocytic cycles. We have demonstrated that the ability of S- parasites to switch to a particular VAT when passaged into a S+ animal changes during the course of an infection in the S- animal, indicating that, although surface antigens are not expressed, the processes leading to antigenic variation occurs even in the S- host. Antibodies directed against these surface antigens inhibit the growth of intra-erythrocytic parasites. The growth inhibition effects of antibodies are also variant specific, indicating that these variant surface antigens are functionally important for parasite survival.

Animals↗
PubMed1987

A metropolitan hospital in a non-endemic area provides a sampling pool for epidemiological studies on vivax malaria in Sri Lanka.

An analysis of records of 494 malaria patients admitted to the General Hospital in Colombo (the capital of Sri Lanka where malaria transmission is not known to occur) from 1981 to 1984 is presented and compared with national malaria data from the entire country. The incidence of predominantly Plasmodium vivax malaria rose sharply over the 3 years; its species distribution and seasonal variation in patients in the General Hospital, Colombo (GHC) generally reflected the disease pattern in the country as a whole. The disease had spread from mainly the endemic dry zone to the non-endemic wet zone. Malaria patients at the GHC were mainly residents of Colombo who had acquired malaria during brief visits to endemic areas, and we have demonstrated how information from them can be used as a sampling method to obtain almost immediate epidemiological information from the whole country. Based on the histories of selected patients we deduced the incubation periods and possible relapse patterns of P. vivax infections in Sri Lanka. This study also provided an insight to the epidemiology of the disease in the city.

Animals↗
PubMed1987

Plasmodium vivax: isolation of mature asexual stages and gametocytes from infected human blood by colloidal silica (Percoll) gradient centrifugation.

The densities of human erythrocytes infected with P. vivax obtained from infected patients were determined by isopycnic centrifugation in continuous gradients of Percoll. The approximate densities of erythrocytes infected with rings were 1.086 to 1.1, trophozoites (amoeboid stages) 1.053 to 1.086, schizonts and gametocytes 1.053 to 1.056 and of the other cellular elements of blood, uninfected erythrocytes, 1.086 to 1.1, polymorphonuclear leucocytes 1.073 to 1.086 and mononuclear cells 1.062 to 1.073 g/ml. Based on these values, a one-step gradient of 47% Percoll was devised to separate erythrocytes infected with the more mature stages (trophozoites, schizonts and gametocytes) from uninfected erythrocytes. By this method it is possible to obtain parasitaemias of 88% to 98% from blood with starting parasitaemias of less than 0.7%. This method is therefore being routinely used for immunological, biochemical and molecular biological studies on P. vivax.

Animals↗
PubMed1987

Demonstration of antigenic polymorphism in Plasmodium vivax malaria with a panel of 30 monoclonal antibodies.

A panel of 30 monoclonal antibodies was established against asexual erythrocytic stages of Plasmodium vivax and used to investigate the antigenic composition of the parasite. At least 38 different antigenic polypeptides of P. vivax were characterized by the Western blot technique. The possible location of these antigens, as well as their stage and species specificity, was determined on the basis of the staining patterns produced by these antibodies on air-dried parasites in the indirect immunofluorescence test. Immunofluorescence performed with 30 different monoclonal antibodies on 50 different isolates of P. vivax obtained from patients showed that a high level of antigenic polymorphism prevailed in P. vivax. Only six monoclonal antibodies reacted with epitopes that were represented in more than 80% of parasite isolates, and therefore, appeared to be relatively conserved among different isolates. The other 24 monoclonal antibodies reacted with only 20 to 70% of parasite isolates.

Animals↗
PubMed1987

Malaria transmission-blocking immunity induced by natural infections of Plasmodium vivax in humans.

Immunity to malarial infections in human populations is known to affect the development of the asexual blood stages of the parasites in the human host and to be capable of conferring significant protection against morbidity and mortality due to the disease. In this study we show that during acute infection with Plasmodium vivax malaria, one of the two main malarial pathogens of humans, most individuals also develop immunity that suppresses the infectivity of the sexual stages of the parasite to mosquitoes. The immunity is antibody mediated and is directed against the parasites in the mosquito midgut shortly after ingestion of blood by a mosquito. This immunity could be expected to have significant effects on the natural transmission of P. vivax malaria.

Animals↗
PubMed1986

Anti-gamete antibodies block transmission of human vivax malaria to mosquitoes.

