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Bovine viral diarrhea
Bovine viral diarrhea, often called BVD, is a viral disease that is very common in cattle farms. Its name is misleading: diarrhea is only part of the problem, and very often the disease is expensive without causing a visible epidemic. The v...
What is it?
Bovine viral diarrhea, often called BVD, is a viral disease that is very common in cattle farms. Its name is misleading: diarrhea is only part of the problem, and very often the disease is expensive without causing a visible epidemic.
The virus weakens immune defenses, disrupts reproduction and weakens young people. We observe repeated returns to heat, abortions, sickly calves and more diarrhea and pneumonia in the herd.
Its key to understanding lies in one concept: the permanently infected immunotolerant animal, often abbreviated “IPI”. If a cow is infected at an early stage of pregnancy, the calf can be born infected for life without ever developing defenses against this virus. It then excretes enormous quantities of virus constantly.
Key point
Disease subject to surveillance and sanitation plans in many countries. Suspicions and abortions must be reported to the veterinarian, who will indicate the steps to follow with the veterinary services.
Commonly observed signs
These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.
Related signs — each one links to its page:
In animals that have just been contaminated, the signs are often discreet: a temporary fever, a drop in appetite, a little throwing, sometimes nothing at all.
In more marked forms: diarrhea, salivation, small sores in the mouth and on the muzzle, drop in milk production, depression.
In the herd, it is mainly indirect signs that warn: more diarrhea in calves, more pneumonia, animals that respond poorly to treatments, disappointing growth.
On the reproduction side: repeated returns to heat, abortions at all periods of gestation, stillborn calves, malformed or blind calves, small and weak calves.
Mucous membrane disease is a particular, fatal form which only affects permanently infected animals: abundant and persistent diarrhea, ulcers in the mouth and between the hooves, rapid weight loss.
A permanently infected animal may also appear normal for months, or only remain small and have a dull coat.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
The disease is caused by bovine viral diarrhea virus, a pestivirus that exists in several types.
This virus attacks immune cells: it lowers the animal's defenses, which aggravates all other infections present in livestock.
When a female is infected during the first part of her gestation, before the fetus knows how to defend itself, the latter considers the virus as part of itself. If it survives, it is born infected for life: it is the permanently infected animal.
Depending on the time of contamination during gestation, we observe resorption of the embryo, an abortion, a malformation, or the birth of a permanently infected calf.
Purchase of animals, particularly pregnant females: a healthy cow can carry a permanently infected calf and give birth to it on your farm.
Absence of quarantine and screening upon introduction.
Adjoining pastures, gatherings, markets, bull loan.
Large herds with lots of internal movement.
Reuse of needles and equipment between animals.
Transmission
By direct contact between cattle: permanently infected animals excrete the virus continuously in nasal secretions, saliva, urine, dung, milk.
A recently infected animal also excretes virus, but for a short period.
From mother to fetus during gestation: this is how permanently infected animals are born.
By the semen of an infected bull.
Through soiled equipment, reused needles, restraint equipment, clothing and hands.
Contact between neighboring herds over a fence is enough to spread the virus.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
The diagnosis cannot be made on clinical signs alone, which are too variable. The veterinarian relies on the laboratory.
Testing for antibodies in blood, or in tank milk in dairy farming, indicates whether the herd has encountered the virus.
The search for the virus itself is done by blood analysis or on a small fragment of skin taken from the ear, often when the calf's identification tag is fitted.
An animal in which the virus is found must be rechecked after a few weeks: if it is still positive, it is permanently infected.
In the event of abortions or malformed calves, the veterinarian also takes samples from the fetus and the mother.
Treatment
There is no treatment for the virus itself.
Affected animals receive supportive care: rehydration, palatable food, quiet isolation, and treatment of additional bacterial infections, on veterinary prescription.
Mucous membrane disease is always fatal: no treatment cures it, and the course of action to be taken is decided with the veterinarian.
The real “treatment” for BVD is that of the herd, not the animal: identifying the permanently infected and removing them from the herd. As long as they remain in place, all vaccination and hygiene efforts are largely neutralized.
A permanently infected animal should never be sold to another breeder: it would carry the infection.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Screen animals upon purchase and isolate them until the result is obtained, paying particular attention to pregnant females and the calf they are carrying.
Search for and eliminate permanently infected animals from the herd: this is the most decisive measure.
Avoid contact with neighboring herds: double fence or sufficient distance.
One needle per animal, equipment cleaned and disinfected between batches.
Regularly monitor the status of the herd, using tank milk or blood samples from control animals, to quickly detect reintroduction.
Only use semen from controlled centers.
Vaccination
Inactivated vaccines and live attenuated vaccines are available.
The main objective of vaccination is the protection of the fetus: this involves avoiding the birth of new permanently infected animals. It must therefore be in place before mating or insemination.
Vaccination never replaces the detection and removal of permanently infected animals: used alone, it gives disappointing results.
The protocol, the age of primary vaccination and the frequency of booster vaccinations depend on the type of vaccine and the management of the herd: they are set by the veterinarian.
Possible complications
Collapse of reproductive results: returns to heat, abortions, extended calving intervals.
Increase in diarrhea and pneumonia in calves, with treatments less effective than expected.
Mucosal disease in permanently infected animals: always fatal.
Worsening of other infections in the herd, due to weakened immune system.
Significant and often underestimated economic losses because they are spread over time.
When to see a veterinarian
You notice several abortions, repeated returns to heat or stillborn calves.
A calf is born small, trembling, unable to stand, or visibly malformed.
Diarrhea and pneumonia in calves are increasing and respond poorly to usual treatments.
An animal presents with persistent diarrhea with ulcers in the mouth and rapid weight loss.
You have just introduced animals, especially pregnant females.
You want to know the BVD status of your herd: this is a process to take with your veterinarian, without waiting for a problem.
Prognosis
An adult bovine infected after birth generally recovers without after-effects and develops lasting immunity.
On the other hand, the prognosis is hopeless for permanently infected animals: they often die young, and those who survive remain a source of contamination for the entire herd.
At the farm level, sanitation is perfectly achievable: screening, removing permanently infected, protecting entrances. Sanitized herds see a marked improvement in the fertility and health of the calves.
Frequently asked questions
What is an “IPI” animal and why should it be removed?
It is a bovine contaminated before its birth, which produces no defense against this virus and excretes it constantly, in large quantities. Just one is enough to maintain infection in an entire herd: as long as it remains in place, vaccination and hygiene will not be enough.
Is this disease dangerous for humans?
No, this virus does not infect humans and milk does not present a risk as a result. The usual precautions remain valid: do not consume milk from an animal undergoing treatment before the end of the waiting period.
I bought a healthy cow, how could I have introduced the disease?
Because an uninfected cow can carry an infected calf before birth. The calf will be born permanently infected on your farm. This is why screening must also concern the calf at birth.
I already vaccinate: why continue to screen?
Because vaccination mainly protects the fetus and limits new cases, but it does not detect or eliminate animals already permanently infected. The two approaches are complementary.
References
WOAH — Organisation mondiale de la santé animale (ex-OIE)
EFSA — Autorité européenne de sécurité des aliments
Content reviewed by the TunisieVet editorial team · Updated 09 August 2026
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