Foot-and-mouth disease outbreaks due to an exotic serotype Asia 1 virus in Myanmar in 2017

Evaluating serological tests for foot-and-mouth disease while accounting for different serotypes and uncertain vaccination status

Controlling foot-and-mouth disease (FMD) by vaccination requires adequate population coverage and high vaccine efficacy under field conditions. To assure veterinary services that animals have acquired sufficient immunity, strategic post-vaccination surveys can be conducted to monitor the coverage and performance of the vaccine. Correct interpretation of these serological data and an ability to derive exact prevalence estimates of antibody responses requires an awareness of the performance of serological tests. Here, we used Bayesian latent class analysis to evaluate the diagnostic sensitivity and specificity of four tests. A non-structural protein (NSP) ELISA determines vaccine independent antibodies from environmental exposure to FMD virus (FMDV), and three assays measuring total antibodies derived from vaccine antigen or environmental exposure to two serotypes (A, O): the virus neutralisation test (VNT), a solid phase competitive ELISA (SPCE), and a liquid phase blocking ELISA (LPBE). Sera (n = 461) were collected by a strategic post-vaccination monitoring survey in two provinces of Southern Lao People's Democratic Republic (PDR) after a vaccination campaign in early 2017. Not all samples were tested by every assay and each serotype: VNT tested for serotype A and O, whereas SPCE and LPBE tested for serotype O, and only NSP-negative samples were tested by VNT, with 90 of them not tested (missing by study design). These data challenges required informed priors (based on expert opinion) for mitigating possible lack of model identifiability. The vaccination status of each animal, its environmental exposure to FMDV, and the indicator of successful vaccination were treated as latent (unobserved) variables. Posterior median for sensitivity and specificity of all tests were in the range of 92-99 %, except for the sensitivity of NSP (∼66%) and the specificity of LPBE (∼71 %). There was strong evidence that SPCE outperformed LPBE. In addition, the proportion of animals recorded as having been vaccinated that showed a serological immune response was estimated to be in the range of 67-86 %. The Bayesian latent class modelling framework can easily and appropriately impute missing data. It is important to use field study data as diagnostic tests are likely to perform differently on field survey samples compared to samples obtained under controlled conditions.

A Vaccine Based on Asia1 Shamir of the Foot-and-Mouth Disease Virus Offers Low Levels of Protection to Pigs against Asia1/MOG/05, Circulating in East Asia

Foot-and-mouth disease (FMD) is one of the most contagious diseases in cloven hoof animals. Vaccination can prevent or control FMD, and vaccine antigens should be matched against circulating viruses. According to phylogenetic analyses, field isolates in this region belonged to genotype V and showed low genetic similarity with the Asia1 Shamir vaccine, the OIE-recommended vaccine strain. In this study, we investigated whether pigs vaccinated with the Asia1 Shamir vaccine could be protected from challenges with the Asia1/MOG/05 virus, one of the genotype V field isolates. Eight pigs were divided into either vaccinated or nonvaccinated control groups. After two vaccinations with Asia1 Shamir, both groups of pigs were challenged with the Asia1/MOG/05 field isolate at 2 weeks after the second vaccination. In the control group, symptoms appeared at 2 days post-infection (dpi). The clinical sign score peaked at 4 dpi, and this coincided with virus shedding through nasal discharge. Neutralizing antibody titers peaked at 17 dpi. In the vaccinated group, clinical signs were delayed compared with the control group, and the highest score was shown at 10 dpi accompanied with virus nasal shedding, which peaked at 11 dpi. Neutralizing antibodies were induced 2 weeks after the second vaccination and peaked at 17 dpi. In conclusion, Asia1 Shamir vaccination in pigs provided partial protection from Asia1/MOG/05 virus infection.

Time-Series Analysis for the Number of Foot and Mouth Disease Outbreak Episodes in Cattle Farms in Thailand Using Data from 2010-2020

