Ruby Singh^1,2 and Prachi Srivastava¹*

¹Amity Institute of Biotechnology, Amity University, Uttar Pradesh, Lucknow Campus, India
²ICAR- Central Institute of Fisheries Education, Versova, Mumbai, Maharashtra, India

*Corresponding Author: Prachi Srivastava, ICAR- Central Institute of Fisheries Education, Versova, Mumbai, Maharashtra, India.

Received: November 06, 2020; Published: March 22, 2021

Introduction and Background

  In the last few years, we have seen the existence of new viruses which has caused serious damage to global health. Recently numerous Coronaviruses isolates have been identified and accordingly their classifications have been revised. Coronaviruses are positive strand RNA viruses that originate from the family Coronaviridae (Order: Nidovirales) which consists of many genera and species and it infects three groups of vertebrates including mammals, birds and fishes [1] and they suffer respiratory, gastrointestinal, cardiovascular and neurological diseases. According to the International committee on taxonomy of viruses (ICTV), Coronaviridae are divided into two subfamilies Coronavirinae and Torovirinae. The members of Coronaviridae infect three groups of vertebrates which includes mammals (genera Alphacaronavirus, Betacoronavirus, Gammacoronavirus and Torovirus), birds (genera Gammacoronavirus and Deltacoronavirus) and fish (genus Bafinivirus) [2].

  The name Coronaviridae, is derived from the Latin term Corona as the name suggests it shows a crownlike structure presented from the prominent surface projections. The virus particles are enveloped and it can bespherical (Coronavirinae), kidney-shaped (Torovirus) or bacilliform (Bafinivirus). The viral envelope consists a unit membrane which is having club-shaped pro­jections of 12–24 nm in length and these projections bearing spike (S) glycoprotein trimers allows the virions to attach to specific receptors which are expressed on the plasma membrane of the host cell [3]. The major feature possessed by coronaviruses are formation of syncytia which are induced by S protein. Animal SARS-CoV could evolve to infect humans by a series of transmission events between animals and humans and among all the structural proteins of SARS-CoV this S protein is the main antigenic component that is mainly responsible for inducing host immune responses, neutralizing antibodies and protective immunity against virus infection [4] The second type of surface projection of coronaviruses comprises a homodimeric hemaglutinin-esterase (HE) glycoprotein which helps in receptor binding. The other protein which plays a main role in viral budding is matrix (M) glycoprotein which is located on the cytoplasmic side of the viral envelope [5-7]. The non-glycosylated envelope E protein plays an important role in assembly of the virus as well as in morphogenesis because of its ion channel and membrane-permeabilizing activity but this E protein is not important for all corona viruses in spite of its loss may cause the inhibition of virus maturation. The major antigens which are expressed by coronaviruses are S and HE glycoproteins which induces the production of neutraliz­ing antibodies and a cell-mediated immune response in the host [8,9]. The N protein which is responsible for genome encapsidation and packaging can also induce a protective immune response [4]. The closely related coronaviruses which show serological cross-reactivity are Human coronavirus 229E (HCoV 229E), Transmissible gastroenteritis virus (TGEV), Porcine respiratory coronavirus ISU-1 (PRCV ISU-1) and Feline infectious peritonitis virus WSU79-1146 (FIPV 79-1146) [10].

Review

  In June 2000, twenty-one harbor seals were found dead on the beaches of Point Reyes near San Francisco, California. Sudden death of so many harbor seals, scientists sought to understand what killed these animals [11].

  According to Schutze., et al. [12], aquatic Coronaviruses which are listed by officially by ICTV are Beluga whale Coronavirus SW1 and the White bream virus (WBV). The other unassigned member are harbor seal coronavirus and Bottle nose dolphin coronavirus. Woo., et al. [13] suggested Beluga whale Coronavirus SW1 (BVCoVSW1) and bottle nose dolphin coronavirus as a distinct species i.e. Cetacean coronavirus.

  In 2008 and 2010 during marine surveillance study in Ocean park in Hongkong, a Coronavirus which was identified in Indo-pacific was from Bottle nose dolphin and even the coronavirus genome was detected in fecal samples from three apparently healthy animals.

  Mihindukulasuriya., et al. [14] published first report about identification of the complete genome from a coronavirus isolated from a marine mammal which was Beluga whale which died from acute liver failure after suffering a short pulmonary disease and this was assigned as genus Gammacoronavirus.

  Bossart and Schwatz in [15] reported the probable case of coronavirus infection in harbor seal. Three harbor seals (Phoca Vitulina) were affected by this virus in 1987. Two seals died without showing any clinical symptoms whereas the third one showed some symptoms such as severe diffuse pulmonary congestion and extensive broncho-alveolar hemorrhage. On the basis of antigenic cross reactivity this virus was confirmed as genus Alphacoronavirus, however the virus is still unassigned.

Coronaviruses in fish was assigned as genus Bafinivirus under the family Coronaviridae.

