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Fulltext Detection of all four dengue virus serotypes and identification of four mismatched nucleotides between DENV4 specific primer rTS4 and DENV 4 sequences in Sandakan and Kudat (2016-2017)

Tin Sabai Aung, Amalina Emran, Chua Tock Hing, Tin Tin Thein, Win Win Than, Aye Aye Wynn, et al.

Malaysian Journal of Medicine and Health Sciences, 2019;15(106):49-49.
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Introduction: Dengue is caused by dengue virus (DENV) which is a member of the genus Flavivirus of the family Flaviviridae. The prevalence of dengue has been increasing all over the world especially in Southeast Asia and Western Pacific regions. In 2016 - 2017 dengue outbreaks were reported in Sandakan and Kudat of Sabah, Malay-sia. The aim of this study was to determine the serotypes of dengue viruses circulating in these two sites during the outbreaks. Methods: A total of 200 dengue patients’ sera tested positive with NS1 and IgM & IgG rapid test (PanBio) were collected from Hospital Duchess of Kent Sandakan and Hospital Kudat between June 2016 and December 2017. PCR was done at the Faculty of Medicine and Health Sciences, Universiti Malaysia Sabah. One-Step Reverse transcriptase PCR (RT-PCR) and nested PCR was performed using C-prM amplimers designed by Lanciotti et al and later redesigned by Chien et al, followed by sequencing some of the PCR products. Results: Out of 200 sera tested 128 were PCR positive. All the four dengue serotypes were detected with PCR products with specific sizes in gel electrophoresis. However, in four samples, no serotype-specific band was amplified by the nested PCR, while they were dengue-positive in RT-PCR showing 511 base pair amplicon. Sequencing results revealed all four samples were found to belong to DENV4. The sequences of these samples were aligned with that of DENV 4 reverse primer rTS4. The DENV4 specific primer rTS4 was found to have four mismatched nucleotides to the DENV4 sequences. Conclusion: There was a co-circulation of DENV1 to 4 in Sandakan and Kudat in the study period. DENV1 was the predominant serotype. DENV4 specific C-prM primer rTS4 should be redesigned for the local DENV4 strain in Sabah in future research.
Fulltext Neonatal melioidosis case reports-Lessons learned

Daim S, Barnad E, Johnny V, Suleiman M, Jikal M, Chua TH, et al.

Clin Case Rep, 2020 Jan;8(1):171-175.
PMID: 31998510 DOI: 10.1002/ccr3.2584

In endemic regions, include melioidosis in the routine differential diagnosis of neonates with respiratory distress, and consider early empirical ceftazidime treatment for neonates with worsening respiratory distress.
Evaluation of new multiplex PCR primers for the identification ofPlasmodium species found in Sabah, Malaysia

Stanis CS, Song BK, Chua TH, Lau YL, Jelip J

Turk J Med Sci, 2016 Jan 05;46(1):207-18.
PMID: 27511356 DOI: 10.3906/sag-1411-114

BACKGROUND/AIM: Malaria is a major public health problem, especially in the Southeast Asia region, caused by 5 species of Plasmodium (P. falciparum, P. vivax, P. malariae, P. ovale, and P. knowlesi). The aim of this study was to compare parasite species identification methods using the new multiplex polymerase chain reaction (PCR) against nested PCR and microscopy.
MATERIALS AND METHODS: Blood samples on filter papers were subject to conventional PCR methods using primers designed by us in multiplex PCR and previously designed primers of nested PCR. Both sets of results were compared with microscopic identification.
RESULTS: Of the 129 samples identified as malaria-positive by microscopy, 15 samples were positive for P. falciparum, 14 for P. vivax, 6 for P. knowlesi, 72 for P. malariae, and 2 for mixed infection of P. falciparum/P. malariae. Both multiplex and nested PCR identified 12 P. falciparum single infections. For P. vivax, 9 were identified by multiplex and 12 by nested PCR. For 72 P. malariae cases, multiplex PCR identified 58 as P. knowlesi and 10 as P. malariae compared to nested PCR, which identified 59 as P. knowlesi and 7 as P. malariae.
CONCLUSION: Multiplex PCR could be used as alternative molecular diagnosis for the identification of all Plasmodium species as it requires a shorter time to screen a large number of samples.
The vectors of Plasmodium knowlesi and other simian malarias Southeast Asia: challenges in malaria elimination

Vythilingam I, Chua TH, Liew JWK, Manin BO, Ferguson HM

Adv Parasitol, 2021;113:131-189.
PMID: 34620382 DOI: 10.1016/bs.apar.2021.08.005

Plasmodium knowlesi, a simian malaria parasite of great public health concern has been reported from most countries in Southeast Asia and exported to various countries around the world. Currently P. knowlesi is the predominant species infecting humans in Malaysia. Besides this species, other simian malaria parasites such as P. cynomolgi and P. inui are also infecting humans in the region. The vectors of P. knowlesi and other Asian simian malarias belong to the Leucosphyrus Group of Anopheles mosquitoes which are generally forest dwelling species. Continual deforestation has resulted in these species moving into forest fringes, farms, plantations and human settlements along with their macaque hosts. Limited studies have shown that mosquito vectors are attracted to both humans and macaque hosts, preferring to bite outdoors and in the early part of the night. We here review the current status of simian malaria vectors and their parasites, knowledge of vector competence from experimental infections and discuss possible vector control measures. The challenges encountered in simian malaria elimination are also discussed. We highlight key knowledge gaps on vector distribution and ecology that may impede effective control strategies.
Fulltext Spatial patterns of mosquito communities and monkey malaria vectors in a tropical riverine forest in Sabah, Malaysian Borneo

Matsuda I, Manin BO, Yahiro T, Lambut P, Tangah J, Huffman MA, et al.

