Every year, tens of thousands of people living in the USA get ill from zoonotic diseases – illnesses that can spread between animals and people.
Six out of 10 infectious diseases in people are zoonotic. You've probably heard of the big-hitters, including rabies, all the flus (bovine, swine, and bird), and anthrax (fun fact: did you know that an anthrax outbreak was once caused by an infected reindeer thawing out?). But which ones should you be most worried about?
The Centers for Disease Control and Prevention (CDC) recently sat down to discuss just that, and have released a list of the zoonotic diseases that should be of most concern to people living in the US.
As zoonotic diseases go, the plague is pretty much your classic. It killed millions of people in Europe during the Middle Ages, though today it is treatable with antibiotics.
Plague is still present in the western United States. In 2017 a county in Arizona had to issue a public health warning after fleas, which transmit the disease, tested positive for the plague.
Brucellosis is an infectious disease caused by bacteria. It can be transferred from animals to humans through contact with the animals or contaminated products.
Animals affected include sheep, cattle, goats, pigs, and dogs.
The CDC had to investigate earlier this year after people became infected with an antibiotic-resistant strain of the disease, which came from drinking raw milk from a farm in Quarryville, Pennsylvania.
Several types of animal flu can't be transferred to humans (such as horse and dog flu), but others can (including swine and bird flu). The ones that can infect people tend to pass from human to human quite slowly. Human zoonotic flu infections usually occur through direct contact with infected animals. If one of these viruses evolved to spread quickly between people, it could cause a pandemic as we'd have little immunity to it.
West Nile virus
West Nile virus (WNV) is the leading cause of mosquito-borne disease in the continental United States, according to the CDC. There are no vaccines or treatments for the disease, which can be serious in about one in every 150 people who contract it, and even fatal.
A total of 2,544 cases of West Nile virus were reported to the CDC in 2018.
Rabies is transmitted through the bite of a rabid mammal. It mostly occurs in wild animals (such as raccoons, skunks, and bats) but can infect more common pets like dogs.
The death rate from rabies has dramatically declined in recent years, falling from 100 annually around 100 years ago to one or two per year since the 1990s. Human deaths now only really occur when medical treatment is not sought, e.g. when people don't realize they're infected.
One of the most common zoonotic diseases, it causes around 1.2 million illnesses, 23,000 hospitalizations, and 450 deaths in the US every year, notes the CDC.
Most sufferers experience diarrhea, fever, and abdominal cramps. Some people have diarrhea so severe that they require hospitalization.
Salmonella is best avoided through proper food hygiene.
Lyme disease is caused by the bacterium Borrelia burgdorferi, which is transferred to humans through blacklegged tick bites. Initial symptoms include headache, fever, fatigue, and a very distinctive skin rash.
Untreated, it can spread to the joints, heart, and nervous system. Most cases can be treated with antibiotics, and prevented with insect repellent.
Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS) fall into this category of diseases. SARS is thought to have originally occurred in bats before transferring to other animals, and was first documented in humans in 2002. There were over 8,000 cases worldwide during an epidemic in 2003, notes the World Health Organization.
MERS was first reported in Saudi Arabia in 2012 and spread to several other countries, including the US. It causes severe acute respiratory illness and can be fatal.