At least a few small members of our ecosystem are pleased by the massive amounts of water inundating parts of Australia.
Mosquitoes will breed well in the masses of stagnant water lying around. As a result, the risk of mosquito-borne diseases will be particularly high in many areas of eastern Australia.
Causes
There are now three main mosquito-borne infections of concern: Along with Murray Valley Encephalitis Virus (MVEV) and Kunjin/West Nile Virus (WNV), Japanese Encephalitis (JE) has been added to the list of significant risks to your horse’s health.
Japanese Encephalitis is a notifiable exotic disease in most states. These viruses are uncommon but can cause serious disease. All three affect the nervous system and can be challenging to diagnose. Japanese Encephalitis primarily affects pigs and is transmitted to horses and humans by mosquitos. Humans are considered end hosts as they don’t produce sufficient viral load to infect mosquitoes.
Murry Valley Enchephalitis is endemic to Australia and also affects humans. It tends to cause outbreaks following flooding, so you need to be on alert in the coming months. The natural hosts of this virus are water birds which will also be increasing in numbers after the rains. Surveys carried out in South Australia recently have estimated that around 8% of horses have antibodies to this virus and so have been exposed but do not necessarily show any symptoms.
Kunjin is a strain of West Nile Virus also endemic to parts of Australia. The virus has been detected in two parts of NSW in four foals which all showed neurological signs of infection. In 2011 after unusually wet conditions, there was an outbreak involving about 300 horses in NSW. Kunjin/West Nile Virus has also been known to infect humans.
Signs to watch out for
These viruses primarily affect the nervous system, and symptoms may appear quite similar.
Symptoms of Japanese Encephalitis range from mild to severe, even fatal.
Clinical signs may include fever, jaundice, lethargy, loss of appetite, incoordination, difficulty swallowing, impaired vision, and in rare cases, the horse can become over-excited. The disease may also be subclinical, meaning the horse shows no signs of disease.
Murray Valley Encephalitis may cause facial paralysis, exaggerated movement, incoordination or muscle twitching. More commonly, however, these symptoms come from depression or weakness.
Kunjin causes similar symptoms, but this virus can also cause overreactions to stimuli, blindness and walking in circles.
Often, one or more blood tests are required to definitively diagnose these infections but occasionally the fluid around the spine may need to be sampled and tested for evidence of infection.
In some areas, health and agriculture departments are using sentinel chickens to run surveillance programs to detect the presence of these diseases. These chickens have their blood regularly sampled, and if disease is detected, an alert may be issued to warn the public of the increased risk.
Treatment
Depending on the symptoms each horse experiences, common treatment for these infections may include anti-inflammatory and sedative drugs. Prevention is much easier than treatment, so take precautions to avoid mosquito bites.
Affected horses usually recover in days to weeks but in severe cases, infections can be fatal.
Prevention
See above- minimise risk by protecting horses with rugs, anti-mosquito masks and insecticides, particularly at dawn and dusk when mosquitoes are more active. Try to minimise stagnant water where mosquitoes breed.