Seen worldwide, all cattle are able to contract bovine respiratory syncytial disease. Sheep and goats are also able to become infected by the respiratory syncytial virus. Animals can die from this disease as a result of secondary infections such as pneumonia and in two out of every ten cases, fatalities can occur.
A viral infection, this disease is caused by the bovine respiratory syncytial virus (BVSV). This virus is known to be a pneumovirus. The virus attacks the lower respiratory tract of the cow causing it to be more at risk of other infections of the lungs. It is in the respiratory tract where it rapidly multiplies leading to tissue damage.
NaÔve herds can show signs and symptoms following the disease but young dairy and beef calves are more susceptible to its most severe form. This is due to their immune system having not yet been adequately developed. Transmission occurs generally as a result of already infected cows spreading the disease via expelling aerosol droplets as the cow breathes or coughs. The virus is not able to survive long outside the host so direct contact with an infected animal is required.
The signs and symptoms vary depending mainly on the age of the animal. There can be a fever, coughing, and nasal and ocular discharge. In some cases the calf will actually die before the owners are ever aware of any infection. The bovine respiratory syncytial virus is very similar to the human respiratory syncytial virus although there are no known zoonotic effects from the BRSV. Vaccines are available to protect against the worst effects of the disease by boosting the animalís immune system.
Transmission of the bovine respiratory syncytial virus
The virus cannot survive for long periods of time outside of its host in the environment. Thus, direct contact is required for the spread of the bovine respiratory syncytial virus. As a result the main sources of infection are cows already infected with this respiratory disease. It has been suggested therefore that the virus is transferred from an infected cow to an unaffected cow via aerosols droplets. The droplets may be expelled into the air via breathing, coughing or sneezing.
Cows in close proximity of each other, especially those exposed to overcrowding can rapidly transfer the virus throughout the herd. As a result areas of intensive beef farming or dairy herds are very likely to spread the disease very quickly once one is infected. From this, it can be deduced that cows are more susceptible during the colder months since they are more likely to be kept in.
Older cows which have become infected may show no signs or symptoms relating to the disease which can become a cause for concern. As a result, they are able to pass on the virus to the more susceptible members of the herd, such as the calves, without the knowledge of the owner.
Signs and Symptoms of BRSV
The signs and symptoms in older cows can vary from relatively mild to severe. In some cases, where the herd has previously been exposed naturally or via vaccination, they may not show any signs or symptoms at all. Dairy cows may experience a sudden drop in milk production during the lactation period. NaÔve herds are more likely to show severe consequences following infection. They can be seen to have difficulty breathing and may actually collapse and die.
Very young calves rarely succumb to infection as they are protected by the maternal antibodies provided by the motherís milk. If infected however, symptoms include a fever and nasal discharge. The calf becomes more susceptible to other respiratory infections and may die as result of contracting pneumonia.
The more severe forms of the disease can usually be observed in weaned or feedlot calves between the ages of two and five months old. There is both ocular and nasal discharge visible as either serous or yellow and viscous, and the cough progresses to sound relatively dry. Signs of depression and a progressive fever can also result from an infection of the bovine respiratory syncytial virus. Gross lesions are often present. The calf may also lose weight following a loss of appetite. Swelling of the eyes and jaw will be seen as well as difficulty in breathing. It may keep its mouth open in order to breathe and bloody or frothy saliva may leave the mouth. Calves of this category often die either as a result of the damage caused by the virus directly or by secondary infections including pneumonia. None of the above signs may even be noticed until the virus does actually prove to be fatal.
Treatment for BRSV
There is no cure against infection from the bovine respiratory syncytial virus. Supportive therapy is therefore the option included in most treatment plans. Fluids lost are replaced intravenously and attempts are made to maintain the correct balance of the electrolyte levels of the cow. Medication with anti-inflammatory effects can be given. In some cases, to prevent secondary bacterial infections, antibiotics will be administered.
Prevention against the bovine respiratory syncytial virus
Preventative measures are vital to reduce any possible outbreaks of infection. Vaccines to protect against the bovine respiratory syncytial virus are available to be injected into the cowís muscle. Cattle appear to be better protected against the disease when vaccinated. They show fewer if any signs of infection and are more likely to survive. To provide long term protection regular vaccinations are required as well as annual boosters. Pregnant cows can be safely given the vaccine and in doing so their calves will also be protected for a short period of time.
Diagnosis of bovine respiratory syncytial virus
One aspect which increases the difficulty of making a diagnosis is the presence of other secondary lung infections. These could be diagnosed, incorrectly, as a cause of the disease. Sampling, such as using nasal swabs, prove to be difficult when attempting to detect the virus. It is not able to survive for long outside its host and so attempts to isolate and identify it are not easy. Detection is more likely if the animal is acutely infected.
Prognosis for BRSV
If caught in time and administered supportive therapy, it is not uncommon for most cases to recover. If the animal contracts a secondary infection then the prognosis is poor and fatalities are more likely to occur.