News Archive

Emerging CPV strain 2c

By Dr. Melissa Kennedy, UTCVM Clinical Virologist 

Parvoviruses remain a significant enteric pathogen of cats and dogs. Parvovirus of dogs is believed to have emerged as a host variant of feline parvovirus, and was designated canine parvovirus-2 (CPV-2). This variant did not infect cats. The virus continued to evolve, and was replaced by CPV-2a and 2b, the latter being the most prevalent currently. The newer variants reacquired the ability to replicate and cause disease in cats. All of these variants are closely related, sharing approximately 99% DNA homology.

In recent years, additional variants have emerged, and differ from CPV-2b by just a few amino acid residues, with some leading to antigenic differences. The nomenclature of these variants is confusing, and has led to the reporting of several distinct CPV-2c isolates. These variants have been identified in Asia, Europe, South America, and most recently, the US. One of these variants contains a mutation at amino acid residue 426 of the major capsid protein, an important antigenic epitope of CPV, leading to substitution of an aspartic acid residue with glutamic acid. This variant is present in dogs in the US - this is the CPV-2c currently getting attention in the US. The disease associated with these newer variants, including the US variant appears to be similar to that seen with earlier strains, including vomiting, diarrhea which may be hemorrhagic, and leukopenia. The mortality rate thus far does not seem to be significantly different from that of previous isolates.

With the emergence of new CPV variants, concern exists over the spectrum of protection by current vaccines. Commercial vaccines containing CPV-2, -2b, or a combination of the two strains have been licensed. At least one study has shown protection against the Asp426Glu-mutant, the US variant with current vaccines. Neutralizing antibody studies demonstrate antigenic differences among these newer variants. These differences could impact protection of puppies and kittens of dams vaccinated with CPV-2, 2b, or FPV, but this has not yet been tested. However, in well-immunized adult dogs, where immunity depends not only on antibodies, but cell-mediated immunity as well, protection with current vaccines should be adequate.

Diagnosis of canine and feline parvovirus is often done in-house at veterinary clinics using commercial ELISA kits. Most kits utilize monoclonal antibodies, specific for a single epitope of the virus, to detect the virus in fecal samples. It is not known if the continued evolution of CPV has affected the sensitivity of these assays, but investigations into this possibility are ongoing. We are investigating this at the Clinical Virology Laboratory here at UTCVM. We are using genetic detection by PCR and genetic analysis of the virus to characterize the strain.

If you have patients you suspect have parvovirus, and 1) want to confirm with additional testing (e.g. it was positive on ELISA) and to genetically characterize the isolate (i.e. if its occurring in a well-vaccinated animal), or 2) the ELISA test was negative yet parvovirus is still suspected, please consider sending us a sample. For further information, contact the virology lab at (865) 974-5643. This testing will be provided at no charge if timely results are not needed to minimize our costs, samples are stored, and processed in batches; thus results will not be available in the usual 2-3 business day period.

 

 

Posted: 09-03-08 Viewed: 1707 times