Abstract:

Respiratory diseases contribute significant economic losses to the swine industry globally. In
Uganda, no detailed studies on pig respiratory pathogens have been undertaken previously. This
doctoral thesis aimed to fill knowledge gaps on epidemiology of important respiratory pathogens,
gastro-intestinal (GIT) parasites and their economic impacts on smallholder pig production systems
in Uganda. The studies were conducted in Lira district from October 2018 to September 2019. Four
respiratory pathogens of economic importance in pigs including porcine reproductive and respiratory
syndrome virus (PPRSv), porcine circovirus type 2 (PCV2), Mycoplasma hyopneumoniae (M. hyo)
and Actinobacillus pleuropneumoniae (App) were studied. The first study was a desk systematic
review on status and gaps of research on swine respiratory pathogens in Africa. This was followed
by three cross-sectional studies: prevalence and risk factors for respiratory co-infections, a slaughter
slab survey which correlated serology to 4 selected respiratory pathogens and pneumonia lesions
and identify PRRSv genotypes. Tissue and blood samples were collected from pigs and used for
genotypying PRRSv and to determine exposure to respiratory pathogens using ELISA assays,
respectively. A mixed effects model was fitted to quantify economic losses due to exposure of pigs
to respiratory pathogens and GIT parasites. Results highlighted major knowledge, information gaps
on epidemiology, and economic impacts of the 4 studied pathogens reported in pigs in Africa. Wc
found that there was dual circulation of both PRRSv PRRSv-1 and PRRSv-2 in Lira district with type 1 more predominant. A high prevalence and severity of pneumonia forms (17.4 — 74.2%) in
slaughtered pigs was observed. The model showed that a grower pig in a given farm exposed to
PRRSv and Ascarisspp infection had significantly lower average daily weight gain by 18.5 and 23.7
grams/pig/day respectively, compared to a similar unexposed pig. Monetary losses encountered by
farmers due to PRRSv and Ascaris spp. infection amounted to USD 7.12 and USD 9.16 respectively,
per pig during 200 days of fattening. In conclusion, these findings strengthened evidence of the role
of housing, hygiene and biosecurity in reducing disease incidence in herds. The most important
respiratory pathogens were PPRSv, App, Ascaris spp and risk factors were use of murrain as floor
type, poor hygiene, biosecurity practices, and concurrent GIT parasite infestations. Associations
between serology and Ifing lesions suggests their potential role in lung disease precipitation. Farmers
should pay close attention to proper housing, hygiene, biosecurity, wastes management and parasite
control and limiting contacts with outside pigs. The findings from this study shall inform national
policy in Uganda.