An investigation of classical swine fever virus seroprevalence and risk factors in pigs in East Nusa Tenggara, eastern Indonesia
Received 7 April 2014, Revised 29 January 2015, Accepted 2 February 2015, Available online 11 February 2015.
https://doi.org/10.1016/j.prevetmed.2015.02.002
Highlights
- •Seroprevalence varied widely at various levels of spatial aggregation.
- •
- •Levels of herd immunity inadequate for disease control.
Introduction
Classical swine fever virus (CSFV), or hog cholera, is a pestivirus associated with high morbidity and mortality rates in pigs. CSFV has been eradicated from several countries including the United States, Australia, and New Zealand, and a number of countries in Central and Western Europe (Artois et al., 2002; Edwards et al., 2000; World Organisation for Animal Health, 2014). However, recent outbreaks in countries previously free of CSFV in domestic pigs have had significant economic and animal health consequences (Elbers et al., 1999, Moennig et al., 2003, World Organisation for Animal Health, 2014), and CSFV remains endemic in parts of Asia, Central America and South America.
East Nusa Tenggara (NTT) is the province with the highest level of pork consumption in Indonesia, and the largest pig population with an estimated size of 1.8 million animals (BPS Statistics, 2013). Smallholder pig farmers (total herd sizes of ≤20 pigs) are the predominant producers in this region, with 85% of households raising pigs (Johns et al., 2009, Santhia et al., 2006) and agriculture is the primary income source for the majority of households (Wang, 2007). In NTT, pigs provide a food source and financial security, and are highly valued socially and culturally (Santhia et al., 2006, Leslie et al., 2015). Therefore, morbidity and mortality events in the pig population impact a large proportion of the human population.
CSFV is a highly contagious transboundary disease. Pigs are generally infected oronasally, and spread is both direct via horizontal and vertical transmission, and indirect via contaminated fomites and pork products. Clinical disease caused by CSFV is classified as acute, subacute, or chronic, and is determined by CSFV strain, as well as host factors, including pig age, breed, stage of pregnancy, previous CSFV exposure status, and CSFV vaccination status. There are no pathognomonic signs for CSFV, and therefore laboratory diagnostics are required to make a diagnosis (Moennig et al., 2003).
CSFV was confirmed in NTT in 1998. It subsequently spread across the province largely through uncontrolled live pig movement, causing substantial losses. It continues to limit pig production in the region (Tri Satya et al., 1999, Christie, 2007). In NTT, districts are classified by CSFV infection status, which is based on clinical case reports to the NTT Livestock Office and limited government-led serological surveys. In 2010, all districts on West Timor and Sumba Island and one district on the eastern end of Flores Island were classified as infected; one district in east Flores Island was classified as suspect; and the rest of Flores Island plus Lembata Island classified as not infected (Fig. 1). Vaccination campaigns are conducted in districts with the highest pig densities and annual reports of cases in an attempt to control disease. However, fluctuations in the size of the pig population have continued, and the NTT Livestock Office has documented an increase in the number of annual reported cases (Dinas Peternakan Propinsi, 2011).
Live attenuated ‘Chinese’ strain (C-strain) vaccine CSFV vaccine is used in NTT to control disease. Its effectiveness has been demonstrated by a number of studies, and protection lasts at least 6–18 months and may be life long (van Oirschot, 2003). Neutralizing antibody usually appears within two weeks and increases until at least 4–12 weeks post vaccination (van Oirschot, 2003). Antibody can persist many years after inoculation with a single dose, but also disappears in some individuals and may disappear at a higher rate under ‘real’ field conditions compared to field trial conditions (van Oirschot, 2003). It is generally accepted that the presence of neutralizing antibody confers CSFV protection (Suradhat et al., 2007). Similarly, pigs that recover from acute CSFV infection develop neutralizing antibody as early as two weeks post infection (Moennig, 2000). These animals are protected against future infection for several years and immunity may be life long (Moennig, 2000).
In spite of the importance of CSFV to NTT, little is known about the seroprevalence and distribution. No serological surveys have been conducted in many parts of NTT, including the western half of Flores Island. Inconsistencies have been noted between the number of CSFV cases reported by the NTT Livestock Office and the few published studies (Santhia et al., 2003, Dinas Peternakan Propinsi, 2011). It has been recognized that as a result of government decentralization, communication between and within different government sectors is lacking, which may be the cause of data inconsistencies (Brandenburg and Sukobagyo, 2002). However, previous studies have also noted that farmers across NTT are reluctant to report CSFV cases (Robertson et al., 2010, Deveridge, 2008). Moreover, Santhia et al. (2003) stated that farmers and animal health workers on Alor Island in NTT were not reporting all CSFV cases.
The overarching aim of the presented study was to better understand CSFV seroprevalence and distribution in NTT to provide information to support decisions on CSFV control. The objectives of this study were: (1) to determine CSFV seroprevalence in West Timor and Sumba islands, both classified as CSFV infected; (2) to detect the presence of CSFV antibody in CSFV suspect and not infected districts on Flores island, and in Lembata island, which was classified as not infected in 2010, and; (3) to investigate pig-level and farmer-level factors to determine their impact on pig CSFV serological status in the islands surveyed.
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Section snippets
Material and methods
The survey was conducted as described from April to September 2010 following approval the University of Sydney's Human Research Ethics Committee (08-2009/11866).
Results
Seven hundred and twenty farmers and 2160 pigs from 805 farmers were surveyed across the four islands. Herd size ranged from 1 to 48 pigs, with an average of 4.6 pigs. One thousand four hundred fifty-two (67.2%) of the 2160 pigs included in the survey were born in the farmer's herd. Approximately 42% (898/2160) of the pigs surveyed were 3–5 months of age, 30% (652/2160) were 6–11 months of age, and the remaining 28% (610/2160) were equal to or greater than 12 months of age. Five percent
Discussion
CSFV is a highly infectious disease of pigs with major animal health and economic consequences. In regions where CSFV is endemic, the first step to controlling the disease is to understand its seroprevalence and distribution. Therefore we undertook a CSFV seroprevalence and risk factor study in the NTT province of eastern Indonesia.
In the sample size calculations for CSFV antibody prevalence, the inputs for test sensitivity and specificity were estimated to be lower than the values reported in
Conclusions
In 2010, Lembata Island was confirmed free of antibody to CSFV. However, the district of Manggarai Barat on the west end of Flores Island contained pigs that were seropositive for CSFV, in spite of no reports of clinical CSFV and no government-led vaccination programs in this region. Pig age and CSFV vaccination status were associated with CSFV serological status, with older pigs and pigs vaccinated for CSFV more likely to test positive for antibody to CSFV. Our results indicate that further
Acknowledgements
The Australian Centre for International Agricultural Research (ACIAR) funded this study under the AH/2006/156 project. The authors gratefully acknowledge the NTT Livestock Office in Kupang, the village leaders and participating farmers for their collaboration. The authors are also indebted to the veterinarians and field staff who assisted with the sample collection and survey administration. The assistance of Navneet Dhand and Peter Thompson (Faculty of Veterinary Science, University of Sydney)
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