Antibodies were raised in rabbits by immunizing against fresh unfixed or cryopreserved female gametes of the human malaria pathogen Plasmodium vivax. The antibodies were shown to react with the surface of gametes by the indirect immunofluorescent test. When parasite isolates from P. vivax infected individuals were fed through a membrane to Anopheles tessellatus mosquitoes in the presence of immune rabbit sera, they completely blocked the infectivity of the parasite isolates to the vector. Immunoglobulins separated from these sera also blocked infectivity to the same extent as did the immune sera indicating that antibodies were responsible for the transmission blocking effect of the sera. This study indicated that P. vivax like other malaria parasites is highly susceptible to anti gamete transmission blocking immunity.

Animals↗
PubMed1983

Immunity to malarial antigens on the surface of Plasmodium falciparum-infected erythrocytes.

An indirect immunofluorescence test with fresh non-fixed infected blood as antigen was used to show that antibody in human sera from the Gambia recognized antigens on the surface of Plasmodium falciparum-infected human erythrocytes. Surface immunofluorescence was detected on 90% of erythrocytes infected with trophozoites and schizonts produced in continuous culture of isolates from the Gambia (FCR 3/K+), Brazil and Thailand. Fluorescence was equally strong with a Gambian parasite clone (FCR 3/K-) that lacked knobs, an ultrastructural modification of the erythrocyte membrane associated with parasite sequestration. Immunofluorescence could not be detected with an isolate from Uganda. The surface antigenicity of parasitized erythrocytes was eliminated by chymotrypsin and trypsin treatment. Fluorescence was specific for the surface of trophozoite- and schizont-infected cells on the condition that fresh erythrocytes were added to cultures every 4-5 days (subculture); if fresh erythrocytes were not added for over 2 weeks, a large percentage of non-infected erythrocytes also bound antibody. Normal erythrocytes incubated with media from these cultures also gave positive surface immunofluorescence. Thus, there are two types of antigenicity on erythrocytes: one expressed on infected erythrocytes and another passively absorbed from media to normal erythrocytes when parasites are not subcultured for long periods.

Absorption↗
PubMed1982

Congenital malaria due to Plasmodium vivax: a case report from Sri Lanka.

A case of Plasmodium vivax malaria in an eight-week-old infant in Colombo is documented, with epidemiological and circumstantial evidence which strongly supports a transplacental route of infection. The malarial antibody levels detected by the indirect fluorescent antibody technique in both mother and child are discussed in terms of the present epidemiological pattern of malaria in the country. We also comment on the species incidence of congenital malaria, this case being the first caused by P. vivax in Sri Lanka, despite this species being more prevalent than P. falciparum which has been reported in six previous cases of congenital malaria in Sri Lanka.

Antibodies↗
PubMed1982

Vaccination to prevent transmission of Plasmodium yoelii malaria.

It was possible to block the transmission of infection of the rodent malaria parasite Plasmodium yoelii nigeriensis to Anopheles stephensi mosquitoes by immunizing mice with a vaccine containing formalin-fixed gametes. Both intramuscular and intravenous routes were effective, immunity was achieved with a single dose and the immunity persisted for 6 months at least. Transmission-blocking immunity was found to reside in a serum factor, probably antibody, and to be directed against extracellular gametes, acting on them in the gut of the mosquito, while gametocytes in the circulation of the vertebrate host remained unaffected. The gamete vaccine afforded partial protection against the disease, but immunization with asexual parasites alone showed that this protection was due largely to the presence of asexual forms as contaminants and that anti-gamete immunity is stage specific.

Animals↗
PubMed1978

Filarial infection of the breast.

The breast is a common site of filarial infection in females in Sri Lanka. We report our experience with 13 cases of filarial breast nodules, 12 containing adult worms and the other only microfilariae. In five of these cases the species was identified as Wuchereria bancrofti.

Adult↗
PubMed1977

Enterobius vermicularis in ectopic sites.

We document six cases in which tissues were invaded by Enterobius vermicularis. These cases illustrate several mechanisms whereby the worms form granulomata in ectopic sites. In three cases, the worms passed through pre-existing breaches in the intestinal mucosa. In one case, a gravid worm migrated via the female genital tract to ther peritoneal cavity. In two other cases, male worms were found on the outer surface of the intestine, suggesting active penetration of the intestinal wall.

