Abstract:
African swine fever (ASF) is an economically devastating disease for the pig industry,
especially in Africa. Identifying what supports infection on pig farms in this region
remains the key component in developing a risk-based approach to understanding the epidemiology of ASF and controlling the disease. Nigeria was used for this matched
case-control study, because there is perpetual infection in some areas, while contiguous
areas are intermittently infected. Risk factors and biosecurity practices in pig farms were
evaluated in association with ASF infection. Subsets of farms located in high-density pig
population areas and high-risk areas for ASF infection were randomly selected for
analysis. Most plausible risk factor variables from the univariable analysis included in the
multivariable analysis include: owner of farm had regular contact with infected farms and
other farmers, untested pigs were routinely purchased into the farm in the course of
outbreaks, there was an infected neighbourhood, other livestock were kept alongside pigs,
there was a presence of an abattoir/slaughter slab in pig communities, wild birds had free
access to pig pens, tools and implements were routinely shared by pig farmers, there was
free access to feed stores by rats, and feed were purchased from a commercial source
Only the presence of an abattoir in a pig farming community (OR = 8.20; CI95% = 2.73;
24.63; P < 0.001) and the presence of an infected pig farm in the neighbourhood (OR =
3.26; CI95% = 1.20; 8.83; P = 0.02) were significant. There was a marginally significant
negative association (protective) between risk of ASF infection and sharing farm tools
and equipment (OR = 0.35; CI95% = 0.12; 1.01; P = 0.05).
Of the 28 biosecurity measures evaluated, food and water control (OR = 0.14; CI95% =
0.04, 0.46; P < 0.001), separation/isolation of sick pigs (OR = 0.14; CI95% = 0.04, 0.53; P
= 0.004) and washing and disinfection of farm equipment and tools (OR = 0.27; CI95% =
0.10, 0.78; P = 0.02) were negatively associated (protective) with ASF infection.
Consultation and visits by veterinarian/paraveterinarians when animals were sick (OR =
8.11; CI95% = 2.13, 30.90; P = 0.002), and pest and rodent control were positively associated with ASF infection of Nigerian farms (OR = 4.94; CI95% = 1.84, 13.29; P =
0.002).
The presentation of sick and unthrifty pigs for slaughter at abattoirs, farmers’ inadvertent
role, an infected neighbourhood, a pig to pig contact, rodents and wild birds may
contribute to infections of farms, whereas washing, disinfection of tools, food and water
control, and separation of sick pigs reduces the likelihood of infections. Underlying
reasons for these observations and strategies for control are discussed.
