SURVEILLANCE FOR AFRICAN SWINE FEVER AND CLASSICAL SWINE FEVER IN BENUE STATE, NIGERIA
A serosurveillance study was conducted to detect the presence of antibodies to African swine fever virus (ASFV) and classical swine fever virus (CSFV) in pigs sampled frompiggeries and Makurdi central slaughter slab in Benue State, Nigeria. Four hundred and sixteen (416) pigs from 74 piggeries across 12 LGAs and 44 pigs at the Makurdi central slaughter slab were sampled for serum. The sera collected were analysed using Indirect Enzyme Linked Immunosorbent Assay (ELISA) test kit to test for antibodies to ASFV while competitive Enzyme Linked Immunosorbent Assay (ELISA) test kit was used to test for antibodies to CSFV. Questionnaire were distributed to 80 respondents consisting of farmers and slaughter slab workers to determine the risk factors associated with ASF and CSF infection. Of the 416 pigs from piggeries and 44 pigs sampled from the slaughter slab, 7 (1.7 %) and 6 (13.6 %) respectivelytested positive to ASFV antibodies and the detection rate was significantly associated with the pigs sampled in the different locations(p < 0.0001),while none tested positive to CSFV antibodies in both locations. Out of the 12 LGAs sampled, Obi LGA had the highest ASFV antibody detection rate of (4.8%)and the detection rate was significantly associated with the pigs sampled in different LGAs (p < 0.0001).Piggeries located within 1km radius of a slaughter slab(OR=9.2, 95 % CI – 3.0 – 28.8), piggeries near refuse dump sites (OR=3.0, 95 % CI – 1.0 – 9.5)and piggeries where farm workers wear their work clothes outside of the piggery premises (OR=0.2, 95 % CI 0.1 – 0.7)were significantlyassociated (p < 0.0001), (p = 0.05)and (p < 0.005)with ASF infection of the sampled piggeries. Sanitary measures in piggeries were observed to be generally very poor,though respondents admitted being aware of ASF. The study concluded that antibodies to CSFV were absent in the sampled pigs in piggeries and at the Makurdi slaughter slab in Benue State. Also that antibodies to ASFV were detected both in sampled pigs in piggeries and at the Makurdi slaughter slab and may pose a great risk in the study area.It is therefore recommended that further studies be carried out to investigate possible sources of infection in ASFV positive pigs and also characterise the ASFV circulating in Benue State. Adherence to hygienic and proper sanitary measures in piggeries, routine surveillance and monitoring of ASFV and CSFV antibodies in pigs in Benue State to provide a comprehensive and readily accessible data base on these diseases to plan for the prevention of any fulminating outbreak were equally recommended.
1.1 Background Information
African swine fever and classical swine fever are the two most feared and important contagious diseases of pigs worldwide (Penrith et al., 2011; Penrith et al., 2013) and are World Organization for Animal Health (OIE) notifiable diseases (Petrov and Salzungen, 2015). African Swine Fever (ASF) is also known as Peste porcine Africaine, fiebre porcina Africana, maladie de Montgomery(Penrith et al., 2013) while Classical SwineFever (CSF) is known as Hog Cholera, Peste du Porc, colera Porcina, Virusschweinepest (Penrith et al., 2011; Petrov and Salzungen, 2015).
While outbreaks of ASF have a long and on-going history in Africa (Fasina et al.,2010), CSF up to now is considered an exotic disease within African member states with exception of Madagascar and Mauritius (Penrith et al., 2011;Aiki-Rajietal., 2014). However, very recently CSF was reported in domestic pigsslaughtered at an abattoir in Ibadan, South-western Nigeria (Aiki-Rajietal., 2014),thereby, making both diseases of high risks to the pig industry in Nigeria.
The two diseases exhibit similar clinical picturebut their causative agents differ greatly (Penrith, et al., 2013;Petrov and Salzungen, 2015). Afican swine feveris caused by African Swine Fever Virus (ASFV),a large, double-stranded DNA virus,belongingto its own genus;Asfivirus, the only member of the family Asfarviridae(Dixon et al. 2004), while CSFis caused by Classical Swine Fever Virus (CSFV),a small enveloped positive single-stranded RNA virus of the genus Pestivirus, family Flaviviridae (Petrov and Salzungen, 2015). Both viruses affect only members of the pig family Suidae (Plowright etal., 1994; Moennig, 2000) and are highly contagious to pigs and their ancestor, the Eurasian wild boar (Sus scrofa ferus).African swine fevervirus is the only known DNA arbovirus that has a biological vector that can maintain and transmit the virus (Dixon et al. 2005).
The pig population in Nigeria is estimated at over 7.4 million and is concentrated mainly in the Middle Belt and Southern parts of the country (FAO, 1998b; NBS, 2010). Small holder farms raise most of these pigs(El-Hicheri, 1998; NBS, 2010 Cited by FLD, 2010).This important pig population contributes highly to the food security of the low income rural and periurban population (Ate and Oyedipe, 2011;El-Hicheri, 1998) thereby contributing significantly to the economic welfare of the rural population as well as playing an important role in the social and cultural life of most of the communities in the southern and middle-belt States of Nigeria, including providing cheap meat for traditional marriages and burial rites (Ate and Oyedipe, 2011). In addition, pigs provide a ready and regular source of cash to meet the rural families’ needs, such as paying educational and health expenses; and procurement of farm inputs on a day to day basis (El-Hicheri, 1998; Ate and Oyedipe, 2011).
The pig industry in Nigeria can be classified into small holder farms(having fewer than 50 pigs in the herd at any point in time); medium holder farms (with 50 to 100 pigs in the herd at any point in time); and large holder farms (of over 100 pigs in the herd at any point in time) (Awosanya etal., 2015). The pig farming industry in Nigeria has a significant presence in the north-central and south-western Nigeria. The pig production system in Benue state Nigeria is predominantly semi-intensive (El-Hicheri, 1998; FAO, 1998a).