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  1. Khor CS, Teoh BT, Sam SS, Khoo HY, Azizan NS, CheMatSeri A, et al.
    J Infect Dev Ctries, 2023 Jan 31;17(1):118-124.
    PMID: 36795935 DOI: 10.3855/jidc.16613
    INTRODUCTION: Chikungunya fever is a mosquito-borne viral disease that usually presents with prominent arthralgia. An outbreak of chikungunya fever was reported in Tanjung Sepat, Malaysia in 2019. The outbreak was limited in size with a low number of cases being reported. The present study sought to determine the possible variables that could have affected the transmission of the infection.

    METHODOLOGY: A cross-sectional study involving 149 healthy adult volunteers from Tanjung Sepat was performed soon after the outbreak had subsided. All the participants donated blood samples and completed the questionnaires. Laboratory detection of anti-CHIKV IgM and IgG antibodies was performed using enzyme-linked immunoassays (ELISA). Risk factors associated with chikungunya seropositivity were determined using logistic regression.

    RESULTS: The majority (72.5%, n = 108) of the study participants tested positive for CHIKV antibodies. Only 8.3% (n = 9) of the participants out of all the seropositive volunteers had an asymptomatic infection. Participants who resided with a febrile (p < 0.05, Exp(B) = 2.2, confidence interval [CI] 1.3-3.6) or a CHIKV-diagnosed person (p < 0.05, Exp(B) = 2.1, CI 1.2-3.6) in the same household were found likely to be tested positive for CHIKV antibodies.

    CONCLUSIONS: Findings from the study support that asymptomatic CHIKV infections and indoor transmission occurred during the outbreak. Hence, widespread community testing and indoor use of mosquito repellent are among the possible measures that can be implemented to reduce CHIKV transmission during an outbreak.

    Matched MeSH terms: Asymptomatic Infections/epidemiology
  2. Anuar TS, Bakar NH, Al-Mekhlafi HM, Moktar N, Osman E
    PMID: 27405127
    The epidemiology and environmental factors affecting transmission of human microsporidiosis are poorly understood. We conducted the present study to determine the prevalence and risk factors associated with asymptomatic intestinal microsporidiosis among aboriginal school children in the Kuala Krau District, Pahang State, Malaysia. We collected stool samples from 255 school children and examined the samples using Gram-chromotrope Kinyoun stain. We also collected demographic, socioeconomic, environmental and personal hygiene information using a pre-tested questionnaire. Sixty-nine of the children was positive for microsporidia: 72.5% and 27.5% were low (1+) and moderate (2+) excretions of microsporidia spores, respectively. Univariate and multivariate analyses showed being aged 10 years (p = 0.026), using an unsafe water supply as a source for drinking water (p = 0.044) and having close contact with domestic animals (p = 0.031) were all significantly associated with microsporidial infection among study subjects. Our findings suggest asymptomatic intestinal microsporidiosis is common in the study population, more than previously reported. In the study population, control measures need to be implemented, such as good personal hygiene, proper sanitation and safe drinking water supply.
    Matched MeSH terms: Asymptomatic Infections/epidemiology*
  3. Shahrul Anuar T, M Al-Mekhlafi H, Md Salleh F, Moktar N
    PLoS One, 2013;8(8):e71870.
    PMID: 24014078 DOI: 10.1371/journal.pone.0071870
    Studies on microsporidial infection mostly focus on immunodeficiency or immunosuppressive individuals. Therefore, this cross-sectional study describes the prevalence and risk factors of microsporidiosis among asymptomatic individuals in Malaysia.
    Matched MeSH terms: Asymptomatic Infections/epidemiology*
  4. Wong J, Abdul Aziz ABZ, Chaw L, Mahamud A, Griffith MM, Lo YR, et al.
    J Travel Med, 2020 08 20;27(5).
    PMID: 32365178 DOI: 10.1093/jtm/taaa066
    Matched MeSH terms: Asymptomatic Infections/epidemiology*
  5. Tan JK, Leong D, Munusamy H, Zenol Ariffin NH, Kori N, Hod R, et al.
    BMC Infect Dis, 2021 Mar 09;21(1):249.
    PMID: 33750347 DOI: 10.1186/s12879-021-05849-7
    BACKGROUND: Presymptomatic COVID-19 patients have been identified as a major stumbling block in efforts to break the chain of transmission. Studies on temporal dynamics of its shedding suggests it peaks 1-2 days prior to any symptom onset. Therefore, a large proportion of patients are actively spreading the disease unknowingly whilst undetected. However, lengthy lockdowns and isolation leads to a host of socioeconomic issues and are impractical. Conversely, there exists no study describing this group and their clinical significance despite their key role in disease transmission.

