What animals carry the most diseases
Disease-Carrying Animals
Animals can carry diseases that are harmful to people. Here is a list of animals and the diseases they may carry.
 Photographed by Ernie Frank, the TAMU Department of Agricultural Communications Tick |  IMSI Master Clips Mosquito |
| Disease | Symptoms | Carrier |
|---|---|---|
| Bubonic plague | Painful swelling, high fever, body aches | Rat, flea |
| Elephantiasis | Rough, thickened skin, body swelling | Worms |
| Lyme disease | Rash, fatigue, muscle and joint pain | Deer tick |
| Malaria | Chills, weakness, fever, excessive perspiration | Mosquito |
| Plague typhus | Fever, skin rashes | Flea, lice, chipmunk, prairie dog, squirrel |
| Rabies | Headaches, muscle spasms, convulsions | Woodchuck, bat, raccoons |
| Rocky Mountain spotted fever | Chills, fever, rash, leg pain | Wood tick |
| Sleeping sickness | Attacks nervous system; results in prolonged sleep | Tsetse fly |
| Trichinosis | Vomiting, fever, pain, face swelling | Worms in pigs |
| Rift Valley fever | fever, muscle pain, joint pain, headache, blurred or loss of vision, memory loss, hallucinations, vertigo, lethargy, coma | contact with any infected animal's blood or organs, hematophagous (blood-feeding) flies, the Aedes mosquito |
Bats Are the Number-One Carriers of Disease
Understanding where new viruses come from is critical for preventing them from rapidly spreading among humans. When it comes to preventing the next pandemic, a new study suggests that bats may be public enemy number one.
In a new study published in the journal Nature, researchers at the nonprofit EcoHealth Alliance collected data on viruses known to infect mammals, which included about 600 viruses found in more than 750 species. They were then able to calculate the number of viruses from each species and identify characteristics that make the transmission to humans more likely. Living more closely to humans and being more closely genetically related to humans increased the odds of transmission.
Out of all the species assessed, bats carried the highest number of these viruses. Researchers are currently looking into why.
A lot of people dont realize that these viruses have been on the planet for a long time, and they are in populations of animals all around the world, says study author Kevin Olival, associate vice president for research at EcoHealth Alliance. What we did in this study is prioritize where we should look if we want to stop the next Ebola or Zika from emerging.
All groups of mammals were found to carry viruses that can spread to humans, and areas around the world most at risk for carrying emerging viruses differed based on the mammal. For bats, these places are most common in South and Central America and areas in Asia. For primates, the areas with the higher risks are in Central America, Africa and Southeast Asia.
The study was funded as part of the United States Agency for International Development (USAID) Emerging Pandemic Threats PREDICT program, a project that seeks to identify new emerging infectious diseases that could become threatening to human health. Olival says his team hopes that scientists will use this research to identify regions and viruses to focus on for prevention efforts.
Bats dont deserve all of the blame, however. The spreading of new diseases often involves activity from both animals and people, Olival points out.
These diseases are not just randomly jumping into people, he says. We see time and time again that it is the human disturbances in the environment that are causing these diseases to emerge, through activities like chopping down forest and hunting animals out of certain areas. It is our interactions with these species that are causing diseases to jump.
The National Academies
Many of the diseases that afflict people todayare caused by
microbeswhose ancestors came from animals first domesticated by early humans. Biologists believe that the
measlesvirus evolved from rinderpest virus, an affliction of cattle; that rhinoviruses, agents of the common cold, came to us from horses; and that
smallpoxis a close cousin of cowpox. Middle East respiratory syndrome coronavirus (MERS-CoV), a virus found circulating in the Arabian Peninsula in 2014, was probably first passed to people by camels, though it may have originated in bats.
Of the 37 new infectious diseases identified in the past 30 years, more than two-thirds sprang from animals.
Infections transmitted from animals to humans are called
zoonosesor zoonotic diseases. Of the more than 1,700 known viruses, bacteria, and other pathogens that infect people, more than half either originated in or now come directly from animals. The rest come from the environment around us, such as soil, water, and air. And of the 37 new infectious diseases identified in the past 30 years, more than two-thirds originated in animals. The next deadly pandemic to sweep the world could very likely jump species in this way.
Direct Transmission
Some zoonotic infections move directly from animals to humans. In such cases, an animal is the natural
hostor reservoirfor the pathogen and through encounters often spurred by ecological change, the pathogen moves from the natural host to humans. Severe acute respiratory syndrome (
SARS) is a recent example of this. In spring 2003, this new and deadly viral illness swept out from Chinas Guangdong Province and spread rapidly around the world before it was contained that summer. SARS virus originated in Chinese horseshoe bats, animals used for food and medicine in many parts of Asia and traded in wildlife markets. There the virus infected both small carnivores called civets as well as the people who worked at the markets where they were sold and in restaurants where these animals were served as food. The virus infected 8,098 people, 774 of whom diednearly a 10 percent mortality rate. Fortunately, no human infections have been found since early 2004.
There are many other examples of direct transmission from animals to humans.
Toxoplasmosis, a parasitic disease that can cause mild flu-like symptoms in humans (but potentially more serious illness in developing fetuses and individuals with a compromised immune system), infects many warm-blooded animals. Cats are essential for this parasite to spread because they become infected by eating infected rodents or small birds and then pass the parasite to humans through their feces.
Leptospirosis, a bacterial disease spread through the urine of infected animals or through soil or water contaminated by infected urine, can cause a wide range of symptoms in humans, including high fever, vomiting, and even
meningitisand liver failure.
