Experts conclude plans to control zoonoses, diseases transmitted from animals to humans

International experts today concluded a three-day international consultation on zoonoses, held by the World Health Organization (WHO) together with the Food and Agriculture Organization (FAO) and the World Organization for Animal Health (OIE), in collaboration with the Dutch Health Council. The experts agreed on numerous conclusions and recommendations for the control and possible prevention of future diseases transmitted from animals to humans (zoonoses).

Conclusions from the meeting and recommendations for public health and animal authorities include:

Conclusions:

• A recognition that human activities and behaviour drives the emergence of zoonoses, including: pet ownership, interaction with and movement of pets, air travel, food preferences, economic development, and the lack of compliance with recommended prevention measures.
• The importance of coordinating the response of doctors and veterinarians in outbreak responses to emerging zoonotic diseases.
• Recognizing that identifying future zoonotic diseases is extremely difficult, due to the complexity of the constantly evolving risk factors.

Recommendations:

• Encouraging research into surveillance data from non-traditional systems, i.e. insect populations, climactic changes, satellite land observation, and animal and human demographics to attempt to predict future zoonotic public health events.
• Integrating the early warning and alert systems of international organizations (WHO, FAO and OIE) to facilitate detection of potentially linked animal and public health events.
• Integrating animal and human health data at national and regional levels, including an inter-sectoral committee for zoonosis preparedness and control.

For WHO, together with FAO and OIE, the next step forward is to mobilize political awareness and support for the implementation of a public and animal health infrastructure. WHO will also begin coordinating an international network to support countries in analyzing their particular emerging zoonotic disease situation, as well as establish guidelines for the core capacities needed to assess the risk for emerging zoonoses.

Examples of recent zoonoses outbreaks

Avian Influenza

Avian influenza is a viral disease of wild and domestic birds that occasionally affects other animal species such as pigs. Human infection is rare. The first documented human outbreak of avian influenza H5N1 occurred in Hong Kong in 1997. During that outbreak, 18 people fell ill, of which 6 died. The source of infection in all cases was traced to contact with diseased birds in farms and in live poultry markets.

A new outbreak began in late 2003. Since December 2003, eight Asian countries have confirmed outbreaks of highly pathogenic avian influenza caused by the H5N1 strain. Most of these countries were experiencing H5N1 outbreaks for the first time in their histories. In several, the disease was detected in poultry flocks in virtually every part of the country. Since December 2003, more than 100 million birds have either died from the disease or been culled to prevent its further spread. Human cases of H5N1 were reported in Thailand (12 cases, of which 8 were fatal) and Vietnam (23 cases of which 15 were fatal).

Monkeypox

Monkeypox was first identified in 1958 in laboratory monkeys. The first human case was detected in 1970 in Zaire (now the Democratic Republic of Congo). Before June 2003, it had never been documented outside of the African continent, when it was reported in prairie dogs and humans in the United States. Monkeypox is a viral disease with symptoms in humans similar to that seen in smallpox patients.

Most monkeypox cases occur in remote villages of Central and West Africa close to tropical rainforests where humans have frequent contact with infected animals. It is thought that monkeypox is transmitted to humans from infected squirrels or primates, via contact with the infected animal's blood or through a bite.

In 2003, investigations into the monkeypox outbreak in the US traced the source of infection to the shipment to Texas of 800 small mammals, intended as pets, including Gambian giant rats and tree squirrels. Gambian rats from this shipment were housed in close proximity to prairie dogs that were later purchased as pets.

Nipah Virus

Nipah virus first emerged in 1999 in Malaysia. Named after the village from where the virus isolate that led to its identification was collected, Nipah virus has caused disease in pigs and in humans. It is believed that certain species of fruit bats are the natural animal reservoir for Nipah virus.

From September 1998-April 1999, Nipah virus was identified as the cause of an encephalitis outbreak that infected 265 people, of whom 105 died. The convergence of bat, pig and human populations in a single location was pivotal to the virus' emergence; from the natural reservoir of bats, the virus was transmitted first to pigs, (which had never before then been raised in such numbers in the area), to their human handlers. Since the emergence of Nipah virus, the Malaysian government has adopted policies designed to prevent another outbreak, by requiring that pig farms and abattoirs not be located in close proximity to bats and large human settlements.

Bovine spongiform encephalopathy (BSE) and variant Cruetzfeld-Jakob Disease (vCJD)

Bovine spongiform encephalopathy (BSE) or "mad cow" disease first emerged in cattle in 1986. BSE is one of several different forms of transmissible brain diseases due to an unconventional agent affecting various animal species. Epidemiological studies suggested that BSE was caused by cattle feed prepared from bovine carcasses contaminated by the BSE agent. About 190 000 cases of BSE have been diagnosed in the world, mostly in the UK (183 000 cases).

Variant Cruetzfeld-Jakob disease (vCJD) is the human form of BSE. Similarities observed between the strain of the agent responsible for vCJD and those of BSE and closely related agents have suggested that vCJD cases are due to the same agent that causes BSE in cattle.

A cluster of 10 cases of vCJD was first documented in March 1996 in the UK. In contrast to CJD, vCJD affects younger patients, and has a longer duration of illness. The disease is inevitably fatal. As of April 2004, the CJD surveillance unit for the UK reported 146 cases of vCJD.