Seroprevalence of leptospirosis and Japanese encephalitis in swine in ten provinces of Vietnam

Emerging zoonotic diseases in Southeast Asia in the period 2011-2022: a systematic literature review

As COVID-19 has shown, pandemics and outbreaks of emerging infections such as Zika, Nipah, monkeypox and antimicrobial-resistant pathogens, especially emerging zoonotic diseases, continue to occur and may even be increasing in Southeast Asia. In addition, these infections often result from environmental changes and human behaviour. Overall, public health surveillance to identify gaps in the literature and early warning signs are essential in this region. A systematic review investigated the prevalence of emerging zoonotic diseases over 11 years from 2011 to 2022 in Southeast Asia to understand the status of emerging zoonotic diseases, as well as to provide necessary actions for disease control and prevention in the region. During the 2011-2022 period, studies on pigs, poultry, ruminants, companion animals and wildlife in Southeast Asia were reviewed thoroughly to assess the quality of reporting items for inclusion in the systematic review. The review was performed on 26 studies of pigs, 6 studies of poultry, 21 studies of ruminants, 28 studies of companion animals and 25 studies of wildlife in Southeast Asia, which provide a snapshot of the prevalence of the emerging zoonotic disease across the country. The findings from the review showed that emerging zoonotic diseases were prevalent across the region and identified a few zoonotic diseases associated with poultry, mainly stemming from Cambodia and Vietnam, as high priority in Southeast Asia.Clinical relevance: Appropriate prevention and control measures should be taken to mitigate the emerging zoonotic diseases in Southeast Asia.

Leptospirosis in Vietnam

Leptospirosis poses a serious public health problem in many countries because about 1 million people suffer annually from this severe, often fatal, infection. At present, its importance has been increasing due to development of integration processes, globalization and intensification of economic activities, inevitable anthropogenic transformation of landscapes as well as rise in number of people with occupational risk of pathogen exposure. The burden of human leptospirosis is expected to rise with demographic shifts and climate change that result in heavy rainfall and flooding. Regarding leptospirosis, Southeast Asia, including Vietnam, is among the most vulnerable global regions. The objective of the review was to analyze available published data on the spread of leptospirosis in Vietnam. More than 100 research articles were analyzed allowing to state that in Vietnam synanthropic rodents (rats), agricultural (buffaloes, cattle, pigs) and domestic animals (cats, dogs) are the main sources of leptospirosis infection in humans. It is essential that rats (cats and dogs also) in Vietnam are used for food. Among all farm animals, pigs are of maximal importance as a source of infection in humans. In Vietnam, Leptospira prevalence in pigs varies widely, up to 73%. It depends significantly on the location, farm size, age and gender of animals, etc. A large variety of Leptospira serovars have been identified in pigs in Vietnam: Tarassovi, Bratislava, Australis, Javanica, Autumnalis, Grippotyphosa, and some others. Official Vietnam reporting of leptospirosis cases based on clinical data does not reflect the real-life incidence rate in humans. However, the available seroprevalence studies reveal that, on average, about 10% of the Vietnamese population are infected with Leptospira. Work in agriculture is the dominant risk factor for acquiring this infection. The highest Leptospira seroprevalence rates were detected in farmers, 63.2%. Serovar diversity is typical for pathogenic Leptospira circulating in Vietnam. In humans, the most frequent are antibodies to Hebdomadis, Wolffi and Icterohaemorrhagiae, but the frequency varied markedly across the country depending on the site, possibly with relation to the environment, as well as with economic activity of the local population. In Vietnam, geographic, climatic and social differences between northern, central and southern regions contribute to the specificity of local leptospirosis epidemiology. This emphasizes the advisability of developing special measures for leptospirosis prevention taking into account regional peculiarities.

A case-control study of agricultural and behavioral factors associated with leptospirosis in Vietnam

Introduction

Leptospirosis is a neglected disease in Vietnam. Until now, there has been limited knowledge about risk factors of this disease in Vietnam. The study was carried out to identify agricultural and behavioral factors associated with the transmission of leptospirosis in Vietnam.

Methods

This matched retrospective hospital-community-based case–control study was conducted from 1 October 2018 to 31 October 2019. We recruited cases from 11 selected government hospitals in three provinces of Vietnam, while controls were selected from the same communes of cases and matched by age (± 2 years) and sex. Microscopic agglutination test (MAT) and enzyme-linked immunosorbent assay (ELISA) were applied to determine confirmed cases, while only MAT was used to identify controls with a single high MAT titer < 1:100.

Results

504 participants (252 cases and 252 controls) were identified. Cultivating (OR 2.83, CI 1.38–5.79), animal farming (OR 8.26, CI 2.24–30.52), pig owners (OR 10.48, CI 5.05–21.73), cat owners (OR 2.62, CI 1.49–4.61) and drinking unboiled water (OR 1.72, CI 1.14 –2.59, p = 0.010) were significantly associated with human leptospirosis in Vietnam. Hand washing after farming/ gardening (OR 0.57, CI 0.38–0.86, p = 0.007) and bathing after farming, gardening, contact with cattle and poultry (OR 0.33, CI 0.19–0.58, p = 0.000) were determined as protective factors for this disease.

