WHY BATS ARE RESERVOIR OF HUMAN DISEASE?

INTRODUCTION

Bats are the the only mammal that can fly but these bats is only a big problematic to human because these carrier of many of the deadliest virus such as ebola, SARS, MERS ect., and so many so to know about the answer we want to know about bat immune system

Photo credit:www.express.co.uk

REASONS FOR BAT AS A RESERVOIR 

• Bats Have an Efficient and Varied Antiviral Response
• It has been observed that viruses which severely affect other mammals, including humans, are apparently non pathogenic for bats.
• Bats have evolved immune mechanisms that allow for benign virus–host relationships.
• Bats seem to possess either an “always ON” interferon strategy plus or a better antiviral ISG defense strategy.

Photo credit:https://doi.org/10.3390/v11020192

• Viral Persistence in Bats
• Detection of virus and absence of disease have led researchers to suggest that bats are likely the reservoirs of these viruses. Asymptomatic infections have been observed in bats for human pathogens such as henipaviruses (Nipah and Hendra viruses), coronaviruses (Middle Eastern Respiratory Syndrome coronavirus (MERS-CoV)), and filoviruses (Marburg virus and ebolaviruses). For a species to be a viral reservoir, the virus needs to persist in the population.
•  Prolonged or latent infection has to occur in some bats for describing persistence of henipavirus in small populations.

•  Stress-Induced Spillover—A Molecular Perspective
• Spillover events are complex and usually require successful alignment of several contributing factors. One such critical factor is increased shedding of viruses by bats.

Photo credit:https://doi.org/10.3390/v11020192

DISEASE SPREAD THROUGH BATS

To know about the disease spread through bats first we want know about virus classification it was described by Baltimore according to baltimore virus classified into

• Double-stranded DNA viruses
• Single-stranded DNA viruses
• Double-stranded RNA viruses
• Positive-sense single-stranded RNA viruses
• Negative-sense single-stranded RNA viruses
• Positive-sense single-stranded RNA viruses that replicate through a DNA intermediate
• Double-stranded DNA viruses that replicate through a single-stranded RNA intermediate.

Photo credit www.wikipedia.com

Bats are the host for all these seven classification by baltimore now we see one by one

• Double-stranded DNA viruses
• Adenoviruses   
• Adenoviruses have been detected in bat guano, urine, and oral and rectal swabs.
• Adenoviruses related illness common cold or flu-like symptoms, fever, sore throat, acute bronchitis (inflammation of the airways of the lungs, sometimes called a “chest cold”), pneumonia (infection of the lungs), pink eye (conjunctivitis), acute gastroenteritis (inflammation of the stomach or intestines causing diarrhea, vomiting, nausea and stomach pain)

• Herpesviruses   
• Diverse herpesviruses have been found in bats in North and South America, Asia, Africa, and Europe.
• Herpesviruses related disease in human such as chickenpox, cold sores, and genital herpes, and also include viruses that can lead to cancer
• New research identified that Novel herpes virus in bat 

• Papillomaviruses
• Papillomaviruses were first detected in bats in 2006, in the Egyptian fruit

• Single-stranded DNA viruses
•  Anelloviruses

 No anellovirus is known to cause disease in humans.

Circoviruses, family Circoviridae, circoviruses are not associated with any disease in humans.

• Parvoviruses

Several kinds of parvoviruses are considered important for human and animal health. 

A bright red rash on the cheeks is a distinctive sign of parvovirus infection.

Parvovirus infection is a common and highly contagious childhood illness.

• Double-stranded RNA viruses 
• Reoviruses

Some disease-causing reovirus species are associated with bats.

• Melaka virus

which was linked to illness in a Malaysian man and his two children in 2006.

• Kampar virus

 Identified a few months later in another Malaysian man. Though he had no known contact with bats, but similar to melaka virus

No astroviruses identified in bats are associated with disease in humans.

