Cultivation techniques for animal coronaviruses: Emphasis on feline infectious peritonitis virus, canine coronavirus, transmissible gastroenteritis virus, and porcine hemagglutinating encephalomyelitis virus

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The on-going SARS-CoV-2 causing COVID-19 discovered in December 2019, is responsible for a global pandemic. The virus belongs to the group of enveloped viruses containing linear, non-segmented, single stranded, positive sense strand RNA as genetic material. Already six different strains Coronaviruses are being reported to infect humans, however the seventh one is genetically similar to the SARS Coronavirus and termed as SARS-CoV-2. Specific crucial macromolecules such as membrane, nuclear, spike and enveloped proteins including HE esterase are present in the virus that interact with ACE2, APN, NEU-5, 9SC2 moiety of humans plays significant role in occurrence and transmission of the devastating disease. This review article summarizes the structure, histopathology, transmission of novel Coronavirus, its symptoms with preventive measures & currently prescribed drugs. Though various drugs and therapy have been administrated or implemented to restrict COVID-19, however it is imperative to develop an antidote against SARS-CoV-2 by the scientific or research community to save life.

The S gene of canine coronavirus, strain UCD-1, is more closely related to the S gene of transmissible gastroenteritis virus than to that of feline infectious peritonitis virus

To gain insight into the genetic relationships among six canine coronavirus (CCV) strains, the variable region of the spike (S) protein gene was sequenced. The CCV strains were: two ATCC reference strains, the Insavc-1 vaccine strain, the National Veterinary Services Laboratories (Ames, IA) challenge strain, and two California field isolates (UCD-1 and UCD-2) from the 1970s. All six strains, downstream of the nucleocapsid (N) protein gene, had sufficient size for an ORF 7b, and thus, none were transmissible gastroenteritis virus (TGEV)-like since TGEV lacks ORF 7b. By sequence analysis of the variable domain at the 5' end of the S gene, five of the six CCV strains had a high degree of identity with feline infectious peritonitis virus (FIPV). However, one CCV field isolate (UCD-1) was different and had a high degree of identity with the 5' end of the TGEV S gene. This suggests that RNA recombination occurred at this site between antigenically related coronaviruses. The low passage field isolates, UCD-1 and UCD-2, varied in their initial infectivity for swine testicular cells suggesting that sequence differences in the variable domain of the S gene may account for biological variation among CCVs.

Differentiation between transmissible gastroenteritis virus and porcine respiratory coronavirus using a cDNA probe

A plasmid, pG3BS, containing a cDNA clone from the 5' coding region of the peplomer glycoprotein gene appears to be specific for enteric transmissible gastroenteritis virus (TGEV) strains and for live-attenuated TGEV vaccines. This cDNA probe is used to differentiate porcine respiratory coronavirus (PRCV) isolates from TGEV field and vaccine strains by a slot blot hybridization assay. Probe pG3BS also hybridizes to canine coronavirus (CCV) RNA but does not hybridize to antigenically related feline infectious peritonitis virus (FIPV) RNA. The RNAs of 13 enteric TGEV isolates from the United States, Japan, and England, 4 US-licensed live-attenuated TGEV vaccines, and antigenically closely related CCV were detected by pG3BS. The RNAs of FIPV and 3 US isolates of PRCV did not react with pG3BS but were detected by a TGEV-derived plasmid, pRP3. Pigs infected with either PRCV or TGEV test serologically positive for TGEV antibody by the serum neutralization test. Characterization of the virus circulating in a swine herd by the pG3BS probe will differentiate between an enteric TGEV and a respiratory PRCV infection.

Evidence for a porcine respiratory coronavirus, antigenically similar to transmissible gastroenteritis virus, in the United States

A respiratory variant of transmissible gastroenteritis virus (TGEV), designated PRCV-Ind/89, was isolated from a swine breeding stock herd in Indiana. The virus was readily isolated from nasal swabs of pigs of different ages and induced cytopathology on primary porcine kidney cells and and on a swine testicular (ST) cell line. An 8-week-old pig infected oral/nasally with the respiratory variant and a contact pig showed no signs of respiratory or enteric disease. These pigs did not shed virus in feces but did shed the agent from the upper respiratory tract for approximately 2 weeks. Baby pigs from 2 separate litters (2 and 3 days old) also showed no clinical signs following oral/nasal inoculation with PRCV-Ind/89. In a third litter, 5 of 7 piglets (5 days old) infected either oral/nasally or by stomach tube developed a transient mild diarrhea with villous atrophy. However, virus was not isolated from rectal swabs or ileal homogenates of these piglets, and viral antigen was not detected in the ileum by fluorescent antibody staining even though the virus was easily recovered from nasal swabs and lung tissue homogenates. Swine antisera produced against PRCV-Ind/89 or enteric TGEV cross-neutralized either virus. In addition, an anti-peplomer monoclonal antibody, 4F6, that neutralizes TGEV also neutralized the PRCV-Ind/89 isolate. Radioimmunoassays with a panel of monoclonal antibodies indicated that the Indiana respiratory variant and the European PRCV are antigenically similar.