Conclusions

In short, the case–control study has revealed the risks in agricultural and animal practices and protective behavioral factors related to human leptospirosis in Vietnam. The findings suggested promotion of communication and health education programs targeting health behaviors in daily life and agricultural practices. Using personal protective equipment such as gowns, gloves, and boots during agricultural practices, especially cultivating and animal farming, is most recommended.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-022-07561-6.

Absence of serological or molecular evidence of Leptospira infection in farmed swine in the Hong Kong Special Administrative Region

Leptospirosis is an important zoonotic disease with several maintenance host species including swine. A cross sectional survey was undertaken between January to October 2020 to investigate the prevalence of leptospirosis in farmed swine in the Hong Kong Special Administrative Region (HKSAR) of China. Serum samples were collected from swine on seven farms (15 swine per farm; ten multiparous sows and five twelve-week-old weaners), while kidney samples were collected from 64 swine submitted for routine post-mortem (26 farms; average 2.4 swine per farm, range 1-6). Microscopic agglutination tests (MAT) to a panel of 24 Leptospira antigens did not reveal any evidence of seroconversion at a titre of 1:100. Polymerase chain reaction (PCR) testing of the kidney samples for Leptospira DNA did not detect any evidence of infection. Bayesian methods were used to compute the probability that the leptospirosis prevalence in farmed swine in the HKSAR was <3%, given none of the 105 swine sampled were positive on the MAT. The results of this study demonstrate no serological or molecular evidence of leptospirosis in farmed swine in the HKSAR. Subsequent statistical analysis supports the conclusion that the prevalence of leptospirosis in farmed swine in the HKSAR is negligible at present.

Immunoinformatic Study of Recombinant LigA/BCon1-5 Antigen and Evaluation of Its Diagnostic Potential in Primary and Secondary Binding Tests for Serodiagnosis of Porcine Leptospirosis

Leptospirosis is responsible for hampering the productivity of swine husbandry worldwide. The aim of this study was to assess the efficacy of bioinformatics tools in predicting the three-dimensional structure and immunogenicity of recombinant LigBCon1-5 (rLigBCon1-5) antigen. A battery of bioinformatics tools such as I-TASSER, ProSA and SAVES v6.0 were used for the prediction and assessment of the predicted structure of rLigBCon1-5 antigen. Bepipred-2.0, DiscoTope v2.0 and ElliPro servers were used to predict linear and conformational epitopes while T-cell epitopes were predicted using NetMHCpan 4.1 and IEDB recommended 2.22 method for MHC Class I and II peptides respectively. The results obtained using various in silico methods were then compared with wet lab experiments comprising of both primary (IgG Dot ELISA Dipstick test) and secondary-binding assays (Latex Agglutination Test [LAT]) to screen 1153 porcine serum samples. The three-dimensional structure of rLigA/BCon1-5 protein as predicted by I-TASSER was found to be reliable by Ramachandran Plot and ProSA. The ElliPro server suggested 10 and three potential linear and conformational B-cell-epitopes, respectively, on the peptide backbone of the rLigA/BCon1-5 protein. The DiscoTope prediction server suggested 47 amino acid residues to be part of B-cell antigen. Ten of the most efficient peptides for MHC-I and II grooves were predicted by NetMHCpan 4.1 and IEDB recommended 2.22 method, respectively. Of these, three peptides can serve dual functions as it can fit both MHC I and II grooves, thereby eliciting both humoral-and cell-mediated immune responses. The prediction of these computational approaches proved to be reliable since rLigBCon1-5 antigen-based IgG Dot ELISA Dipstick test and LAT gave results in concordance to gold standard test, the Microscopic Agglutination Test (MAT), for serodiagnosis of leptospirosis. Both the IgG Dot ELISA Dipstick test and LAT were serodiagnostic assays ideally suited for peripheral level of animal health care system as "point of care" tests for the detection of porcine leptospirosis.

Leptospira infection among human-close-contact animals in different geographical areas in Vietnam

Leptospirosis is a neglected disease in Vietnam. Only a few studies have evaluated the status of Leptospira infection in both humans and animals. To our knowledge, this is the first serological survey of Leptospira in both domestic and wild animals, which may act as reservoirs of this agent. This study aimed to evaluate the seroprevalence of Leptospira in animals that are in close contact with humans in different geographical areas in Vietnam. Sera were collected from 1205 individual animals of six species, including buffaloes, cattle, cats, dogs, swine, and rats. The microscopic agglutination test (MAT) against 25 serovars of Leptospira spp. has been employed to detect serovars of Leptospira among the studied population. Overall, 44.2% of buffaloes, 24.9% of cattle, 10.2% of swine, 32.9% of dogs, 12.2% of cats, and 16% of rats were seropositive. A total of 17 different serovars were detected, of which serovars Hebdomadis and Canicola circulated in all the studied animal species. Variability of the predominant serovars circulating in animal species and in different geographical areas of Vietnam has been noted. We conclude that this study showed a high prevalence of Leptospira circulating in animals that are in close contact with humans, raising an alert of the important sources of pathogenic leptospires transmission to humans in Vietnam. These findings prove an imperative need for effective measures for disease prevention.