Nipah virus, which can cause fatal encephalitis (inflammation of the brain), emerged in 1998 in Malaysia. This virus is carried by fruit bats, but it moved into pigs and then spread to pig farmers and slaughterhouse workers who were exposed.
Vector-Borne Diseases
Diseases transmitted to humans indirectly via an insect or an arthropod (animals with jointed appendages and
exoskeletons, such as ticks) are called vector-borne diseases. Vectors carry disease-causing viruses, bacteria, or parasites from one host to another, delivering these pathogens to humans and other warm-blooded hosts. The vectors themselves typically suffer no ill effects from the organisms they carry. In 1999, for example, a mosquito-borne infection
West Nile virussuddenly began affecting New Yorkers. Seven people died and 62 were hospitalized. Until then the virus had been confined to Africa, Europe, the Middle East, and West Asia. Today, the infection caused by West Nile virus has fully established itself in North America, flaring up in the summer and continuing into the fall. Since 1999 the virus has also spread geographically, moving rapidly across North America and into Latin America. According to 2015 data, there were 1,996 reported cases of West Nile virus in the United States, with 111 deaths.
Wild or domestic animals are natural reservoirs for many vector-borne diseases. The main reservoir host for West Nile virus is wild birds. The New York City strain of the virus was virtually identical to a strain taken the previous year from a dead goose in Israel. Scientists speculate that an infected mosquito, human, or bird may have brought the pathogen to this country on a plane or ship, again showing the unintended consequences that global trade and travel can have on the spread of infectious disease.
Dengue fever, also known as break-bone fever, is a mosquito-borne virus that results in flu-like symptoms. It was detected in Key West, Florida, in 2009 and by the end of 2010 there were 21 cases reported in Key West, prompting concern that the virus had emerged in the United States and could become endemic.
Chikungunya, a rarely fatal virus also transmitted by mosquitoes, crossed the Atlantic Ocean in 2013. Since then it has been detected in more than 10 countries in the Americas and has resulted in more than 780,000 suspected cases, with 15,000 being confirmed.
Zika, originally identified in Africa more than 60 years ago, was first recognized in the Americas in Brazil in 2015. It has since spread to almost 50 countries, including the United States.
Many other infections, including
malaria,
Lyme disease,
yellow fever, and typhus, are spread to humans from animals (including from other humans), via the bites of insects and other arthropods.
13 Animal-to-Human Diseases Kill 2.2 Million People Each Year
Diseases that can be transmitted between animals and humans, such as bird flu and tuberculosis, can wreak havoc on the health of both organisms. Now researchers have found 13 so-called zoonoses are responsible for 2.2 million human deaths every year.
The study, detailed this week in the report "Mapping of Poverty and Likely Zoonoses Hotspots," shows the vast majority of these illnesses and deaths occur in low- and middle-income countries. For instance, Africa's Ethiopia, Nigeria and Tanzania, along with India, had the highest rates of associated illness and death.
"From cyst-causing tapeworms to avian flu, zoonoses present a major threat to human and animal health," lead study author Delia Grace, a veterinary epidemiologist and food safety expert with the International Livestock Research Institute (ILRI) in Kenya, said in a statement. "Targeting the diseases in the hardest-hit countries is crucial to protecting global health as well as to reducing severe levels of poverty and illness among the world's 1 billion poor livestock keepers."
The new global zoonosis map, an update of one published in the journal Nature in 2008, also revealed the northeastern United States, Western Europe (particularly the United Kingdom), Brazil and parts of Southeast Asia may be hotspots of "emerging zoonoses." An emerging zoonosis is a disease that is newly infecting humans, has just become virulent, or has just become drug-resistant. [10 Deadly Diseases That Hopped Across Species]
Animal-human disease
About 60 percent of all human diseases and 75 percent of all emerging infectious diseases are zoonotic, according to the researchers. Most human infections with zoonoses come from livestock, including pigs, chickens, cattle, goats, sheep and camels.
Out of 56 zoonoses studied, the researchers found 13 that were most important in terms of their impact on human deaths, the livestock sector and the severity of disease in people, along with their amenability to agriculture-based control.
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These were, in descending order: zoonotic gastrointestinal disease; leptospirosis; cysticercosis; zoonotic tuberculosis (TB); rabies; leishmaniasis (caused by a bite from certain sandflies); brucellosis (a bacterial disease that mainly infects livestock); echinococcosis; toxoplasmosis; Q fever; zoonotic trypanosomiasis (sleeping sickness), hepatitis E; and anthrax.
They found many livestock were infected with these zoonoses in poor countries, where:
- 27 percent of livestock showed signs of current or past infection with bacterial food-borne disease that causes food contamination (a type of zoonotic gastrointestinal disease)
- 12 percent of animals have recent or current infections with brucellosis
- 10 percent of livestock in Africa are infected with trypanosomiasis
- 7 percent of livestock are currently infected with TB
- 17 percent of smallholder pigs show signs of current infection with cysticercosis
- 26 percent of livestock show signs of current or past infection with leptospirosis
- 25 percent of livestock show signs of current or past infection with Q fever
Dependence on livestock
Nearly three-quarters of rural poor people and about one-third of the urban poor depend on livestock for food, income, manure and other services, the researchers say.
As such, the loss of one milking animal can devastate these households, though even worse, the researchers point out, is the loss of a loved one to a zoonotic disease.
The new map of hotspots will give researchers and officials places on which to focus their efforts. The highest zoonosis burden, they found, occurs in just a few countries, particularly Ethiopia, Nigeria and India. These three countries also have the highest number of poor livestock keepers and the highest number of malnourished people.
"These findings allow us to focus on the hotspots of zoonoses and poverty, within which we should be able to make a difference," Grace said in a statement.
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