Opportunities and Limitations of Molecular Methods for Studying Bat-Associated Pathogens

Rapid detection of bat coronaviruses from fecal samples using loop-mediated isothermal amplification assay in the field

The global impact of the COVID-19 pandemic has emphasized the critical need for effective viral diagnostics. Although polymerase chain reaction (PCR) is a well-established nucleotide amplification technique, its limitations, such as the need for expensive equipment and skilled technicians, have led to the exploration of alternative methods, including loop-mediated isothermal amplification (LAMP). Bats, as a crucial natural reservoir of coronaviruses (CoVs), particularly Scotophilus bat coronavirus 512 (Scotophilus bat-CoV 512) prevalent among Taiwan's bat population, are the focus of this study. We aimed to detect Scotophilus bat-CoV 512 from bats in field conditions using loop-mediated isothermal amplification (LAMP) assay for on-site detection. Therefore, our study delves into the specificity of the LAMP reaction, emphasizing the careful design of primers to prevent false positive results. A cross reactivity and primer specificity test involving seven different microorganisms, including closely related bat CoVs and two bacterial species typically found in feces, revealed that the LAMP assay uniquely detected Scotophilus bat-CoV 512. The developed colorimetric reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay was optimized for the primers targeting nucleocapsid (N) gene, and the sensitivity test revealed a detection limit of 2.4 × 103 copies/µL. Our findings indicate the potential of the RT-LAMP assay for on-site detection in the field and subsequent laboratory analysis for comprehensive sampling and further research on bat CoV isolation. The surveillance and monitoring of bat CoVs contribute substantially to mitigating human threats, particularly concerning the emergence of new pandemic variants.

Henipaviruses: an expanding global public health concern?

Nipah virus (NiV) and Hendra virus (HeV) are highly pathogenic zoonotic viruses of the genus Henipavirus, family Paramyxoviridae that cause severe disease outbreaks in humans and also can infect and cause lethal disease across a broad range of mammalian species. Another related Henipavirus has been very recently identified in China in febrile patients with pneumonia, the Langya virus (LayV) of probable animal origin in shrews. NiV and HeV were first identified as the causative agents of severe respiratory and encephalitic disease in the 1990s across Australia and Southern Asia with mortality rates reaching up to 90%. They are responsible for rare and sporadic outbreaks with no approved treatment modalities. NiV and HeV have wide cellular tropism that contributes to their high pathogenicity. From their natural hosts bats, different scenarios propitiate their spillover to pigs, horses, and humans. Henipavirus-associated respiratory disease arises from vasculitis and respiratory epithelial cell infection while the neuropathogenesis of Henipavirus infection is still not completely understood but appears to arise from dual mechanisms of vascular disease and direct parenchymal brain infection. This brief review offers an overview of direct and indirect mechanisms of HeV and NiV pathogenicity and their interaction with the human immune system, as well as the main viral strategies to subvert such responses.