Laurence J. Gleeson

Village level risk factors for foot-and-mouth disease in Northern Thailand

Abstract A study was undertaken in northern Thailand to identify factors which put some villages at higher risk of foot-and-mouth disease (FMD) outbreaks than others. The number of FMD outbreaks experienced in the previous 5 years and data on 145 putative risk factors were obtained by interview from 60 villages during 1991–1992. Univariable analyses identified 27 factors for further investigation using logistic regression. When villages were classified into three FMD frequency groups of zero to one, two to three or four or more outbreaks in the last 5 years, the important factors explaining the differences in risk were the total number of cattle and buffaloes purchased in the previous year, the number of neighbouring villages which shared a common water source and whether agriculture was the most important source of cash income for the village. These factors were also the most important variables in explaining the difference in risk when comparing villages with zero or one outbreak with those having four or more. We concluded that the greatest impact on reducing spread of FMD among villages would be obtained through the development of strategies to reduce the likelihood of introduction through livestock purchases and for villagers to take greater care when livestock are grazed with those from neighbouring villages and when sharing common water supplies.

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 Peoples 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.

Genetic typing of classical swine fever viruses from Lao PDR by analysis of the 5' non-coding region

The 5′ non-coding region (5′-NCR) of 27 classical swine fever virus (CSFV) isolates from Lao People’s Democratic Republic (Lao PDR) during 1997 and 1999 were amplified by RT-PCR. A 150-bp region of the 5′-NCR amplicons was analysed and compared with reference CSFV of European and Asian origin and a phylogenetic dendrogram constructed. Following analysis, all viruses were determined to belong to genogroup 2. Viruses from Lao PDR grouped on a geographical basis with the majority of northern/central isolates falling into subgroup 2.1 and southern/central isolates falling into subgroup 2.2. These results concur with previous studies of CSF viruses from Lao PDR, although this study recognized the first occurrence of subgroup 2.1 in southern Lao PDR.

Comparative susceptibility of indigenous and improved pig breeds to Classical swine fever virus infection: practical and epidemiological implications in a subsistence-based, developing country setting.

This study investigated the comparative susceptibility of indigenous Moo Laat and improved Large White/Landrace pig breeds to infection with classical swine fever virus (CSFV) under controlled conditions in the Lao People’s Democratic Republic (Lao PDR). The Moo Laat (ML) and Large White/Landrace crossbreed (LWC) pigs were inoculated with a standard challenge strain designated Lao/Kham225 (infectivity titre of 102.75 TCID50/ml). The results demonstrated that both the native breed and an improved pig breed are fully susceptible to CSFV infection and the mortality rate is high. LWC pigs demonstrated lower (or shorter) survival times (50% survival time: 11 days), earlier and higher pyrexia and earlier onset of viraemia compared to ML pigs (50% survival time: 18 days). In the context of village-based pig production, the longer time from infection to death in native ML pigs means that incubating or early sick pigs are likely to be sold once an outbreak of CSF is recognized in a village. This increased longevity probably contributes to the maintenance and spread of disease in a population where generally the contact rate is low.

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.

A modified liquid phase (LP) blocking ELISA used to assess type O foot-and-mouth disease virus antigenic variation in Thailand

A selection of type O foot-and-mouth disease (FMD) viruses isolated in Thailand between 1986 and 1989 were compared to the reference viruses O1 Thailand 1960 (O BKK/60) and O Nakorn Pathom 1965 (O NPT/65) using a liquid-phase blocking ELISA (LP ELISA) to derive serum titres and associated r values. Interpolation techniques were used to increase the precision for estimation of r values through a more accurate estimation of serum titres at predicted equivalent levels of antigen input. Mean r values were 0.45 (for 56 field viruses) relative to O BKK/60 reference virus and 0.56 (for 51 field viruses) relative to O NPT/65. While only two viruses showed considerable difference (r < 0.20) to a reference virus (O BKK/60), 41% and 31% gave r values less than 0.4 for O BKK/60 and O NPT/65 respectively. This indicated antigenic differences between reference and field viruses which may result in a reduction in vaccine efficacy.

Diagnosis of classical swine fever virus in a limited resource setting: the influence of pig breed on methodology and sample selection.

S. D. Blacksell ( ) CSIRO Australian Animal Health Laboratory, Geelong, Victoria, Australia; Department of Microbiology and Parasitology, University of Queensland, St. Lucia, Brisbane, Queensland, Australia e-mail: stuart@tropmedres.ac The disease causes severe economic impact in both commercial and village pig production systems owing to its ease of spread and highly pathogenic nature. Laboratory diagnosis is required to confirm CSF virus (CSFV) infection since the clinical signs mimic many other less-contagious infections. Tissues including tonsil, spleen and lymph node are the most suitable for CSF diagnosis (Kamolsiriprichaiporn et al., 1992a,b; Shannon et al., 1993) Breed-related factors influence the susceptibility to CSFV infection (Brugh et al., 1964; Depner et al., 1997); however, it is not clear whether these factors affect disease diagnosis and epidemiology. Four breeds of indigenous domestic pig have been described in the Lao People’s Democratic Republic (Lao PDR), namely Moo Laat, Moo Chid, Moo Nonghaet and Moo Daeng (Vannasook et al., 1997), with the Moo Laat being the most prevalent in the village-based pig production systems. The only recognized improved (imported) pig breeds in Lao PDR are the Large White/Landrace crossbreed and Duroc, although production using these breeds is generally restricted to the urban and peri-urban centres. Some smallholder breeders use cross improved breed boars to breed native bred sows. This study investigated the influence of pig breed on the diagnosis (serology, antigen detection, gross pathology) of CSF infection in the limited resource setting of Lao PDR and aimed to develop a simple strategy to improve diagnosis of CSF by the animal health services.