Swinepox is an acute, often mild, infectious disease characterized by skin eruptions that affects only pigs. It is present in the USA, particularly in the Midwest, and has been reported from all continents, although the incidence is generally low.
Historically, vaccinia virus was involved in some outbreaks; currently, swinepox virus appears to be the only cause. The disease described here is that caused by the latter. Swinepox virus is distinct from other poxviruses and does not protect against infection with vaccinia virus. It will grow on pig cell cultures, but not embryonating eggs. It is relatively heat stable and survives for ~10 days at 37°C (98.6°F).
The disease is most frequently seen in young pigs, 3–6 weeks old, but all ages may be affected. After an incubation period of ~1 week, small red areas may be seen most frequently on the face, ears, inside the legs, and abdomen. These develop into papules and, within a few days, pustules or small vesicles may be seen. The centers of the pustules become dry and scabbed and are surrounded by a raised, inflamed zone so that the lesions appear umbilicated. Later, dark scabs (1–2 cm in diameter) form, giving affected piglets a spotted appearance. These eventually drop or are rubbed off without leaving a scar. Successive crops of lesions can occur so that all are not at the same stage. The early stage of the disease may be accompanied by mild fever, inappetence, and dullness. Few pigs die of uncomplicated swinepox.
Virus is abundant in the lesions and can be transferred from pig to pig by the biting louse (Haematopinus suis). The disease also may be transmitted, possibly between farms, by other insects acting as mechanical carriers.
Recovered pigs are immune. There is no specific treatment. Eradication of lice is important.