Major Epidemic Diseases
of Sheep and Goats

The following definition of Epidemic Disease is offered by Smith (1995): "A disease is epidemic when its frequency within the population during a given time interval is clearly in excess of its expected frequency." When considering epidemic diseases, the term, trans-boundary is often mentioned.

Cause for Concern Disease Control Vaccination Management Practices Important Epidemic Diseases of Small Ruminants References and Further Reading

Epidemic diseases are, therefore, those which show such fluctuations in their pattern of occurrence. Other characteristics of epidemic disease are described by Perry et al., (2002): "Epidemic diseases … are those that characteristically occur at a frequency above the expected, are highly infectious and exert their influence at both farm and national level on local marketing and international trade". It should also be noted that a disease, which is considered to be epidemic in some locations may be endemic in others

The epidemic diseases which cause the greatest concern are those leading to large losses in terms of mortality or decreased production. If the flocks of poor livestock keepers are affected by a serious epidemic disease, which leads to the deaths of many animals, the impact on livelihoods can be severe. If ewes or does die, a poor household’s access to milk for home consumption or sale will be reduced. In other cases income from the sale of wool may be affected. Nutritional standards and/or cash income levels will be reduced.

Sheep and goats often act as a form of savings at the household level and are sold to meet expenses which arise such as school fees or health expenses. If flock sizes are reduced by disease, poor households have fewer assets with which to meet these problems. Similarly, poultry can provide poor households with an important and regular supply of protein - greatly improving nutrition, and general levels of health of household members. In the event of an epidemic disease outbreak, livestock movement restrictions may be put in place. While the measures are important for disease control, they may have an adverse effect on the livelihoods of the poor. For example access to markets for selling livestock may be affected, or patterns of livestock migration may be disrupted. Epidemics involving poultry may, for example, require culling of all poultry in an area of outbreak, and this clearly has a major impact on poorer households.

Additionally, epidemic diseases frequently lead to restrictions on the international trade in livestock and livestock products. In such cases, the term "transboundary disease" is often used. The term is sometimes used as a synonym for epidemic diseases, but in reality refers in particular to diseases, which affect international trade in livestock and livestock products due to the potential spread of the disease across national boundaries.

The control of many epidemic diseases is regarded as an important objective by national animal health services and by international organizations such as the World Organisation for Animal Health (OIE). The following diseases of sheep and goats are notifiable to the OIE:

• Ovine epididymitis (Brucella ovis),
• Caprine and ovine brucellosis (excluding B. ovis),
• Caprine arthritis/encephalitis,
• Contagious agalactia,
• Contagious caprine pleuropneumonia,
• Enzootic abortion of ewes (ovine chlamydiosis),
• Ovine pulmonary adenomatosis,
• Nairobi sheep disease,
• Salmonellosis (S. abortusovis),
• Scrapie,
• Maedi-visna,
• Peste des petits ruminants,
• Sheep pox and Goat pox.

Additionally, the following diseases, which affect multiple species including sheep and/or goats are also notifiable:

• Anthrax,
• Aujeszky's disease,
• Echinococcosis/hydatidosis,
• Heartwater,
• Leptospirosis,
• Q fever,
• Rabies,
• Paratuberculosis,
• New world screwworm (Cochliomyia hominivorax),
• Old world screwworm (Chrysomya bezziana),
• Foot and mouth disease,
• Vesicular stomatitis,
• Lumpy skin disease,
• Bluetongue,
• Rift Valley fever.

For many diseases data on disease status by year and by country are published by the OIE.

A number of control measures may be implemented against epidemic diseases depending on the epidemiology of the disease and the resources available. The objective may be to eradicate the disease from a country or region. If this is the case, strict criteria for the declaration of "disease free"’ status are set out by the OIE. If eradication is the objective, a "stamping out" policy may be implemented in the case of the occurrence of the disease. In such cases, infected animals and those which have come into contact with a source of infection are slaughtered and the carcasses destroyed.

The eradication of a disease may be of great significance to the export of livestock products from a given country. As such, the dedication of large amounts of resources for surveillance and stamping out programmes may be justifiable to the national economy. However, poor livestock keepers are often not involved in international trade. The impacts in terms of poverty reduction may therefore be less dramatic. The poor clearly benefit from the absence of diseases which can seriously affect their flocks. However, it is possible that animal health policies directed specifically towards improving the livelihoods of the poor would give rise to different priorities.

 

For many epidemic diseases vaccination is an option for control. Vaccination programmes may be part of progress towards the eradication of a disease. Alternatively, the objective may be simply to reduce the impact of a disease, which is likely to continue to be a problem.

Where poor livestock keepers are concerned, the delivery of the required vaccinations may be problematic. A number of factors are of significance. Poor livestock keepers often live in remote locations and access to animal health services may be inadequate. Vaccines may need to be kept at low temperatures and maintaining a cold chain can be a problem. Livestock keepers also have to be willing to take up vaccinations. Services have to be delivered in a manner that is appropriate to the culture of the area and which does not interfere with other livelihood activities of the poor. A further problem may be a general lack of knowledge on the part of poor livestock keepers regarding the causation and means of preventing diseases. The poor often have limited access to information and training on animal health.

Affordability is another issue to be considered. Poor livestock keepers may wish to have their animals vaccinated, and be well aware of the advantages, but there are likely to be many other demands on a household's resources. In some cases free vaccinations may be delivered by state veterinary services, particularly due to the "public goods" involved in the control of many epidemic diseases. However, resources are often limited and service delivery, particularly to the poor, may be inadequate. The use alternative providers such as of Community-based Animal Health Workers is a possible means of delivering services at lower costs.

 

A number of management practices can be important in preventing the spread of epidemic diseases. In particular it is important to prevent contact between infected and uninfected animals. Infection can also be spread by people, by wildlife or animals such as dogs and cats, in livestock feed, on vehicles or other tools and implements. A lack of knowledge regarding the causality of diseases and how to prevent them may limit the uptake of such measures by the poor. Additionally, it may be difficult for the poor to implement the appropriate controls. Poor livestock keepers often make use of common grazing areas and watering places. Animals from different flocks mix together and potentially spread infection. It may not be possible to isolate sick animals or quarantine new introductions to the flock due to lack resources such as fencing, housing or labour.

There are a number of particularly important epidemic diseases of small ruminants (seep and goats). These are listed below, and described on the linked pages.