Zoonotic Diseases

Animals can sometimes carry harmful germs that can spread to people and cause illness - these are known as zoonotic diseases or zoonoses. Zoonotic diseases are caused by harmful germs like viruses, bacterial, parasites, and fungi. These germs can cause many different types of illnesses in people and animals, ranging from mild to serious illness and even death.

How do germs spread between animals and people?

Direct contact: Coming into contact with the saliva, blood, urine, mucous, or other body fluids of an infected animal. Examples include petting or touching animals, and bites or scratches.

Indirect contact: Coming into contact with areas where animals live and roam, or objects or surfaces that have been contaminated with germs. Examples include aquarium tank water, pet habitats.

Since the beginning of the 21st century, there has been emergence and outbreaks of multiple zoonotic diseases. Zoonotic disease is a type of disease that passes from an animal or insect to a human.

DISEASES:

Nipah

Nipah virus (NiV) infection is zoonotic disease that causes severe disease in both animals and humans. Fruit bats are natural host of the virus. It was first identified during outbreak of disease that took place in Kampung Sungai Nipah, Malaysia.

• The virus spread fast and is mostly fatal.
• Infected bats shed virus in their excretion and secretion.
• The virus cannot be transmitted through air. But it is transmitted through direct contact with infected bats, pigs.
• Pigs can act as intermediate hosts.
• Human to Human transmission from other NiV-infected people is also reported.
• It is capable of causing diseases in domestic animals too.

Zika

Zika is a viral infection, spread by mosquitoes, the vector is the Aedes aegypti mosquito, which also spreads dengue and chikungunya. Additionally, infected people can transmit Zika sexually.

• Most people infected with the virus do not develop symptoms, the symptoms are similar to those of flu, including fever body ache, headache etc.
• Fears around Zika primarily involve microcephaly, especially when pregnant women are infected.
• Microcephaly is a condition in which babies are born with small and underdeveloped brains.
• Generally, the virus is not considered dangerous to anyone other than pregnant women.
• Some countries that have had a Zika outbreak, including Kerala in India.
• There are no reports of infants getting Zika virus through breastfeeding. Because of the benefits of breastfeeding, mothers are encouraged to breastfeed even in areas where Zika virus is found.

Ebola

Ebola virus disease (EVD) formerly known as Ebola haemorrhagic fever is a severe often fatal illness in humans. It was first discovered in 1976 near the Ebola River in what is now the Democratic Republic of Congo.

• It is transmitted to people from wild animals and then spreads in the human population through human-to-human transmission.
• Symptoms include fever, intense weakness, muscle pain and a sore throat. It progresses to vomiting, diarrhoea and both internal and external bleeding.
• There is no proven treatment for Ebola but interventions early on includes rehydration with fluids and body salts and treatment of specific symptoms such as low blood pressure, vomiting, diarrhoea and infections.
• An investigational vaccine called rVSV-ZEBOV has shown to be safe and protective against the Ebola virus.

Avian / Bird Flu

Bird flu or avian influenza is a disease caused by avian influenza Type A viruses found naturally in wild birds worldwide. The virus can infect domestic poultry including chickens, ducks, turkeys and there have been reports of H5N1 infection among pigs, cats, and even tigers in Thailand zoos.

• Human infections occur through infected bird-to-human contact or contact with surfaces and objects contaminated by their droppings.
• Avian Influenza type A viruses are classified based on two proteins on their surfaces - Hemagglutinin (HA) and Neuraminidase (NA).
• Symptoms of avian influenza include - Fever, cough, sore throat, muscle aches, nausea, abdominal pain, diarrhoea, vomiting, severe respiratory illness, and Neurologic changes.
• Human to human transmission is limited. There have been reports of avian and swine influenza infections in humans including A(H1N1), A(1N2), A(H5N1), A(H7N9) among others. There is no sufficient evidence suggesting the spread of the virus through properly cooked meat.

Swine Flu

H1N1 influenza or swine flu is a highly contagious acute respiratory disease of pigs caused by type A influenza virus. It is called swine flu because it was known in the past to occur in people who had been in the vicinity of pigs.

• The symptoms of Swine flu include fever, body aches, loss of appetite, sore throat, vomiting among others.
• Most people with flu including swine flu require only symptom relief.
• Medications do not cure the illness but they may shorten the duration and make symptoms less severe.

Kyasanur forest disease

Kyasanur Forest disease is caused by a Kyasanur Forest disease virus. The disease primarily affects humans and monkeys. The disease was first identified in the Kyasanur forest of Shimoga district in Karnataka during an investigation of monkey mortalities in 1957.

