Patterns of Flavivirus Seroprevalence in the Human Population of Northern Laos.

A total of 1,136 samples from 289 households in four provinces in northern Laos were subjected to Japanese encephalitis virus (JEV) and dengue virus hemagglutination inhibition (DENV HI). Overall, antibodies to JEV were detected by HI in 620 (54.6%) of 1,136 people; of which 217 (19.1%) had HI activity against JEV only. Antibodies to DENV4 were detected by HI in 526 (46.3%) of 1,136 people; of which 124 (10.9%) had HI activity against DENV4 only. Antibodies to DENV1-3 were detected by HI in 296 (26.1%), 274 (24.1%), and 283 (24.9) of 1,136 people, respectively; of which 7, 1, and 0, respectively, had HI activity against DENV1-3 only. JEV was the most prevalent Flavivirus in Oudomxay, Luangprabang, and Huaphan provinces and DENV4 was the most prevalent in Xiengkhouang province. Seroprevalence for JEV increased with increasing age and wealth and was higher in villages where rice was cultivated in paddy fields and highest for people of Lao-Tai ethnicity.

Prevalence of Endemic Pig-Associated Zoonoses in Southeast Asia: A Review of Findings from the Lao People's Democratic Republic.

The increasing intensification of pork production in southeast Asia necessitates an urgent requirement to better understand the dual impact of pig-associated zoonotic disease on both pig production and human health in the region. Sharing porous borders with five countries and representing many regional ethnicities and agricultural practices, the Lao People's Democratic Republic (Lao PDR) appears well placed to gauge the levels of pig-associated zoonoses circulating in the wider region. Despite this, little is known about the true impact of zoonotic pathogens such as leptospirosis, Trichinella, hepatitis E virus (HEV), Japanese encephalitis (JE), and Taenia solium on human health and livestock production in the country. A comprehensive review of the published prevalences of these five pig-associated zoonoses in Lao PDR has demonstrated that although suspicion remains high of their existence in pig reservoirs across the country, epidemiological data are scarce; only 31 epidemiological studies have been undertaken on these diseases in the past 25 years. A greater understanding of the zoonoses prevalence and subsequent risks associated with pork production in the southeast Asian region could help focus public health and food safety interventions at key points along the value chain, benefiting both livestock producers and the broader animal and human health systems in the region.

Patterns and risks of trichinella infection in humans and pigs in northern Laos.

Several outbreaks of trichinellosis associated with the consumption of raw pork have occurred in Laos since 2004. This cross-sectional study was conducted in four provinces of northern Laos to investigate the seroepidemiology of trichinellosis in the human population and determine the prevalence and species of Trichinella infection in the domestic pig population. Serum samples and questionnaire data were obtained from 1419 individuals. Serum samples were tested for Trichinella antibodies by ELISA using larval excretory-secretory (ES) antigens and a subset of 68 positive samples were tested by western blot. The seroprevalence of Trichinella antibodies was 19.1% (95% confidence interval (CI) = 17.1-21.1%). The risk of having antibodies detected by ELISA using ES antigens increased with age, being of Lao-Tai ethnicity, living in Oudomxay province and being male. Tongue and diaphragm muscle samples were collected from 728 pigs and tested for Trichinella larvae by the artificial digestion method. Trichinella larvae were isolated from 15 pigs (2.1%) of which 13 were identified as T. spiralis by molecular typing; the species of the two remaining isolates could not be determined due to DNA degradation. Trichinella spp. are endemic in the domestic environment of northern Laos and targeted preventative health measures should be initiated to reduce the risk of further outbreaks occurring.

The economic impact of pig-associated parasitic zoonosis in Northern Lao PDR.

