Detection of Coronavirus in Giant Anteater (Myrmecophaga tridactyla) by Transmission Electron Microscopy in São Paulo, SP, Brazil
Abstract
Coronaviruses belong to the order Nidovirales, family Coronaviridae and have four genera, Alphacoronavirus, Betaconavirus, Gammacoronavirus and Deltacoronavirus. They infect humans and several animal species, causing various diseases. Coronavirus constitute zoonotic risk to global public health because of their ability to adapt to new species and establish sppilover events. In this study, we evaluated the presence of coronavirus particles in the feces of giant anteaters (Myrmecophaga tridactyla). Under the transmission electron microscope, particles with coronavirus-like morphology, pleomorphic, rounded or elongated with radial projections forming a corona and measuring 80-140 nm in diameter, were visualized in all examined samples. The technique used was extremely useful for rapid viral diagnosis in affected animals. This report is the first occurrence of coronavirus in Giant anteater (Myrmecophaga tridactyla).
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Introduction
Coronaviruses infect humans and a wide diversity of animal and bird species causing respiratory, enteric, neurologic and hepatic disorders [1].
They constitute a zoonotic risk to global public health because their ability to adapt to new species and establish sppilover events [2].
Due to their zoonotic potential, they have a strong tendency to cause catastrophic impacts, such as the recent human viral pandemics, originating from bat, including severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), and Covid 19 [3].
In animals, the coronavirus has also caused devastating diseases, such as porcine epidemic diarrhea (PEDV) that eliminated 10% of the US pig population in less thana year [4, 5, 6] and the infectious bronchitis virus that decimated flocks of chicken and turkey indifferent parts of the world, causing economic losses to the poultry industry [7].
Coronaviruses are positive-stranded RNA viruses, belong to the order Nidovirales, family Coronaviridae and have four genera, Alphacoronavirus (human coronavírus NL63 (HCoV-NL63), porcine transmissible gastroenteritis coronavírus (TGEV), PEDV, and porcine respiratory coronavírus-PRCV), Betacoronavirus (SARS-CoV, MERS-Cov, bat coronavírus HKU4, mouse hepatites coronavírus (MHV), bovine coronavírus (BCoV), and human coronavírus OC43, Gammacoronavirus (avian (infectious bronchitis coronavírus-IBV) e Deltacoronavirus (porcine deltacoronavirus (PdCV) [8].
Companion animals, such as cats, dogs, ferrets, horses and alpacas can also be infected [9]. The electron micrographs of coronavirus revealed a diverging spherical outline with some degree of pleomorphism, virion diameters varying from 60 to 140 nm, and distinct spikes of 9 to 12 nm, giving the virus the appearance of a solar corona [10].
Coronavirus genome measures 27 to 32 kband encodes three tipos of proteins, structural, accessory, and non-structural proteins. The structural proteins comprise the nucleocapsid (N), spike (S), membrane (M), and envelope (E) proteins [11]. The S protein mediates attachment of the virus to the host cell surface receptors resulting infusion and subsequent viral entry.
TheM protein is the most abundant protein and defines the shape of the viral envelope and the pleomorphic variability indifferent species. TheE protein is the smallest of the major structural proteins and participates in viral assembly and budding. TheN protein is the only one that binds to the RNA genome and is also involved in viral assembly and budding [12]. The roles of most of the accessory proteins remain poorly understood, but, the SARS coronavirus encodes accessory proteins that antagonize the development of type I interferon (IFN) responses [13]. The nonstructural proteins reassemble to form a viral replicase-transcriptase complex, consisting of the RNA-dependent RNA polymerase (RdRp, nsp12), helicase (nsp13), nsps with accessory functions [14].
Viral replication occurs quickly and mainly in the villous epithelial cells of the small intestine, resulting in marked villous atrophy due to necrosis [15, 16].
Animals become infected through the faecal-oral route, respiratory or inhalation of aerossol [17, 18]. The incubation period is 2–8 days [19] and the morbidity is very high, up to 100% [20].
The giant anteater (Myrmecophaga tridactyla) is the largest known species of anteater and the only species in Myrmecopahaga [21], listed as "vulnerable" by IUCN. It has become extinct in some parts of its geographic distribution, such as Uruguay. In Brazil it is considered extinct in the states of Vitoria, ESand Rio de Janeiro, RJ, and in condition of vulnerability in other states at great risk of disappearance in Central America [22].
The main threats to the survival of the species are hunting and habitat destruction, being an animal susceptible to being fatally hit by fires and traffic-accidents [21].
The incidence of studies on the presence of coronavirus in animals with potential reservoir has been little discussed, especially in animals at risk of vulnerability [23].
Electron microscopy techniques (rapid preparation) allow an accurate detection of viral particles, especially those of the coronavirus, enabling a rapid diagnosis in samples of different specimens [24].
To the detriment of the efficiency of detection by means of electron microscopy, this study sought to evaluate the presence of coronavirus particles in fecal samples of giant anteaters from the Ecological Park of the State of São Paulo, SP, Brazil.