Thailand is one of the countries where foot and mouth disease outbreaks have resulted in considerable economic losses. Forecasting is an important warning technique that can allow authorities to establish an FMD surveillance and control program. This study aimed to model and forecast the monthly number of FMD outbreak episodes (n-FMD episodes) in Thailand using the time-series methods, including seasonal autoregressive integrated moving average (SARIMA), error trend seasonality (ETS), neural network autoregression (NNAR), and Trigonometric Exponential smoothing state−space model with Box−Cox transformation, ARMA errors, Trend and Seasonal components (TBATS), and hybrid methods. These methods were applied to monthly n-FMD episodes (n = 1209) from January 2010 to December 2020. Results showed that the n-FMD episodes had a stable trend from 2010 to 2020, but they appeared to increase from 2014 to 2020. The outbreak episodes followed a seasonal pattern, with a predominant peak occurring from September to November annually. The single-technique methods yielded the best-fitting time-series models, including SARIMA(1,0,1)(0,1,1)12, NNAR(3,1,2)12,ETS(A,N,A), and TBATS(1,{0,0},0.8,{<12,5>}. Moreover, SARIMA-NNAR and NNAR-TBATS were the hybrid models that performed the best on the validation datasets. The models that incorporate seasonality and a non-linear trend performed better than others. The forecasts highlighted the rising trend of n-FMD episodes in Thailand, which shares borders with several FMD endemic countries in which cross-border trading of cattle is found common. Thus, control strategies and effective measures to prevent FMD outbreaks should be strengthened not only in Thailand but also in neighboring countries.

First Report of Lumpy Skin Disease in Myanmar and Molecular Analysis of the Field Virus Isolates

Lumpy skin disease virus (LSDV) causes lumpy skin disease in cattle and buffaloes, which is associated with significant animal production and economic losses. Since the 2000s, LSDV has spread from Africa to several countries in the Middle East; Europe; and Asia; including, more recently, several south-east Asian countries. In November 2020, Myanmar reported its first LSD outbreak. This study reports on the first incursion of LSD in Myanmar and the molecular analysis of the LSDV detected. Staff from the Livestock Breeding and Veterinary Department (LBVD) of the Ministry of Agriculture, Livestock, and Irrigation collected samples from cattle with suspected LSD infection. The Food and Agriculture Organization (FAO) of the United Nations’ Emergency Centre for Transboundary Animal Diseases (ECTAD) and the Joint International Atomic Energy Agency (IAEA)/FAO program’s Animal Health and Production laboratory provided LSDV diagnostic support to two regional veterinary diagnostic laboratories in Myanmar. Samples from 13 cattle tested positive by real-time PCR. Selected samples underwent sequence analysis in IAEA laboratories. The results show that the Myanmar LSDV sequences clustered with LSDV isolates from Bangladesh and India, LSDV Kenya, and LSDV NI-2490. Further characterization showed that the Myanmar LSDV is 100% identical to isolates from Bangladesh and India, implying a common source of introduction. These findings inform diagnosis and development of control strategies.

What drives small-scale farmers to vaccinate their multiple livestock species animals against common infectious diseases in Myanmar?

Livestock rearing is an important income source for small-scale farmers in Myanmar, but Foot and Mouth Disease (FMD) and Newcastle disease (ND) are major constraints to livestock production. A study was conducted to identify perceptions of farmers about FMD and ND disease risks and perceptions about vaccination practices by using the modified health belief model. The majority of livestock farmers (>70%) reported that they were aware of the risk and impact of FMD and ND and were willing to vaccinate their livestock (>60%). Focusing on three main livestock farmer groups, about 17.0% of cattle, 15.4% of village chicken, but only 2.3% of small ruminant owners, indicated that the non-availability of vaccinations in the villages was the major constraint to vaccinations (p<0.001), while in contrast twice as many small ruminant farmers compared to cattle and village chicken farmers indicated they had no knowledge about vaccinations and no funds to conduct vaccinations. Limited accessibility to vaccines and vaccinators was related to size of villages (p = 0.001 for cattle; p = 0.027 for small ruminants; p = 0.005 for village chicken). Willingness to vaccinate small ruminants against FMD was associated with the perceived impact of the disease on sales and accessibility of information about vaccination. Accessibility to information about ND vaccination influenced the willingness of village chicken farmers to conduct vaccinations. In addition, beliefs in the effectiveness of vaccinations played a major role in the willingness to carry out vaccinations on both, cattle (β = 0.3, p = 0.018) and village chicken farms (β = 0.5, p<0.001). Our study highlights that policies that increase the accessibility of vaccines and the dissemination of information about disease prevention and vaccination practices in villages of all sizes, have the potential to increase FMD and ND vaccination rates and thereby reduce outbreak occurrence in Myanmar. On the other hand, indirect factors, such as village size strongly influenced the availability of vaccinations.

