Zoonotic Spillover

Zoonotic Spillover

Subject : Science and technology

Section: Biotechnology

Concept :

• The Energy Department’s conclusion, with “low confidence,” that an accidental laboratory leak in China most likely caused the coronavirus pandemic has renewed questions about what sparked the worst public health crisis in a century — and whether the virus at the heart of it was somehow connected to scientific research.
• Scientists who have studied the genetics of the virus, and the patterns by which it spread, say the most likely cause is that the virus jumped from live mammals to humans — a scientific phenomenon known as “zoonotic spillover” — at the Huanan Seafood Wholesale Market in Wuhan, China, the city in which the first cases of COVID-19 emerged in late 2019.

Zoonotic Spillover

• Zoonotic Spillover refers to a phenomenon in which a disease jumps from animals to human hosts i.e. the pathogen infects a novel host- a species different from its usual reservoir host.
• A variety of disease causing pathogens can cause spillovers- bacteria, virus, parasites, etc.
• The SARS CoV 2, the pathogen behind the COVID-19 pandemic, is a notable example of this phenomenon. Other examples include Ebola virus from bats and the Salmonella bacteria from farm animals.

How does it happen?

• For a pathogen to be capable of causing such spillover event, several factors need to be fulfilled.
• The pathogen mustn’t be too effective in its primary host population. This is so that host species viability isn’t destroyed and it continues to act as a reservoir for the pathogen.
• There needs to be close contact between the primary host species and the novel host species for the transmission to take place.
• Then the pathogen has several more barriers to break through- such as biological incompatibility between the pathogen and the new host and the latter’s immune response.
• The pathogen also needs to develop the ability to transmit between members of the new host species.

Why is it concerning?

• Though not all pathogens are capable of causing such spillover events, it is noteworthy that 3/4th of all new infectious diseases among humans originated from animals.
• These events are difficult to detect.
• While not all pathogens that jump to human hosts pose a risk, the more frequently this happens, greater the chances are for the advent of a dangerous new pathogen to take root- as in case of the SARS CoV 2.
• Viral spillovers are especially concerning as they undergo very quick and random genetic mutations, making them capable of acquiring the spillover ability more easily.
• The ongoing climate change, habitat destruction and anthropogenic encroachment into natural habitats is increasing the risk of such events.
• This is because shrinking habitats mean increasing number of animals are being crowded into smaller areas- favouring disease transmission.
• As human settlements expand closer to wildlife habitats, the chances of reservoir host animals coming into contact with people and farm animals increases.
• For instance, the recent avian flu outbreak in the USA is because of spillover from migrating duck to domestic chicken.