Find out more about ten zoonotic diseases – including mpox – as well as their symptoms and how they spread from animals to humans
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There are more than 200 zoonotic diseases – diseases that spread between humans and animals – known in the world, including the recent mpox disease outbreak declared last week. Some zoonotic diseases, such as rabies, are entirely preventable through vaccination and other methods. Others, like HIV, began as zoonotic diseases, but mutate into strains only transmissible via human-to-human contact.
Here are ten examples of zoonotic viruses, along with their symptoms and how they are transmitted:
1) Mpox
Mpox – whose outbreak was declared as a public health emergency on an international level last week – is a disease that transmits to humans via both contact with infected humans, as well as animals with mpox. Although the exact source of mpox is unknown, scientists believe that small mammals – such as giant-pouched rats and African dormice – carry the virus.
In 1958, mpox was first discovered in colonies of monkeys kept for research purposes, but it wasn’t until 1970 that the first human case of the disease was reported in the Democratic Republic of Congo (DRC). The first symptoms of mpox include a high temperature, exhaustion and muscle aches, with the rash occuring one to five days after.
2) Rabies
Each year, around 59,000 people die from rabies, with 40 per cent of cases in children under the age of 15. If medical care is not sought immediately, rabies – spread through the bite and scratches of an infected animal – can lead to severe brain disease and death. Most cases of human rabies – up to 99 per cent – are caused by transmission via dogs.
Fewer than ten deaths are recorded in the United States from rabies per year – with the most common cause via contact with infected bats – but its high mortality rate means the disease is still a serious public health threat across the world.
Symptoms include confusion, hydrophobia (fear of water) and partial paralysis, which usually appear within three to twelve weeks of exposure, but can take as long as several months or years to show.
3) Ebola
Transmitted firstly from wild animals, including fruit bats and porcupines, Ebola is then able to spread to humans through bodily fluids or contaminated surfaces or objects.
With a mortality rate of 50 per cent, the most recent outbreak of Ebola occurred in West Africa between 2014-2016, leading to the deaths of 11,000 people and spreading to an additional seven countries, including the United Kingdom, the USA, Nigeria and Italy.
Symptoms include sickness, skin rash and yellowing of the eyes.
4) Anthrax
Caused by the Bacillus anthracis bacteria, anthrax is found naturally in soil across the world as well as live animals and livestock. Exposure to infected animals, or contaminated animal products, is the most common source of infection.
There are four main ways in which anthrax can enter the human body: eating undercooked meat (gastrointestinal anthrax), exposure through a skin wound (cutaneous anthrax), inhaling spores (inhalation anthrax) or injection of illegal drugs (injection anthrax).
By treatment with antibiotics, most cases of anthrax can be cured – although exposure caused via inhalation, as opposed to the bacteria entering a skin wound – is more difficult to treat.
5) Lyme disease
Lyme disease is caused by Borrelia bacteria and is transmitted to humans via tick bites. It is commonly found in Europe, the upper Midwest, the northeastern and mid-Atlantic states of the US, and south-central and southeastern Canada.
Early symptoms of Lyme disease may include a rash that resembles the bull’s eye on a dart board—developing between three and 30 days after exposure to the bacteria—although one in three infected individuals do not report this symptom.
Lyme disease is often successfully treated with antibiotics, but in some cases, individuals can experience ongoing effects including tiredness and loss of energy.
6) Avian influenza
Avian influenza is caused by the influenza A or B virus – the two types known to cause seasonal epidemics within humans – found in birds. In recent years, four strains have been identified as able to infect humans: H5N1 (since 1997), H7N9 (since 2013), H5N6 (since 2014) and H5N8 (since 2016).
Although human transmission is rare, exposure to live or dead poultry, touching droppings or bedding, or visiting live bird markets can increase the risk of infection. Symptoms include temperature, shortness of breath, and stomach pain, with possible complications such as pneumonia and acute respiratory distress syndrome. Treatment of avian influenza is often through antiviral medications.
7) E. coli
E. coli refers to a large group of bacteria – many of which are harmless and form a healthy part of human digestive tracts. However, six major types of E-coli are harmful and can cause diarrhoea, stomach cramps, vomiting and fever.
E. coli is spread by contact with the bodily fluids of an infected person, eating contaminated food or water, or contact with animals, their faeces, or the environment. Cattle are the main reservoir for a particular strain of E. coli, but animals, including sheep, goats, deer, and horses, have been found to be infected.
8) Cat scratch disease
Most cases occur after scratches from cats – domestic or feral – cat scratch disease is caused by the Bartonella henselae bacteria found in flea faeces.
Fleas – which can reside on cats – can carry the B. henselae bacteria, that are transmitted from the cat to humans through scratches. An infected cat licking a human’s open wound can also be a source of infection.
Symptoms begin with a low fever and pustules where the scratch is located. After 1-3 weeks, individuals may also report enlarged lymph nodes. Treatment include over-the-counter anti-inflammatory medicines or antibiotics, but most individuals’ symptoms clear up on their own.
9) Yellow fever
Yellow fever is spread by the bite of Aedes and Haemagogus mosquitoes – found in parts of sub-Saharan Africa and South and Central America – which breed around houses, forests and jungles. As of 2023, 34 African countries and 13 countries in Central and South America were either endemic, or have regions that are endemic for, the disease.
It can be prevented by vaccination, of which a single dose can offer life-long protection. Symptoms begin with high temperature, headache and loss of appetite, but can also lead to more fatal symptoms including jaundice, stomach pain and bleeding from the eyes, nose, mouth or stomach.
10) Brucellosis
Brucellosis is caused by consuming unpasturised dairy products, or contact with infected animals – mainly cattle, swine, goats, sheep and dogs – and their bodily fluids. It is found globally and most cases occurs through eating raw milk or similar derivative products from sheep or goats.
Symptoms include back and joint pain, sweating and loss of appetite. Although no vaccine exists for brucellosis, measures can be taken to prevent the disease, including wearing protective clothing when working with animals and covering wounds with plasters before handling animals.
