Presence of zoonotic pathogens in the wildlife market for human consumption in Laos

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In a recent study published in Emerging infectious diseasesan interdisciplinary team of researchers from different countries examined various animal species from wildlife trade sites for the presence of zoonotic pathogens in Laos, Southeast Asia.

Study: Zoonotic pathogens in wildlife traded in markets for human consumption, Laos. Image Credit: Vaclav Matous/Shutterstock

The trade and consumption of wild animals amplified by human encroachment on the natural ecosystem has led to the emergence of various infectious diseases. The trade and consumption of wild animals has been responsible for various epidemics such as Human Immunodeficiency Virus (HIV-1), Ebola, Monkeypox and even the current Coronavirus Disease 2019 (COVID-19).

Wildlife trade markets bring together various pathogenic species in close contact, usually in unsanitary and dense conditions, resulting in the amplification, mixing and transmission of zoonotic pathogens between different species, including humans.

At present, determining pathogens in wildlife in trade is essential in order to develop adequate measures to control zoonotic diseases and assess the future environmental and societal costs of wildlife trade.

study design

In this study, the authors collected samples from nine wildlife trade hotspots and two roadside stalls called trade sites in Laos. Other samples were taken from wild animals confiscated in the markets by three provincial offices of forest inspection (POFI).

A total of 717 wildlife samples from 359 animals were collected. Of these, more than 461 samples from 324 animals were collected from wildlife trade sites and 256 samples from 35 animals were collected from POFI.

Different animal samples such as urogenital swabs, urine samples, blood samples, and liver, kidney, and spleen tissues were collected depending on whether the animals were alive, dead, or slaughtered.

Nucleic acid was extracted using a QIAGEN kit. Polymerase chain reactions (PCR) targeting Leptospira sp., Rickettsia spp., AnaplasmataceaeOrientia tsutsugamushi, Ehrlichia chaffeensis, Coxiella burnetti, Anaplasma phagocytophilum, hantavirus, flavivirus, Zika virus, dengue virus and universal bacterial 16S RNA was conducted. PCR samples were sequenced and compared using the Baseline Local Alignment Search Tool (BLASTN).

The authors performed univariate, descriptive, and multivariate analyses, and a mixed-effects logistic regression model estimated the impact of wild meat processing status on the risk of Leptospira detection.

Results

The results of the study demonstrated that among the animals sampled in the wildlife market, more than 37% belong to vertebrate species from 12 different families. Over 73% of sampled animals were Sciuridae squirrels representing 16 species and 20.3% were Pallas squirrels (Callosciurus erythraeus).

Among animals collected from wildlife trade sites, more than 20% of animal specimens had at least ≥1 positive sample by PCR for ≥1 zoonotic pathogen in 90.9% of total sites. Of the 324 animals tested, 20.1% were positive for Leptospira spp., 9.8% for Rickettsia spp, 4.9% for Anaplasmataceae and 0% for O.tsutsugamushi.

In wildlife collected from POFI sites, more than 71% of animals tested positive by PCR for ≥ 1 zoonotic pathogen. Of these, 25.7% of animal species were positive for Leptospira spp, 57.1% for Rickettsia spp, 17.1% for Anaplasmataceae and 5.7% for O. tsutsugamushi. Sequencing identity match identified R. felis, R. conorii, R. typhi and Anaplasma species (either A. capra, A. centralWhere A. marginale), A.platys, A. phagocytophilic, A. bovis, Lactococcus garvieae, Ehrlichia chaffeensisand Popular Kurthia. No animal species tested positive for C. burnetii, dengue virus, flavivirus and Zika virus.

The team observed that two animal species – variable squirrel (Callosciurus finlaysonii) and the common palm civet (Hermaphroditic paradox) had 45.5% and 46.4% of Leptospira spp.–positive samples, respectively. Leptospira spp.–positivity during the dry season was 25.6% while it was 11.6% during the rainy season.

Disaggregation of data by species and by province demonstrated that the observed seasonality was driven by findings in variable squirrels and common palm civets in Champasak Province. The authors observed no association between the likelihood of an animal testing positive for Leptospira species and the animal being alive, freshly dead or frozen.

In the multiple samples of a subset of Leptospira spp.– positive animals, 75% of urogenital samples and 50% of blood samples were positive. Rickettsia spp has been exclusively detected in solid organs such as liver, spleen and kidney of animal species.

Conclusion

The results of the study demonstrated a substantial risk of exposure to zoonotic pathogens for the human population through the consumption and handling of meat from wild animals.

In this study, squirrels had the highest pathogen diversity and were frequently traded in the Laos market. Leptospira spp. was the most infectious and frequently detected pathogen in the majority of animal species, followed by Rickettsia typhi and R. felis.

The frequent presence of Leptospira in wild animals, which can be transmitted through mucous membranes and abraded skin, poses a substantial health risk for hunters, sellers and consumers.

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