Inefficient Transmission of African Swine Fever Virus toSentinel Pigs from an Environment Contaminated byASFV-Infected Pigs under Experimental Conditions

Abstract

Knowledge about African swine fever virus (ASFV) transmission and its survival in the environment is mandatory to developrational control strategies and combat this serious disease in pigs. In this study, the risk that environmental contamination posesfor infection of naïve pigs was investigated. Naïve pigs were introduced as sentinels into contaminated pens kept at ambienttemperature (about 18–22˚C) either on the same day or up to 3 days after ASFV-infected pigs were removed. Three experimentswere carried out in which four to six pigs per pen were inoculated with virulent ASFV isolates OURT88/1 (genotype I), Georgia2007/1, or POL/2015/Podlaskie (genotype II), respectively. The majority of the inoculated pigs developed acute disease but with noevident haemorrhagic lesions or haemorrhagic diarrhoea and were culled at the predefined humane endpoint. The levels of ASFVDNA detected in the blood of the infected animals reached 107−9 genome copies/ml before euthanasia. Environmental swabs weretaken from different surfaces in the animal rooms, as well as from faeces and urine, close to the time of introduction of the naïveanimals. Relatively low quantities of virus DNA were detected in the environmental samples, in the range of 103−7 genome copiesper swab or per gram and ml of faeces and urine. No infectious virus was recovered from these environmental samples. Neitherclinical signs nor virus genomes were detected in the blood of any of the sentinel pigs over a period of 2 to 3 weeks after exposure,indicating that transmission from the ASFV-contaminated environment did not occur. Interestingly, viral DNA was detected innasal and oral swabs from some of the sentinel animals at early days of exposure (ranging between 10 3.7−5.8 genome copies perswab), though none of them developed ASF. The results indicate a relatively low risk of ASFV transmission from a contaminatedenvironment under the conditions provided in these experimental studies and in the absence of bloodshed from infected animals.