Adult↗
PubMedDate not supplied

Infectivity of Plasmodium vivax and P. falciparum to Anopheles tessellatus; relationship between oocyst and sporozoite development.

The assessment of malarial infectivity, for example in the evaluation of transmission blocking immunity, is generally based on counting oocysts in mosquitoes fed on infected blood. Ultimate transmission of the disease may, however, depend on the sporozoite load in the mosquito and its relationship to the size of the inoculum introduced to man. We conducted a laboratory study on Anopheles tessellatus infected with 108 different natural isolates of Plasmodium vivax from patients and 24 of P. falciparum to determine the relationship between oocyst numbers, sporozoite loads, and the effect of these on mosquito mortality. It was found that the P. vivax parasite density was positively correlated with the proportion of mosquitoes infected by a given feed at both the midgut and gland stages of parasite development (correlation coefficient [r] = 0.77, P < 0.001 and r = 0.6, P < 0.05 respectively). A significant positive linear correlation was observed between the number of oocysts and sporozoites in P. vivax (r = 0.5; P < 0.05); the proportions of mosquitoes infected with oocysts and sporozoites were also similarly related, although in general about 15% of mosquitoes infected with oocysts failed to develop salivary gland infections with sporozoites. The number of mosquitoes infected with P. falciparum parasites was too low for statistical analysis. Infection with either species of parasite did not appear to affect mosquito survival, nor was parasite density in the mosquito correlated with mosquito mortality.

Animals↗
PubMedDate not supplied

Cognitive performance at school entry of children living in malaria-endemic areas of Sri Lanka.

In a cross-sectional study, carried out in January 1997 at the beginning of the school year, the impact of repeated attacks of malarial infection on the cognitive performance of children at school entry in moderate malaria-endemic areas of Sri Lanka was investigated. The cognitive performance of 325 schoolchildren in grade 1 (mostly aged 5-6 years) in 2 districts of Sri Lanka which are endemic for malaria (Anuradhapura and Moneragala) was assessed by an entry performance test developed by the National Institute of Education, Sri Lanka. The indices assessed included writing, language and mathematical skills. There was no difference in any of the cognitive performance indices between children from Anuradhapura and Moneragala districts. The scores of most of the indices decreased as the number of malaria infections experienced by a child increased and the ability to identify letters was significantly impaired by the number of malaria infections a child had experienced after controlling for socio-economic and nutritional status. These findings suggests that repeated attacks of malaria in children can have an adverse impact on their development.

Child↗
PubMedDate not supplied

Features of recrudescent chloroquine-resistant Plasmodium falciparum infections confer a survival advantage on parasites and have implications for disease control.

This paper reports on the features of recrudescent infections of chloroquine-resistant Plasmodium falciparum (CQRPf) malaria from a study in vivo of patients from a malaria endemic (n = 527) and non-endemic (n = 129) region of Sri Lanka where the incidence of RI resistance was 30% and 55%, respectively. In both groups of patients, the recrudescent infections which emerged after treatment of the primary infection with chloroquine (CQ) and primaquine had significantly lower peripheral parasitaemia (0.036% and 0.108% in endemic and non-endemic patients, respectively) compared to their primary infections (mean parasitaemia 0.13% and 0.49%; P = 0.021 and 0.002, respectively). The recrudescences of CQ resistant infections also gave rise to clinical disease of markedly reduced severity (average clinical scores of 10.1 and 8.2) compared to their primary infections (average clinical scores of 12.4 and 12.3; P = 0.003 and 0.001, respectively, in endemic and non-endemic patients). CQ resistant recrudescent infections therefore had a lower probability of being diagnosed and treated. In endemic patients, a higher proportion of CQRPf infections (57%) had gametocytaemia compared to the chloroquine sensitive ones (29%) (P = 0.014, chi 2 = 5.96) and were significantly more infective to mosquitoes (P = 0.047). these findings imply that, in areas where CQ resistance is prevalent, the continued use of the drug may confer a survival and propagation advantage on resistant parasites and favour the rapid expansion of their reservoir. In support of this, we also present epidemiological evidence showing that, in endemic areas, the proportion of P. falciparum patients carrying gametocytes has increased significantly since the emergence of chloroquine resistance. These findings are relevant to the management of drug resistance and malaria control in countries where P.falciparum is only partially resistant to CQ.

Adolescent↗