An immunohistochemical assay was developed combining an avidin-biotin-glucose oxidase complex procedure (ABC-GO) with light microscopy to detect specific antibody against Plasmodium falciparum. Thin blood films were prepared from culture material of P. falciparum and fixed with acetone. Antibody was detected by successive incubations with test serum, biotinylated goat antihuman antibody, avidin-biotin-glucose oxidase complex, and glucose oxidase substrate. In the presence of reactive serum, a blue precipitate formed on the parasites and could be visually observed with a 40x objective. Sera from patients with single infections for P. vivax or P. ovale were unreactive. No cross-reactivity was observed with sera from patients with rheumatoid arthritis, filariasis, amebiasis, schistosomiasis, dengue, scrub typhus, leptospirosis, or toxoplasmosis. The sensitivity of ABC-GO is comparable to that of the indirect fluorescent antibody test.
The indirect hemagglutination test was used to measure malaria antibody levels in residents of an endemic area of Malaysia. Blood specimens were collected at 4-week intervals for a year. Seropositivity rates increased with age and number of episodes of malaria in young children. Although antibody levels were variable, titers tended to rise with parasitemia and fall in the absence of detected parasites. In general, the serologic indices tended to reflect the parasitologic findings.
A cohort of 62 persons living in a malaria-endemic area was examined by serology and by blood film 14 times over a 56-week period. Serologic responses (indirect hemagglutination test) of the group as a whole reflected the malaria transmission as determined by blood slide examination. The serologic responses of individuals showed titer changes that were not always consistent with blood slide results. The use of chloroquine may have modified the host's immune response.
The indirect hemagglutination (IHA) test done with turkey red cells was applied to 173 serum samples obtained from patients and persons exposed to Wuchereria bancrofti and Brugia malayi in endemic areas of Peninsular Malaysia. A crude extract of adult worms of the rat filaria, Breinlia booliati, was used as the antigen. When a titer of 1:16 was taken as negative, positive IHA test rates in sera from microfilaria-negative persons in endemic areas, microfilaremic cases, and patients with clinical filariasis were 13%, 75%, and 80%, respectively. Results of the IHA test correlated well with results obtained with the indirect fluorescent technique.
Two hundred and seventy-five Orang Asli volunteers living in nine villages in the Pos Legap Valley of Perak State, peninsular Malaysia, participated in a prospective study designed to characterize the epidemiological, parasitological, and entomological characteristics of Plasmodium falciparum, P. vivax, and P. malariae malaria transmission. Prevalence rates for the three plasmodial species at initiation of the study ranged from 56% in the 0-4-year-old age group to 0% in individuals over the age of 40. Entomological surveys were conducted, enabling us to determine mosquito salivary gland-positive rates and entomological inoculation rates of 1.2 infectious mosquito bites per person per month for P. falciparum, 2.4 for P. vivax, and 0.3 for P. malariae. Cumulative incidence rates over the 16 weeks of the study, following radical cure of all volunteers, were 22.5% for P. falciparum, 12.7% for P. vivax, and 1.5% for P. malariae. The median baseline antibody titer against the immunodominant repetitive B cell epitope of P. falciparum or P. vivax circumsporozoite protein was significantly higher for volunteers who did not become parasitemic. Volunteers were selected for further study if they had evidence of being challenged with P. falciparum sporozoites during the study, based on a two-fold or greater increase in antibody titer against the immunodominant repetitive B cell epitope of the circumsporozoite protein. Resistance to infection was seen in six of 10 individuals who had high (greater than 25 OD units) baseline ELISA titers, compared with only three of 24 individuals who had low baseline ELISA titers (chi 2 P less than 0.02). A similar analysis for P. vivax did not show a significant correlation.
Systematic surveys of the wild macaques of South Asia by blood culture resulted in the discovery that trypanosomiasis is enzootic in the simians of Indonesia, Malaysia, India, and Thailand. The isolates obtained differ in morphology, metabolism, and ability to multiply in arthropods. Following this discovery, interest focused on possible transmissions of these trypanosomiases. Laboratory-reared and wild-caught insects were studied to determine which are satisfactory intermediate hosts and potential natural vectors. Successful results were obtained with insectary-reared reduviids and Indonesian isolates. In Rhodnius prolixus and Triatoma rubrofasciata the Indonesian trypanosomes multiply for periods which can exceed 40 days. The flagellate infections are in the digestive tract, whereas trypanosomes have never been seen in the salivary glands or in the hemolymph. The feces of trypanosome-carrying reduviids are infective, suggesting a stercoreal method of infection of mammals, and infection was produced in experiments in which feeding by the insects was not possible. The relevance of these findings to natural transmission in Indonesia is not known. Experiments with insects and all other trypanosomal isolates have been negative. The natural transmission mechanism(s) of the simian trypanosomiases in South Asia remains an unsolved problem.
