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Zoonotic Diseases in Livestock


Zoonotic diseases are characterised by their ability to spread between animals and humans either through direct contact or contaminated material. There are many important zoonotic diseases in livestock which are caused by parasites and non-parasitic vectors such as viruses. 

  

  1. Hydatids (also known as hydatidosis or echinococcosis) is a zoonotic disease caused by a parasite which occurs throughout the world especially in grazing areas. In a recent article published by Beef Central it was reported that the financial loss to abattoirs was more than $450,000 from the disposal of offal not fit for human consumption. The article also documented annual losses up to $1,200,000 due to reduced body weight of animals infected with hydatids.

Hydatids is a potentially serious, sometimes fatal human disease caused by cysts containing the larval stages of tapeworm. When canines are infected with tapeworms, they shed tapeworm eggs in faeces which can be ingested by humans directly. Tapeworm eggs passed through the dog faeces can survive in the soil and on pastures for months. Livestock however play a direct role. Sheep, cattle and goats can become infected by eating contaminated grass.  Hydatid cysts can then form in meat and offal of livestock and the cycle back to dogs is completed when this infected product is consumed.

To prevent hydatids it is important to practice good hygiene around dogs, cook or freeze offal before being consumed by dogs, don’t allow dogs to eat roadkill or dead stock and contact your veterinarian to ensure all canines on farm are part of a regular worming program (including praziquantel) that targets hydatids.    

  

Adult liver fluke (marked x) on cut surface of liver. Source: Bruce Watt Central Tablelands LLS
Adult liver fluke (marked x) on cut surface of liver. Source: Bruce Watt Central Tablelands LLS
  1. Liver fluke (fasciolosis) is the next zoonotic disease caused by a parasite and in this case the source for humans is raw vegetables. Fasciolosis is found in more than 70 countries worldwide, especially where there are sheep or cattle. Humans usually become infected by eating raw watercress or other water plants contaminated with parasite larvae that have contaminated plants after leaving their intermediate host, a water snail.

In sheep and cattle, disease can result in liver damage leading to weight loss, ill-thrift, anaemia and bottle jaw. There is also an economic cost to the meat industry due to condemnation of livers. Using an integrated approach Fasciola infections are both treatable and preventable. Ensure good quarantine practices, fence off waterways, monitor animals with fluke egg count test and use an effective drench when required.  

  

  

3. Q fever is an illness caused by the bacteria Coxiella burnetii and is the first of our non-parasitic zoonotic diseases. It is carried by animals such as cattle, sheep and goats and transferred to humans usually by breathing in droplets or dust contaminated by birth fluids, faeces, or urine from infected animals.

Humans such as farmers, abattoir workers, research personnel and agricultural workers whose employment may potentially expose them to high-risk animals, animal products and animal excreta may develop Q fever.  A Q fever vaccine is available to protect humans against the disease.  As with all other zoonotic diseases good hygiene practices are also important.  

 

 

4. Japanese encephalitis is caused by the Japanese encephalitis virus (JEV) spread by insects, so it can therefore be characterised as a vector-borne zoonotic disease. It is spread through mosquito bites and infects pigs (feral and domestic), deer, water birds and horses but can also infect humans. It is for this reason we have heard of more cases recently due to the large quantities of water on the eastern sea-board creating the perfect environment for mosquito populations.

Infection in humans is asymptomatic, but on rare occasions it can result in severe disease and even death. Humans living in areas with high mosquito populations and those in the pig industry should be careful to cover up and prevent mosquito bites. There is a human vaccine available which is recommended for people working in the pig industry.  

 

 

5. Scabby mouth is a non-parasitic zoonotic disease caused by a virus common in sheep and goats that sometimes infects humans. It causes scabs and pustules around the mouth and face of animals. These are then shed onto the pasture and easily transferred. Animals become infected through abrasions in the skin. Sheep grazing stubble and hard feeds can therefore be more vulnerable.

The disease is most common in younger stock over the summer months, older animals are less prone as immunity is easily established through exposure. Animals tend to recover without intervention in a few weeks. However, there is a live vaccine available.

Scabby mouth remains a particularly significant disease for the live export markets. Trading partners may reject consignments of sheep with scabby mouth. Sheep held in confined areas can quickly spread the disease. It is important that all sheep being sold to a live exporter are vaccinated and immune. Prevent the disease occurring in humans by stopping sheep infections through vaccination and practicing good hygiene including wearing appropriate protective gear e.g. gloves when handling infected animals.