The parasitic zoonoses human cysticercosis (Taenia solium), taeniasis (other Taenia species) and trichinellosis (Trichinella species) are endemic in the Lao People's Democratic Republic (Lao PDR). This study was designed to quantify the economic burden pig-associated zoonotic disease pose in Lao PDR. In particular, the analysis included estimation of the losses in the pork industry as well as losses due to human illness and lost productivity. A Markov-probability based decision-tree model was chosen to form the basis of the calculations to estimate the economic and public health impacts of taeniasis, trichinellosis and cysticercosis. Two different decision trees were run simultaneously on the model's human cohort. A third decision tree simulated the potential impacts on pig production. The human capital method was used to estimate productivity loss. The results found varied significantly depending on the rate of hospitalisation due to neurocysticerosis. This study is the first systematic estimate of the economic impact of pig-associated zoonotic diseases in Lao PDR that demonstrates the significance of the diseases in that country.

A cross-sectional study of Taenia solium in a multiple taeniid-endemic region reveals competition may be protective.

We conducted cross-sectional surveys for taeniasis and cysticercosis in humans, pigs, and dogs in four northern provinces of Laos. Human cysticercosis and taeniasis prevalence was 2.2% (95% confidence interval [CI] = 1.4-3.0%) and 8.4% (95% CI = 6.9-9.9%), respectively. Eating uncooked beef, being male, province of residence, age, and ethnicity were significant risk factors for taeniasis and only province of residence was a significant risk factor for cystiercosis. Thirty-five human tapeworms were recovered during the survey and 33 (94.3%) and 2 (5.7%) were identified as Taenia saginata and T. solium, respectively. Maximum-likelihood adjusted prevalence of T. solium and T. hydatigena in pigs was 4.2% (95% CI = 0.5-7.9%) and 55.9% (95% CI = 47.5-64.3%), respectively, and T. hydatigena taeniasis in dogs was 4.8% (95% CI = 0.0-11.3%). Taenia hydatigena and T. saginata were the most prevalent taeniids in the respective pig and human populations and together may suppress T. solium transmission.

Serologic study of pig-associated viral zoonoses in Laos.

We conducted a serologic survey of four high-priority pig-associated viral zoonoses, Japanese encephalitis virus (JEV), hepatitis E virus (HEV), Nipah virus (NiV), and swine influenza virus (SIV), in Laos. We collected blood from pigs at slaughter during May 2008-January 2009 in four northern provinces. Japanese encephalitis virus hemagglutination inhibition seroprevalence was 74.7% (95% confidence interval [CI] = 71.5-77.9%), JEV IgM seroprevalence was 2.3% (95% CI = 1.2-3.2%), and HEV seroprevalence was 21.1% (95% CI = 18.1-24.0%). Antibodies to SIV were detected in 1.8% (95% CI = 0.8-2.8%) of pigs by screening enzyme-linked immunosorbent assay, and only subtype H3N2 was detected by hemagglutination inhibition in two animals with an inconclusive enzyme-linked immunosorbent assay result. No NiV antibody-positive pigs were detected. Our evidence indicates that peak JEV and HEV transmission coincides with the start of the monsoonal wet season and poses the greatest risk for human infection.

Seroprevalence of major bovine-associated zoonotic infectious diseases in the Lao People's Democratic Republic.

Bovine-associated zoonotic infectious diseases pose a significant threat to human health in the Lao People's Democratic Republic (Lao PDR). In all, 905 cattle and buffalo serum samples collected in northern Lao PDR in 2006 were used to determine seroprevalence of five major bovine zoonotic infectious diseases that included Taenia saginata cysticercosis, bovine tuberculosis, Q-fever, bovine brucellosis, and bovine leptospirosis. Five enzyme-linked immunosorbent assays (ELISAs) were used to test for the presence of antibodies to the diseases, except Taenia saginata, for which we tested for the presence of Taenia metacestode circulating antigens. The overall highest prevalence was for T. saginata (46.4%), with lower prevalence for Q-fever (4%), leptospirosis (3%), tuberculosis (1%), and brucellosis (0.2%). Although there were no significant differences in the proportion of seroprevalence between sex and age of the animals sampled, there were significant differences between the provincial distributions. Further studies are required to determine the seroprevalence of these infections in other locations in Lao PDR, as well as other animal species including humans, in order to develop effective prevention and control strategies. This is the first study to investigate the prevalence of bovine zoonotic infectious agents in the Lao PDR. Positivity was demonstrated for all diseases investigated, with the highest prevalence for T. saginata antigen and Coxiella burnetti antibodies. For T. saginata, there were significant differences in the provincial distribution. Approximately 16% seroprevalence of Coxiella burnetti was noted in Xayabuly Province; however, there are no clear reasons why this was the case, and further studies are required to determine risk factors associated with this observation.

