Swinepox virus: an unusual outbreak in free-range pig farms in Sicily (Italy)

Abstract

Background: Two outbreaks of swinepox were investigated in free-range domestic pig farms located in the northeastern side of Sicily, Italy. The disease is generally self-limiting with a low mortality rate, but morbidity can reach high rates in case of poor sanitary conditions, improper husbandry practices and ectoparasitic infestation. The presented cases are the first ever reported on the island and part of the few cases reported in domestic pigs.

Case presentation: Carcasses condemned at the slaughterhouse and deceased pigs from Farm A and Farm B respectively, were referred for post-mortem examination and further investigations, with a strong suspect of SwinePox virus (SWPV) infection. Twelve deceased pigs were examined in total, showing poor body condition and pustular lesions scattered all over the cutaneous surfaces. Moreover, pigs from Farm B showed ocular lesions classified from Grade I to IV (from mild conjunctivitis to severe keratoconjunctivitis with corneal oedema, opacity, and ulcers). Final diagnosis was pursued by the microscopic assessment of skin lesions in both farms, which revealed the typical SWPV-lesion appearance, such as severe and disseminated ulcerative dermatitis and suspected inclusion bodies multifocally observed in the epidermis. Moreover, negative staining Electron Microscopy (nsEM) was performed on skin lesions and ocular swabs from Farm B, revealing in two samples the presence of brick-shaped viral particles, 220 nm long and 160 nm wide, with irregularly arranged surface tubules, identified as SWPV. The gene encoding the 482-bp fragment of the virus late transcription factor-3 was detected by PCR and sequencing revealed 99.79% identity and 100% query-cover with a strain previously isolated in Germany. Field clinical assessment was then performed in Farm B, revealing high overcrowding, poor sanitary conditions and improper husbandry practices, which are relevant risk factors for SWPV transmission.

Conclusions: The present is the first case report of SWPV in free-range pigs raised in Sicily, an island of the Southern coast of Italy, and wants to raise awareness on a neglected disease, and cause of animal health and welfare issues.

Keywords: Haematopinus suis; Poxvirus; Skin lesions; Swine; Swinepox virus; biosecurity.

Fig. 1

Multifocal, eruptive dermatitis caused by SWPV in Farm B. Multifocal distribution of skin lesions in the abdomen and inner surface of the limbs (A), peri-labial area (B) and periocular area (C). Lesions evolved from macules to papules and pustules with a central umbilicated area (D). Severe pustular and ulcerative blepharitis with severe conjunctival hyperemia, chemosis mucous- suppurative ocular discharge and severe diffuse corneal oedema and opacity in a pig from Farm B (E)

Fig. 2

Microscopic assessment of PCR/nsEM positive skin sample (A-B) and eye (C) lesions from a Farm B affected piglet. (A) Severe erosion with epidermal destruction (arrow) and ballooning degeneration (arrowhead), necrosis and mixed inflammation (circled). Neoformation of blood vessels and lymphoplasmacytic infiltrates in the epidermal base was also seen. HE, 50x. (B) detail of the ballooning degeneration at the epidermal base with suspected inclusion bodies (circled). HE, 200x. (C) Severe corneal ulceration with neovascularization and mixed inflammatory infiltration of the corneal stroma. (HE,4x).

Fig. 3

Electron micrograph. Swinepox virus particle at nsEM (2% PTA. Bar = 100 nm) performed on a eye swab coming from Farm B

Fig. 4

A-B: Lack of biosecurity measures and severe overcrowding in Farm B. C: Individual affected by ocular lesions. D: Poor body condition scores in deceased weaned pigs