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Airborne viruses: easily transmitted and spread

Watch Prof. Simarro explain about respiratory zoonotic viruses which produce SARS, MERS and influenza.
Air is one of the most efficient routes of transmission for different infectious agents. A large number of human respiratory diseases have their origin in animal viruses. As examples, we may include some of the human respiratory diseases that have generated more social and health alarms in recent years. One of them, the severe acute respiratory syndrome (SARS), emerged in 2002 in China, without any apparent relationship with any other human or animal coronavirus characterized so far. It was considered as the first pandemic of the 21st century, and it affected more than 33 countries on 5 continents. It produced more than 8000 cases of infection and over 700 deaths in the human population.
Subsequently, its origin was related to the circulation of the virus in different animal species which would have acted as reservoirs (such as bats), while civets would have served as the main intermediary host. Contact with live animals in markets, fairs, transportation, close-by restaurants, etc., would have served as an origin and spread the infection amongst the human population. The second example, the Middle East respiratory syndrome (MERS) also caused by a coronavirus, appeared in 2012. To date, 1791 human cases have been confirmed and 640 deaths in 27 countries have been reported. Bats may act as reservoirs of the coronavirus and camelids as intermediate hosts.
But of all respiratory viral diseases, the more representative is influenza, a very old disease already described by Hippocrates around the year 400 BC. Human populations all over the world have historically suffered pandemics of this disease. In the last century, just three of them alone, the “Spanish flu” (between 1918 and the year 1919), the “Asian flu” (in 1957) and the “Hong Kong flu” (1968), produced millions of human deaths on different continents. Flu is considered a non-eradicable disease. It is highly contagious and has demonstrated the ability to “jump the interspecies barriers”. This means that influenza viruses are able to multiply and be efficiently transmitted between different animal species.
To understand how this disease behaves, it is necessary to consider flu as a “combination of viruses”. Influenza viruses circulate in nature and have been isolated from very different animal species, such as ducks, hens, whales, horses, seals, etc. and of course, from humans. Amongst the domestic species of interest, there are avian viruses, swine viruses, and equine viruses that maintain their own cycle of natural and temporary transmission. In certain circumstances, a genetic exchange between different viruses from various animal species may take place. This could lead to the emergence of new variants that would potentially cause an epidemic or a pandemic.
Thus, during an epidemic, and due to the emergence of these new viruses or new variants, we may observe the disease simultaneously in the human population and/or in different animal populations, such as swine, poultry, etc. As veterinarians, we deal with the animal influenzas, their prevention and control. They are a major problem for animal health and production, and also from the point of view of public health, since they are zoonoses. This week we will address different aspects of the disease, starting with the study of orthomixovirus, their causal agents.

Why are airborne viruses so important?

Many of the airborne viruses produce very severe diseases, associated with high mortality, which may be spread along long distances and cause outbreaks of the disease in different locations. In addition, many of them are zoonoses.


At the end of December 2019, a new coronavirus was described in Wuhan, China, causing acute and severe respiratory syndrome in people. This initial outbreak rapidly spread to other parts of China and then to other countries, first in Europe and then in America, Asia, Africa, and Australia. The causative virus is called severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) because of its genetic similarity to the previous one that caused SARS in 2002. The disease is known as corona virus disease 2019 (COVID-19).

The WHO declared the outbreak a public health emergency of international concern on January 30th, 2020, and then on March 11th, 2020, the WHO assessed that COVID-19 can be characterized as a pandemic. This is the first pandemic caused by a coronavirus.

The COVID-19 pandemic is evolving rapidly. The distribution of reported cases of COVID-19 worldwide can be found on these websites:

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Animal Viruses: Their Transmission and the Diseases They Produce

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