First, let’s define panleukopenia. Panleukopenia describes a state in which the body experiences a decrease in the number of white blood cells, that then subsequently endangers the body to become more susceptible to infections.
Feline panleukopenia virus refers to a feline parvovirus infection. One of the symptoms that feline parvovirus causes is panleukopenia, which can enable other secondary infections.
Why is it called feline panleukopenia instead of feline parvovirus? The disease was discovered in the 1920’s. They thought it was caused by a virus, but they did not know the exact causative agent.
Nowadays, veterinary scientists are making a concerted effort to refer to feline panleukopenia virus as feline parvovirus (FPV). The renaming is significant and important for several reasons, one of which is that sometimes feline panleukopenia is referred to as feline distemper.
Referring to FPV as feline distemper sets everyone up for confusion because canine distemper refers to a virus that belongs to the genus Morbillivirus within the Paramyxoviridae family. At this time, domestic cats cannot contract canine distemper.
Canine parvovirus-2 (CPV-2) and FPV both belong to the genus Protoparvovirus within the family Parvoviridae.
May officially renaming feline panleukopenia virus as feline parvovirus cause confusion with canine parvovirus? Possibly. However, there are several additional good reasons to do so.
FPV and CPV-2 are distinct from one another. At this time, dogs cannot contract FPV. It has been demonstrated that cats can contract strains of CPV-2 such as CPV-2a, 2b and 2c. However, this occurrence is rare in Western Europe and North America. Of course, if your companion dog is diagnosed with CPV-2, it is best to keep him away from all household animals.
Many viruses can live outside the body, but usually only for a short period of time and can be eliminated with disinfectants. These parvoviruses are different from other viruses. They can live in many environments (cold, room temperature, etc.) for a year or more, can be transported long distances via shoes and clothing, and are more difficult to inactivate.
Once infected, a dog or cat sheds CPV-2 or FPV, respectively, through all secretions, particularly feces. Food bowls, water, hands, clothing, kennels…basically any surface can be a source of infection for both viruses.
Mechanism of Action
FPV and CPV-2 attack bone marrow, lymph nodes, and cells that line the small intestine. This results in shortages of all types of white blood cells and red blood cells.
FPV and CPV-2 can cause a drop in white blood cells, vomiting, bloody diarrhea, high fever, lethargy, loss of appetite, dehydration, and death.
Predominantly, cats shed FPV for approximately 1-2 days and dogs can shed CPV-2 for up to 14 days.
CPV-2 emerged in the 1970’s. It is hypothesized that CPV-2 is probably the result of a couple of genetic mutations of FPV that allowed it to expand its host range to dogs.
Nowadays, evidence of recombination between FPV and CPV-2 variants exists.
So, keeping the name “FPV” helps remind us there is always a possibility for a new breakthrough parvovirus that could affect cats, dogs, and many other animals.
Why haven’t any new and novel parvovirus outbreaks occurred due to recombination? More than likely this is due to effective vaccination against FPV and CPV-2.
FPV Vaccine Protocol
Dr. Dodds does recommend vaccinating indoor and indoor/outdoor cats against FPV. Her protocol is to give the combination vaccination of FPV, calicivirus, feline viral rhinotracheitis (feline herpesvirus-1) between 8-9 weeks of age and boosted at 12-13 weeks of age. As well, she specifies an additional booster of this combination at 1 year of age. This vaccine is often written as FVRCP.
The FPV vaccine provides cross-protection against CPV-2 and produces sterilizing immunity. Sterilizing immunity typically lasts between 5-7 years. Companion cats that were actually immunized and thus have sterilizing immunity not only prevents clinical disease but also prevents them from being infected with FPV.
The American Animal Hospital Association’s (AAHA) feline vaccination guidelines committee recommends vaccinating against FPV every 3 years after the initial kitten vaccinations. The committee appears to waver – but is not definitive – on whether indoor-outdoor cats should receive the booster because they would have boosted their natural immunity. The reason being is FPV is basically everywhere.
Dr. Dodds understands their position. However, since the duration of sterilizing immunity is clearly longer than 3 years, she prefers serum antibody titer testing due to potential vaccinal adverse events performed every three years or more often until geriatric age, to determine if a vaccine is necessary.
Vaccinating an immunized companion cat against FPV would cause only a temporary increase in antibody titer, and hypersensitivity reactions to vaccine components may develop. Therefore, the animal does not need to be revaccinated and should not be revaccinated since the vaccine could cause an adverse reaction.
It is accepted by many veterinarians that cats can develop injection site sarcomas. AAHA has provided guidelines on how to minimize these reactions.
2020 AAHA/AAFP Feline Vaccination Guidelines, American Animal Hospital Association, https://www.aaha.org/aaha-guidelines/2020-aahaaafp-feline-vaccination-guidelines/feline-vaccination-home/. Accessed 14 Jan. 2024.
Dodds, Jean. Canine Parvovirus Outbreak in Michigan, Hemopet, 30 Sept. 2022, https://hemopet.org/canine-parvovirus-outbreak-in-michigan/.
Dodds, Jean. Dodds Reviews the 2020 AAHA/AAFP Feline Vaccination Guidelines, Hemopet, 21 Sept. 2020, https://hemopet.org/dodds-reviews-the-2020-aaha-aafp-feline-vaccination-guidelines/.
Dodds, Jean. Parvovirus Variants and Vaccines, Hemopet, 26 Feb. 2021, https://hemopet.org/parvovirus-variants-and-vaccines/.
Sykes, Jane E. “Feline Panleukopenia Virus Infection and Other Viral Enteritides.” Canine and Feline Infectious Diseases (2014): 187–194. doi:10.1016/B978-1-4377-0795-3.00019-3, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7151839/.