Calicivirus infections commonly cause acute gastroenteritis, which is the inflammation of the stomach and intestines

Photo credit: Sheng-Fan Wang, Department of Medical Laboratory Science and Biotechnology, Kaohsiung Medical (www.researchgate.net) 

• Positive-sense single-stranded RNA viruses
• Coronaviruses

SARS-CoV

SARS-CoV-2

MERS-CoV

• Middle East respiratory syndrome-related coronavirus electron micrograph Several zoonotic coronaviruses are associated with bats, including severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome-related coronavirus (MERS-CoV).
• Severe acute respiratory syndrome coronavirus 2 is another zoonotic coronavirus likely originating in bats.
•  SARS-CoV causes the disease severe acute respiratory syndrome (SARS) in humans. 
•  It is believed that MERS-CoV originated in bats, though camels are likely the intermediate host through which humans became infected. Human-to-human transmission is possible, though does not easily occur. 

Photo credit: https://doi.org/10.3390/mi11030306

• Flaviviruses
• Bats might play a job within the ecology of some species.
• Several strains of dengue fever virus are found in bats within the Americas, and West Nile River virus has been known in fruit around the bend in South Asian nation.
• Japanese encephalitis virus or its associated antibodies are found in many bat species throughout Asia

Picornaviruses are known from a various array of bat species round the world

• Negative-sense single-stranded RNA viruses
• Arenaviruses

Arenaviruses are primarily related to rodents, although some will cause unwellness in humans.

Bat hantaviruses aren't related to unwellness in humans. 

EBOLA VIRUS

Photo credit: www.cdc.gov.in

Rabies-causing viruses

• lyssaviruses are transmitted by mammals, most often through biting.
• After transmission has occurred, the typical human is well for 2 months, although the time period are often as short as per week or as long as many years.
• Italian scientist Antonio Carini was the first to theorise that lyssa virus may well be transmitted by bats, which he did in 1911. This same conclusion was reached by Hélder Queiroz in 1934 and Joseph Lennox Pawan in 1936.
• Investigations of the two reported human cases discovered that each infections may well be explained by means that nonetheless aerosol transmission.

Photo credit:https://doi.org/10.1038/nrmicro.2018.11

• Orthomyxoviruses
• The circulation of influenza A viruses. influenza A viruses in bats probably originated in birds.
• influenza A infections are common among bats within the New World.

Hendra

Nipah

Menangle viruses

• Hendra virus was 1st known in 1994 in Hendra, Australia.
• Seven humans are known to own been infected by Hendra virus, with four fatalities
• It was 1st a horse infection however it conjointly transmitted to horse-horse transmission then to horse-human transmission
• The first human outbreak of Nipah virus was in 1998 in Malaysia.
• Outbreaks have conjointly occurred in Asian nation, India, Singapore, and also the Philippines. In Asian nation, the first mode of transmission of Nipah virus to humans is thru the consumption of Phoenix dactylifera sap.
• Pots began to gather the sap are contaminated with fruit bat excreta and guano, {and the|and therefore the|and conjointly the} bats also lick the sap streams flowing into the pots.
• Menangle virus, that was 1st known at a hog farm in New South Wales, Australia.
• Two workers of the hog farm became sick with flu-like diseases, later shown to be a results of the virus.

Photo credit: https://www.researchgate.net/figure/Transmission-of-the-Nipah-virus-1-Fruit-bats-acts-as-natural-reservoir-of-Nipah_fig2_332558975

Togaviruses embody alphaviruses, that are detected in bats. Alphaviruses cause encephalitis in humans. Alphaviruses that are detected in bats.

• Positive-sense single-stranded RNA viruses that replicate through a DNA intermediate   
• Retroviruses

Bats often infected with retroviruses. 

• Double-stranded DNA viruses that replicate through a single-stranded RNA intermediate
• Hepadnaviruse

 The hepadnavirus found within the tent-making bat, that could be a New World species, was the closest relative of human hepadnaviruses.

REFERENCE: 

If you have any suggestions or correction please comment below it will be more helpful to make this blog content better

Thank you….