Every year, tens of thousands of Americans get sick from zoonotic diseases. Also known as zoonoses, these are infectious diseases that are spread between animals and people.
Zoonotic diseases are caused by harmful microbes like viruses, bacteria, parasites, and fungi. They can cause many different types of illnesses in people and animals ranging from mild to serious illness and even death. Some animals can appear healthy even when they are carrying infectious agents that can make people sick.
Scientists estimate that more than 6 out of every 10 known infectious diseases in people are spread from animals, and 3 out of every 4 new or emerging infectious diseases in people are spread from animals.
Zoonotic diseases can cause epidemics and pandemics.
Because zoonotic diseases are very common around the world and are a serious public health threat, several federal agencies have been collaborating to address associated challenges. In late April, those agencies released the first federal report on zoonotic diseases, in which they included a list of the top eight of concern for the US.
The report, which prioritizes zoonotic diseases based on feedback from December 2017’s One Health Zoonotic Disease Prioritization Workshop for the United States workshop, was compiled by the Centers for Disease Control and Prevention (CDC), US Department of Agriculture (USDA), and the US Department of the Interior (DOI).
The eight illnesses were chosen based on the potential for the disease to cause an epidemic or pandemic, the severity of the disease, the economic impact, the potential for the introduction or spread of the disease in the US, and the potential for bioterrorism. To clarify, an epidemic refers to when a disease affects more of a given population than expected, and a pandemic refers to a worldwide epidemic.
Here’s a list of the prioritized zoonotic diseases for the US:
- Zoonotic influenza
- Salmonellosis (illness caused by Salmonella bacteria)
- West Nile virus
- Emerging coronaviruses (e.g., severe acute respiratory syndrome and Middle East respiratory syndrome)
- Lyme disease
Let’s take a brief look at each of these zoonotic diseases.
Influenza A viruses are found in many different animals, including ducks, bats, chickens, pigs, whales, horses, seals, and cats. Certain subtypes of influenza A virus are specific to certain species, except for birds, which are hosts to all known subtypes of influenza A viruses. Influenza B viruses circulate widely only among humans.
Although certain strains of flu virus are typically contained within certain species, the strains change all the time. In rare cases, the virus can mutate in a way that allows it to hop from whichever animal it usually infects to humans, and from there, spread to other humans.
For example, bat flu viruses could eventually become capable of infecting humans, explains the CDC:
Because the internal genes of bat flu viruses are compatible with human flu viruses, it is possible that these viruses could exchange genetic information with human flu viruses through a process called “reassortment.” Reassortment occurs when two or more flu viruses infect a single host cell, which allows the viruses to swap genetic information. Reassortment can sometimes lead to the emergence of new flu viruses capable of infecting humans.
However, the conditions needed for reassortment to occur between human flu viruses and bat flu viruses remain unknown. A different animal (such as pigs, horses, dogs or seals) would need to serve as a “bridge,” meaning that such an animal would need to be capable of being infected with both this new bat flu virus and human flu viruses for reassortment to occur. (source)
While it is unusual for people to get influenza infections directly from animals, sporadic human infections and outbreaks caused by certain influenza A viruses have been reported, according to the CDC.
Infectious disease experts monitor flu viruses that circulate in animals because of the previous pandemics. The 1918 flu pandemic, which killed millions of people around the world, originated in birds. And, the 2009 H1N1 pandemic started with a virus that originated in pigs (hence, the nickname “swine flu”). By the way – the H1N1 virus that caused that pandemic is now a regular human flu virus and continues to circulate seasonally worldwide.
Speaking of bird flu, last year the federal government decided to allow previously suspended research on the deadly avian H5N1 influenza virus resume. This research is controversial because it is dangerous – very dangerous – it could make the bird flu virus more easily transmitted to humans.
Salmonellosis is an illness caused by Salmonella bacteria. The CDC estimates Salmonella causes about 1.2 million illnesses, 23,000 hospitalizations, and 450 deaths in the United States every year.
