BVD

Bovine viral diarrhoea/mucosal disease is an infectious disease of cattle caused by a virus. In humans, the virus does not cause disease.

Occurrence

The disease is spread worldwide

Host animals

cattle, sheep, goats and wild ruminants

Route of infection

Transmission mainly occurs via persistently (permanently) infected animals (PI animals). These animals become infected while still in the womb and excrete virus throughout their lives via all bodily excretions and secretions.

Symptoms

The majority of infections with BVD viruses are asymptomatic. Possible symptoms are diarrhoea, fever, respiratory diseases, erosions of the mucous membranes, feeding instability, reduced milk yield, fertility problems. Pregnant animals can give birth to malformed or weak calves. A special variant of the disease is the fatal mucosal disease.

Therapy

There is no therapy against the BVD virus.

Prevention

In Austria, cattle herds are monitored by antibody tests in serum and milk.

The successful and continuously positive development of BVD control (in 2006 - thus two years after the start of nationwide control - for example, 2,600 PI animals were still detected in approx. 1,700 farms) can be seen in recent years: Austria's farms subject to the BVD Ordinance were almost completely officially recognised as BVD-free, and no new outbreaks occurred in 2018 and 2019.Figure 1: Development of the number of PI animals from 2012 to 2019.

Bovine Viral Diarrhoea/Mucosal Disease is one of the most economically important infectious diseases of cattle worldwide. Many countries have opted for active control and surveillance programmes of BVD/MD. The disease is caused by a pestivirus, family Flaviviridae, and is distributed worldwide. Host animals are cattle, sheep, goats and wild ruminants.

Transmission

The route of transmission of BVD is mainly through persistently (permanently) infected animals (PI animals). They are the main source of virus spread. A PI animal develops by infection of the unborn calf via the dam between the 40th and 120th day of gestation. At this time, the immune system of the fetus is not fully developed, immune tolerance to the virus develops, and the animals remain infected throughout their lives and excrete the virus. Excretion takes place via all bodily excretions and secretions.

Symptoms

The majority of infections with BVD virus (BVDV) are asymptomatic. Possible symptoms are diarrhoea, fever, respiratory diseases, erosions of the mucous membranes, feeding instability, reduced milk yield, fertility problems. Pregnant animals can give birth to malformed or weak calves.

Mucosal disease (MD) occurs as a special disease variant. It occurs when a PI animal is additionally infected with another strain of the virus. MD is characterized by a severe course of the disease and is fatal. Symptoms of MD are bloody diarrhoea, high fever, erosions of the mucous membranes and ulcerations (on the muzzle, nose, interclaws).

Control

To control BVD, virus excretors (PI animals) present in the herd are eliminated to protect the herd from reinfection.Phylogenetic analyses of the virus strains can provide valuable information on infection routes for epidemiological questions. Pathogen analyses are extremely useful in tracing sources of infection. In order to obtain data on circulating BVDV and BDV (Border Disease Virus) strains in Western Austria in 2005 and 2006, a comprehensive study was carried out by AGES (Hornberg, A.; Revilla-Fernández, S.; Vogl, C.; Vilcek, St.; Matt, M.; Fink, M.; Köfer, J.; Schöpf, K. (2008): Genetic diversity of pestivirus isolates in cattle from Western Austria. Vet Microbiol. 2009 Mar 30;135(3-4):205-13). The study carried out in the veterinary institutes of Mödling and Innsbruck was based on the genetic heterogeneity of BVDV strains. This was determined by molecular biological sequence analysis. The typing of the samples showed a very high genetic variability of the BVDV strains circulating in Tyrol and Vorarlberg. A total of 8 different BVDV-1 subtypes were found, 3 of which were isolated for the first time in Austria. The BVDV-1h subtype occurred most frequently (143 isolates), but subtype 1f (79 isolates) was also widespread. In addition, two BVDV-2 strains and, for the first time, a BDV isolate in cattle could be classified. On farm level, only a low geographical correlation in the occurrence of the different strains could be found.

BVD in red deer

Cattle and red deer(Cervus elaphus) can come into direct or indirect contact with each other on pastures or mountain pastures, so that pathogen transmission between these two animal species becomes possible. In several European countries, as well as in the USA, evidence of pestivirus transmission between cattle and wild ruminants has been found.In the course of a study at the Institute for Veterinary Investigations of the AGES in Innsbruck, the occurrence of BVDV in the Austrian red deer population was determined by means of virus detection from ear tissue samples. Between 2007 and 2009, as part of an officially ordered monitoring programme for chronic wasting disease in Austrian red deer, a total of 567 animals from the wild and 133 from cages were examined not only for brain samples but also for one ear tissue sample per animal from the ears sent in. In the laboratory, the ear tissue samples were tested for BVDV using HerdCheck BVDV antigen ELISA and commercial real-time RT-PCR. No BVDV was detected in all 700 tissue samples tested by ELISA and real-time RT-PCR.Recent literature from AustriaSchöpf, Karl; Revilla-Fernández, Sandra; Steinrigl, Adolf; Fuchs, Reinhard; Sailer, Andreas; Weikel, Joachim; Schmoll, Friedrich (2016): Retrospective epidemiological evaluation of molecular and animal husbandry data within the Bovine Viral Diarrhoea (BVDV) control programme in Western Austria during 2009-2014. Berl Münch Tierärztl Wochenschr 129:196-201. doi 10.2376/0005-9366-129-15102, http://vetline.de/open-access/158/3216/)

Antibody detection: Infection with BVDV leads to the formation of antibodies (detectable in serum, individual and tank milk).

Antigen detection: Direct pathogen detection (serological and molecular biological methods from blood, tissue, secretion and organ samples)Detection in ear tissue samples : In spring 2005, an innovative and efficient control programme for the detection of PI animals was introduced in Tyrol. For the first time, the examination of ear tissue samples for antigen detection was carried out on all newborn calves nationwide. In 2008, the system was improved with the aim of already taking an ear tissue sample during the legally required animal identification with the same work step (confusion-proof sampling procedure!). One of the most important goals in BVD diagnostics is the timely detection of a PI animal. Maternal antibodies (antibodies that are passed from the mother to the young animals via colostrum) can mask BVDV in the blood, making early detection impossible. This so-called "diagnostic gap" does not play a role in the examination of tissue samples and the detection and eradication of PI animals is already possible in the first week of life. Equally problematic is the delayed rise in antibodies following BVD infection. BVD antibodies are only detectable from about the 7th day after infection. This time delay is even greater when tank milk is tested.