Animals transmit diseases to humans. What are zoonoses?

Feb 18, 2020 | 2 comments

By Jaime Moreno
Zoonoses cross the species barrier. Let’s remember Neil Armstrong when he had the first moonwalk in 1969 and pronounced his famous phrase,  “That’s one small step for man, one giant leap for mankind.” He took another “second small step” when he went to the Tayos Caves, Morona Santiago in 1976.

With minor adjustments, Neil Armstrong could have been referring to one of the most important distinctions between limited outbreaks called epidemics, and unlimited pandemics. Although emerging infectious diseases will continue to take small steps across the species barrier, the prize will be the avoidance of giant jumps to mankind. (Klempner, Shapiro 2004; Stan Hall, 2007).

There are hundreds of diseases known as zoonoses that are transmissible from lower vertebrates such as fish, birds, and other animals to humans. The many modes of transmission include direct contact, scratch, bite, inhalation, contact with urine or feces, and ingestion of meat, dairy products, eggs, or feces, as well as contact with arthropod intermediate hosts. Many emerging and reemerging diseases are zoonoses, including hantavirus infections and most viral hemorrhagic fevers.

Human immunodeficiency viruses probably originated and evolved from a lower primate source. (Marcus, NEJM 1998). Carl Flügge, Munich 1847-1923, described the droplets responsible for airway transmission. Currently, there is a need for a better understanding of aerosol-acquired diseases. Experts find it more useful to classify the inhalation of diseases as obligate (tuberculosis), preferential, or opportunistic, based on the agent’s capacity to be transmitted and to induce disease through fine-particle aerosols and other routes. The clinical implications of airborne transmission are particularly important for infection control in hospitals and in public indoor settings such as airplanes and schools. (Roy, Milton, NEJM 2004).

Coronaviruses are a large group of viruses, so named because when studied under the electron microscope they look like a “crown.” Coronaviruses are the cause of about 30 percent of mild to severe respiratory infections in children and adults. Sometimes coronaviruses cause gastrointestinal and even uncommon neurologic presentations. Coronaviruses which have worried the world in the past are Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) and Middle East Respiratory Syndrome Coronavirus (MERS-CoV).

Whilst the situation of the COVID-19 virus outbreak is still evolving, the epicentre remains in China, where 99% of cases have been detected. Credit: European Commission

Novel Coronavirus (2019-nCoV) Epidemic
A novel coronavirus, designated 2019-nCoV, was identified as the cause of a cluster of pneumonia cases in Wuhan, a city of 11 million people in the Hubei Province of China, at the end of 2019. At the moment, there are thousands of laboratory-confirmed cases in China and other countries, with mortality especially in elderly individuals and those with comorbidities.

This is an ongoing epidemic with an impending risk of propagation and transformation into a devastating pandemic. Researchers at Wuhan identified an initial association with a seafood market where most patients had worked or visited and which was subsequently closed for disinfection. The seafood market also sold live rabbits, snakes, and other animals including bats. However, as the outbreak progressed, most laboratory-confirmed cases had no contact with this market, and cases were identified among health care workers and other contacts of patients with 2019-nCoV infection. Human-to-human transmission has been confirmed in China and has also been identified in other countries, including the United States. Understanding of the transmission risk is incomplete. (UpToDate February 2020).


  • Inadequate information is more dangerous than any disease; trust only serious references and search for scientific evidence.
  • More important than to precisely determine the origin of 2019-nCoV is the global effort of its containment, in other words, to prevent a pandemic.
  • Zoonoses could be blocked not allowing human beings to have intimate contact with animals and birds, avoiding their saliva, immunizing pets.
  • Make sure you and your relatives are vaccinated (Influenza), not neglecting other diseases. Consult your physician.
  • It is mandatory that you follow the evolution of this changing epidemic, appraising official publications, such as the Ecuadorian Ministry of Health, World Health Organization, USA CDC, Chinese CDC, reliable publications as the New England Journal of Medicine, UpToDate, and others.
  • Promote examining patients, isolating them, diagnosing and managing them.
  • Report suspicious 2019-nCoV individuals to health authorities.

Frequent Questions and Answers, the World Health Organization (WHO)

  1. What is a coronavirus? Coronaviruses are a large family of viruses found in both animals and humans, that can cause different sickness, going from the mild common cold to more severe infections as the coronavirus causing the Middle East Respiratory Syndrome (MERS-CoV) or the Severe Acute Respiratory Syndrome (SARS-CoV).
  2. What is the 2019 Novel Coronavirus? A novel coronavirus (CoV) is a new strain of coronavirus that has not been previously identified in humans.  The new, or “novel” coronavirus, now called 2019-nCoV, had not previously been detected before the outbreak was reported in Wuhan, China in December 2019.
  3. Can animals transmit a new coronavirus to humans? Comprehensive research proved that in 2002, in China, the civet cat transmitted to humans the coronavirus causing SARS, and that in 2012, in Saudi Arabia, the dromedary transmitted the coronavirus causing MERS. There are other known coronaviruses circulating in animals that have not infected humans yet. It is likely that with better epidemiologic surveillance, the detection of coronaviruses will increase.
  4. What symptoms have the persons infected with coronavirus? It depends on the virus. Nevertheless, symptoms of 2019 Novel Coronavirus appear within two to 14 days after exposure and include fever, cough, runny nose and difficulty breathing. In more serious cases these infections can cause pneumonia, severe acute respiratory distress syndrome, kidney failure, and even death.
  5. Do we have vaccines for the novel coronavirus? When a new disease appears, there are no vaccines available, and it could take years in obtaining it.
  6. How is it treated? There is currently no FDA approved medication for the 2019 Novel Coronavirus. People infected with this virus should receive supportive care (rest, fluids, fever control) to help relieve symptoms and for severe cases, treatment should include care to support vital organ functions.
  7. How does Coronavirus spread? It is primarily spread through respiratory droplets, produced when a person coughs or sneezes. To become infected, people generally must be within six feet of someone who is contagious and come into contact with these droplets.
  8. Are health professionals at risk of contracting a new coronavirus infection? Yes, they are because of their higher exposure to patients than the general population. WHO recommends them to abide by preventive measures at all times.
  9. What does WHO recommend to countries? To improve and optimize surveillance of serious acute respiratory infections.
  10. Where can you find more information about known coronaviruses? In the WHO web on MERS-CoV and SARS-CoV. Click here for more.

Definitions: The element dem in epidemic, endemic, and pandemic comes from the ancient Greek word demos, which meant people or district. Thereby, en (in) + demos = endemic, is defined as the habitual presence of a disease within a given geographic area. It may also refer to the usual occurrence of a given disease within such an area; epi (among) + demos = epidemic, is defined as the occurrence in a community or region of a group of illnesses of similar nature, clearly in excess of normal expectancy, and derived from a common or from a propagated source; pan (all) + demos = pandemic, refers to a worldwide epidemic. (Gordis, Epidemiology, p 22).

Dr. Jaime Moreno Aguilar is an internist with specialties in hematology and oncology, with offices in Cuenca.

Dr. Moreno writes the InfoHealth blog.
For more information and the InfoSalud Spanish language version please click here.
Dr. Jaime Moreno Aguilar
Consultorios Santa Inés, Torre 1, Oficinas 003 y 102
Daniel Córdova y Federico Proaño
Teléfonos: 072843136 – 0997281884 – 0997257585



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