The past two decades have seen some remarkable emergence of new and deadly pathogens, from SARS to avian influenza H5N1 and the novel 2009 H1N1influenza strain. It is often pointed out that a majority of recent emerging infections are “zoonotic” (transmitted from animals to people) in origin. The movie “Contagion” follows on this theme by depicting a novel virus sweeping the globe. About halfway through the movie, we learn that the virus has genetic sequences from both bats and pigs, implying that at some point “the wrong bat met up with the wrong pig”.
At the end of the movie, there is a montage that hints at the origin of the new lethal virus. Fruit bats in disturbed rain forest are seen flying and having contact with pigs in a large barn. The montage follows the pigs and presumably the virus as the pigs go to market and slaughter and into a restaurant in Asia where blood on the chef’s hands and apron appears to infect the business traveler character played by Gwyneth Paltrow, who then becomes the “index” patient spreading the epidemic from person to person around the globe.
This bat-to-pig-to-human scenario hearkens back to the real emergence of a novel virus called "Nipah virus" from a fruit bat reservoir in Malaysia into pig farms located close to areas of recently logged rain forest (see review by Chua 2003 ) . In 1999, Nipah virus caused a new and fatal encephalitis in Malaysian pig workers and a milder disease in pigs. It is thought that the movement of sick pigs spread the disease to other parts of the country, often infecting other pig workers.
The Nipah outbreak in Malaysia is a reminder about how often it is the people working closely with animals or their products who first experience disease from a viral or bacterial pathogen crossing from animals to humans.
Similarly, with SARS, while we now think that the virus may have emerged from a natural reservoir in bats and spread to humans via intermediate host animals such as civets, the initial animal to human transmission events may have involved workers in animal markets, who have been found to have elevated rates of antibodies to the virus, suggesting that they had become infected through their work with animals (CDC MMWR 2003).
With avian influenza, the majority of human case have been among people performing tasks associated with poultry production, trade, and consumption, such as working on farms, in animal markets, or butchering and preparing poultry for consumption.
And with the 2009 H1N1 virus, while the emergence events remain unknown there is a suspicion that one of the key events was zoonotic transmission from swine influenza viruses to humans working closely with the animals.
So, what if emerging infectious diseases can be seen as a problem of animal workers? It might lead us to pay greater attention to these workers than we do currently.
Agricultural animal workers work worldwide across a large spectrum of activities, from backyard farms to large industrialized facilities, to large and small slaughter facilities to animal markets. They deal on a daily basis with a wide range of hazards, from injuries, to inhalation of dusts, to the possibility of infection from the animals. Regardless of whether these animal workers are members of the “informal work sector” (such as workers on family farms), or salaried employees in large mechanized facilities, in general, in contrast to, say, factory workers, there are no regular programs to monitor or foster their health and safety. Their health and safety concerns, including their risk of occupational infections, are ‘off the radar’ of most physicians who practice the specialty “occupational and environmental medicine” (the diagnosis, treatment, and prevention of diseases caused by exposure to hazards at work and in the environment). In addition, due to their often marginal economic status, they may also not be receiving medical care benefits or have access to regular basic medical care.
In the U.S., many agricultural animal workers are recent immigrants who may be less aware of their health and safety conditions, and due to language and cultural barriers less likely to access such information if it is provided by the employer or others.
What is needed is more awareness of the work these people do and better ways to help them do it in a healthy way that reduces the risk of disease transmission. Ironically, doing so may be also be better for animal health, since we have seen that “zoonotic” pathogens can sometimes move in both directions, from animal to human or from human to animal (‘humanosis’ or ‘reverse zoonosis’). An example is H1N1 influenza, which, as it spread globally, demonstrated many more instances of humans apparently infecting animals (pigs, cats, etc.) than the other way around. So keeping animal workers healthy may help keep animals healthy as well!
In addition to the occupational medicine aspects of emerging zoonotic infections, it is also important to look at the environmental aspects. When Nipah virus emerged in Malaysia, it was related to the way that the farms were impacting the forest ecosystem. And many of the recent episodes of food safety problems seem to be caused by persistence of pathogens in the environment related to the way that animal waste and human waste are handled.
Perhaps in the future there can be greater emphasis on a “One Health” approach to animal agriculture, one that brings together experts in agriculture, veterinary medicine, environmental health, and human occupational health, and that emphasizes the value of healthy workers and healthy animals, and the need to raise animals in such a way that the environment is enhanced. It would seem that to take our attention off of any of these three issues (the health of animals, animal workers, and the environment), and their interrelationships, in our push as a society to produce greater amounts of animal protein to feed a growing human population is to risk big problems in the long run.
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