Detection of zoonotic-borne parasites in Rattus spp. in Klang Valley, Malaysia

Zoonotic importance of ecto- and endoparasites in rodents in Malaysia: a review

IMPORTANCE

Rodents, particularly those inhabiting urban areas, are sources of infections that cause major human diseases. The number of recorded zoonotic infections has increased in recent decades, exacerbating public concerns. Zoonotic diseases in humans, such as capillariasis, hymenolepiasis, and toxoplasmosis, are life-threatening in severe cases, particularly in immunocompromised individuals. A thorough understanding of pathogens, particularly the parasites infecting rodents, is critical for predicting future zoonotic disease outbreaks and developing effective mitigation strategies. This review summarizes the information on parasites in rodents inhabiting Malaysia to identify the knowledge gaps that could serve as a foundation for future research.

OBSERVATIONS

Thirty-eight previous parasite studies in rodents conducted in Malaysia were reviewed, and 44 ectoparasites species and 58 endoparasites species across 19 rodent species were revealed. Six ectoparasite and eight endoparasite species were identified as zoonotic among these parasites. Morphological identification of parasite species typically succeeded only at the genus level because of their identical morphological characteristics. However, these studies used a molecular approach to identify parasites at the species level using species-specific primers. The pathological findings of various organs of infected rodents were also summarized, including gross and histological lesions exhibited by parasites.

CONCLUSIONS AND RELEVANCE

This review highlights the list of parasites infecting rodents in Malaysia, provides information on the molecular and pathological findings from previous studies, and identifies some of the limitations and knowledge gaps that suggest future research to address the issues, including the paucity of information on blood parasites, molecular, and histopathological studies of parasites in rodents.

Trypanosoma lewisi in blood of Rattus rattus complex residing in human settlements, Nakhon Si Thammarat, Thailand: Microscopic and molecular investigations

Trypanosomes are blood parasites infected in various mammals, including rats. The presence of rats in human settlements can increase the chance of Trypanosoma transmission to humans. The molecular study of multispacer in Trypanosoma spp. in naturally infected rodents in Thailand is scanty. The objective of this study was to detect Trypanosoma in the blood of the captured rats in Nakhon Si Thammarat, Thailand, using microscopic and molecular techniques. This was a cross-sectional study conducted in human settlement areas. Ninety-nine blood samples were collected using cardiac puncture. A blood sample was smeared on a glass slide and examined using a compound light microscope and a scanning electron microscope. Moreover, polymerase chain reaction was applied to detect Trypanosoma evansi and T. lewisi in the blood. An additional primer set was used to confirm the species of the detected trypanosome. Approximately 18% of the rats had positive Trypanosoma infections. All Trypanosoma-positive blood samples were matched with sequences of T. lewisi. The stumpy form of trypanosome had higher nucleus related parameters than the slender form. Interestingly, the partial sequences of the alpha-tubulin gene of T. lewisi were first reported in the naturally infected RrC in this study. Based on the results obtained, T. lewisi biology, particularly the virulent components and route of transmission, pathogenesis, and in vitro experiments, are strongly recommended for further study.

Screening of West Nile Virus, Herpesvirus, and Parvovirus in Rattus spp. in Klang Valley, Malaysia

Free-roaming and scavenging lifestyles of Rattus spp. in densely populated urban areas expose them to multiple pathogens that facilitate the transmission of infection to the human population more rapidly, raising public health concerns. There is limited information on the status of rat susceptibility to virus infection, particularly West Nile virus (WNV), herpesvirus, and parvovirus, to prepare for emerging zoonosis. A total of 23 (n = 23) blood samples collected from Rattus spp. in the wet market areas of Klang Valley, Malaysia, were subjected to molecular assay using a one-step reverse transcription-polymerase chain reaction (RT-PCR) to detect the highly conserved region of the WNV capsid and pre-membrane protein via nested polymerase chain reaction (PCR) assay targeting highly conserved amino acid motifs within the herpesviral DNA-directed DNA polymerase gene (DPOL) and polymerase chain reaction (PCR) assay targeting the parvovirus non-structural (NS) protein. As a result, 4 out of 23 (17.39%) rats were positive for herpesvirus DNA, but none were positive for WNV RNA and parvovirus DNA. The positive PCR amplicons of herpesvirus DNA were subjected to partial DNA sequencing analysis, 100% identical to Acomys herpesvirus SVMS 226,222 from Betaherpesvirinae, which is highly suggestive of rat cytomegalovirus (RCMV). This study has successfully demonstrated the presence of RCMV from Rattus spp. in the Klang Valley. The RCMV potentially crosses species barriers and establishes infection, raising public health concerns. The non-viraemic state of WNV or parvovirus infection, low sample size, and limited niche distribution emphasise the need for the expansion of this study in the future.