Analyzing risk factors for herd seropositivity to classical swine fever in West Timor, Indonesia

 

Elsevier

Research in Veterinary Science

Volume 131, August 2020, Pages 43-50
Research in Veterinary Science

Analyzing risk factors for herd seropositivity to classical swine fever in West Timor, Indonesia

https://doi.org/10.1016/j.rvsc.2020.04.011Get rights and content

Highlights

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    Three potential risk factors for the presence of antibodies to CSF were identified.
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    Introducing new pigs was associated with the presence of antibodies to CSF.
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    Keeping goats was also associated with the presence of antibodies to CSF.
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    Vaccinated pigs were 2 times more likely to be seropositive than non-vaccinated pigs.

Abstract

A cross-sectional study was undertaken to identify factors associated with herd-level seropositivity to Classical Swine Fever (CSF) in smallholder pig farms in West Timor, Indonesia. Questionnaires were distributed to 240 pig farmers from 8 villages in two districts to collect information about farm structure and herd information, reproductive management and performance, husbandry, pig introductions and exits, health status, farmers' knowledge and history of vaccination. Three risk factors were found to be associated with the presence of antibodies to CSF in the herd in a multivariable logistic regression model. Seropositivity was associated with the introduction of pigs in the 12-month period preceding the survey (OR 4.78, 95% CI: 1.46, 15.71). Farmers who kept goats were 3.42 (95% CI: 1.20, 9.81) times more likely to have seropositive pigs than farmers without goats. Herds that had been vaccinated against CSF were also 2.33 (95% CI: 1.10, 5.12) times more likely to be seropositive than non-vaccinated herds. This latter positive association is likely to be as a result of antibodies induced by vaccination rather than a true risk factor for infection. The results of the questionnaire highlighted the lack of implementation of biosecurity measures by smallholder farmers in West Timor, which has the potential to increase the risk of their pigs to CSF, as well as other diseases.

Introduction

Classical Swine Fever (CSF) is a serious and highly infectious viral disease of domestic pigs and wild boar (Paton and Greiser-Wilke, 2003). The causative agent, Classical Swine Fever Virus – CSFV, is a small (40 ± 60 nm) enveloped ribonucleic acid (RNA) virus with a single stranded genome with positive polarity (Horzinek et al., 1971; Moennig and Greiser-Wilke, 2008). The virus is one of three pestiviruses that forms a group of economically important pathogens (Moennig et al., 1990) belonging to the Flaviviridae family. CSFV has a close antigenic relationship with the other pestiviruses - bovine viral diarrhoea virus (BVDV) and border disease virus (BDV), as demonstrated by immunodiffusion and immunofluorescence tests, and their similar morphology and nucleic acid homology (Wengler, 1991; Wengler et al., 1995).
Indonesia was free from CSF until 1993. Between 1994 and 1996 thousands of pigs were reported to have died from the disease in the Indonesian regions of North Sumatera, Jakarta, Bali, Central Java, and North Sulawesi (Satya and Santhia, 2009). An outbreak of CSF was reported in Dili, East Timor in August 1997 and the disease then spread to the Kupang district of West Timor in March 1998 (Satya and Santhia, 2009) and subsequently to all five districts of West Timor (Santhia et al., 1997; Santhia et al., 1998). When the disease first appeared the pig population was estimated to have decreased by 23 and 45% in Belu and Kabupaten Kupang in West Timor, respectively (Christie, 2007), with up to 80% mortality reported in some herds (Christie, 2007; Satya and Santhia, 2009).
The existence of CSF in an area and the potential for its introduction into a new area can be associated with the presence of certain risk factors. Identification of these risk factors is important in understanding the transmission of disease and for developing effective prevention, control and eradication programs (Robertson, 2019). Farmers are a valuable source of information about potential risk factors and associated management and husbandry practices linked with disease as they often have many years of experience in raising or trading livestock. In many South-East Asian nations farmers own only a small number of livestock and hence are generally very aware of the health and well-being of their animals. This knowledge can be used to identify risk factors for disease so that effective region-specific control programmes can be developed.
The objective of the current study was to identify potential farm level risk factors associated with CSF seropositivity in West Timor. In particular factors involved in the management and husbandry of pigs were investigated. West Timor was selected because of two main reasons: firstly, Timor is an island with a pig population of almost 550,000 (Provincial Livestock Service of Nusa Tenggara Timur, 2010), which represents over one-third of the total pig population in the province of Nusa Tenggara Timur (NTT). Secondly, in line with the increase in the pig population, clinical cases of CSF have also reportedly increased in West Timor and the disease can result in significant economic losses to farmers through reduced productivity and mortalities (Satya and Santhia, 2009; Christie, 2007).

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Section snippets

Study area

A cross-sectional study was undertaken in 2 districts of West Timor in April and May 2010 (Fig. 1). West Timor is situated on the island of Timor along with the Democratic Republic of Timor–Leste. The economy in West Timor is mainly based on agriculture, and pigs play an important role in animal production, with “backyard” pigs representing the vast majority of pigs where villagers raise pigs to provide an income source, protein and for cultural reasons (Provincial Government of Nusa Tenggara

Results

The univariable analyses identified 32 risk factors (Table 1, Table 2) that were linked with the serological status of pig herds in West Timor (P < .25) and these were offered to the multivariable logistic regression model.
The final model generated through backward conditional binary logistic regression is displayed in Table 3. Three factors were retained in the final model. The most strongly associated factor with herd seropositivity to CSF was introducing pigs in the preceding 12-month period 

Discussion

Classical swine fever is a major disease of pigs (Moennig, 2000) and identifying risk factors for infection and understanding factors influencing the transmission and dissemination of this disease is essential when developing control programs.
Even though there were no reported outbreaks of clinical disease of CSF in the region during the study, 126 of 720 pigs tested were seropositive (test seroprevalence of 17.8%; 95% CI: 15.1–20.8%); and of the 240 herds tested 93 herds (38.8%; 95% CI 32.6,

Acknowledgements

The authors would like to acknowledge the input by the pig farmers interviewed in West Timor; the support of the Dinas Peternakan Provinsi NTT and the support of the Directorate of Higher Education of Indonesia for providing the lead author Post Graduate Scholarship. This paper represents part of a thesis submitted by the lead author for award of a master degree at Murdoch University.

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