This report summarizes the results of a comparative study of the virulence of the "S-M," H, and C strains of P. knowlesi for Indian rhesus monkeys (Macaca mulatta) and cynomolgus monkeys [M. irus (fascicularis)] of Malayan (West Malaysia) and Philippine origins. Each of the above strains produced fulminating, uniformly fatal infections in the rhesus monkey and mild, chronic infections, characterized by relatively low level parasitemias in cynomolgus monkeys of Philippine origin. In striking contrast, the H and C strains produced infections in cynomolgus monkeys of Malayan origin which were indistinguishable in severity from infections produced in M. mulatta. The circumstances of the study precluded evaluation of the virulence of the "S-M" strain for M. irus of Malayan origin. Even so, the available data make it necessary to qualify the long-held belief that infections with P. knowlesi in M. irus invariably follow a benign course.
Fluorescent antibodies were detected in 89% of 288 Orang Asli (Malaysian aborigines) with Plasmodium falciparum antigen and in 62% with P. brasilianum (for P. malariae) antigen. Blood films from 18 donors were positive for P. falciparum; 2 of them had mixed infection with P. vivax. Seven of the P. falciparum-positive blood films were from children in the 2- to 9-year age group. Of 17 sera from cord blood, 16 had significant levels of P. falciparum antibody and 14 of P. malariae antibody, the levels being the same as those of the mothers. None of these babies had congenital malaria. A higher percentage of male donors reacted to both antigens. There was an age dependent increase in the number positive and the maximum titers.
Plaque reduction neutralization tests, using five group A arboviruses (chikungunya, Ross River, Getah, Bebaru and Sindbis), were done on sera from human populations in 44 Southeast Asia and Pacific island localities. Specificity of the plaque neutralization test was determined by examining convalescent sera from patients with known alphavirus infections. Chikungunya-specific neutralizing antibodies were demonstrated in sera of persons living in South Vietnam, Northern Malaysia, Indonesia (Kalimantan and Sulawesi), as well as Luzon, Marinduque, Cebu and Mindanao islands in the Philippines. Evidence of Ross River virus infection was found among populations living in West New Guinea and Papua New Guinea mainland, the Bismark Archipelago, Rossel Island and the Solomon Islands. There appeared to be no geographic overlap in the distribution of chikungunya and Ross River viruses, with the separation in their distribution corresponding with Weber's line in the Pacific. Sindbis neutralizing antibodies were found in 7 of 21 populations sampled, but in general the prevalence of infection was low. Four sera, from Vietnam, Malaysia and Mindanao gave monospecific reactions with Getah virus. No evidence of specific Bebaru virus infection was detected. The epidemiology of these five alphaviruses in Southeast Asia and the Pacific islands is discussed.
The ultrastructure of the cyst wall and zoites of a species of Sarcocystis from the skeletal muscles of a naturally-infected Malaysian long-tailed monkey, Macaca fascicularis, is described in detail. The wavy, electron-dense primary cyst wall is thin (55 nm) and invaginated. Cytophaneres are absent. The ground substance contains electron-dense granules and bundles of parallel, fibrillar elements in some areas. Thin trabeculae are present. The zoites measure 1.2 X 4.7 microns and have an interior conoid, 22 subpellicular microtubules, 50-60 micronemes, 4-6 rhoptries, and a posteriorly situated nucleus. Some ultrastructural aspects of the cyst wall and the zoites of this parasite resemble those of Sarcocystis species of the moonrat, rhesus monkey, tamarin, and baboon. The light microscopic appearance of this species from M. fascicularis also bears some resemblance to that of parasites from the four cases of human Sarcocystis reported in Malaysia. The cyst in all these human cases were thin-walled, with no cytophaners. Although the final hosts of these species of Sarcocystis are not known, it is quite possible that man, monkeys, and perhaps the moonrat (an insectivore) may serve as common intermediate hosts for one or several species of Sarcocystis.