    METHODS: As a result, we devised a retrospective study to look at the prevalence of presymptomatic patients with COVID-19 from data sourced via our medical records office. Subsequently, we identify early indicators of infection through demographic information, biochemical and radiological abnormalities which would allow early diagnosis and isolation. In addition, we will look into the clinical significance of this group and their outcome; if it differs from asymptomatic or symptomatic patients. Descriptive statistics were used in addition to tabulating the variables and corresponding values for reference. Variables are compared between the presymptomatic group and others via Chi-square testing and Fisher's exact test, accepting a p value of

    Matched MeSH terms: Asymptomatic Infections/epidemiology*
  6. Gupta N, John A, Kokkottil MS, Varma M, Umakanth S, Saravu K
    Drug Discov Ther, 2021 Mar 10;15(1):1-8.
    PMID: 33642450 DOI: 10.5582/ddt.2020.03068
    Despite the high number of coronavirus disease-19 (COVID-19) cases from India, there are few reports from India describing the clinical epidemiology of COVID-19. This study aimed to describe the clinical/epidemiological characteristics and outcomes of asymptomatic vs. symptomatic COVID-19 patients. This was a retrospective chart review of all admitted patients with COVID-19 above 18 years with a history of travel within one month of the admission. The patients were categorized into asymptomatic and symptomatic. The symptomatic patients were further classified into mild, moderate and severe. The demographic profile, risk factors, clinical features, laboratory parameters, treatment details and outcome of all patients were recorded. The clinical and laboratory parameters were compared between symptomatic patients and asymptomatic patients. Of the 127 recruited patients, 75 were asymptomatic. Of the 52 symptomatic patients, 41 patients were classified as a mild illness. The mean age of the patients was 44.5 ± 15 years. A total of 73 patients had one or more risk factors. The male patients were more commonly found to be symptomatic compared to female patients. Neutrophil-lymphocyte ratio, C-reactive protein and lactate dehydrogenase were significantly elevated in symptomatic patients. A total of five individuals required supplemental oxygen therapy, and one of them required mechanical ventilation. All the patients had favourable outcomes. Asymptomatic and mild illness form a significant proportion of positive patients and have excellent outcomes without therapeutic interventions.
    Matched MeSH terms: Asymptomatic Infections/epidemiology*
  7. Fornace KM, Brock PM, Abidin TR, Grignard L, Herman LS, Chua TH, et al.
    Lancet Planet Health, 2019 04;3(4):e179-e186.
    PMID: 31029229 DOI: 10.1016/S2542-5196(19)30045-2
    BACKGROUND: Land use changes disrupt ecosystems, altering the transmission of vector-borne diseases. These changes have been associated with increasing incidence of zoonotic malaria caused by Plasmodium knowlesi; however, the population-level distributions of infection and exposure remain unknown. We aimed to measure prevalence of serological exposure to P knowlesi and assess associated risk factors.

    METHODS: We did an environmentally stratified, population-based, cross-sectional survey across households in the Kudat, Kota Marudu, Pitas, and Ranau districts in northern Sabah, Malaysia, encompassing a range of ecologies. Using blood samples, the transmission intensity of P knowlesi and other malaria species was measured by specific antibody prevalence and infection detected using molecular methods. Proportions and configurations of land types were extracted from maps derived from satellite images; a data-mining approach was used to select variables. A Bayesian hierarchical model for P knowlesi seropositivity was developed, incorporating questionnaire data about individual and household-level risk factors with selected landscape factors.

    FINDINGS: Between Sept 17, 2015, and Dec 12, 2015, 10 100 individuals with a median age of 25 years (range 3 months to 105 years) were sampled from 2849 households in 180 villages. 5·1% (95% CI 4·8-5·4) were seropositive for P knowlesi, and marked historical decreases were observed in the transmission of Plasmodium falciparum and Plasmodium vivax. Nine Plasmodium spp infections were detected. Age, male sex, contact with macaques, forest use, and raised house construction were positively associated with P knowlesi exposure, whereas residing at higher geographical elevations and use of insecticide were protective. Agricultural and forest variables, such as proportions and fragmentation of land cover types, predicted exposure at different spatial scales from households.

    INTERPRETATION: Although few infections were detected, P knowlesi exposure was observed in all demographic groups and was associated with occupational factors. Results suggest that agricultural expansion and forest fragmentation affect P knowlesi exposure, supporting linkages between land use change and P knowlesi transmission.

    FUNDING: UK Medical Research Council, Natural Environment Research Council, Economic and Social Research Council, and Biotechnology and Biosciences Research Council.

