|BAUERMANN, FERNANDO - Universidade Federal De Santa Maria|
Submitted to: Journal of Clinical Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/13/2016
Publication Date: N/A
Interpretive Summary: Bovine viral diarrhea virus (BVDV) causes a disease, bovine viral diarrhea (BVD) present in all parts of the world. BVD has a major economic impact on the dairy and beef industries. Recently it has been found that another distantly related virus, HoBi-like virus, could also cause BVD. So far HoBi-like virus has not been detected in the United States, but have been found in South America, Europe and Asia. When pregnant cattle are exposed to either BVDV or HoBi-like virus in the first trimester of gestation, there is a high chance that the fetus will became persistently infected (PI). This means that the virus will be present in the animal for life and will be shed in the animal’s milk, saliva, nasal secretions, urine and feces. The female that carries the PI fetus will be constantly re-infected with the virus that the fetus is producing. This constant exposure stimulates a strong immune response against that virus in the cow and that prevents subsequent fetuses from becoming infected. The purpose of this study was to see if this strong immune response also protected subsequent fetuses from infection with HoBi-like virus. To this end, we inoculated pregnant heifers with BVDV and they generated PI animals. The following season these cows were rebred and exposed to HoBi-like virus during the first trimester of pregnancy. At the time of exposure to HoBi-like virus, all cows had strong immune responses against BVDV. Six days after exposure HoBi-like virus was found in the blood of 4 out of 6 cows. One of the cows lost its fetus and 30 days post inoculation, HoBi-like virus genetic material was detected in the tissues of the five remaining fetuses. These five fetuses weighed less and were shorter than normal fetuses. These results illustrate that previous exposure to BVDV is not protective against HoBi-like virus infection. This in turn indicates that cattle in the United States, while having previous exposure to BVDV, will not be protected against infection with HoBi-like virus. Thus introduction of HoBi-like virus into the United States would have significant negative effects on cattle health and the agricultural industry.
Technical Abstract: The ability of bovine viral diarrhea viruses (BVDV) to establish persistent infection (PI) following fetal infection is central to keeping these viruses circulating. Similarly, an emerging species of pestivirus, HoBi-like viruses, is also able to establish PIs. Dams that are not PI, but carrying PI calves, are constantly exposed to virus during gestation and develop high levels of immunity. This immunity prevents BVDV infection of the dam’s fetus in subsequent pregnancies. The goal of this study was to determine if this immunity is great enough to prevent the infection of a subsequent fetus with a HoBi-like virus. Six second pregnancy cows were inoculated with a HoBi-like virus about day 85 of gestation, and three were mock inoculated. Of the six challenged cows, four had birthed BVDV-1 PI calves in a previous pregnancy, while two cows had birthed BVDV-2 PIs. On the day of challenge, the serum titers ranged from 1148 to 5793 against the BVDV strain found in the PI calf from the first pregnancy. At day 6 post-challenge, HoBi-like RNA was detected in the serum of all four BVDV-1 cows but not in the two BVDV-2 cows. The fetuses harvested from five of the exposed dams at day 30 post-challenge were positive for HoBi-like virus RNA. The sixth cow, BVDV-1 cow #541, while pregnant at the time of exposure, had no fetus 30 days after exposure. Compared to the fetuses of control dams, fetuses from HoBi-like virus exposed dams were significantly smaller and lighter (p=0.04). While HoBi-like RNA was detected in samples of all challenged fetuses, no viable virus was recovered. The identification of viral RNA in the serum of 4 cows at day 6 post-challenge, as well as viral RNA detection in all fetuses 30 days post-inoculation indicates that the fetuses of dams with high antibody titers against BVDV-1 or BVDV-2 would not be protected if challenged with a HoBi-like virus.