Pestivirus Infection

Why Should We Worry About Pestivirus?

If you intend to be breeding cattle, you need to be very aware of this virus, as it occurs in more than 70% of the beef herds in Australia, and appears as fertility problems, birth of abnormal calves and abortions. These are very unwelcome problems if you are dealing with your very own Highland cattle, especially when they are as sort after as they are and the price they fetch is more than just a beef animal purchased through the sale yards.

What is it?

The virus is actually known as BVD (Bovine Viral Diarrhoea) and while by far the majority of animals exposed to it when young will just fend off the virus and become naturally immune, very rarely, an animal will become persistently infected (“PI”) with BVD and shed the virus to others, without necessarily showing symptoms themselves.  Some PI cattle will show profuse diarrhoea and weight loss and die by the age of 1-2 years old, some just look like every other animal in the paddock.

Even though 80% of cattle that are exposed to the virus when young, or that are vaccinated, will develop immunity to the virus, there will be animals that have no immunity, or you may have a herd that is naive & has never had a chance to build up immunity, and exposure to a constantly shedding PI while the cattle are pregnant can be devastating (causing abortion storms and birth deformities).

It can be carried by goats and deer as well, so be aware of these species on your property as sources of infection.

Symptoms

As mentioned above, PI animals can appear normal, or classically look like the “runt of the litter” skinny, scouring yearling that you would normally hide up in the back paddock, or sell off because it wasn’t doing well. If you are not aware or not testing, this animal’s infection will go unnoticed.

If you have a PI in your herd, and not all the rest of your cattle are immune, you may see any or all of the following signs:

• early (1st trimester) abortion (may look like cows that just don’t get in calf)
• poor fertility in your herd (only 70-90% of cows exposed to the bull calving)
• increased susceptibility to other diseases
• weak, stunted or deformed calves
• transient fever and lethargy for some cattle that are exposed to the virus and recover (many show no symptoms at all)

If a female is exposed during pregnancy, you can see the following depend on the stage of pregnancy when the foetus is infected:

• Month 1 of pregnancy – the pregnancy is terminated either by abortion or resorption of the foetus by the dam.
• Months 2-6 of pregnancy – the foetus may still be aborted (this does not necessarily occur straight away), but more often the foetus survives full-term with the resultant offspring born malformed, weak, ‘dwarfed’, stillborn, or clinically healthy but ‘persistently infected’ with pestivirus. Persistently infected calves may grow well, but generally are unthrifty compared to others the same age, and they often suffer from chronic scours or pneumonia.
• Months 3-5 of pregnancy – the virus affects the developing nervous system of the foetus. Calves may not be able to stand or suck, or may develop convulsions after birth because they are missing parts of their brain (cerebellar hypoplasia). These calves may also have eye abnormalities such as blindness and cataracts, or bent-up front legs. Some calves will survive, but have a wobbly gait and may have a permanent head tremor.
• Months 6-9 of pregnancy – the foetus is generally resistant to any adverse effects of the virus although some growth retardation of the developing calf may occur.

Infected cattle develop strong immunity when they recover.

Diagnosis

Pestivirus is sometimes difficult to diagnose. The range of symptoms is great and the number of animals affected is usually just a few and sporadic. Strong suspicions can be held when poor conception rates are seen, in combination with still births and abnormalities in the calves that are born.

Testing is straight forward for a veterinarian – blood tests from suspect animals. Both an antigen test (for animals with active infection, like a PI) and antibody tests (to see if they have had exposure in the past, but likely to be immune now).

Treatment

As with all viruses, there is no treatment. If you have the virus in your herd, or want to prevent it from causing problems in your herd, read the next section.

Management / Prevention

• Farm Biosecurity – management of cattle moving on and off your property (whether intentional, or unintentional fence jumpers) is extremely important. Nothing gets into your paddocks without a test to see if it is a PI.
• Vaccinate – the Pestigard vaccine is pretty good at protecting against active infection (protecting at least 80% of animals). Two doses 2-4 weeks apart as calves, then a booster dose annually, 2-4 weeks prior to joining is ideal.
• Deliberate exposure to a PI – some farms use this to “biologically vaccinate” their heifers just prior to joining.
• PI Testing – this is extremely useful to keep your finger on the pulse in your won herd (even if you vaccinate & have a strict Farm Biosecurity Plan), and also gives a guarantee to the purchasers of that animal if you sell them as a breeder.

Purchasing Cattle from Another Breeder

If you bring in breeding bulls or cows, these animals need to be PI tested prior to getting on your property. It is also a good idea to get an idea of the pestivirus situation on the property of origin (Do they vaccinate? Have they had PI cases in the past? Do they trade cattle or agist cattle regularly?) If you can not test, keep the newcomer separate until you have the result of the PI test back.