Detection of Foot-and-Mouth Disease Virus in the Absence of Clinical Disease in Cattle and Buffalo in South East Asia

Foot-and-mouth disease virus (FMDV) is widespread throughout much of the world, including parts of South East Asia. Surveillance is often limited in endemic areas, relying predominantly on passive outbreak reporting. As part of the World Organisation for Animal Health (OIE)'s South East Asia and China Foot-and-Mouth Disease Project (SEACFMD), field sampling was performed to help understand evidence of widespread virus exposure observed in previous studies. Serum and dry mucosal swabs were collected to evaluate the presence of FMDV RNA on the nasal, oral, and dorsal nasopharyngeal mucosal surfaces of 262 healthy cattle (n = 84 in Laos; n = 125 in Myanmar) and buffalo (n = 48 in Laos; n = 5 in Myanmar) immediately following slaughter in three slaughterhouses. Swabs and serum were tested by the OIE/FAO World Reference Laboratory for foot-and-mouth disease (WRLFMD) using pan-serotypic real-time reverse transcription-PCR (rRT-PCR) and serum was evaluated using the FMD PrioCHECK non-structural protein (NSP) ELISA. In total, 7.3% of animals had detectable FMDV RNA in one or more of the three sites including 5.3% of nasopharyngeal swabs, 2.3% of oral swabs, and 1.5% of nasal swabs. No FMDV RNA was detected in serum. Overall, 37.8% of animals were positive for NSP antibodies, indicating likely past natural exposure to FMDV. Results were comparable for Laos and Myanmar, and for both cattle and buffalo, and were not significantly different between age groups. Detectable FMDV RNA present on the oral and nasal mucosa of clinically-healthy large ruminants in Laos and Myanmar demonstrates the importance of sampling asymptomatic animals as part of surveillance, and may indicate that subclinical infection plays a role in the epidemiology of FMD in these countries.

Efficient protection against Asia1 type foot-and-mouth disease using a chimeric vaccine strain suitable for East Asia

The type Asia1 genetic group(G)-V lineage foot-and-mouth disease (FMD) virus was identified in the East-Asian region in 2009. To date, only Shamir has been used as a standard vaccine strain worldwide for type Asia1. To prevent type Asia1 FMD in eastern Asia, two vaccine strains (ASM-R: G-V and ASM-SM: G-V/Shamir fusion) were developed and tested against type Asia1 virus strains. After immunization with the two experimental vaccines, the ASM-SM strain showed a higher level of protection against Shamir virus in mice. Additional immunogenicity tests were carried out in cattle and pigs, revealing sufficient antibody production capable of protecting the animals against the viral challenge. In cattle, the immune response started just 2 weeks after vaccination. Immunogenicity was lower in pigs, but antibody production was greatly increased to a high level after a second vaccination round. In particular, herein, 60 % and 100 % of the vaccinated pigs challenged with the Asia1 Shamir virus were determined to be clinically protected after one and two vaccination rounds with ASM-R, respectively. Pigs vaccinated twice produced sufficient antibody titers with low virus shedding for short time. Moreover, ASM-SM single-vaccinated pigs showed 100 % protection when challenged with the Asia1 Shamir virus. In summary, the vaccine strain ASM-SM designed for the defense of the Asian region efficiently granted protection to pigs against the typical Asia1 virus, Shamir.

High seroprevalence of Foot and Mouth Disease in Laos: Call for nationwide vaccination campaigns and disease surveillance

Foot and mouth disease (FMD) virus remains enzootic in Lao People's Democratic Republic (Lao PDR) due to insufficient control measures, including low vaccination coverage. We assessed virus epidemiology and evaluated knowledge, attitude and practice of Lao farmers and animal health stakeholders towards FMD to support politics in devising evidence-based control measures. Sera were collected from 972 domestic ruminants in three provinces of Lao PDR: Vientiane Capital, Vientiane and Xiengkhouang provinces. Seroprevalence of antibodies directed against non-structural proteins of FMD virus was assessed using a commercial ELISA. Positive sera were further characterized by detecting antibodies directed against the structural proteins of FMD serotypes O, A and Asia 1. Information about farm management, biosecurity practices, livestock trade, and past FMD outbreaks was obtained. Overall 35% (340/972) of the ruminants had antibodies against FMD virus with a similar seroprevalence in each province. Seroprevalence depended significantly on the ruminant species (p < .001): 61% of buffaloes, but only 41% of cattle and 15% of goats were seropositive. While antibodies against FMD serotype Asia 1 were absent, 87% (297/340) of the seropositive animals had antibodies against FMD serotype O and 32% (110/340) against FMD serotype A. Many seropositive animals (31%) had antibodies against both serotypes O and A. The majority of the farmers could name the symptoms of FMD and the susceptible animal species. Although many had likely observed FMD outbreaks in their herd and were aware of FMD vaccines, only few vaccinated their animals. This study confirms that FMD remains enzootic in at least three provinces of Lao PDR where vaccination coverage is low. It also shows the relevance of nationwide active and passive disease surveillance, as well as of vaccination campaigns using bivalent FMD vaccines and targeting all susceptible animal species.

