Feline Panleukopenia Overview

Feline Panleukopenia

• Feline panleukopenia virus (FPV) is a highly contagious and resistant virus.
• The virus remains infectious for weeks or even months in contaminated environments.
• Diseased carnivores shed high titres of virus (up to 10⁹ TCID50 per gram of faeces).
• The virus quickly accumulates in affected shelters and catteries.
• Susceptible animals can become infected even after disinfection.
• Only vaccinated kittens and cats should enter affected environments.

Pathogenesis

• FPV causes a systemic infection.
• Transmission is faecal-oral.
• Initial replication occurs in oropharyngeal tissues.
• Cell-free viraemia distributes the virus to other tissues.
• Replication is restricted to dividing cells in the S-phase, primarily active tissues.
• Enteritis results from gut infection.
• Parvoviruses require cellular DNA polymerases to synthesize complementary DNA.
• Synthesis is the first step in replication and a prerequisite for transcription.

Pathogenesis (Continued)

• The hallmark of FPV replication is the shortening of intestinal villi, sometimes resulting in a complete loss of epithelial cells in the gut.
• The virus replicates in rapidly dividing cells in Lieberkühn's crypts. This impairs regeneration of the epithelium and results in specific lesions.
• Lesion severity correlates with epithelial turnover rate, and co-infection with enteric viruses (like feline coronavirus) can worsen disease.

Pathogenesis (Further)

• FPV infects lymphoid tissues to cause cellular depletion and functional immunosuppression.
• Lymphocytolysis and lymphocyte emigration into tissues can cause lymphopenia.
• Bone marrow is also affected. Virus replicates in early progenitor cells, significantly impacting myeloid cell populations.
• This deficiency in white blood cells is called panleukopenia.

Intrauterine Transmission

• Intrauterine transmission or perinatal FPV infection can affect central nervous system development.
• This can cause "Feline ataxia syndrome."
• This results from impaired cerebellum development due to Purkinje cell infection in kittens.

Immunity - Passive

• Antibodies play a critical role in the immune response to FPV, effectively protecting kittens from fatal infection.
• Maternal antibodies (MDA) are derived from the mother.
• The endotheliochorial placentation in cats restricts maternal-foetal antigen passage, allowing only IgG transfer in the last trimester of gestation (accounts for <10% of kitten's immunity).
• Adequate colostrum ingestion is essential for reaching protective neutralising antibody levels.

Immunity - Passive (Continued)

• Maximum antibody absorption occurs within the first 8 hours of life.
• The intestinal lining changes to no longer absorb antibodies after this initial period.
• Kitten serum antibody levels are generally about half that of the mother.
• These levels depend on the individual colostrum intake.
• Titres decrease during the first few weeks of life due to decay and dilution.

Immunity - Passive (Further)

• Maternal antibodies have a biological half-life of approximately 10 days in kittens.
• Antibody levels that fall below 40-80 (measured by haemagglutination inhibition) may not provide significant protection against infection but can interfere with active vaccination.

Immunity - Active

• Passively acquired immunity is eventually replaced by an active immune response.
• This active response can develop from either vaccination or natural infection.
• Acquired immunity is solid and long lasting.
• Vaccination can be achieved via inactivated or modified live virus (MLV) vaccines.
• FPV antiserum assists in passive immunisation for immunocompromised cats.
• Parvoviruses produce a range of immune responses, including reactions from T-helper CD4+ and possible also CD8+ cytotoxic T lymphocytes.

Diagnosis

• Post-mortem examination is essential.
• Histopathology of intestinal tract (specifically the jejunum and ileum) may reveal intestinal crypt necrosis, dilated crypts filled with mucus and sloughed necrotic cell debris.
• Neonatally infected kittens can present with cerebellar hypoplasia.
• Laboratory changes may include significantly reduced white blood cell counts (as low as 0.05-3 x 10⁹/l).
• Microscopically, profound neutropenia and lymphopenia can be present.
• Thrombocytopenia is sometimes observed.
• Serum biochemistry changes can be non-specific and include hypoalbuminaemia, hypochloraemia and hyponatraemia.
• Diagnostic imaging findings in FPV infected cats may include small intestinal mucosal layer thinning, muscular layer thickening, and mucosal hyperechogenicity.
• FPV antigen detection in faeces is typically conducted using ELISA or immunomigration-based point-of-care tests.
• PCR is more effective for confirming negative results.