Dogs as Sentinels for Flavivirus Exposure in Urban, Peri-Urban and Rural Hanoi, Vietnam

Diseases caused by flaviviruses, including dengue fever and Japanese encephalitis, are major health problems in Vietnam. This cross-sectional study explored the feasibility of domestic dogs as sentinels to better understand risks of mosquito-borne diseases in Hanoi city. A total of 475 dogs serum samples from 221 households in six districts of Hanoi were analyzed by a competitive enzyme-linked immunosorbent assay (cELISA) for antibodies to the pr-E protein of West Nile virus and other flaviviruses due to cross-reactivity. The overall flavivirus seroprevalence in the dog population was 70.7% (95% CI = 66.4–74.8%). At the animal level, significant associations between seropositive dogs and district location, age, breed and keeping practice were determined. At the household level, the major risk factors were rural and peri-urban locations, presence of pigs, coil burning and households without mosquito-borne disease experience (p < 0.05). Mosquito control by using larvicides or electric traps could lower seropositivity, but other measures did not contribute to significant risk mitigation of flavivirus exposure in dogs. These results will support better control of mosquito-borne diseases in Hanoi, and they indicate that dogs can be used as sentinels for flavivirus exposure.

Seroprevalences of multi-pathogen and description of farm movement in pigs in two provinces in Vietnam

Background

In Vietnam, lack of animal health information is considered a major challenge for pig production. The main objective of this study was to assess the seroprevalences of five pathogens [porcine circovirus type 2 (PCV2), porcine reproductive and respiratory syndrome virus (PRRSV), mycoplasma hyopneumoniae (M. hyo), Japanese encephalitis virus (JEV) and leptospirosis] and to better characterize the farm movements through a survey.

Results

A total of 600 samples were collected from 120 farms from Bac Giang and Nghe An. Among unvaccinated herds, the highest seroprevalence was found for JE with 73.81% (95% CI: 68.39–78.74) in Bac Giang and 53.51% (95% CI 47.68–59.27) in Nghe An. Seroprevalences for PCV2 and M.hyo were 49.43% (95% CI: 45.06–53.80) and 46.06% (95% CI: 41.48–50.69) among unvaccinated animals. Accumulative co-infections for JE (86.25%) showed the highest level followed by M. hyo (66.25%) and PCV2 (62.50%). Three co-infections with JE had the highest positive rate (28.75%) followed by four co-infections (25.0%). Medium farms had relatively higher herd prevalences for all pathogens, except from leptospirosis. Overall, farmers exported/imported their pigs at the most 1–2 times every 6 months. Some respondents (5% for exportation and 20% for importation) had moved pigs more than 6 times over the last 6 months.

Conclusions

Our study provided another pool of evidence that showed that PCV2, PRRS and H. hyo are endemic in pigs in Vietnam. Given the economic impacts of these pathogens elsewhere, the findings confirm the need for studies to evaluate the association between antibody response and clinical relevance as well as to assess the economic impact of co-infections at farm level. We also found that high seroprevalences of JE and leptospirosis were detected in pigs. From a pubic health point of view, it is crucial to raise public awareness especially for high risk occupations (mainly pig farm workers).

Serological evidence of Japanese encephalitis virus infection in pigs in a low human incidence state, Goa, India

Japanese encephalitis (JE) is a mosquito-borne zoonosis caused by Japanese encephalitis virus (JEV). It is a leading cause of encephalitis in humans especially children in Asia. Aquatic wading birds are the reservoirs and pigs serve as amplifying hosts for JEV. Humans and horses are dead-end hosts. JE is endemic in several states of India. Goa, a small state on the west coast of India, had witnessed JE outbreaks in the past and as on date human JE cases are reported sporadically. Although human JE cases are well documented in Goa, the status of JEV exposure of pigs has not been well documented. Hence the present study was undertaken with an objective of identifying JEV exposure in the pig population of Goa state in the light of declining human JE cases. To achieve the objective, between January 2017 and May 2019, serum samples from 666 pigs were screened using enzyme-linked immunosorbent assay (ELISA) for the detection of anti-JEV IgG. The apparent prevalence of anti-JEV IgG in pigs was found to be 7.1 % (95 % confidence interval 5.3 %-9.3 %) and true prevalence was 4.6 % (95 % confidence interval 2.7 %-7.1 %). The seroprevalence of JE recorded in pigs of Goa state was low compared to other endemic states in India, which may also be one of the reasons for the lower prevalence of human JE cases in Goa state. Univariate analysis revealed that the age of the pigs and district did not significantly influence the JE seroprevalence in pigs of Goa state. However, in multivariable logistic regression, the North Goa district was found to significantly (p = 0.017) influence the JE seroprevalence in pigs. The study identified that JEV is still circulating in the Goan pig population and hence constant vigil is required to monitor the intensity of JEV circulation in pigs. Besides forewarning possible human outbreaks in the locality, evidence of JEV exposure in pig population provides valuable data on the magnitude and extent of geographical spread.