    Matched MeSH terms: Asymptomatic Infections/epidemiology
  8. Nhidza AF, Naicker T, Stray-Pedersen B, Chisango TJ, Sibanda EP, Ismail A, et al.
    J Microbiol Immunol Infect, 2020 Aug;53(4):612-621.
    PMID: 30583941 DOI: 10.1016/j.jmii.2018.11.005
    BACKGROUND: Asymptomatic Entamoeba histolytica infections in pregnant women puts infants at risk of infection through vertical transmission or transmission during breastfeeding in high HIV prevalence areas. The study aimed at investigating the immune response to asymptomatic E.histolytica infection in pregnant women and their infants in a high HIV burdened setting in Harare, Zimbabwe.

    METHODOLOGY: Serum samples from 39 predominantly breastfeeding mother-infant pairs were analyzed for inflammatory cytokine and immunoglobulin profiles using BIOPLEX. The infants' ages ranged from 10 days to 14 weeks.

    RESULTS: IL-1r, IL-4, IL-9, IL-12p70, IL-17a, G-CSF and PDGF-BB were significantly raised in E. histolytica infected compared to non-infected lactating mothers (p 

    Matched MeSH terms: Asymptomatic Infections/epidemiology*
  9. Siner A, Liew ST, Kadir KA, Mohamad DSA, Thomas FK, Zulkarnaen M, et al.
    Malar J, 2017 Oct 17;16(1):417.
    PMID: 29041929 DOI: 10.1186/s12936-017-2064-9
    BACKGROUND: Plasmodium knowlesi, a simian malaria parasite, has become the main cause of malaria in Sarawak, Malaysian Borneo. Epidemiological data on malaria for Sarawak has been derived solely from hospitalized patients, and more accurate epidemiological data on malaria is necessary. Therefore, a longitudinal study of communities affected by knowlesi malaria was undertaken.

    METHODS: A total of 3002 blood samples on filter paper were collected from 555 inhabitants of 8 longhouses with recently reported knowlesi malaria cases in the Betong Division of Sarawak, Malaysian Borneo. Each longhouse was visited bimonthly for a total of 10 times during a 21-month study period (Jan 2014-Oct 2015). DNA extracted from blood spots were examined by a nested PCR assay for Plasmodium and positive samples were then examined by nested PCR assays for Plasmodium falciparum, Plasmodium vivax, Plasmodium malariae, Plasmodium ovale, Plasmodium knowlesi, Plasmodium cynomolgi and Plasmodium inui. Blood films of samples positive by PCR were also examined by microscopy.

    RESULTS: Genus-specific PCR assay detected Plasmodium DNA in 9 out of 3002 samples. Species-specific PCR identified 7 P. knowlesi and one P. vivax. Malaria parasites were observed in 5 thick blood films of the PCR positive samples. No parasites were observed in blood films from one knowlesi-, one vivax- and the genus-positive samples. Only one of 7 P. knowlesi-infected individual was febrile and had sought medical treatment at Betong Hospital the day after sampling. The 6 knowlesi-, one vivax- and one Plasmodium-infected individuals were afebrile and did not seek any medical treatment.

    CONCLUSIONS: Asymptomatic human P. knowlesi and P. vivax malaria infections, but not P. cynomolgi and P. inui infections, are occurring within communities affected with malaria.

    Matched MeSH terms: Asymptomatic Infections/epidemiology*
  10. Fornace KM, Herman LS, Abidin TR, Chua TH, Daim S, Lorenzo PJ, et al.
    PLoS Negl Trop Dis, 2018 Jun;12(6):e0006432.
    PMID: 29902171 DOI: 10.1371/journal.pntd.0006432
    BACKGROUND: Primarily impacting poor, rural populations, the zoonotic malaria Plasmodium knowlesi is now the main cause of human malaria within Malaysian Borneo. While data is increasingly available on symptomatic cases, little is known about community-level patterns of exposure and infection. Understanding the true burden of disease and associated risk factors within endemic communities is critical for informing evidence-based control measures.

