Infectious Respiratory Disease in Cattle
The main infectious agents involved in bovine respiratory disease in Ireland are viruses and bacteria. Antibiotics can be used to combat bacteria but are ineffective at fighting viruses. Those viruses and bacteria most commonly linked with bovine respiratory disease are listed below.
Infectious bovine rhinotracheitis virus (IBR) Mannheimia haemolytica Bovine respiratory syncitial virus (BRSV) Pasteurella multocida Bovine parainfluenza 3 virus (PI3) Haemophilus somnus Bovine viral diarrhoea virus (BVD) Mycoplasma spp Chlamydia spp. Salmonella spp.
Probably only these four viruses are capable of acting alone to cause respiratory disease in cattle although pulmonary infections by bovine coronavirus, rhinovirus, reovirus, enterovirus and adenovirus can also be involved. It is very common for two or more of the above agents to interact to overcome the animal's immune defences and thereby produce bovine pneumonia - such super infections can also greatly increase disease severity and subsequent losses incurred.
Proper animal management helps to make outbreaks of respiratory disease self-limiting and even clinically unapparent. Stress, poor nutrition, and high worm burdens render animals more susceptible to outbreaks of respiratory disease, by their negative impact on host immune status. The bacteria Mycoplasma spp. and Chlamydia spp. are considered significant predominantly in younger stock.
Vets and farmers need to work closely together when dealing with outbreaks of bovine respiratory disease. Intervening earlier rather than later, regular temperature checks of at-risk stock and the operation of sick-bays, are just some of the tasks that must be discussed, planned and shared if success is to be achieved.
In both human and veterinary medicine, vaccination remains the dominant intervention measure to combat viral disease.
Respiratory disease in Irish cattle costs money.
There are the direct and obvious costs such as deaths, failure to thrive, "screw" cattle, and the veterinary /drug bills.
There are also the hidden, less obvious costs such as the significant drop in feed conversion efficiencies and daily weight gains across the group; the loss of specialist markets (AI, export) due to unfavourable health/disease status; and the amount of farmer time wasted on each outbreak, attending sick animals.
In addition, drug residue and welfare issues increasingly contribute to the overall negative impact of bovine respiratory disease as does the ratchetting up of antibiotic resistances on farms .
It is unlikely that specific diagnosis can be attempted in every case of bovine pneumonia attended. But for cases with severe clinical signs, cases where the problem continually recurs or cases proving intractable and non-responsive, there are many advantages in knowing which agent(s) are involved.
- Often specific management changes can do a lot to alleviate the problem - when you know which agents are involved.
- The viruses BVD and IBR are important in herd health programmes and for those herds which supply exports and the AI stations. The earlier you know of their arrival on your farm, the earlier you can eliminate them.
- Vaccines can be used to face down an outbreak, similar to how firebreaks are used in larger forest fires. For success however, it is crucial that agent and vaccine are specifically matched in this case.
- The viruses BVD and IBR have developed special strategies (persistent infection and latent infection), which make their spread more difficult to control than other viruses. To help protect your breeding herd, it is important to know if these two viruses are circulating on your farm.
- Respiratory disease in cattle is rarely caused by a single agent - it becomes a more complicated problem to solve when you are dealing with two, three or more agents. Knowing the problem allows you to solve it.
- With viruses being the primary cause of many outbreaks of respiratory disease, reaching for the latest (and more expensive) antibiotic for treatment is of dubious value. With an ever-growing problem of antibiotic resistance, a more tempered approach would be to tailor treatment to cause.
Bovine respiratory disease is often a unique interaction of environment, management and pathogen, particular to that farm.
Sampling for bovine respiratory disease
In any disease outbreak, it is extremely rare for all animals to be exposed at once - disease outbreaks tend to snowball and expand as more and more animals become infected - especially the case in larger herds.
So on any given day of an outbreak, different animals will be at different stages of infection.
The exposure or dose, which each animal receives during an outbreak will also vary greatly. Housed or grazing, animal density, group size, pen position, house size, ventilation, mixing rate are just some of the factors behind this variation.
Different animals (and people) react differently (speed of response, magnitude of response, length of response, severity of signs, etc) to any set infection. This is due to a mixture of previous disease history, genetics, and age for that particular animal as well as the group disease history and management factors such as vaccination.
The period that an animal is actively shedding virus is often very short - frequently between 3-5 days. With such a brief "window" it can often be difficult to collect samples useful for diagnosis. BVD and IBR are exceptions, commonly with much longer shedding phases - this is partly why they need special consideration.
This is the reason why obtaining the correct samples at the correct stage of infection is often far from easy.
Sampling for bovine respiratory disease
1) Use the submission form to provide as much information as possible
2) Take two nasal swabs, one plain cotton, one with transport media from each of 5-10 animals.
Send the plain swabs for virology.
Send the transport media swabs for bacteriology
More detail... (pdf 91Kb)
3) Take a single, clotted blood from each of 5-10 animals
If possible use different groups to highlight the disease's effects eg. recovered group versus currently affected group, etc
More detail... (pdf 87Kb)
Some caution is always required to prevent over-interpretation of actual numerical ELISA readings but the following tables may be used to place in context, results received
Interpreting BRSV serology results (pdf 178Kb)
Interpreting PI3 serology results (pdf 178Kb)
4) Use post-mortem sampling as appropriate
More detail... (pdf 74Kb)
5) Use lung wash samples as appropriate
More detail... (pdf 80Kb)