Zoonotic diseases: How do they affect the public?
This month, a highly contagious strain of avian influenza broke out in poultry farms in Gimje and Jeong-eup, North Jeolla Province and Nonsan in South Chungcheong Province. This is the third outbreak of avian influenza in Korea since 2003.Livestock farms and related food industries have been severely damaged by the spread of avian influenza (bird flu) viruses.
Above all, the general public is very concerned that humans can be infected by the viruses.
In fact, a soldier, who was dispatched to destroy infected birds, recently had to be treated at a hospital since he was suspected of being infected by the virus.
Recently, zoonotic diseases, or contagious diseases infecting both humans and animals, have become global pandemics, including bird flu, severe acute respiratory syndrome (SARS), the human form of mad cow disease and brucellosis.
Bird flu has spread to 40 countries and caused 239 deaths since 2003.
What are zoonotic diseases?
Zoonotic diseases are diseases caused by infectious agents that both animals and humans can catch. Zoonotic diseases make up 70 percent of all epidemic diseases.
The carriers of the diseases are bacteria, viruses and parasites. The diseases are transmitted when people come into direct or indirect contact with infected animals.
What effects do these diseases have on humans?
Historically, zoonotic diseases have been lethal to humans.
The reason why the diseases are so lethal is that they develop diverse strains of viruses through genetic mutation. Thus, the human body does not have time to adjust to a new strain of virus and its immune system does not work properly. This is why zoonotic diseases cause significant deaths in a short time.
In the past 100 years, three influenza pandemics caused by new viruses have occurred around the world.
The 1918 Spanish flu resulted in 50 million deaths. The 1957 Asian flu and the 1968 Hong Kong flu caused 1 million and 700,000 deaths, respectively. In total, the number of deaths exceeded the number of those killed during World War I and II.
What causes zoonotic disease?
Experts say that zoonotic diseases began occurring after humans adopted agriculture. As people started raising animals such as cows, pigs, sheep or horses and used them for food or cultivation, diseases were transferred from animals to humans.
Rabies, a viral disease affecting mammals, is most often transmitted from dogs or raccoons to humans. It was mentioned in a legal document from ancient Mesopotamia 4,000 years ago.
The reason why zoonotic diseases are more prevalent these days is that the diseases’ infectious agents are rapidly spread by the movement of animals.
For instance, scientists once thought migrant birds transmitted avian influenza. However, the current outbreak of avian influenza in South Korea occurred after winter migratory birds had left the country. Others raised skepticism about this theory.
Some claim that the primary cause of zoonotic diseases is people’s greed.
“The fundamental cause of zoonotic disease is modern mass production in animal husbandry in a bid to maximize profit and minimize costs,” said Park Sang-pyo, director of a civic group of veterinarians.
“Animals, raised in overcrowded factory farms, tend to have very weak immune systems and are easily exposed to viruses such as avian influenza.”
Mad cow disease, or bovine spongiform encephalopthy, is known to have emerged because people fed meat and other animal food to herbivores to save on feed costs.
“While humans recklessly tinkered with nature, they destroyed the environment by distorting the ecosystem. Thus the number of viruses and insects that transmit diseases to wild animals or livestock increased,” said Lee Hang, a professor the Seoul National University College of Veterinary Medicine. “Zoonotic diseases were created by humans themselves.”
Other scientists cite the growing mobility of people and animals, thanks to advances in transportation and trade, as one of the reasons behind the spread of infectious zoonotic diseases.
What should be done to prevent these diseases?
The most important thing to prevent the spread of these diseases is to track their routes. Humans conquered the Black Death after the discovery that the epidemic was transmitted by infected rat fleas.
In addition, individuals have to pay careful attention to sanitation in their everyday lives, such as washing their hands more often. Viral diseases could be lethal when a person has a weak immune system; therefore it is important to strengthen the immune system by improving nutrition.
“To prevent the spread of zoonotic diseases, people have to understand that animals and plants have direct contact with viruses,” said Park Seung-cheol, professor of Samsung Medical Center. “For this goal, close cooperation among doctors, veterinarians and government ministries is needed.”
Some experts claim that we should conduct research on diseases among wild as well as domestic animals.
As current research on zoonotic diseases focuses on domestic animals such as cows and chickens, it is not enough to prevent a new epidemic.
Some experts argue that humans can only conquer these diseases when we realize that humans should coexist safely with domestic animals and wild animals.
By Jang Wook JoongAng Ilbo[soejung@joongang.co.kr]
with the Korea JoongAng Daily
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