Photo: Wayne Southwood
By Paul Donovan
Livestock can be carriers of diseases that can make you ill and might even be fatal, warns Paul Donovan.
A zoonosis is a disease that can be transmitted from animals to humans, or from humans to animals. The example that springs to mind most readily is rabies. If a dog or other animal with rabies bites you, you will also get rabies. But other diseases too can cross the animal/human barrier. Bovine spongiform encephalopathy (BSE) – ‘mad cow disease’ – and avian influenza (AI) both made headlines in recent years. Anthrax, brucellosis and tuberculosis are other zoonotic diseases.
Theoretically, to stop such diseases from spreading to humans we need to prevent their occurrence in animals. In reality, infectious diseases caused by pathogenic microbes (viruses, bacteria) or by parasites (worms, protozoans) are many and varied, and occur in different parts of the body. There are therefore many ways in which they can be transmitted from animal to human.
Furthermore, an animal can act as a carrier of a microbe or parasite without showing symptoms. For example, a chicken can spread salmonella without showing symptoms of the bacteria. It is important that livestock owners or poultry farmers understand the importance of these diseases, and how they can be contracted from the animals. Most zoonotic diseases can be prevented by simple measures such as vaccination and good husbandry. These will also improve the health of the animal and boost profits.
Some evidence suggests that the small-scale rural farmer is more at risk of contracting a zoonotic disease than a farmer on a large-scale operation. This is mainly due to a lack of adequate veterinary care, increased contact between owner and animals, and increased interaction between livestock and wildlife.
The way in which animals are slaughtered can also increase the risk from zoonoses. Backyard slaughtering is common, and is unregulated. Therefore the risk of buying a sick animal or meat at a local market is higher, as is the risk of becoming ill as a consequence.
Humans and wildlife
Evidence suggests that the appearance of new zoonotic pathogens in human populations is increased by greater contact between humans and wildlife. This can be through encroachment of human activity into wilderness areas, or by the movement of wild animals into areas of human habitation. A good example is the outbreak of Nipah virus in Malaysia in 1999. In order to expand pig farming, the government encouraged farmers to use land occupied by fruit bats, little knowing the bats were infected with the Nipah virus.
Over time the pigs developed a mysterious infection and eventually transmitted the virus to farmers. More than 100 people died. (The name ‘Nipah’ refers to the place where the virus was first isolated in a human patient.)
How the diseases are spread
There are several ways in which microbes can be transmitted from animals to humans: direct contact with the infected animal, contact with its secretions or faeces, or via vectors such as flies and mosquitoes. As noted, many zoonotic diseases show no clear symptoms in the animal, making them difficult to identify. However there are some symptoms that should set the alarm bells ringing. Sudden deaths in cattle (excluding the effects of being hit by lightening, for example) may point to anthrax. Do not touch the animal, but call a vet or the local veterinary authority.
Animals that abort can be carriers of brucellosis, which can cause pregnant women to miscarry. Aborted foetuses or fluids should not be touched; rather call a vet immediately. We should always be conscious of the diseases that animals can harbour and transfer to us, and take sensible precautions when working with, or around, livestock.
These will be covered in the next issue.
Sources: Daszak, P, Cunningham, AA, Hyatt, AD (2001): ‘Anthropogenic environmental change and the emergence of infectious diseases in wildlife’, Act Trop. 78 (2): 103-116. Field, H, Young, P, Yob, JM et al (2001): ‘The natural history of Hendra and Nipah viruses’, Microbes and Infection 3 (4): 307-314.
Issue date: 20 June 2014
Related Articles >>
Livestock Disease Trends – June 2014
Livestock Disease Trends – May 2014
Livestock Disease Trends – April 2014
FMD-free status: Sorry, but it’s just not enough!