PLoS Negl Trop Dis, 2026 Nov 03;20(11):e0014849.
PMID: 42976202 DOI: 10.1371/journal.pntd.0014849

BACKGROUND: Understanding how vector ecology intersects with host behaviour is essential for predicting zoonotic malaria risk in tropical ecosystems. In Malaysian Borneo, zoonotic transmission of monkey malaria parasites such as Plasmodium knowlesi is shaped by interactions among mosquito vectors, non-human primate reservoir hosts, and human activities across heterogeneous landscapes. However, fine-scale spatial structuring of mosquito communities within tropical riverine forests remains poorly characterized.
METHODOLOGY/PRINCIPAL FINDINGS: We conducted a two-year mosquito survey (November 2016-October 2018) in a lowland riverine forest along the Menanggul River, Sabah, Malaysian Borneo. Mosquitoes were sampled on 44 nights using CO2-baited light traps repeatedly deployed across horizontal (0 m, 250 m, and 500 m from the river) and vertical (ground and canopy) gradients, yielding 244 trap collections. A total of 9,928 mosquitoes were collected, dominated by Culex spp. (91.4%), whereas Anopheles spp. were rare (153 individuals; 1.5%). Female Anopheles mosquitoes (n = 57) were more frequently detected near the river and tended to occur more often in ground traps. Zero-inflated negative binomial generalized linear mixed models based on the female mosquito dataset revealed significant effects of river distance and trap height on mosquito abundance, while short-term microclimatic variation showed little explanatory power. The Anopheles assemblage was dominated by Anopheles balabacensis, a recognized vector of monkey malaria parasites in Sabah. Molecular screening detected monkey Plasmodium DNA in two An. balabacensis individuals, including P. knowlesi, together with other monkey Plasmodium species.
CONCLUSIONS/SIGNIFICANCE: Our findings suggest that river-edge habitats may function as localized contact hotspots where mosquito vectors, non-human primate reservoir hosts, and human activities repeatedly overlap in space and time, potentially facilitating zoonotic malaria transmission even when vector densities are low. These results support the growing view that zoonotic malaria risk in tropical landscapes is shaped less by overall vector abundance than by fine-scale ecological overlap among vectors, wildlife, and humans.
Fulltext A Non-severe Coronavirus Disease 2019 Patient With Persistently High Interleukin-6 Level

Hambali NL, Mohd Noh M, Paramasivam S, Chua TH, Hayati F, Payus AO, et al.

Front Public Health, 2020;8:584552.
PMID: 33304877 DOI: 10.3389/fpubh.2020.584552

Interleukin 6 (IL-6) is one of the markers of immune system activation indicating existent infection and inflammation. We present here a case of a 55-year-old male COVID-19 patient with an unusual high level of interleukin 6 (IL-6). Further investigation revealed he had hepatocellular carcinoma (HCC) with underlying hepatitis B. He did not present with respiratory symptoms although a baseline chest x-ray showed changes, and the patient was categorized as Class 3A of COVID-19. Routine investigations proceeded with high-resolution computed tomography and IL-6 to monitor for progression to severe COVID-19. Notably, there was a high IL-6 level but other parameters did not show he was in severe COVID-19. In this report, we conclude that elevated IL-6 level in a COVID-19 patient is not necessarily associated with severe COVID-19.
Simian malaria: a narrative review on emergence, epidemiology and threat to global malaria elimination

Fornace KM, Zorello Laporta G, Vythilingham I, Chua TH, Ahmed K, Jeyaprakasam NK, et al.

Lancet Infect Dis, 2023 Dec;23(12):e520-e532.
PMID: 37454671 DOI: 10.1016/S1473-3099(23)00298-0

Simian malaria from wild non-human primate populations is increasingly recognised as a public health threat and is now the main cause of human malaria in Malaysia and some regions of Brazil. In 2022, Malaysia became the first country not to achieve malaria elimination due to zoonotic simian malaria. We review the global distribution and drivers of simian malaria and identify priorities for diagnosis, treatment, surveillance, and control. Environmental change is driving closer interactions between humans and wildlife, with malaria parasites from non-human primates spilling over into human populations and human malaria parasites spilling back into wild non-human primate populations. These complex transmission cycles require new molecular and epidemiological approaches to track parasite spread. Current methods of malaria control are ineffective, with wildlife reservoirs and primarily outdoor-biting mosquito vectors urgently requiring the development of novel control strategies. Without these, simian malaria has the potential to undermine malaria elimination globally.
Fulltext Exposure and infection to Plasmodium knowlesi in case study communities in Northern Sabah, Malaysia and Palawan, The Philippines

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.