Vibrio parahaemolyticus was isolated from 47 of 2,699 stools examined primarily for the exclusion of cholera. All strains grew well in alkaline peptone water containing 0.5% NaCl and in Monsur's medium. Serotyping showed them to be of various types. Adults were mainly affected. The importance of looking for V. parahaemolyticus in clinical specimens from cases of diarrhea is emphasized.
The COVID-19 pandemic caught the world by surprise, causing millions of confirmed cases and hundreds of thousands of deaths. Hence, the Malaysian government announced a Movement Control Order at the start of the containment phase to flatten the epidemiological curve. Universiti Malaysia Sabah (UMS), a public university in Borneo, was accelerated into alert phase because of high risk of case importation from more than 400 China incoming undergraduates. Measures to mitigate the potential COVID-19 outbreaks in its population were taken by using conventional public health measures with special attention to task-shifting and widespread community mental health interventions. A Preparedness and Response Centre was established to overseer the mitigating measures happening inside the university. Measures taken included empowerment of frontline staff, strengthening of restrictions, strengthening university health center, vigorous contact tracing, widespread health education, maintaining cultural sensitivity, and establishment of early standard operating procedures and university continuity plans. Hence, UMS was able to ensure no importation of cases into its campus during both acute and containment phases at the nationwide level.
A simple and rapid reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay was developed for the detection of SARS-CoV-2. The RT-LAMP assay was highly specific for SARS-CoV-2 and was able to detect one copy of transcribed SARS-CoV-2 RNA within 24 minutes. Assay validation performed using 50 positive and 32 negative clinical samples showed 100% sensitivity and specificity. The RT-LAMP would be valuable for clinical diagnosis and epidemiological surveillance of SARS-CoV-2 infection in resource-limited areas as it does not require the use of sophisticated and costly equipment.
Mosquito-borne flaviviruses are emerging pathogens of an increasing global public health concern because of their rapid increase in geographical range and the impact of climate change. Japanese encephalitis virus (JEV) and West Nile virus (WNV) are of concern because of the risk of reemergence and introduction by migratory birds. In Singapore, human WNV infection has never been reported and human JEV infection is rare. Four sentinel vector surveillance sites were established in Singapore to understand the potential risk posed by these viruses. Surveillance was carried out from August 2011 to December 2012 at Pulau Ubin, from March 2011 to March 2013 at an Avian Sanctuary (AS), from December 2010 from October 2012 at Murai Farmway, and from December 2010 to December 2013 at a nature reserve. The present study revealed active JEV transmission in Singapore through the detection of JEV genotype II in Culex tritaeniorhynchus collected from an Avian Sanctuary. Culex flavivirus (CxFV), similar to the Quang Binh virus isolated from Cx. tritaeniorhynchus in Vietnam and CxFV-LSFlaviV-A20-09 virus isolated in China, was also detected in Culex spp. (vishnui subgroup). No WNV was detected. This study demonstrates the important role that surveillance plays in public health and strongly suggests the circulation of JEV among wildlife in Singapore, despite the absence of reported human cases. A One Health approach involving surveillance, the collaboration between public health and wildlife managers, and control of mosquito populations remains the key measures in risk mitigation of JEV transmission in the enzootic cycle between birds and mosquitoes.
Leptospirosis is a zoonotic bacterial disease caused by pathogenic species of the genus Leptospira. Disease incidence is known to be attributed to environmental and social conditions which promote the spread of reservoir hosts, primarily rodents. A well-being program was conducted to determine the seroprevalence and risk factors associated with leptospirosis in urban poor communities occupying low-cost flat accommodation and squatter settlements in the vicinity of Wilayah Persekutuan, Kuala Lumpur. Blood samples from a total of 532 volunteers were screened for the detection of IgG and IgM antibodies against leptospirosis using ELISA. Demographic data were collected for each participant through a questionnaire survey before blood collection. The overall seroprevalence was low (12.6%, n = 67/532; 95% CI: 9.9-15.7%), with 8.1% (n = 43/532) being seropositive for anti-Leptospira IgG, indicating previous infection, and 4.9% (n = 26/532) for anti-Leptospira IgM, indicating current infection. Two significant factors such as host age (P ≤ 0.01) and knowledge of disease transmission (P = 0.017) significantly influenced the presence of anti-Leptospira IgM, whereas the detection of anti-IgG indicated the presence of clean drinking water sources (P = 0.043). Despite the low prevalence, the transmission of leptospirosis does occur among urban poor communities, suggesting the need for undertaking public awareness programs.