Diseases transmitted from animals have been troubling humans for centuries. From the Great plague to smallpox, from yellow fever to the ever-infectious coronavirus, animal diseases have resulted in great epidemics which have caused deaths of millions of people and continue to haunt humanity to this day. Below are ten most infectious diseases ever encountered by humans:
- COVID-19:
COVID-19 is a disease caused by SARS-CoV-2 that can trigger what doctors call a respiratory tract infection. It can affect your upper respiratory tract (sinuses, nose, and throat) or lower respiratory tract (windpipe and lungs).It spreads the same way other coronaviruses do, mainly through person-to-person contact. Infections range from mild to deadly. SARS-CoV-2 is one of seven types of coronavirus, including the ones that cause severe diseases like Middle East respiratory syndrome (MERS) and sudden acute respiratory syndrome (SARS). Nobody exactly knows where this virus came from. Some say bats, some say, it came from an animal Market from a city in China. Some even say it was leaked from a lab. If the latter is the case then it could be one of the worst man-made disasters ever in recorded history.
2. Influenza pandemics:
The 1918 influenza pandemic swept the world within months, killing an estimated 50 million people — more than any other illness in recorded history for the short time frame involved. The H1N1 influenza virus that infected more than one-third of the globe had an avian origin. First identified in the United States by military personnel in the spring of 1918, the virus killed an estimated 675,000 Americans, according to the Centers for Disease Control and Prevention (CDC).
3. Bubonic plague:
Nothing beats the 14th-century Black Death (also called Bubonic Plague) for the sheer global impact of a single disease outbreak and bringing civilization to its knees. It is the epitome of plague. Corpses piled in the streets from Europe to Egypt and across Asia. Some 75 million people died, at a time when there were only about 360 million living on Earth. Death came in a matter of days, and it was excruciatingly painful.Plague is a bacterial disease caused by Yersinia pestis. It is carried by rodents and even cats, and hops to humans through bites from infected fleas (often rat fleas). The disease becomes most deadly to us when transmitted between people, as became the case in the 1300s. Symptoms include fever, chills, weakness, and swollen and painful lymph nodes. Even today, if not treated, the disease is deadly.
4. HIV/AIDS:
HIV, the virus that causes AIDS, has been traced to a type of chimpanzee in Central Africa, according to the CDC. The chimp version of this disease was likely passed to humans when they hunted these animals for meat, getting exposed to their infected blood. Once they were exposed, the virus mutated into HIV. Studies suggest the virus may have jumped to humans as far back as the 1800s. HIV destroys the immune system, opening the door to a host of deadly infections or cancers. For example, Tuberculosis (TB) kills nearly a quarter of a million people living with HIV each year. In 2018, 770, 000 people died from causes related to HIV, and 1.7 million people were infected with the virus that year. At the end of 2018, 37.9 million people were living with HIV, according to the WHO. Two-thirds of HIV infections are in certain countries in Africa.
5. Ebola:
Ebola virus disease, which is caused by one of five strains of the Ebola virus, is a widespread threat to gorillas and chimps in Central Africa. The disease may have spread to humans from infected bats or infected non-human primates, the CDC says. It was first identified in 1976 near the Ebola River in what is now called the Democratic Republic of the Congo. People can catch four strains of the virus through contact with infected blood or bodily fluids from an animal carrying the virus. That person can then spread the virus to others through close contact. The awful symptoms include: sudden onset of fever, intense weakness, muscle pain, headache and sore throat, often followed by vomiting, diarrhoea, rash, impaired kidney and liver function, and in some cases, both internal and external bleeding.
6. Cysticercosis:
People can get cysticercosis after swallowing water or food containing the eggs of the parasitic tapeworm called Taenia solium. These larvae then creep into muscle and brain tissues, where they form cysts. Humans can also pick up the parasite if they eat raw or undercooked pork containing these cysts, which then attach to the lining of the small intestine; over about two months, those cysts develop into adult tapeworms. The most dangerous form of the disease occurs when the cysts enter the brain, called neurocysticercosis. Symptoms can include headaches, seizures, confusion, brain swelling, difficulty balancing and even stroke and death.
7. Bird flu:
Bird flu (avian influenza) is a disease caused by strains of influenza virus that primarily affects birds. In the late 1990s, a new strain of bird flu arose that was remarkable for its ability to cause severe disease and death, especially in domesticated birds such as ducks, chickens, or turkeys. As a result, this strain was called highly pathogenic (meaning very severe and contagious) avian influenza and termed H5N1.Human cases of highly pathogenic bird flu have been largely confined to Southeast Asia (India, Bangladesh) and Africa. Although easy transmission between humans has not yet developed, H7N9 avian influenza virus has infected about 1,565 individuals; about 39% of these individuals died from the infection. The majority of these infections were due to exposure to infected birds or their droppings.
8. Lyme disease
Lyme disease, also known as Lyme borreliosis, is an infectious disease caused by the Borrelia bacterium which is spread by ticks. The most common sign of infection is an expanding red rash, known as erythema migrans, that appears at the site of the tick bite about a week after it occurred.
9. Rabies
Rabies is a deadly virus spread to people from the saliva of infected animals. The rabies virus is usually transmitted through a bite. In developing countries of Africa and Southeast Asia, stray dogs are the most likely to spread rabies to people.
Once a person begins showing signs and symptoms of rabies, the disease nearly always causes death. For this reason, anyone who may have a risk of contracting rabies should receive rabies vaccinations for protection.
10. Zika fever
Zika virus is similar to dengue fever, yellow fever and West Nile virus. Carried by infected Aedes aegypti mosquitoes, Zika is largely transmitted through bites. If a woman is bitten by an infected mosquito and becomes infected, Zika can cross into the placenta and affect the foetus. While anyone can contract Zika, pregnant women are the most at risk due to the potential for neurologic abnormalities. Sexual transmission of this virus can occur. Transmission has been reported from infected men and women to their sexual partners. The virus can be transmitted through anal, oral or vaginal sex. Symptoms of this virus are generally mild, with fever, rash and joint pain present. Most people who develop the virus do not have symptoms.
