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The epidemiology of foot and mouth disease in Malaysia

Ramanoon, Siti (2016) The epidemiology of foot and mouth disease in Malaysia. PhD thesis, Murdoch University.

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The objectives of the present study were to determine the prevalence of foot and mouth disease (FMD) and the serotypes of foot and mouth disease virus (FMDV) in Malaysia; to describe the temporal and spatial distribution of FMD in Malaysia; to evaluate the risk of the introduction of FMD to Malaysia; to evaluate the effectiveness of mitigation strategies adopted in Malaysia during outbreaks of FMD; and ultimately to give recommendations on FMD control to the Malaysia-Thailand-Myanmar (MTM) Tri-state Commission and Zoning Working Groups.

The first documented outbreak of FMD in Peninsular Malaysia was in the 1860s and, although there have been periods where no outbreaks have been reported, the disease is now endemic in Peninsular Malaysia. Serotypes A, O and Asia 1 have been involved in the outbreaks of FMD in Peninsular Malaysia. In contrast the states of Sabah and Sarawak, located on Borneo have never had a reported outbreak of FMD. The virus strains involved in outbreaks in Peninsular Malaysia are closely related to those in southern Thailand and outbreaks have occurred in both countries at similar times.

A total of 622 outbreaks of FMD were reported between 2001 and 2011 in Peninsular Malaysia. Serotype O was responsible for 92% of the 253 outbreaks serotyped and A in 8%. The number of outbreaks of FMD differed significantly between years (χ2=621, P<0.01, df=10), month (χ2=621, P<0.01, df=11) and states (χ2=621, P<0.01, df=10). The highest number of outbreaks (110) occurred in 2009, while the lowest number (23) was in 2007. The monthly outbreak pattern of FMD showed a significant increase during the northeast monsoon season (November to March). It is hypothesised that the seasonal increase in outbreaks was related to animal movement to meet the demand for fresh meat for cultural events held during those months. Outbreaks of FMD in Peninsular Malaysia were most prevalent in Kedah (n=95). There was a significant correlation between the number of outbreaks and the average population size of cattle (r=0.731, P=0.007), buffalo (r=0.625, P=0.03) and goats (r=0.652, P=0.021). Cattle were involved in most outbreaks (87%). The overall prevalence of clinical disease was highest in cattle (15.4%), followed by buffalo (9.9%), goats (6.8%), sheep (6.6%) and pigs (6.5%). Cattle (odds ratio, OR=2.6, 95% CI 2.5, 2.8) and buffalo (OR=1.6, 95% CI 1.4, 1.8) were significantly more likely to be reported with clinical signs of disease than pigs. The case-fatality rate in cattle was 0.2% and goats 0.5%. The main sources of outbreaks were hypothesised to be the introduction of new animals or the illegal movement of animals (66% of outbreaks). A combination of control measures, including ring vaccination, animal movement management and quarantine, were implemented during outbreaks.

The animal seroprevalence of FMD by the NSP test in cattle, buffalo, goats and sheep were 24.2% (95% CI: 23.8, 24.6), 52.7% (95% CI: 50.5, 55), 11.8% (95% CI: 11, 12.6) and 9.5% (95% CI: 6.9, 12.6), respectively. These findings indicate natural infection and provide evidence that the virus was circulating in the livestock population. Males were 2.2 (OR 95% CI: 2.04, 2.3) times more likely to be NSP positive than were females. Cattle belonging to the Murrah breed (OR=1.6, 95% CI: 1.3, 2.0) and dairy breeds (OR=1.3, 95% CI: 1.2, 1.5) were more likely to be seropositive than were meat breeds. The whole peninsula was infected with FMD (range of point prevalences 6 to 37% in Kuala Lumpur and Kelantan, respectively).

In cattle, the overall seroprevalence based on the liquid phase blocking ELISA titre (LPBET) (positive titre >45) for type O (n=3025) was 74% (95% CI: 72, 76) and 52% (95% CI: 50, 53) of animals had protective titres (titre > 90). The findings indicate that, on average, the protective levels of antibody to type O in cattle were below the recommended level. In imported cattle (n=3295), more than 90% were positive on the LPBE percentage inhibition (PI) to type O and 49% were NSP positive indicating that they had been vaccinated and also exposed to a natural infection. This finding highlights that infected imported cattle may be an important source of FMD outbreaks, thus livestock consignments should be closely monitored. Based on the results of the LPBET adequate protective levels were present to serotype O in buffalo but not in goats, sheep or pigs.

The results from the simulation study for the risk of introduction of FMD via importation of live cattle from Thailand showed that there is almost a 100% probability that there will be at least one infectious animal that is capable of transmitting infection being accepted for importation into Peninsular Malaysia in any given year. The estimated total number of outbreaks was 26 per year (range: 10-182; 95% CI: 1, 27) and the probability of outbreaks following effective contact was 92%. This indicates that importation of live cattle from Thailand is a strong factor contributing to the likelihood of outbreaks in Peninsular Malaysia. Furthermore, Malaysia is at continuous risk as long as the importation of live animals continues from infected countries. To reduce risk, interventions, including pre-arrival testing, vaccination and improved farm biosecurity, should be adopted on farms, irrespective if the new animals are from another country or from within Peninsular Malaysia.

In conclusion, FMD is endemic in Peninsular Malaysia and movement of animals plays a major role in the spread of FMD. The protective level of immunity induced by vaccination was below the recommended level. Imported live cattle from Thailand could be infected with FMD and a potential source for introducing new strains of virus to Peninsular Malaysia. Therefore, studies should be conducted to trace the farms of origin of these imported cattle. The findings from this study could be used to improve the existing control strategy for FMD in Peninsular Malaysia thus ultimately underpinning the MTM FMD Campaign.

Item Type: Thesis (PhD)
Murdoch Affiliation: School of Veterinary and Life Sciences
Supervisor(s): Robertson, Ian
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