When watching bats in Austin, Texas at the South Congress Bridge, one does not think that these critters carry a coronavirus. The emergence of the Mexico free-tail bats every evening from March to November between 5:30 PM to 6:30 PM is a major spectacle in Austin. Many evenings, bat enthusiasts and watchers wait at lookout spots below and above the South Congress Bridge until the bats emerge in huge flocks, mostly visible as a vibrating cloud. Images of a Townsend's big-eared bat, a horse-shoe bat, and the Mexican free-tailed bat are shown below.
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Townsend's big-eared bat Horseshoe bat Mexican free-tailed bat
Many viruses are found in bats
Horseshoe bats in China harbor SARS-like coronaviruses. The suggestion that wildlife markets led to the spillover of the newly emerged corona virus SARS-CoV-2 has now given bats a bad reputation. Bats can be carriers of rabies as well as of coronaviruses but are no danger to humans unless people come in contact with their blood or saliva. This is very rare in the western world.
Approximatelly 60 to 80% of emerging infectious diseases in humans originated from wild life. Bats are a natural reservior for a large variety of viruses. The origin and evolution of bat viromes can be studied using modern molecular biology technologies such as the construction of viral nucleic acid libraries, genome analysis via next-generation sequencing, and phylogenetic analysis.
In 1989, Steece and Altenbach found that a rabies virus infected young Mexican free-tailed bats shortly after birth. However, an immunological study carried out by these two scientists determined that the Mexican free-tailed bats readily recovered from their rabies virus infection. Bats are known to harbor a wide range of human pathogens, including Nipah, Hendra, rabies, Ebola, Marburg, and severe acute respiratory syndrome coronavirus (SARS-CoV). Hence, there is a need to monitor the presence of infectious pathogens, including for the existence of coronaviruses (CoVs).
Anthony et al., in 2013, investigated the presence of CoVs in bats from Mexico and found that an individual bat from the species Lonchorhina aurita or Tomes’s sword-nosed bat testes positive for the novel coronavirus α-CoV Mex-CoV-3. The research group screened 606 bats from 42 different species in Campeche, Chiapas, and Mexico City and identified 13 distinct CoVs. Nine were alpha (α)-CoVs; four were β-CoVs.
However, it is essential to remember that most of the viruses carried by bats will not pose any clinical risk. Therefore, bats should not be stigmatized ubiquitously as significant threats to public health.
In recent years, our knowledge of coronaviruses has increased exponentially. Several outbreaks of zoonotic diseases caused by several pathogenic CoVs, including SARS, MERS, and more recently SARS-CoV-2 (COVID-19), stimulated a new era of coronavirus research.
SARS-Cov-2 is the cause of COVID-19. SARS-CoV-2 is a betacoronavirus like MERS-CoV and SARS-CoV. A large family of coronaviruses exists, and many are common in people as well as in different animal species. Sequence analysis suggests that SARS-CoV-2 recently emerged from an animal reservoir in Wuhan, China.
In a dispatch by the CDC, Lau et al. suggested that the genome of SARS-CoV-2 is closest to that detected in a related virus from horseshow bats. Phylogenetic analysis of coronavirus genomes indicated that the genomic region of SARS-CoV-2 is closely related to SARSr-Ra-BatCoV-RaTG13 from an intermediate horseshoe bat in Yunnan. In contrast, its receptor-binding domain (RBD) resembles that of pangolin-SARSr-CoV/MP789/Guangdong/2019 observed in smuggled pangolins in Guangzhou. Identified potential recombination sites around the RBD region, suggest that SARS-CoV-2 maybe a recombinant virus. The genomic backbone appears to have evolved from the Yunnan bat virus-like SARSr-CoVs, and the RBD region came from pangolin virus-like SARSr-CoVs.
The availability of next-generation sequencing (NGS) technologies allows increased surveillance of wild animal species. As of 2019, an enormous number of novel coronaviruses were identified. So far, over 200 novel coronaviruses have been found in bats. Approximately 35% of the sequenced bat virome is from coronaviruses.
Bats are known to be natural reservoirs of a large variety of viruses, including coronaviruses. Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) and Middle East Respiratory Syndrome Coronavirus (MERS-CoV), are thought to have originated from bats. Various species of horseshoe bats in China harbor genetically diverse SARS-like coronaviruses. Some strains are highly similar to SARS-CoV, even in the spike protein sequence. Some CoVs use the same receptor as SARS-CoV for cell entry. Bat also harbor coronaviruses genetically related to human coronavirus 229E and NL63.
Reference
Anthony, Simon & Ojeda-Flores, Rafael & Rico, Oscar & Navarrete-Macias, Isamara & Zambrana-Torrelio, Carlos & Rostal, Melinda & H. Epstein, Jonathan & Tipps, Teresita & Liang, Eliza & Sanchez-Leon, Maria & Sotomayor-Bonilla, J & Aguirre, A. Alonso & Avila-Flores, Rafael & Medellín, Rodrigo & Goldstein, Tracey & Suzan, Gerardo & Daszak, Peter & Lipkin, W. (2013). Coronaviruses in bats from Mexico.The Journal of general virology. 94. 10.1099/vir.0.049759-0. [PMC]
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Richard Steece and J. Scott Altenbach; PREVALENCE OF RABIES SPECIFIC ANTIBODIES IN THE MEXICAN FREE-TAILED BAT (TADARIDA BRASILIENSIS MEXICANA) AT LAVA CAVE, NEW MEXICO. Journal of Wildlife Diseases 1989 25:4, 490-496. [Article]
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