Rotaviral diarrhoea is one of the main infections causing calves to scour between five to fourteen days of age. Both the rotavirus, which is seen more often, and the coronavirus together make up over half of diarrhoea problems in calves. Most cattle herds are exposed to the disease and can shed the rotavirus although an onset of signs and symptoms occurring in calves older than four weeks is not commonly seen. Other animals able to catch the disease include dogs, horses, rabbits, sheep, some rodents, pigs and chicken. The disease can prove fatal if it leads to extreme dehydration and emaciation.
The bovine rotavirus is scientifically said to be categorised into the viral family which is called the Reoviridae. Upon entering the small intestine, the virus attacks the villi thus reducing the calf’s ability to absorb material into the body effectively. This produces a concentration gradient and the change in water potential results in water loss from the epithelial cells and therefore from the body causing dehydration.
All cattle are susceptible to infections. Calves, in particular under one month of age are more susceptible to the severe signs and symptoms of the bovine rotavirus following the contraction of the disease. Transmission generally occurs as a result of oral contact with infected faeces. Other sources of infection include re-infected cows which show no symptoms at all. These cows are able to shed the virus without the knowledge of the farmer.
Symptoms include runny diarrhoea, dehydration and a loss of appetite. As the severity is increased, the more likely fatalities will result. The disease is considered to be zoonotic. This means that the rotavirus can be transmitted to humans, which is a cause for concern. Vaccines are available and may even by administered to neonatal calves.
Transmission of the bovine rotavirus
One method of transmission for the bovine rotavirus is if an unaffected cow has contact orally with contaminated material. This material can include the faeces from an infected cow and contaminated feed. If there is poor hygiene in the living quarters then this also acts as a source of infection. Some cows become re-infected and shed the virus throughout the whole of their life whilst remaining asymptomatic. In cows showing signs and symptoms, it is estimated that they are able to shed the virus for as long as a week.
The bovine rotavirus is a hardy virus which can survive for many months outside of the host and it cannot be destroyed by a large number of disinfectants. Therefore, due to the difficulty in the eradication of the virus and due to its rapid transmission, the disease can spread very quickly throughout the herd.
Signs and Symptoms of the bovine rotavirus
There are a few factors which are taken into account when judging the severity of an infection from the bovine rotavirus. These include the age of the animal and the external conditions of the environment it resides in.
Generally, the main sign or symptom of the disease is runny diarrhoea which may have the appearance of water rather than normal faeces. The diarrhoea is often yellow in colour and blood and mucous may be present. The calf will appear depressed and be disinclined to drink or feed. As a result severe dehydration will occur. Some calves may drool and some may be seen to continually attempt and fail to defecate. These symptoms are more commonly seen in calves between four days and three weeks of age. It is rarely symptomatic when the cow is older than a month old.
In calves or adult cows older than four weeks of age, there are often no signs or symptoms shown at all following re-infection. These cows are able to regularly shed the virus at certain periods of time without the knowledge of the farmer.
Treatment of the bovine rotavirus
There is no cure as such for calves and cows infected with the bovine rotavirus although supportive therapy is usually effective. The treatment plan usually consists of replacing lost fluids and restoring the balance of the body’s important electrolytes. These may be administered intravenously or orally depending on whether the oral rehydration therapy works. The infected animal must be kept in a warm and dry area, and adequate amounts of colostrum may be given to young calves to induce recovery. These are generally given for most cases of viral diarrhoea.
The use of antibiotics is not required to treat the viral infection since they do not destroy viruses. However, in cases where there is a possibility or a presence of a secondary bacterial infection the antibiotics are administered. This is because once a secondary infection comes into play, the severity and risk of the diseases to the animal’s health significantly increases.
Prevention of the rotaviral diarrhoea
Preventing the disease can significantly reduce economic loss and stress for the cattle farmer. The prevention methods are very similar to the majority of measures used to treat viral diarrhoea. The key points to keep are high hygiene standards, ensuring the calves have adequate amounts of colostrum, and in some cases having a good vaccination programme.
Concerning hygiene, good cleanliness can prevent the transmission of the bovine rotavirus. Calves and cows living indoors should be provided with clean and dry bedding in addition to good ventilation. Infected animals should be isolated and restricted from having contact with the other members of the herd in order to reduce the possibility of rapid transmission. It has also been suggested that animals of different ages should be separated.
In terms of keeping calves healthy, the ingestion of a good amount of colostrum is essential. This is especially true for calves under the age of five days old. The calf gains the necessary immuno-globulins in the gut from the colostrum. All of this strengthens the immune system of calves and so decreases any risk of infection from the majority of diseases. Calves should be kept free of stress at the age of below five days as this can also contribute to infection.
Vaccines are available to protect against the virus and also come with added protection against other diseases. Vaccinated cows are able to pass on the necessary antibodies in their colostrum to a suckling calf for as long as week. Neonatal calves are also able to be vaccinated. Additionally, to further protect calves, cows may be administered the vaccine in the last one to three months of pregnancy.
Diagnosis of the bovine rotavirus
Initially the signs and symptoms are observed. Following this, any medical history is taken into count for the individual as well as the entire present or past herd. Faecal and tissue samples can be taken and sent for laboratory tests. Antigens and antibodies may be detected here in order to identify the rotavirus.
Prognosis of the bovine rotavirus
In calves where severe dehydration or emaciation has occurred as a result of infection the prognosis is rarely good. In these cases it can prove fatal. However, with the correct treatment the calf may recover despite the fact it may not grow into adulthood achieving its full potential.