Brucellosis (Animal)

Primary reference(s)

WHO, 2020. Brucellosis. World Health Organization (WHO). Accessed 9 October 2020.

Additional scientific description

Brucellosis is one of the most widespread zoonoses transmitted by animals and in endemic areas human brucellosis has serious public health consequences. Expansion of animal industries and urbanisation, and the lack of hygienic measures in animal husbandry and in food handling, partly account for brucellosis remaining a public health hazard (WHO, 2020).

Brucellosis is found globally and is a reportable disease in most countries. It affects people of all ages and both sexes. In the general population, most cases are caused through direct contact with infected animals, by eating or drinking contaminated animal products or by inhaling airborne agents. Most cases are caused by ingesting unpasteurized milk or cheese from infected goats or sheep (WHO, 2020).

The disease is also considered an occupational hazard for people who work in the livestock sector. People who work with animals and are in contact with blood, placenta, foetuses and uterine secretions have an increased risk of contracting the disease. This method of transmission primarily affects farmers, butchers, hunters, veterinarians and laboratory personnel (WHO, 2020).

Brucellosis is mainly caused by Brucella abortus, biovars 1-6, 9; B. melitensis, biovars 1-6; B. suis, biovars 1-5; and B. canis (WHO, 2001). Worldwide, B. melitensis is the most prevalent species causing human brucellosis, owing in part to difficulties in immunising free-ranging goats and sheep (WHO, 2020).

Brucellosis typically causes flu-like symptoms, including fever, weakness, malaise and weight loss. However, the disease may present in many atypical forms and which, in the absence of specific treatment, may persist for weeks or months. In many patients the symptoms are mild and, therefore, the diagnosis may not be considered. The incubation period of the disease can be highly variable, ranging from 1 week to 2 months, but usually 2 to 4 weeks (FAO, OiE and WHO, 2006; WHO, 2020). Human-tohuman transmission is very rare (WHO, 2020).

Metrics and numeric limits

Disability adjusted life years (DALYs) are used as a measure to evaluate the impact of the morbidity caused by brucellosis in humans.

Examples of drivers, outcomes and risk management

Drivers: introduction of sub-clinically infected animals.

Outcomes include abortion in animals; disease in humans after consuming unheated dairy products (e.g., raw milk); and trade implications. These may involve substantial economic losses, including loss of income and manpower, medical care costs, and loss of food due to inadequacy of processing or spoilage. Therefore, public health education should be included among the essential activities to be performed within the framework of brucellosis control programmes or even as an independent activity (FAO, OIE and WHO, 2006).

Risk management includes movement control; treatment with antimicrobials (in humans); tracing back/forward of infected animals, depopulation of infected herds (in cattle); vaccination of animals (prevention). It also involves routine surveillance, particularly among high-risk groups (farmers, shepherds, workers in slaughterhouses, butchers, veterinarians, laboratory personnel). Another element of risk management is the mandatory early case-based reporting by health care providers or laboratories to upper levels of the public health sector as well as to the appropriate level of the animal health sector. In endemic countries where investigation of all reported cases may not be feasible, a representative proportion of reported cases should be investigated routinely.

Control activities must be coordinated and shared between both public health and animal health sectors. Administrative arrangements between the two sectors must facilitate immediate cross-notification of cases, as well as joint investigations and control. Control programmes must be promoted in goat-raising areas (FAO, OiE and WHO, 2006).

Equally important, complementary control of animal and human brucellosis activities on the ground at the community level, where local veterinary and public health services interact and collaborate, are key to ensuring the application of adapted approaches for improving surveillance, enhancing community awareness, promoting milk pasteurisation and hygiene practices and delivering effective vaccination campaigns (FAO, 2014).

Guidance on brucellosis surveillance and standards is available from the Food and Agriculture Organization of the United Nations (FAO), the World Health Organization (WHO), the World Organisation for Animal Health (OIE), and the United States Centres for Disease Control and Prevention (CDC).

The FAO has produced guidelines for coordinated human and animal brucellosis surveillance. The purpose of these general guidelines on surveillance in both human and animal populations is to provide a set of principles and techniques that can be used to develop and monitor new or existing brucellosis control programmes. The guidelines can also help in assessing the effectiveness of regulatory and advisory measures designed to safeguard public health (FAO, 2003).

The WHO provides technical advice to member states through the provision of standards, information and guidance for the management of brucellosis in humans and animals. The WHO works to support the coordination and sharing of information between the public health and animal health sectors. In collaboration with the FAO, the OIE and the Mediterranean Zoonoses Control Programme (MZCP), the WHO supports countries in the prevention and management of the disease through the Global Early Warning System for Major Animal Diseases (GLEWS) (WHO, 2020).

The OIE Terrestrial Animal Health Code provides guidance on infection with Brucella abortus, B. melitensis and B. suis, specifically Article 8.4 on the mitigation of the risk of spread of, and the risk to human health from, Brucella abortus, B. melitensis and B. suis in animals (OIE, 2019).

The CDC Brucellosis Reference Guide: Exposures, Testing, and Prevention is an example of a country approach. This guide includes the Brucella species as one of the biological agents and toxins that may pose a severe threat to public health, stating that the Brucella species are easily aerosolised and have a low infectious dose, cited at levels of between 10 and 100 microorganisms (CDC, 2017).