Magazine article The World Today

Hooves and Humans

Magazine article The World Today

Hooves and Humans

Article excerpt

There is relief that human cases of Swine Flu have so far turned out to be less lethal than expected for many people. Understanding of the need to be prepared is beginning to replace annoyance over expensive unused vaccine stockpiles. But pandemic alerts might be avoided altogether with a new approach aiming to deal with diseases before they spread from animals.

'wHEN YOU HEAR hoof beats in the barnyard, think of horses, not zebras'. This age-old adage is often used when teaching medical students not to overlook common causes of disease in patients. But based on our current understanding of new or emerging infectious diseases, we might have to rethink this advice.

Emerging infectious diseases are often associated with animals; some common, some not. Their names indicate their origin: Bovine Spongiform Encephalopathy (BSE) or Mad Cow Disease; Human Monkeypox; and Avian Influenza. Thinking of zebras in addition to horses is essential to ensure early detection of these infections that are usually caused when microbes cross the species barrier from animals to humans.

The recent pandemic of Swine Flu (H1N1) is a good example. It was first detected in humans in north America in April last year; is thought to have come from pigs, in which the mutant virus has been found, and has infected millions of humans. The death rate is similar to that of seasonal influenza, though the deaths from this virus predominately occur in younger age groups. However, as long as the virus continues to circulate, there is a risk it could mutate into a more virulent form.

To prevent a potential epidemic or pandemic, the detection and response to outbreaks of emerging infections must be rapid. Detection most often occurs in infected humans, and the response is frequently aimed at culling the animals from which the infectious agent has come.

A change in approach is required if human sickness and death from emerging infections, and negative impact on economies, are to be minimised. The shift must ensure that microbes with the potential to cross the species barrier are first identified and controlled in animals, to prevent human infection.

It is also important to bear in mind that domestic livestock are not the only animals involved in the emergence of infectious diseases in humans. Wild animals can also play a role. The outbreak of Severe Acute Respiratory Syndrome (SARS) in 2003 is thought to have been caused by a mutant virus from wild animals sold in markets in the Guangdong Province of China. Infected urine from wild rodents in Malaysia was implicated in an outbreak of Leptospirosis among athletes participating in a jungle triathlon in 2000.

A number of factors are thought to be involved in the increased risk of new infections emerging from livestock and wild animals, and of their spread to humans. Habitat loss to accommodate cities and agricultural land has brought wild animals and humans into closer proximity. Rising demand for meat and dairy products - driven in particular by income growth and urbanisation in the major developing economies - has led to more intensive livestock production, while human population growth and urbanisation have resulted in higher population densities. These trends are thought to ease breeches in the species barrier between animals and humans. Increased trade, travel and human migration in turn allow infectious diseases to spread quickly around the world.

ECONOMIC STAKES

The need for a new approach is particularly apparent where major economic and trade interests are at stake. And with global meat exports valued at around $92 billion dollars in 2007, the potential risks are high.

Avian Influenza (H5N1) among chickens has been most acute in east and Southeast Asia, where the majority of human infections and confirmed deaths have also been recorded. Infection has spread to Europe through the poultry trade, and is thought by some to have also resulted from the migration of infected wild birds. …

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