• The disease is characterized by chills, frontal headache, body ache, and high fever for five to 12 days with a case fatality rate of 3 to 5%.
• Rodents, shrews, and monkeys are common hosts for KFDV after being bitten by an infected tick.
• Transmission to humans may occur after a tick bite or contact with an infected animal, most importantly a sick or recently dead monkey.
• Diagnosis can be made in the early stage of illness. It can be done by molecular detection by PCR or virus isolation from blood.
• There is no specific treatment for KFD. A vaccine (Formalin inactivated KFDV vaccine) does exist for KFD and is used in endemic areas of India.

West Nile Virus

West Nile fever is a zoonotic disease. It is caused by the West Nile Virus. Birds are the natural hosts of West Nile virus (WNV). It transmits to humans through bites from infected Culex mosquitoes.

• Mosquitoes become infected when they feed on infected birds.
• It may also be transmitted through contact with other infected animals, their blood, or other tissues.
• No human-to-human transmission from casual contact has not been documented.
• Symptoms of the virus infection include cold, fever, fatigue and nausea. It can cause fatal neurological disease in humans.
• West Nile Virus was first isolated in a woman in the West Nile district of Uganda in 1937. An epidemic of WNV was reported in humans in Israel in 1951.

Monkeypox

Monkeypox virus (MPXV) is an orthopox virus that causes a viral disease with symptoms in humans similar but milder to those seen in smallpox patients.

• It is endemic in villages of Central and West Africa. The occurrence of cases is often found close to tropical rainforests where there is frequent contact with infected animals.
• There is no evidence to date that person-to-person transmission alone can sustain monkeypox in the human population.
• Monkeypox is transmitted from animals to humans through contact with the blood, bodily fluids, or cutaneous or mucosal lesions of infected animals.
• Gambian giant rats and squirrels with rodents being the most likely reservoir of the virus.
• There are no specific treatments or vaccines available for monkeypox virus infection but outbreaks can be controlled.

Dengue

Dengue is a mosquito-borne tropical disease caused by the dengue virus (Genus Flavivirus), transmitted by several species of mosquito within the genus Aedes, principally Aedes aegypti.

• This mosquito also transmits chikungunya, yellow fever and Zika infection.
• There are 4 distinct, but closely related, serotypes (separate groups within a species of microorganisms that all share a similar characteristic) of the virus that cause dengue (DEN-1, DEN-2, DEN-3 and DEN-4).
• Symptoms include sudden high fever, severe headaches, pain behind the eyes, severe bone, joint, and muscle pain, etc.
• Diagnosis of dengue infection is done with a blood test. There is no specific medicine to treat dengue infection.

Malaria

Malaria is caused by the bite of the female Anopheles mosquito, if the mosquito itself is infected with a malarial parasite.

• There are five kinds of malarial parasites — Plasmodium falciparum, Plasmodium vivax (the commonest ones), Plasmodium malariae, Plasmodium ovale and Plasmodium knowlesi.
• In India, out of 1.57 lakh malaria cases in the high-burden states of Odisha, Chhattisgarh, Jharkhand, Meghalaya and Madhya Pradesh in 2019, 1.1 lakh cases (70%) were cases of falciparum malaria.
• Note: According to the World Malaria Report 2020, cases of Malaria in India dropped from about 20 million in 2000 to about 5.6 million in 2019.

Hantavirus

Hantavirus are a family of viruses which are spread mainly by rodents.

• It does not spread from one person to another but it can be contracted if someone comes in contact with a rodent that carries the virus.
• Symptoms include fatigue, fever, muscle aches, abdominal problems, coughing and shortness of breath.
• Hantavirus pulmonary syndrome (HPS) and haemorrhagic fever with renal syndrome (HFRS).
• There is no specific treatment, cure or vaccine for Hantavirus infection.

Yellow fever

It is a tropical disease that is spread to humans by infected mosquitoes and is caused by the yellow fever virus.

• Yellow fever is caused by a virus that is spread by the Aedes aegypti mosquito. These mosquitoes thrive in and near human habitations where they breed in even the cleanest water.
• It is often associated with jaundice, hence the name yellow. The disease is found in urban and rural areas of tropical zone countries in Africa and South America.
• Yellow fever virus belongs to the Flaviviridae family, other members of which cause dengue fever.
• The virus is introduced into the bloodstream via the saliva of the mosquito as it bites.
• Vaccine available named 17D.

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