Controlling IBR – the debate goes on

IBR is a disease which has been increasingly discussed by vets and consultants in recent months.  It is an important disease causing significant economic losses on farms where outbreaks occur. It is essential for UK farmers to understand the disease, particularly the aspects of its eradication if they have an interest exporting cattle, embryos or semen.  Many European countries have either eradicated the disease or are implementing programmes with this goal in mind.  Here, vet adviser at Intervet UK, Rosemary Booth gives an insight into the discussion.

A growing movement across the EU to eradicate IBR could be seen as a barrier to trade by those countries without control or eradication schemes.  With Scandinavia, Austria and some parts of Italy now IBR-free, plus national eradication programmes in Germany, Hungary, the Czech Republic and Slovakia, the UK could be missing out on new markets.

(See table 1 for incidence rates).

Control strategies are varied and the advice from those who have developed eradication programmes is to choose a strategy to suit the individual farm.  However, all strategies include the use of IBR marker vaccines which allow animals that have been naturally infected with the virus to be identified from those vaccinated with a marker vaccine.  At Intervet’s recent international conference on IBR, the advising vets and organisations also stressed the importance of including vets and farmers where governments develop such programmes.  A clear understanding of biosecurity and management changes is essential, otherwise eradication will simply not work.  

Table 1: IBR incidence in 1996

Sweden, Finland, Austria, Denmark, Norway and Switzerland are all IBR-free.

CLINICAL SIGNS

IBR is caused by Bovine Herpes Virus-1.  It is a very contagious virus which is spread rapidly if introduced into a group of cattle with no immunity.  All ages of stock can be affected, however the disease is most common in growing cattle over 6 months of age, and in adults. 

Once infected with IBR, animals usually carry the virus for life.  Stressful situations such as transport, overcrowding or calving can all reactivate the IBR virus in carriers. While there is a broad spectrum of symptoms in young and adult stock (ranging from mild to severe and sometimes fatal), respiratory problems and milk drop are those most commonly seen.  

EXPERIENCES FROM EU COUNTRIES IMPLEMENTING IBR ERADICATION SCHEMES

HOLLAND

A high density of livestock and annual losses totalling 24 million Euros led the Netherlands to set up a national IBR eradication programme using Bovilis IBR.  This reduced herd prevalence from 85% in 1995 to today’s 15%.  Now at least 30% of herds are officially IBR-free.

Some 42% of the country’s 1.6 million dairy cows were infected with IBR but culling at this level was impractical, making eradication unlikely.  So why was the scheme adopted?  “We export semen, embryos and 50,000 cattle a year.  New EU regulations meant we needed IBR-free bull stations, and although milk losses were not catastrophic we saw an outbreak on the AI stations every 2-3 years and had to slaughter all 600 bulls,” explains Dr Franken of the Animal Health Service in Deventer.

Table 2: Dutch losses in 1995

Dr Franken says two key issues in control were a strategy for infected herds and monitoring IBR-free herds, plus identifying any new outbreaks quickly to minimise damage and spread.  In Holland farmers pay for blood and milk tests, the culling of positive animals, certification and vaccination. There are no compensation schemes for culling.

The decision was made to use live marker vaccines in IBR-infected herds and surveillance through frequent bulk milk tests in IBR-free certified herds.  Vaccines were administered intramuscularly twice a year, but intranasally in an emergency, such as during an outbreak.

HUNGARY

A national survey in 1993 showed that 79% of the country’s large herds were IBR positive.  By 2002 Dr Laszlo Ozsvari at the Veterinary Faculty in Budapest had calculated the average loss per cow in a 1,000-cow herd due to subclinical IBR was £23.80 (see table 3).

Table 3: Estimated subclinical losses from IBR in 1000-cow herd

Source: Dr Laszlo Ozsvari, Veterinary Faculty in Budapest

When the first live marker vaccines became available in 2002, the country made IBR a notifiable disease and applied a national eradication programme using Bovilis IBR.  Dr Jozsef Foldi of Intervet Hungaria in Budapest warned that even the perfect strategy, without support from all farmers and vets is likely to fail.

It is clear from these examples, that IBR and its control or eradication is very complex.  That said, outbreaks are economically damaging and units seeing IBR or buying in stock from herds with known IBR outbreaks, should discuss control with their vet. 

Bovilis IBR has been used in all the eradication schemes across Europe.  In the UK, Bovilis IBR is the only non-marker vaccine that can be administered by either the intranasal or intramuscular route.