Most people associate Salmonella with contaminated food – and the CDC does estimate that it is the source of about 1 million infections every year. Of those, there are approximately 19,000 hospitalizations and 380 deaths, the agency says.
However, Salmonella can be transmitted to humans via contact with some animals, including reptiles, amphibians, and hedgehogs. Use caution when handling reptiles, including turtles, lizards, and snakes, and amphibians like frogs and salamanders (and their droppings). Currently, there is a multistate outbreak of Salmonella infections that has been linked to contact with pet hedgehogs.
West Nile Virus
West Nile virus (WNV) is the leading cause of mosquito-borne disease in the continental US. It is most commonly spread to people by the bite of an infected mosquito. About 1 in 5 people who are infected develop a fever and other symptoms. About 1 out of 150 infected people develop a serious, sometimes fatal, illness. Cases of WNV occur during mosquito season, which starts in the summer and continues through fall. To learn how to scare off mosquitoes, give What You Can Do to Repel Mosquitoes (And Why They Bite Some of Us More Than Others) a read.
Yes, THAT plague – the one that killed millions of people in Europe during the Middle Ages.
Plague is a disease that affects humans and other mammals. It is caused by the bacterium, Yersinia pestis. Infection in humans usually occurs after a bite from a rodent flea that is carrying the plague bacterium, or by handling an animal infected with the plague. Modern antibiotics are effective in treating plague, but without prompt treatment, the disease can cause serious illness or death. Human plague infections sometimes occur in the western US, but significantly more cases occur in parts of Africa and Asia, according to the CDC.
Even though the plague is treatable, the report concluded that one form of the plague – the deadly pneumonic plague – has the potential to spread until it’s an epidemic, and the bacteria could also be used as a bioterrorism agent.
Coronaviruses are common in many different species of animals, including camels and bats. Rarely, these same coronaviruses can infect and spread between humans. Recent examples of this include SARScoronavirus and MERS coronavirus.
Most coronaviruses infect animals, but not people. However, in the future, one or more of these other coronaviruses could potentially spread to humans, as has happened in the past. Experts still aren’t sure why only certain coronaviruses infect people.
Rabies is a preventable viral disease that is most often transmitted through the bite of a rabid animal. Transmission via other means is rare, but there are documented cases of infection occurring via other routes, including contamination of mucous membranes (i.e., eyes, nose, mouth), aerosol transmission, and corneal and organ transplantations.
While all species of mammal are susceptible to infection, only a few are common reservoirs for the disease. The vast majority of rabies cases reported to the CDC each year occur in wild animals like raccoons, skunks, bats, and foxes.
Brucellosis is an infectious disease caused by bacteria. People can get the disease when they are in contact with infected animals or animal products contaminated with the bacteria. Animals that are most commonly infected include sheep, cattle, goats, pigs, and dogs, among others. The most common way people become infected is by eating undercooked meat or consuming unpasteurized or raw dairy products. Brucellosis can also enter the body via inhalation and through wounds.
Lyme disease is caused by the bacterium Borrelia burgdorferi and is transmitted to humans through the bite of infected blacklegged ticks. Most cases are treated with antibiotics. Ticks can transmit many other diseases to people – for a full list, see the CDC’s Tickborne Diseases of the United States resource.
There are things you can do to prevent infection with zoonotic diseases.
Wash your hands with soap and clean water after handling or being around animals. Even if you didn’t touch them, wash your hands anyway.
If soap and water are unavailable, use an alcohol-based hand sanitizer that contains at least 60% alcohol to clean hands. Keep in mind that sanitizers do not eliminate all types of pathogens, so it is important to wash your hands as soon as soap and water are available.
Know the simple things you can do to stay safe around your pets.
Prevent bites from mosquitoes, ticks, and fleas.
Learn more about ways to handle food safely (including your pet’s food).
Be aware of zoonotic diseases both at home, away from home (such as at petting zoos or other animal exhibits), in child care settings or schools and when you travel.
Avoid bites and scratches from animals, and seek prompt medical care if they do occur.
What do you think?
Do you think any (or all) of these diseases are a big threat or will be in the future? Please share your thoughts in the comments.