  Granzow., et al. [16] isolated White bream virus from a healthy white bream (B. Bjoerkna L) in Germany during monitoring of pathogen in wild fresh water fish. Other WBV isolates from cyprinids was Gold fish, Tench and Grass carp [17].

  In 2014 Lord., et al. [18] isolated a bafinivirus from Chinook Salmon which was the first report of Coronavirus in Salmonidae. This virus was related to white bream virus and FHMV (Fathead Minnow Virus) according to the amino acid alignment however the virus is still unassigned member of the Nidovirales.

  In 2002, Fathead minnow virus was isolated from Moribund fathead minnows on a Baitfish farm in Central Arkansas in 1997 [19]. According to Batts., et al. [20]. FHMNV is closest relative of WBV (white bream virus), however FHMNV is still the unassigned member of the Nidovirales.

  Ahne., et al. [21] isolated an unknown virus from a healthy grass carp (C. idella) and the isolate was named as CIVH 33/86 (Ctenopharyngodon idella virus hungary). This virus was finally confirmed as genus torovirus from the family Coronaviridae.

  Miyazaki., et al. [22] published an another accepted Coronavirus which was named as Carp viremia-associated ana-aki-byo, caused a high mortality in Colored Carp (C. Carpio) in 1997 and 1998 in Japan.

  Sano., et al. [13] isolated a coronavirus from common carp that died after suffering an acute infection.

  According to Schutze., et al. 2016. Coronaviruses belong to the family Coronaviridae and in aquatic organism it infects the aquatic species coming under the genus alphacoronavirus, betacoronavirus, gammacoronavirus and deltacoronavirus under the subfamily coronavirinae as well as the species of the genus torovirus and bafinivirus from the subfamily Torovirinae. Beluga whale coronavirus and dolphin coronavirus are in the genus gammacoronavirus whereas harbor seal corona virus belong to the genus alpha coronavirus and white bream, fathead minnow and chinook salmon belong to the genus bafinivirus. They are classified according to ICTV and among all these virus only two are assigned mainly Beluga whale coronavirus in aquatic mammals and white bream in aquatic fishes [12]. There are no reports for delta and beta coronavirus in aquatic organisms.

  According to Bossart and Schwartz in 1987 three harbor seals (Phoca vitulina) housed at the Miami Seaquarium were infected by Coronavirus and showed symptoms of acute necrotizing enteritis. Two of the seals died without showing any clinical signs and the third one displayed marked leukocytosis, dehydration, hyperna­tremia and hyperchloremia. Extensive focal bronchoalveolar hemor­rhage and edema with severe diffuse pulmonary congestion were revealed by pathological sections from all the three harbor seals. There was detection of moderate-to-severe lymphoid depletion in the spleen, visceral and in peripheral lymphnodes. Coronavirus-specific antigens were detected in the intestinal mucosa. According to the antigenic cross-reactivity, the coronavirus infecting the harbor seals most probably belonged to the genus Alphacoronavirus and all alphacoronaviruses including Canine coronavirus yielded positive results by Immunofluorescence staining.

  Beluga whale exhibited acute liver failure and died after suffering a short generalized pulmonary disease. According to histological examination acute hepatic necrosis was confirmed and a great number of round viral particles was observed in the cytoplasm of hepatic cells during electronic microscopic examination [12]. Bottlenose Dolphin showed no clinical symptoms except the viral genome was detected during infectious stage and in fecal sample from the healthy animals.

  Effected fish exhibited hemorrhage of the skin and eyes, as well as hepatic, splenic and renal lesions including White Bream, carp and gold fish. In 2009 Fichtner., et al. suggested that Other WBV-like pathogens were isolated from tench and carp after clinical events and fatalities in Germany in 2007 and clinical signs shown such as exhaustion, reduced food intake, increased mucus production, pseudofeces and petechiae.

  According to current report Schutze., et al. 2016, at present there are no information is available regard¬ing the ecology, route of infection, cell tropism, mode of transmission or vectors of coronaviruses that infect aquatic organisms but the principle features of the viral infection cycle are as reviewed by de Vries., et al. (1997) and Ruch and Machamer [24]. Virus replication takes place entirely within the cytoplasm of the infected cell.

  As per current report there are no treatments yet and still the information about the disease is lacking.

  This review suggest that coronaviruses are prevalent in cyprinids, salmonids, beluga whale and dolphin too. The first outbreak of coronavirus infecting humans was in 2003 and then recently in 2019 in China and before the outbreak of coronavirus in humans it was seen in fishes as well as in aquatic mammals including blue whale (1987) and in 2001 there were 21 harbor seals died in California [11]. So this study can help in the identification of root of the coronavirus outbreak as still there are no reports for the source of this coronavirus which has recently emerged in 2019 and still is the major cause of death to humans as well as to some animals. It is hoped that this review will enable the discovery and identification of source of coronaviruses and facilitate further research into their molecular biology, phylogeny and evolution [25-34].