By Bruce S. Ribner, MD
Diseases transmitted from animals to humans are called zoonotic diseases. Even though we hear about a disease such as swine flu and think this type of transmission must be uncommon, animal to human spread of infection is more common than you think.
Zoonotic diseases can be caused by all types of pathogens, viruses, bacteria, and parasites, and can cause various symptoms such as diarrhea, muscle aches and fevers. Sometimes infected persons experience severe symptoms that can be life threatening.
Swine Influenza (swine flu) is a respiratory disease of pigs caused by type A influenza viruses that causes regular outbreaks in pigs. People do not normally get swine flu, but human infections can occur, most often in persons who work directly with pigs. Swine flu viruses have been reported to spread from person-to-person, but in the past, this transmission was limited.
About 75 percent of the new diseases affecting humans in the past decade can be traced to animals or animal products. You can get a disease directly from an animal, or indirectly, through the environment. Over 200 “zoonoses” have been described and they have been known for centuries.
Examples of zoonoses include rabies (from small mammals such as the dog, cat, fox, raccoon, bat, and rodent), tularemia (from rabbits and wild rodents), psittacosis (from birds of the parrot family), glanders (from horses), anthrax (from ruminants, horses, and swine), brucellosis (from domestic livestock), cat scratch disease (from cats), diarrhea (from reptiles such as snakes and turtles) and a variety of respiratory infections from domestic animals and house pets.
Foods can be contaminated if animals such as cows and pigs are infected with parasites such as Cryptosporidium and Trichinella. People can acquire trichinosis by ingesting Trichinella-infected, undercooked meat such as bear, boar, or domestic pigs.
Some dog and cat parasites can infect people. Young animals, such as puppies and kittens, are more likely to be infected with ascarids and hookworms. Contact with wild animals or places where wild animals have been can expose people to parasites. For example, people can be infected by the raccoon parasite Baylisascaris when they handle soil that is contaminated with infected raccoon feces.
Spread of the current swine flu virus is thought to be happening in the same way that seasonal flu spreads. Flu viruses are spread mainly from person to person through coughing or sneezing of people with influenza, or even touching something. However, consumption of food such as pork products will not result in infection with the swine flu.
While everyone is calling the current influenza virus swine flu, it is, in fact, more complicated than that. The current virus infecting people around the world is made up of genetic material from avian, pig and human viruses. It is this combination that raises the potential for widespread infection. The genetic material from swine and avian viruses has created a new virus that most people are not immune to, even if they received a flu shot this past season. The genetic material from human influenza viruses is probably what is allowing this virus to spread between persons.
There are simple steps you can take to prevent common infections from animals. Washing hands frequently, especially after touching animals, and avoiding contact with animal feces can help prevent infections. Following proper food-handling procedures and cooking potentially contaminated food well will reduce the risk of transmission from contaminated food. People with compromised immune systems should be especially careful to avoid contact with animals that could transmit these infections.