Analysis of airborne transmission of Bovine Viral Diarrhea Virus among weaned piglets

Bovine Viral Diarrhea Virus (BVDV) has cattle as natural hosts, but it can infect other animals, such as sheep, goat and swine. Once infected, pigs usually do not present clinical signals of infection, which can leads to a silence viral dissemination among animals. Furthermore, the transmission of BVDV between pigs and ruminants requires direct or indirect contact, but virus transmission among pigs remains unknown. Thus, the aim of this work was to evaluate the possibility of BVDV airborne transmission from infected piglets to healthy animals.

For analysis of airborne transmission two experiments, one with 18 days and other with 25 days, were conducted using insulators designed for epidemiological studies with weaning piglets. In each experiment, six piglets were divided into three groups, of which the first was the control, the second was compound by the infected animals and the last one was related to the sentinels. The two animals of the second group were inoculated with BVDV type-1, 10^5,5 TCID⁵⁰ viral titer, through nasal catheter and orally. Blood samples were collected by jugular puncturing every four days and nasal swabs samples were collected daily. In the end of experimental period, all piglets were euthanized and necropsied to collect tissue samples (spleen, ileum, mesenteric lymph nodes, mediastinal lymph nodes, inguinal lymph nodes, lung, liver, kidney, tonsil and blood). The seroconversion by the animals was detected through virus neutralization test. The presence of the virus in the nasal swabs and tissue samples was detected by RT-PCR technique using the set of primers designed by Weinstock et al. (2001).

It was not observed the airborne transmission of BVDV among pigs because there was no detection of BVDV in any sample of sentinel groups. Two piglets of the infected group of the first experiment seroconverted on the 16 day after inoculation. However, the excretion of the virus by only one animal was detected on the 17 day after inoculation, which did not persist on the next day. In the second experiment, one piglet of the infected group seroconverted on the 13 day and the other on 22 day after inoculation, but the viral excretion was not detected in nasal swabs samples.

This experimental study demonstrated that the interval between seroconversion and excretion might be only one day. However, the possibility of airborne transmission of BVDV among pigs was not proven within the period evaluated, suggesting that BVDV is not transmitted among piglets in this route, or, it is very limited. This study had financial support provided by grant 2014/13590-3, São Paulo Research Foundation (FAPESP).

Disclosure of Interest: None Declared.