Zoonotic diseases, or zoonoses, are on the rise. That may first bring to mind exotic diseases like Ebola, but the reality is that many zoonotic infections happen closer to home, often during everyday activities.
In 2018, we saw an outbreak of psittacosis in poultry plant workers, drug-resistant brucellosis linked to drinking raw (unpasteurized) milk, dog lick–related Capnocytophaga infections, and Salmonella infections linked to pet guinea pigs, hedgehogs, and backyard poultry. These were among many other illnesses and outbreaks caused by contact with a range of animals and other vectors like mosquitos and ticks. Over the past decade, outbreaks of zoonotic infections have been linked to animals—from pets to farm animals to wildlife—in virtually all settings, whether at home or away.
Zoonotic diseases can cause illnesses that range from minor skin infections like ringworm to deadly illnesses like rabies and anthrax. Many zoonotic pathogens are enteric, with Campylobacter, Cryptosporidium, Salmonella, and Shiga toxin–producing Escherichia coli being the most common enteric pathogens linked to animal contact. From 2009 to 2017, more than 350 outbreaks of human zoonotic diseases caused by enteric pathogens were linked to animal contact and reported to CDC. Other zoonotic pathogens of concern include Bartonella, Brucella, Capnocytophaga, hantaviruses, Streptobacillus moniliformis, and Toxoplasma gondii.
Anybody who comes in contact with animals—pet owners, zoo workers, travelers, attendants and participants in the summer ritual of county agricultural fairs, and more—is at risk. And that means almost any patient who walks into a clinic or emergency department. Clinicians should always have this potential on their radar.
Zoonotic diseases aren't going away anytime soon, so it's important to understand the risks and recommendations. Here are five things to know.
1. More than half of all known infectious diseases in humans are zoonotic.
Approximately 60% of all known infectious diseases in humans are zoonotic. An even larger percentage (70%) of new or emerging infectious diseases of humans have an animal origin.[3,4] Zoonotic diseases are estimated to be responsible for at least 2.5 billion cases of human illness and 2.7 million deaths worldwide annually. Growth of the human population, changes in the environment and agricultural practices, and increases in international travel and trade have all given both recognized and emerging zoonotic diseases new opportunities to spread.
2. Any contact with any animal can pose a risk.
Any contact with any animal in any setting can present a risk for zoonotic disease transmission. Direct contact is not always necessary, and the infected animal may not seem sick. Even asymptomatic animals or those that appear healthy can spread infections to people. Transmission can also occur via contact with areas where animals live and roam (including beds, cages, tanks, coops, stalls, and barns); their food, water, waste (feces or urine), or other body fluids; and belongings (including toys, bowls, and other supplies).
Zoonotic diseases can resemble common illnesses, so a thorough patient history should be taken. In addition to the basics—fever, malaise, gastrointestinal symptoms, respiratory symptoms, rashes—ask about any contact with animals. A family may need prompting to remember that they stopped at a pet store on their last trip to the mall or played with a neighbor's new puppy. They are even less likely to be aware of potential exposures they may have had without even touching an animal, like stepping in feces while hiking or visiting the zoo.
Patients also may not be aware of specific but serious risks like bat bites, which can be very small but can carry a risk for rabies. If the patient has had exposure to an animal, additional questions could include whether the animal has recently appeared sick, might have been exposed to wildlife, is under the care of a veterinarian, and is up-to-date on vaccinations for zoonoses—such as rabies—that are vaccine-preventable.
3. Several recent outbreaks have been linked to pets.
Although some animals are more likely to transmit certain pathogens, no animal is completely without risk.
More than half of US households own a pet, and pets have the potential to spread a variety of illnesses. Nontraditional pets such as reptiles, amphibians, and small mammals are increasingly common. Additionally, farm animals like backyard chickens and other poultry are increasingly being treated as pets.
Pets that are more likely to transmit zoonotic pathogens include reptiles (lizards, snakes, and turtles), amphibians (frogs, newts, toads, and salamanders), and rodents (mice, rats, hamsters, and guinea pigs). In the past decade, reported outbreaks of human illness have been linked to contact with pet hedgehogs, turtles, lizards, rats, mice, guinea pigs, puppies, and other animals. Every year, backyard poultry, including chickens, ducks, geese, and turkeys, have been linked to multiple outbreaks of Salmonella infections. Additionally, dry pet food and frozen or live feeder rodents for reptiles and amphibians have been associated with outbreaks of human illness.
4. Certain types of patients are at higher risk.
As is true for most infectious illnesses, children younger than 5 years of age, adults over 65 years of age, immunocompromised individuals, and in some cases, pregnant women, are more likely to have serious consequences from infection with zoonotic pathogens. Children under 5 years of age are also more likely to acquire zoonoses for obvious reasons, like putting their hands and other objects in their mouths after playing with animals or touching contaminated objects. Despite best efforts of adults, they are also less likely to properly wash their hands.
Infants can get infected through indirect contact and cross-contamination, even if they do not directly touch an animal. For example, if someone cleans a pet's habitat in the kitchen sink and then prepares a baby bottle in the same sink, germs from the habitat can cross-contaminate the baby bottle. CDC recommends that children younger than 5 years of age avoid contact with reptiles, amphibians, poultry, and rodents.
Pregnant women are at higher risk for a number of zoonotic infections and their complications. Infection with the protozoan parasite Toxoplasma gondii during pregnancy can cause congenital infection that can result in miscarriage, stillbirth, or congenital toxoplasmosis. CDC has long advised pregnant women with pet cats to avoid changing cat litter. If no one else can perform the task, they should wear disposable gloves and wash their hands with soap and water afterwards. The cat's litterbox should be changed daily. Pregnant women do not need to rehome cats they already own, but they should not adopt a new cat or handle stray cats, especially kittens.
Other zoonotic diseases of concern for pregnant women include psittacosis, lymphocytic choriomeningitis virus (LCMV), and Q fever. Obstetricians should consider household pets and occupation when advising patients on risks for pregnancies, and recommend that patients with pets consult with their veterinarian about ways to reduce risk.
These higher-risk groups do not need to avoid contact with all animals, but they do need to avoid contact with animals that pose a higher risk for illness, including reptiles, amphibians, poultry, and rodents. Keep in mind that pets and other animals can shed and transmit pathogens even when they appear healthy. People at higher risk should always practice healthy habits around all animals to decrease the risk for zoonotic diseases.
5. Patients need to hear from you about how to stay healthy around animals.
It's always a good idea to remind patients about healthy habits around pets and other animals to reduce the risk for zoonotic infections. Animals are an important part of patients' lives, and studies have shown that the bond between people and their pets can increase fitness, lower stress, and bring happiness to their owners. Many people don't realize the hidden risks associated with puppy kisses, handling pet food, cleaning reptile tanks in the kitchen sink, or leaving dog poop in the yard. As a trusted source of information, you can help your patients—especially those at higher risk for infection or complications—understand the risks and take steps to stay healthy both at home and away from home.
Opportunities for interactions with animals are expanding, and so are zoonoses. Resources for physicians and patients are available on CDC's Healthy Pets, Healthy People website, and a downloadable patient handout is included here.
Public Information from the CDC and Medscape
Cite this: Animal Lovers and Zoonotic Diseases: 5 Things to Know - Medscape - Sep 16, 2019.