Sunday, 2 December 2012

Science Sunday; Respiratory Disease

In the past I have talked about recurrent airway obstruction, this post is going to focus on other respiratory diseases.

There are a number of defence mechanisms in nose, airways and lungs (respiratory tract) in order to try and prevent diseases taking hold of this system. There are mechanisms that filter the air and throw the air around in the air in order to trap bacteria or viruses that may be entering through the nose. There are also other mechanisms such as the cough reflex and there are tiny hairs in the tract called cilia that waft mucus up the the airways away from the lungs carrying any foreign particles with it. If bacteria does reach the lungs there are also cells there called macrophages that eat them up to stop them causing problems.

Viral infections
Viruses can be spread by direct and indirect contact. After horses have been infected by a virus they may also be infected by bacteria as it will take the opportunity to attack while the immune system is low. A virus can damage cilia (the hairs that waft mucus up the airways) and this leads to mucus staying in the airways and not being removed

Horses are often diagnosed by the clinical signs and the history. Sometimes swabs may be taken within 48-72 hours. After 72 hours the virus may be isolated in the blood so blood tests can be taken. I will now talk about a few viral diseases.

  • Equine influenza can be spread by direct contact. It is incubated in the horse for 1-3 days before symptoms may be seen. The virus will be shred for 10 days. Vaccines are difficult as there are many different strains and it can mutate, there are however vaccines that cab be given that cover a number of different strains. It is under global surveillance. The clinical signs are a high temp, depression, anorexia, nasal discharge, dry cough, and enlarged lymph nodes. Horses are rested for at least 4 weeks to allow the airways to regenerate. They are kept in a dust-free environment. 
  • Equine herpes virus has 2 strains. Equine herpes virus 1 (EHV1) can cause abortion and neurological disease and is contagious. EHV4 is a respiratory disease and is occasionally contagious. It is spread by direct contact and horses show problems in 3-6 days. Horses will have a high temp, depression, serious nasal discharge and a mild cough. Again they are treated with rest but vaccinations don't work for this virus as yet. Horses should be isolated for 21 days and kept unstressed.

Bacterial infections

  • Strangles is also called streptococcus equi, it can survive in water for 1-2 months. It can be diagnosed with nasal swabs but repeat sampling may be necessary as they need 3 negatives before they get the all clear. It causes fever, anorexia, nasal discharge, enlarged lymph nodes and other complications. It mainly affects horses aged 1-5 years and has an incubation period of 7-12 days. Carrier horses may not show symptoms but may pass it on to other horses. Antibiotics cab be given but may not work well. After coming into contact with the disease they are immune for up to 4 years.
  • Rhodococcal infection in foals causes pneumonia. It is usually chronic, they get a high temp, cough, nasal discharge, increased heart rate and breathing rate, enlarged joints, diarrhoea and nervous system problems. This happens due to the immature immune system in foals. They may be diagnosed by clinical history, blood tests and ultrasounds. Vaccinations may be given.

Other respiratory diseases
  • Parasites can cause infections in the lungs. This is uncommon but may happen in the late summer or autumn. Dictyocaulus arnfield is an example of this and may be carried by donkeys.
  • Allergies may also be a problem. Recurrent Airways Obstruction (RAO) is an example of this, I have previously written a post on this which is linked at the top of this one. 

Love Laura

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