Soil-transmitted helminthiasis in Laos: a community-wide cross-sectional study of humans and dogs in a mass drug administration environment.

We conducted a community cross-sectional survey of soil-transmitted helminthiasis in humans and dogs in four provinces in northern Laos. We collected and tested human and dog fecal samples and analyzed results against sociodemographic data. The prevalence of Ascaris lumbricoides, Trichuris trichiura, hookworm, and Strongyloides stercoralis was 26.1% (95% confidence interval [CI] = 23.7-28.4%), 41.5% (95% CI = 38.8-44.1%), 46.3% (95% CI = 43.3-49.0%), and 8.9% (95% CI = 7.4-10.4%), respectively. We observed strong heterogeneity for helminthiasis by ethnicity, province, and wealth status, which coincided with a risk profile demonstrating that Mon-Khmer persons and the poorest households are highly vulnerable. Necator americanus was the dominant hookworm species infecting humans and Ancylostoma ceylanicum was the only Ancylostoma species detected. Hookworm prevalence in village dogs was 94%, and the dominant species was A. ceylanicum. Necator americanus was also detected in dogs. It appears that dogs have a role in human hookworm transmission and warrant further investigation.

A review of parasitic zoonoses in a changing Southeast Asia.

Parasitic zoonoses are common and widely distributed in the Southeast Asian region. However, the interactions between parasites, hosts and vectors are influenced by environmental, socio-cultural and livestock production changes that impact on the distribution, prevalence and severity of disease. In this review we provide an update on new knowledge in the context of ongoing changes for the food-borne pig associated zoonoses Taenia solium and Trichinella spp., the food-borne trematodes Opisthorchis viverrini and Clonorchis sinensis, the water-borne trematodes Schistosoma spp., the vector-borne zoonotic protozoa Plasmodium knowlesi and Leishmania spp. and the soil-borne zoonotic hookworm Ancylostoma ceylanicum. These various changes need to be considered when assessing or developing regional control programs or devising new research initiatives in a changing SE Asia.

Hepatitis E virus is prevalent in the pig population of Lao People's Democratic Republic and evidence exists for homogeneity with Chinese Genotype 4 human isolates.

The objective of this study was to determine the prevalence and genotypic range of Hepatitis E virus (HEV) in the pig population of northern Lao People's Democratic Republic (PDR). We collected 181 faecal samples from indigenous-breed pigs ≤ 6 months of age and the faeces was stored in RNA stabilisation buffer due to cold-chain and transport limitations. Twenty-one (11.6%) pigs had detectable HEV RNA and 43.5% of village pig herds were infected. Based on a 240 base pair-nucleotide sequence flanking the junction of open reading frames 1, 2 and 3 (ORF1, ORF2 and ORF3) the isolates were phylogenetically classified within genotype 4. Phylogenetic analyses revealed distinct genetic groupings of the Lao HEV isolates and two groups clustered with human and pig HEV isolates from China. This was the first study to demonstrate genotype 4 HEV in Lao PDR and indicates pigs are a potential reservoir for human HEV infection.

Does interspecific competition have a moderating effect on Taenia solium transmission dynamics in Southeast Asia?