    METHODOLOGY/PRINCIPAL FINDINGS: We conducted comprehensive surveys in three areas where P. knowlesi transmission is reported: Limbuak, Pulau Banggi and Matunggung, Kudat, Sabah, Malaysia and Bacungan, Palawan, the Philippines. Infection prevalence was low with parasites detected by PCR in only 0.2% (4/2503) of the population. P. knowlesi PkSERA3 ag1 antibody responses were detected in 7.1% (95% CI: 6.2-8.2%) of the population, compared with 16.1% (14.6-17.7%) and 12.6% (11.2-14.1%) for P. falciparum and P. vivax. Sero-prevalence was low in individuals <10 years old for P. falciparum and P. vivax consistent with decreased transmission of non-zoonotic malaria species. Results indicated marked heterogeneity in transmission intensity between sites and P. knowlesi exposure was associated with agricultural work (OR 1.63; 95% CI 1.07-2.48) and higher levels of forest cover (OR 2.40; 95% CI 1.29-4.46) and clearing (OR 2.14; 95% CI 1.35-3.40) around houses. Spatial patterns of P. knowlesi exposure differed from exposure to non-zoonotic malaria and P. knowlesi exposed individuals were younger on average than individuals exposed to non-zoonotic malaria.

    CONCLUSIONS/SIGNIFICANCE: This is the first study to describe serological exposure to P. knowlesi and associated risk factors within endemic communities. Results indicate community-level patterns of infection and exposure differ markedly from demographics of reported cases, with higher levels of exposure among women and children. Further work is needed to understand these variations in risk across a wider population and spatial scale.

    Matched MeSH terms: Asymptomatic Infections/epidemiology
  11. Noordin NR, Lee PY, Mohd Bukhari FD, Fong MY, Abdul Hamid MH, Jelip J, et al.
    Am J Trop Med Hyg, 2020 09;103(3):1107-1110.
    PMID: 32618263 DOI: 10.4269/ajtmh.20-0268
    Asymptomatic and/or low-density malaria infection has been acknowledged as an obstacle to achieving a malaria-free country. This study aimed to determine the prevalence of asymptomatic and/or low-density malaria infection in previously reported malarious localities using nested PCR in four states, namely, Johor, Pahang, Kelantan, and Selangor, between June 2019 and January 2020. Blood samples (n = 585) were collected and were extracted using a QIAamp blood kit. The DNA was concentrated and subjected to nested PCR. Thin and thick blood smears were examined as well. Of the 585 samples collected, 19 were positive: 10 for Plasmodium knowlesi, eight for Plasmodium vivax, and one for Plasmodium ovale. Asymptomatic and/or low-density malaria infection is a threat to malaria elimination initiatives. Eliminating countries should develop guidance policy on the importance of low-density malaria infection which includes detection and treatment policy.
    Matched MeSH terms: Asymptomatic Infections/epidemiology*
  12. Jiram AI, Ooi CH, Rubio JM, Hisam S, Karnan G, Sukor NM, et al.
    Malar J, 2019 May 02;18(1):156.
    PMID: 31046769 DOI: 10.1186/s12936-019-2786-y
    BACKGROUND: Malaysia has declared its aim to eliminate malaria with a goal of achieving zero local transmission by the year 2020. However, targeting the human reservoir of infection, including those with asymptomatic infection is required to achieve malaria elimination. Diagnosing asymptomatic malaria is not as straightforward due to the obvious lack of clinical manifestations and often subpatent level of parasites. Accurate diagnosis of malaria is important for providing realistic estimates of malaria burden and preventing misinformed interventions. Low levels of parasitaemia acts as silent reservoir of transmission thus remains infectious to susceptible mosquito vectors. Hence, the aim of this study is to investigate the prevalence of asymptomatic submicroscopic malaria (SMM) in the District of Belaga, Sarawak.

    METHODS: In 2013, a total of 1744 dried blood spots (DBS) were obtained from residents of 8 longhouses who appeared healthy. Subsequently, 251 venous blood samples were collected from residents of 2 localities in 2014 based on the highest number of submicroscopic cases from prior findings. Thin and thick blood films were prepared from blood obtained from all participants in this study. Microscopic examination were carried out on all samples and a nested and nested multiplex PCR were performed on samples collected in 2013 and 2014 respectively.

    RESULTS: No malaria parasites were detected in all the Giemsa-stained blood films. However, of the 1744 samples, 29 (1.7%) were positive for Plasmodium vivax by PCR. Additionally, of the 251 samples, the most prevalent mono-infection detected by PCR was Plasmodium falciparum 50 (20%), followed by P. vivax 39 (16%), P. knowlesi 9 (4%), and mixed infections 20 (8%).

    CONCLUSIONS: This research findings conclude evidence of Plasmodium by PCR, among samples previously undetectable by routine blood film microscopic examination, in local ethnic minority who are clinically healthy. SMM in Belaga district is attributed not only to P. vivax, but also to P. falciparum and P. knowlesi. In complementing efforts of programme managers, there is a need to increase surveillance for SMM nationwide to estimate the degree of SMM that warrant measures to block new transmission of malaria.

    Matched MeSH terms: Asymptomatic Infections/epidemiology*
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