Zoonotic Diseases of Smallstock

Zoonotic diseases are defined those which can be passed between vertebrate animals and humans. The term was originally used to describe a group of diseases that humans may acquire from domestic animals. This definition has since been modified to include all human diseases that are acquired from or transmitted to any other vertebrate. Infections may be naturally transmitted between animals and humans.

What is a Zoonosis? Zoonotic Diseases and Poverty Examples of Zoonotic Diseases Factors in Disease Emergence References and Further Reading

The majority of pathogen species causing disease in humans are zoonotic - estimated at over 60% of all human diseases. Zoonotic species are also considered to be twice as likely to be associated with emerging diseases than non-zoonotic disease causing species.

Zoonotic diseases are common throughout the world, and in developing countries and constitute an important threat to human health. A high proportion of notifiable human diseases are zoonotic. They exclude diseases transmitted from human to human via an arthropod vector (e.g. malaria).

Zoonotic diseases have both direct and indirect effects on livestock health and production. Indirect effects occur as a result of the risk of human disease, the viability of livestock producers through barriers to trade, the costs associated with control programs, the increased cost of marketing produce to ensure it is safe for human consumption and the loss of markets because of decreased consumer confidence.

Zoonoses include two major and important characteristics:

1. Successful control requires both veterinary and medical inputs, and
2. Their impact extends beyond human public health to include economic losses associated with the infections in the animal hosts.

Until recently, both of these issues, particularly the latter, have tended to be largely neglected in the study of zoonoses (see in Coleman 2002).

Zoonotic diseases are typically endemic and occur naturally, tending to foci. However, ecological change and meteorologic or climatic events can promote epidemic expansion of host and geographic range. Similarly, land use change may also result in new human and animals contacts and the emergence of new disease problems. For practical reasons, surveillance of zoonotic agents normally often relies on the identification of problems in human cases. Surveillance in natural hosts is difficult because of the ecological complexity of zoonoses.

Zoonotic diseases can be caused by bacteria, viruses, fungi and parasites. Different zoonoses are transmitted to humans in a different ways:

• the disease may be directly infectious,
• it may be transmitted by vectors
• it may be transmitted in food or water.

Disease-causing organisms can spread or be transmitted from livestock to humans through direct contact such as touching animals or handling manure. They can also be transmitted by animal scratches, bites and saliva. Recent outbreaks of severe acute respiratory syndrome (SARS) and avian influenza have shown the potential of microorganisms from animal reservoirs to adapt to human hosts.

In addition to infectious diseases, parasites are also a concern for those who have close contact with animals. Hookworms, roundworms, and tapeworms are common in both domestic animals and wildlife. They are also transmissible to humans. Parasites are usually passed through contact with faecal matter, where the eggs are deposited. However transmission can occur even with out direct contact with animal waste.

Similarly, diseases can spread from wildlife to livestock as well as from livestock to wildlife. Several zoonotic diseases may be maintained by cyclical movement from wildlife to livestock and back again to wildlife. Local breeds of livestock have developed endemic stability to some of the pathogens that constantly cycle between them.

Zoonoses have an impact both in terms of human health and economic impact through reduced production. The control of zoonotic diseases requires both medical and veterinary interventions. The emergence or re-emergence of zoonotic diseases is regarded as serious threat to public health on a global scale. Important factors in the potential spread of zoonotic diseases include the globalization of trade in food, microbiological adaptation; environmental changes; changes to human behaviour patterns; and the decline of public health systems (WHO/FAO/OIE, 2004). Effective surveillance and coordinated international action is regarded as important in order to prevent the spread of zoonoses (ibid.) An additional concern is that infection with HIV/AIDS can make individuals more susceptible to zoonotic diseases (Pasquali, 2004).

Increased demand for livestock products in many developing countries is viewed as a market, which can potentially be exploited by poor livestock keepers and offer a pathway out of poverty for some (Delgado et al., 1999). However, the zoonotic and food borne diseases may lead to restrictions on the sale of livestock products and therefore limit the access of the poor to these new markets.

Zoonotic diseases are found throughout the world. However, some are particularly associated with southern countries. The poor in particular may tend to be at risk from zoonotic diseases for a number of reasons.

• The poor often live in close contact with their livestock, and are thus at increased risk of contracting zoonotic diseases.
  
• Access to education on the prevention of zoonotic diseases is often unavailable to the poor livestock keepers.
  
• Poor consumers may be at greater risk from food-borne diseases.
  
• Informal sales of animal products make the maintenance of hygienic conditions and the control of food quality very difficult.
  
• In poor and remote areas, hygienic abattoirs and facilities for meat inspection are often limited.
  
• Crowded conditions in poor urban areas potentially increase the risk that zoonotic diseases spread to livestock keepers and their neighbours.

In addition to the immediate physical suffering inflicted by zoonotic diseases, the impact on the livelihoods of the poor may be considerable. Contracting a zoonotic disease may have serious consequences for a poor person, who will probably have poor access to healthcare, and can ill afford to have his/her ability to work impaired by sickness.