Zoonotic diseases and their far-reaching effects, and why healthy animals make for healthy humans
It was on the tip of everyone’s tongue last year, prompting panicked vacationers to cancel flights and unprecedented CDC travel bans: Zika. Equally notorious but an ocean away from Miami mosquitoes, West Africa battled the most deadly Ebola outbreak in history. The two viruses cause an array of different problems, but are spread similarly, through animals. Ebola’s likely reservoir host is bats, while Zika is hosted within the ubiquitous mosquito.
While these were the hot topics in the last couple years, there are many other zoonotic diseases that can adversely affect both humans and animals in a given population. One of the messages of Veterinarians International is: “Given that 75% of new emerging diseases, and 60% of all human diseases, come from animals, we must have healthy animals to have healthy people.” Read on for an overview of five zoonotic diseases, where you’ll find them, and their animals of origin.
Where: Most recently West Africa, but sporadic outbreaks have been reported throughout the continent.
Who: Humans and non-human primates.
What: According to the CDC, there are five species of the Ebola virus, one of which affects only non-human primates. It is believed to be hosted within bats, thus, it can be transmitted via direct contact with a host bat or host primate. It is also extremely contagious within humans, and can be transmitted between humans through body fluid. This includes contact with the body of someone who has died from Ebola. The virus causes fever, bleeding, and organ failure, and can lead to death.
Where: All over. Historically common in tropical Africa, Southeast Asia, and the Pacific Islands. The recent outbreak began in Brazil and spread throughout South, Central, then eventually North America.
Who: Humans, although there have been some cases in which non-human primates have had the disease, but no symptoms. According to the CDC, more research is needed to determine if non-human primates can be host reservoirs.
What: Zika causes rash, headache, and fever but may present as fairly mild, with symptoms gone within a week or so. No deaths have been reported in this phase of initial infection. Where Zika gets scary is when it infects pregnant women and causes birth defects. The New England Journal of Medicine reported abnormalities in 42% of live births. The virus is mosquito-borne, but it can also be transmitted sexually.
Who: Humans and many other land mammals including dogs, cats, cows, deer, and beavers
What: Person-to-person transmission and drinking contaminated water are the two main ways of contracting giardia, but there are other ways to contract it from the environment. Giardia is found all over, and it is protected by an outer shell that makes it resistant to disinfection and able to survive outside the body for long periods of time, up to several months. It is not only found in the ground and in soil, but also in undercooked foods. It is also found in feces, which is one of the reasons cleaning up after your dogs is important, as it limits the spread of the disease (Giardiasis). The risk of contracting giardia from your infected dog or cat is small, as the CDC believes that different strains affect different species, but it can easily be spread from dog to dog. Its symptoms in humans and in other animals are is similar; it wreaks havoc on the gastrointestinal tract and causes diarrhea, gas, cramps, and nausea.
Who: Up to 13 types can cause disease in humans, according to The Center for Food Security and Public Health. It is transmitted by both wild and domestic animals, most commonly by rodents.
What: Leptospirosis is an infection which causes symptoms of headache and fever in mild cases, with more severe cases escalating to cause bleeding in the lungs. Without treatment, it can be deadly. Animals with the infection can range from having no symptoms to exhibiting severe symptoms. Leptospirosis is spread through the urine of the infected animal, and as long as the urine is still moist, it’s contagious. Thus, it can survive in grass or soil that has been wet with the urine of an infected animal, as well as in puddles and other water. It is commonly contracted by people who enjoy water sports. Dogs who enjoy swimming in lakes or ponds, or sampling puddles, should be vaccinated.
Where: Worldwide except Antarctica, and some small, isolated island nations, according to the CDC. The vast majority of human deaths from rabies (95%) occur in Africa and Asia, according to the World Health Organization.
Who: All warm-blooded species.
What: Perhaps the best known disease of this list, rabies conjures an image of a dog foaming at the mouth, thanks in part to Stephen King’s “Cujo,” wherein a St. Bernard is bit by a bat, infected with rabies, and proceeds to terrorize his family. The disease causes inflammation of the brain and eventually leads to death, almost always. The disease is spread when someone is bit or even scratched by an infected animal. Most commonly in the Americas, this infected animal is a bat; worldwide, dogs are the most common. Fortunately, preemptive vaccination has greatly decreased the risk of rabies in recent decades. People who work with bats or who spend long periods of time in areas where the disease is common should be vaccinated, according to the WHO.
As medical research continues to evolve, there is hope that the world’s people and animals will become healthier and happier. As shown by just this snapshot of zoonoses, it is paramount that human populations understand the way animals can impact their health. Wildlife, insects, livestock, and domestic pets all have the potential to deleteriously affect human health. While diseases will never be completely eradicated, one of the easiest ways to ensure a healthy human population is to vaccinate the pets who share our homes, not just for our health, but for theirs, too. A little prevention can go a long way.