In Africa, FMD viruses are maintained in cattle and African buffaloes (Syncerus caffer) in domestic and wildlife ecology, respectively (Vosloo, et al., 2004). However, it has been reported that the pig-adapted Cathay strain of FMD virus apparently does not infect large ruminants in the field or experimentally and requires cells of porcine origin for primary isolation (OIE, 2012).

Typical cases of FMD are characterized by high fever, loss of appetite, salivation and vesicular condition of the feet, buccal mucosa and, in females, the mammary gland (Thomson, 1994). Clinical signs can vary from mild to severe, and fatalities may occur, especially in young animals (OIE, 2012). Even though FMDV outbreaks in pig have been reported in other countries, especially where pig production is intensive, no clinical case of FMD has been reported in swine in Nigeria. In previous related studies, no evidence of antibodies to FMDV was demonstrated in sera of pigs (Lazarus, et al., 2012). However, seroprevalence of FMD antibodies in cattle, sheep and goats were reported (Ehizibolo, et al., 2010; Fasina, et al., 2013; Ishola, et al., 2011; Lazarus, et al., 2012). Nigeria has a limited swine population of 9 million compared to the 17 million heads of cattle (WAHID, 2013). The pig production in most part of the north is backyard piggery system which is on a small scale production. In the country’s southwest, more intensive commercialized piggery systems are in place with good market for pork. This study investigated the presence of antibodies against FMDV in pig sera collected as part of a National ASF Surveillance Programme in two states of Taraba and Adamawa north-eastern Nigeria.

Study area and sample selection

Two States were conveniently selected from a list of states that submitted samples to the National Veterinary Research Institute, Vom for the National ASF Surveillance Programme in 2009.These are Taraba and Adamawa states; they are the second administrative unit in Nigeria administrative structure. These states share land borders with the Adamawa Province of Cameroun where most pastoralist cattle within the Northeast come from. These states also have suitable vegetation  and  climate  that  supports  the  local livestock industry in the country. Farmers in these areas practice the backyard piggery system in addition to keeping other livestock. FMD outbreak is a seasonal occurrence in this area and pigs reared on backyard piggery system normally come in contact with cattle reared within the community. More samples were selected from Taraba relative to Adamawa state, considering the distribution of piggery in Taraba to Adamawa. .

Serology

The ELISA serology was performed according to the manufacturer’s instructions for PRIOCHECK FMD-3ABC NS protein ELISA (Sorensen et al., 1998; Brocchi et al., 2006). Briefly described, 80 μl of the ELISA buffer and 20 μl of the test sera were added to the 3ABC-antigen coated test plates. Negative, weak positive and strong positive control sera were added to designated wells on each test plate, gently shaken and incubated overnight (18 h) at 22°C. The plates were then emptied and washed six times with 200 μl of washing solution and 100 μl of diluted conjugate was added to all wells. The test plates were sealed and incubated for 60 min at 22°C. The plates were then washed six times with 200 μl of the washing solution and 100 μl of the chromogen (Tetra-Methyl Benzidine) substrate was dispensed to all wells of the plates and incubated for 20 minutes at 22°C following which 100 μl of stop solution was added to all the wells and mixed gently. Readings were taken on a spectrophotometer Multiskan® ELISA reader (Thermo Scientific, USA) at 450 nm and the OD450 values of all samples was expressed as Percentage Inhibition (PI) relative to the OD450 max using the following formula PI = 100 - (OD450 test sample/OD450 max) × 100. Samples with PI = ≥ 50% were considered positive, while those with PI < 50% were declared negative. Since the 3-ABC ELISA for FMD was = 100% specific and > 99% sensitive, the percentage prevalence was taken as true prevalence. All samples that tested positive for NSP using the 3ABC ELISA were further typed  for structural proteins using a Solid Phase Competitive ELISA (SPCE) for antibodies to FMDV serotype A and O, (IZSLER Brescia, Italy),the test was performed  according to the manufacturer’s instructions. 

The result showed an overall seroprevanlence of 1.11% (5/450) in the study area. 1.26% (5/389) were positive in Taraba State and 0% (0/56) in Adamawa state as indicated in Table 1. Furthermore, serotype specific ELISA test for FMDV serotype A and O revealed 1 out of the 5 positive samples, positive for FMDV serotype A.

This is the first report of serological evidence for FMDV serotype A in pigs in Nigeria without obvious clinical signs. Although it has not been reported that pigs may play an obvious role in the epidemiology of FMDV in Nigeria, this study demonstrates that they can be infected and could become important in the epidemiology of the disease when exposed to a virulent strain of FMDV. Therefore, we recommend that contacts between cattle and pigs in communal grazing areas should be limited to avoid interspecies transmission of FMDV and other important animal pathogens. This study is limited by small sample size and incomplete epidemiological data generated. Another major limitation to the study is the SPCE Kit used which was able to detect serotypes A and O. It may be necessary to serotype all NSP positive samples in future studies for all the FMDV endemic serotypes within Nigeria.

We therefore recommend more in depth research into the possible role of pigs in the epidemiology of FMDV in Nigeria and possibly attempt to isolate and characterize FMDV in pigs.  

The authors have not declared any conflict of interest.

We thank the National Animal Disease Information System (NADIS), Federal Department of Livestock Nigeria, Staff and management of the Foot and Mouth Disease Research Laboratory, National Veterinary Research Institute, Vom.