Disease Management and Treatment

• Cats showing clinical signs of FPV should be isolated and treated supportively with barrier nursing to prevent fomite transmission.
• Addressing severe dehydration is crucial for disease progression.
• Electrolyte replacement (preferably intravenous) is paramount to prevent further health complications.
• Blood glucose should be monitored and supplemented if necessary.
• Vomiting treatment involves using antiemetics like maropitant or metoclopramide.
• Oral intake of water and food should be avoided if vomiting persists, but continued as long as possible.
• Highly digestible food is preferred.

Disease Management and Treatment (Continued)

• Administering broad-spectrum antibiotics targeting gram-negative and anaerobic bacteria is crucial for preventing and treating sepsis.
• Options include ampicillin, amoxicillin/clavulanic acid, fluoroquinolones, and/or cephalosporins (parenterally administered).
• Supportive care and good nursing are key aspects of comprehensive care.
• Vitamin supplements, particularly B vitamins, can help prevent thiamine deficiencies, which might occasionally accompany FPV.
• Consider intestinal parasite medication if indicated based on faecal analysis and appropriate anthelmintics.

Prognosis

• FPV causes a severe, sometimes potentially fatal, disease in cats.
• Even with intensive treatment, mortality ranges from 30-50%.
• Presence of antibodies related to FPV on admission is linked to enhanced survival prospects.
• Lethargy, lower body weight, and lower rectal temperatures at hospitalisation are all indicators of improved survival chances.
• Leukopenia developing after the third day of hospitalization signifies a poorer prognosis.

Vaccination

• MLV (modified live virus) and inactivated FPV vaccines are available for injection.
• Both vaccines offer strong disease protection.
• MLV vaccines often provide faster protection and greater efficacy at overcoming maternal antibodies.
• Inactivation vaccines can rapidly induce good antibody responses in naïve kittens.
• However, no vaccine brands demonstrate significant superiority.
• MLV vaccines should not be used in pregnant queens due to the possibility of placental virus passage to the fetus, potentially damaging the developing cerebellum.
• Kittens under four weeks should also not receive MLV vaccinations due to the still-developing cerebellum.
• FPV vaccine is generally deemed a core vaccination.
• Three doses of vaccine are commonly recommended, the first at 8-9 weeks, second at 3-4 weeks later, and the third at 3-4 weeks later (minimum of 16 weeks).

Vaccination (Continued)

• In high-risk situations where maternal antibodies are likely to be poor, additional earlier vaccinations (even as early as 4 weeks),using inactivated vaccines, are recommended.
• Reinforcements (3-4 week intervals) should continue until the kitten reaches 12 weeks of age.
• An additional vaccine dose (10-16 months of age) is often recommended to bolster vaccine-induced immunity in cats that did not respond adequately to the primary course.

Disease Control in Specific Situations

• In shelters, all cats over 4-6 weeks should be vaccinated, regardless of housing status.
• Recommendations for pregnant cats should consider individual cases but usually involve avoiding live FPV vaccination.
• Kittens should be vaccinated at 4 weeks or 6 weeks in cases of outbreaks.

Vaccination Considerations

• MLV vaccines are recommended due to faster action, increased efficacy and likelihood of conferred immunity.
• Concerns about virulence reversion in MLV has not been supported by documentation.
• Vaccination should be given with frequency of 3-4 weeks up until 16 weeks of age.
• Adult cats that show ill health or compromise at the time of initial vaccination should be given a second injection after at least two weeks.
• Cats with unknown vaccination status should not be housed together to avoid potential infection risk.

This quiz covers the critical aspects of Feline Panleukopenia Virus (FPV), including its contagious nature and pathogenesis. It explores transmission methods, effects on infected cells, and the importance of vaccination in controlling outbreaks. Test your knowledge on this significant feline disease.