Antigenic properties of a novel vaccine strain for type Asia1 foot-and-mouth disease in pigs

Newly developed vaccine strains to prevent foot-and-mouth disease caused by the emerging serotype Asia1 virus were evaluated. To protect against the group (G)-VIII strain, which occurred recently, we produced an infectious cDNA clone of Asia1 Shamir cDNA (Asia1 Shamir-R). In addition, by adding a site 1 epitope of VP1 of the G-VIII lineage virus to this virus, we produced a new virus (Sham GVIII- EPI), and another virus(Sham GVIII-VP1) was replaced with that of G-VIII lineage in the VP1 region of Shamir. Test vaccines were produced using these three types of vaccine virus, and their immunogenicity and protection capabilities were evaluated in mice. Immunized mice were challenged with the Asia1 Shamir or G-VIII virus, and the results show that all the vaccines have similar protective effects. As they showed similar antigenicity, we chose the Shamir-R vaccine. Pigs maintained relatively high neutralizing antibody levels against homologous viruses of the Shamir and G-VII or G-VIII lineage three to four weeks after immunization. However, they formed relatively low levels of antibodies to G-IV and G-V viruses. In conclusion, we produced a vaccine candidate capable of protection against the G-VIII virus in the vaccine experiment for the type Asia1 serotype vaccine. This Shamir-R vaccine virus was found to protect against the viruses of the Asia1 genotype G-VII and G-VIII lineages, which occurred recently in Asia.

Evaluation of novel inactivated vaccines for the SAT 1, SAT 2 and SAT 3 serotypes of foot-and-mouth disease in pigs

Background

The foot-and-mouth disease (FMD) virus is classified into seven serotypes, of which the South African types have South African Territories (SAT)1, SAT2, and SAT3 that are prevalent in Africa. Especially SAT2 have spread to Arabian Peninsula and the Palestinian Autonomous Territories. Of these viruses, the incidence of SAT2 is the highest. It is important to prepare for the spread of the virus to other continents, even though most FMD viruses are bovine-derived. In particular, due to the high breeding density of pigs in Asia, more attention is usually paid to the immunity and protection of pigs than cattle. For this reason, this study investigated the immunity and protection of pigs against the SAT viruses.

Methods

Specific vaccines were developed for SAT1, SAT2, and SAT3 serotypes. These vaccine viruses were designed to be distinguished from the wild-type strain. An immunogenicity test was conducted using these vaccines in both cattle (n = 5/group) and pigs (n = 20/group).

Results

High virus-neutralizing titer of antibodies (> 1:100) was induced in only 2 weeks after the immunization of cattle with the individual vaccine for SAT1, SAT2 or SAT3, and a clear immune response was induced after the second immunization in pigs. When the vaccinated pigs (n = 4–5/group) were challenged by the homologous wild-type virus strain 4 weeks after immunization, all the pigs were protected from the challenge.

Conclusions

This study confirmed that these vaccines can be used against SAT1, SAT2, and SAT3 viruses in cattle and pigs. The vaccine strains developed in this study are expected to be used as vaccines that can protect against FMD in the event of a future FMD outbreak in pigs in consideration of the situation in Asia.

Emergence of novel lineage of foot-and-mouth disease virus serotype Asia1 BD-18 (G-IX) in Bangladesh

Foot-and-mouth disease virus (FMDV) is a highly evolutionary divergent pathogen causing great economic havoc in many countries. Among its seven existing serotypes, Asia1 is the least divergent with a single topotype both genetically and antigenically. It is reported sporadically in Indian subcontinent and was classified under lineage G-VIII. In 2018, serotype Asia1 re-emerged in Bangladesh after 2013, along with circulation of a novel serotype Asia1 BD-18 (G-IX) lineage. VP1 phylogeny and sequence variation clearly demonstrated the novel strains which was estimated to have at least >5% nucleotide divergence with distinct clade formation. Also, the Bayesian phylogeographic inferences traced back to the origin time of lineage G-IX in early 2017 and a possible origin in Bangladesh. Mutational analysis considering established eight lineages revealed that the virus strains belonged to lineage G-IX contained a unique mutation at 44 position in the B-C loop region of VP1. Inappropriate vaccination and inefficient outbreak surveillance possibly contributed to the current episode of emergence. Therefore, active surveillance and continued vigilance are essential to assess and timely detect the occurrence, extent and distribution of this novel Asia1 strains in Bangladesh and the neighbouring countries.