It is well understood that sociocultural practices strongly influence Taenia solium transmission; however, the extent to which interspecific parasite competition moderates Taenia transmission has yet to be determined. This is certainly the case in Southeast Asia where T. solium faces competition in both the definitive host (people) and the intermediate host (pigs). In people, adult worms of T. solium, T. saginata and T. asiatica compete through density-dependent crowding mechanisms. In pigs, metacestodes of T. solium, T. hydatigena and T. asiatica compete through density-dependent immune-mediated interactions. Here, we describe the biological and epidemiological implications of Taenia competition and propose that interspecific competition has a moderating effect on the transmission dynamics of T. solium in the region. Furthermore, we argue that this competitive ecological scenario should be considered in future research and surveillance activities examining T. solium cysticercosis and taeniasis in Southeast Asia.

Molecular epidemiology of foot-and-mouth disease viruses from South East Asia 1998-2006: the Lao perspective.

Foot-and-mouth disease (FMD) causes sporadic disease outbreaks in the Lao People's Democratic Republic (Lao PDR) and appears to be endemic within a livestock population largely susceptible to infection. As Lao PDR is a major thoroughfare for transboundary animal movement, regular FMD outbreaks occur causing economic hardship for farmers and their families. The dominant serotype causing outbreaks between 1998 and 2006 was type O. Using phylogenetic analysis, type O isolated viruses were divided into two topotypes: South East Asia (SEA) and the Middle East-South Asia (ME-SA). Type A virus was reported only in 2003 and 2006 and type Asia 1 only in 1996 and 1998.

Development and evaluation of a rapid immunomagnetic bead assay for the detection of classical swine fever virus antigen.

Classical swine fever (CSF) is a highly contagious and severe viral disease of swine resulting in substantial production losses in different farming systems in many regions of the world. The accurate and rapid detection of CSF outbreaks is reliant on sensitive and specific laboratory testing and is a key component of disease control. Specific detection of CSF virus can be achieved by virus isolation in tissue culture, antigen capture or the detection of viral RNA using molecular techniques. In order to reduce the time taken to achieve a diagnostic result and simplify testing methods, an antigen capture ELISA using immunomagnetic beads (IMB) as the solid phase was developed and compared to a microplate-based antigen capture (AC)-ELISA. The IMB-ELISA has up to 64-fold greater analytical sensitivity than the AC-ELISA and initial estimates of diagnostic sensitivity and specificity are 100%. The IMB-ELISA has a highly robust, rapid and stable test format and is simpler to perform than the AC-ELISA. The IMB-ELISA has the added advantage that a result can be sensitively and specifically determined by eye, lending it to the possibility of adaptation to a near-to-field test with minimal equipment or expertise needed.

Biological, antigenic and phylogenetic characterization of the flavivirus Alfuy.

Alfuy virus (ALFV) is classified as a subtype of the flavivirus Murray Valley encephalitis virus (MVEV); however, despite preliminary reports of antigenic and ecological similarities with MVEV, ALFV has not been associated with human disease. Here, it was shown that ALFV is at least 10(4)-fold less neuroinvasive than MVEV after peripheral inoculation of 3-week-old Swiss outbred mice, but ALFV demonstrates similar neurovirulence. In addition, it was shown that ALFV is partially attenuated in mice that are deficient in alpha/beta interferon responses, in contrast to MVEV which is uniformly lethal in these mice. To assess the antigenic relationship between these viruses, a panel of monoclonal antibodies was tested for the ability to bind to ALFV and MVEV in ELISA. Although the majority of monoclonal antibodies recognized both viruses, confirming their antigenic similarity, several discriminating antibodies were identified. Finally, the entire genome of the prototype strain of ALFV (MRM3929) was sequenced and phylogenetically analysed. Nucleotide (73 %) and amino acid sequence (83 %) identity between ALFV and MVEV confirmed previous reports of their close relationship. Several nucleotide and amino acid deletions and/or substitutions with putative functional significance were identified in ALFV, including the abolition of a conserved glycosylation site in the envelope protein and the deletion of the terminal dinucleotide 5'-CU(OH)-3' found in all other members of the genus. These findings confirm previous reports that ALFV is closely related to MVEV, but also highlights significant antigenic, genetic and phenotypic divergence from MVEV. Accordingly, the data suggest that ALFV is a distinct species within the serogroup Japanese encephalitis virus.