BackgroundRabies is an incurable neglected zoonosis with worldwide distribution characterized as a lethal progressive acute encephalitis caused by a lyssavirus. Animal venoms and secretions have long been studied as new bioactive molecular sources, presenting a wide spectrum of biological effects, including new antiviral agents. Bufotenine, for instance, is an alkaloid isolated from the skin secretion of the anuran Rhinella jimi that inhibits cellular penetration by the rabies virus. Antimicrobial peptides, such as ocellatin-P1 and ocellatin-F1, are present in the skin secretion of anurans from the genus Leptodactylus and provide chemical defense against predators and microorganisms.MethodsSkin secretion from captive Leptodactylus labyrinthicus was collected by mechanical stimulation, analyzed by liquid chromatography and mass spectrometry, and assayed for antiviral and cytotoxic activities. Synthetic peptides were obtained using solid phase peptide synthesis, purified by liquid chromatography and structurally characterized by mass spectrometry, and assayed in the same models. Cytotoxicity assays based on changes in cellular morphology were performed using baby hamster kidney (BHK-21) cells. Fixed Rabies virus (Pasteur Virus – PV) strain was used for virological assays based on rapid fluorescent focus inhibition test.ResultsHerein, we describe a synergic effect between ocellatin-F1 and bufotenine. This synergism was observed when screening the L. labyrinthicus skin secretion for antiviral activities. The active fraction major component was the antimicrobial peptide ocellatin-F1. Nevertheless, when the pure synthetic peptide was assayed, little antiviral activity was detectable. In-depth analyses of the active fraction revealed the presence of residual alkaloids together with ocellatin-F1. By adding sub-effective doses (e.g. < IC50) of pure bufotenine to synthetic ocellatin-F1, the antiviral effect was regained. Moreover, a tetrapetide derived from ocellatin-F1, based on alignment with the virus’s glycoprotein region inferred as a possible cell ligand, was able to maintain the synergic antiviral activity displayed by the full peptide.ConclusionsThis novel antiviral synergic effect between a peptide and an alkaloid may present an innovative lead for the study of new antiviral drugs.Electronic supplementary materialThe online version of this article (doi:10.1186/s40409-015-0048-1) contains supplementary material, which is available to authorized users.

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Bats belong to the second-largest order in a number of species diversity within the Mammalia class, containing 21 families and more than 1300 species. It is estimated that more than 200 viruses from 28 families have been isolated or detected in 37 different bat genera, many of them related to emerging infectious diseases with the potential to cross species barriers and infect other animals. The group of coronaviruses (CoV) is one of these viruses, which includes CoVs that can cause serious diseases in humans and animals, such as severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), porcine epidemic diarrhea (PED), swine acute diarrheal syndrome (SADS) and coronavirus disease 2019 (COVID-19). Some of the human and animal coronaviruses appear to be originated from bats. With the advent of new generation molecular techniques and increased surveillance of wild animal species, many new coronaviruses have been identified. The coronaviruses belong to the Nidovirales order and Coronaviridae family. The subfamily Coronavirinae is divided into four genera, Alphacoronavirus (alphaCoV), Betacoronavirus (betaCoV), Deltacoronavirus, and Gammacoronavirus. Since the first report of coronavirus in a Miniopterus pusillus bat, the coronavirus occurrence in a bats population of different regions in the world has been studied and, until now, both alphaCoV and betaCoV have been detected. The aim of this study was to perform a literature review regarding the detection of coronavirus (alphaCoV or betaCoV) in different bat species around the world and their immune response against coronavirus. This review reinforces the importance of these animals as hosts, reservoirs, or sources of viruses, including emerging viruses.

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