By Barry C. Fox, M.D., University of Wisconsin
Seventy percent of infectious diseases originate from wildlife. It is important to be aware of the many ways you can contract infections from animals, and know of the ways you can protect yourself. What do we know about some of these exotic diseases?
Tularemia: A Bacterial Infection
Tularemia is a zoonotic bacterial infection. The most common cause of acquiring tularemia is from direct contact with the blood or flesh of wild rabbits—for example, skinning and eating wild rabbit meat. Tularemia skin disease in humans is most similar to cat-scratch disease, but more severe.
Another way to contract tularemia is by inhaling contaminated aerosolized bacteria generated during the skinning of animals.
Since the tularemia bacterium has high infectivity potential, it can cause a deadly pneumonia. Since it can spread easily through the air, there is a concern that it could become an effective bioterrorism agent.
This is a transcript from the video series An Introduction to Infectious Diseases. Watch it now, Wondrium.
Chronic Wasting Disease
Another emerging disease of wildlife is Chronic Wasting Disease, or CWD. CWD is a contagious animal neurological disease affecting deer, elk, and moose. It is caused by transmission of a prion-associated protein. These proteins are not even alive, nor do they have nucleic acid building blocks of DNA or RNA.
They cause a spongy degeneration of the brain resulting in wasting, abnormal behavior, and death in animals. The disease is transmittable among animals through saliva and blood, and also from contaminated pastures. There is no treatment.
But the big question that you are probably wondering about is what happens if I eat a piece of venison that is infected with CWD? Scientists don’t know the answer to this yet. A clinical diagnosis relies on special testing of the brain for prion proteins.
But another prion-associated disease has caused a degenerative neurological disorder in humans—bovine spongiform encephalopathy. This illness was first discovered in England in the mid-1990s with several dozen citizens dying from eating contaminated beef.
Cooking meat does not destroy the prions nor reduce the risk of disease acquisition. The risk of transmission of CWD to humans is generally thought to be low, which is good news.
Learn more about how bacteria can cause disease.
Foodborne Illnesses
We consume many farm animal products, like pasteurized milk and cheese. Recently, goat cheese, which is frequently under-pasteurized, has appeared regularly in gourmet dishes or on tapas plates.
The Centers for Disease Control, or CDC, deems drinking raw milk as one of the riskiest behaviors for the acquisition of foodborne illness. This is because of the range of germs in raw milk, which includes E. coli, Salmonella, shigella, campylobacter, and Listeria—to name a few. These are usually killed by pasteurization.
Brucellosis
Another bacterium, Brucella, most commonly affects cattle, pigs, sheep and goats by causing an unintended late-term animal abortion. Sometimes transmitted to humans through milk and cheese from an infected animal, brucellosis causes fever and a body-wide illness that can be life threatening.
The United States has maintained a federal program for the eradication of brucella from domestic livestock for many years. It is very near its goal of being brucellosis-free. Since 2001, for the first time we reached a point of having no cattle herds quarantined. However, there have been rare cases detected in buffalo herds since then.
According to the U.S. Dairy Association, cattle and bison in infected geographic areas are recommended for brucella vaccination. The vaccine is a live weakened bacterium.
Query Fever
Q or Query fever, named for the original disease with an unknown cause, was first discovered in Queensland, Australia in 1935. It is a worldwide disease caused by an unusual germ, Coxiella burnetii. This is neither a virus nor a bacterium.
Cattle, sheep, and goats are the primary reservoirs. Organisms are excreted in low numbers in milk, urine, and the excrement of infected animals. But the transmission potential of this germ is especially high during animal birthing, when the germ can be aerosolized.
Humans get infected by inhaling contaminated barnyard dust. Very few organisms are required to cause infection. Veterinarians, farmers, and slaughterhouse workers are particularly at risk.
In spite of its deadly potential, most human infection is actually asymptomatic. Twenty percent of farmers of the United States show serological or blood evidence of exposure to this germ, but don’t remember being ill. When humans do become sick, they usually have pneumonia, but the germ has the potential to spread to all body systems and cause life-threatening infections.
Learn more about the food-borne illnesses.
One Health Initiative
So, how are we handling the burden of human and animal transmission of infectious diseases? Since the 1800s, scientists have noted the similarity in disease processes among animals and humans. But, human and animal medicine were practiced separately until the late 20th century—until links in the epidemiology and abnormal physiology of diseases were recognized to be common.
In the present time, there is an important collaborative worldwide effort by environmental scientists, human physicians, and veterinarians to prevent, control, and eradicate infectious diseases—and to improve the health of all species. It’s called the One Health Initiative.
We are now able to appreciate the potential for repetitive patterns of infections to occur among animals, their environments, and human/animal contacts. This paradigm for global health also recognizes that most new human infectious diseases will emerge from animal reservoirs.
Checking the Impact of Man-made Disasters
Deliberate human environmental changes—whether due to road or dam construction, or cutting down rainforests around the world, or human settlement—has led to increased contact between people, domestic animals and wildlife. This can affect the ecological balance of species.
In these situations, new habitats for viruses, parasites, and their host vectors can provide opportunities for exchange and transmission of disease. This has the potential to negatively impact the health of each species.
We have already witnessed this scenario with malaria, Ebola, and HIV. The One Health Initiative will help provide essential information in anticipating and controlling future infectious disease outbreaks, epidemics, and even the next worldwide pandemic.
Common Questions about Exotic Diseases: From Animals to Humans
The most common way to contract tularemia is through direct contact with the blood or flesh of wild rabbits—for example, skinning and eating wild rabbit meat. Another way is by inhaling contaminated aerosolized bacteria generated during the skinning of animals.
Chronic Wasting Disease, or CWD is a contagious animal neurological disease affecting deer, elk, and moose. It is caused by transmission of a prion-associated protein.
One Health Initiative is an important collaborative worldwide effort by environmental scientists, human physicians, and veterinarians to prevent, control, and eradicate infectious diseases—and to improve the health of all species.
