Feline Immunodeficiency Virus

Chapter 9 Feline Immunodeficiency Virus

Robert G. Sherding

ETIOLOGY

• Feline immunodeficiency virus (FIV) is a member of the lentivirus subfamily of retroviruses. It is an RNA virus with outer envelope and nucleocapsid. FIV originally was isolated in 1986 from a cattery in northern California; however, retrospective assays of stored cat sera have shown that FIV has been widely distributed worldwide since at least the 1960s.
• FIV causes a lifelong infection and gradually progressive decline in immune function that leads to an acquired immunodeficiency syndrome. Manifestations include chronic weight loss, opportunistic infections, chronic inflammatory conditions, and increased risk for malignant neoplasia.
• At least 5 FIV subtypes (clades A through E) have been identified based on genetic differences. Subtypes vary in regional distribution and influence cell tropism and pathogenicity. Subtype A predominates in the Western United States, and subtype B is seen most often in the Eastern United States.
• Numerous wild feline species are susceptible to various subtypes of FIV, including lions, tigers, jaguars, snow leopards, panthers, and bobcats.

Epidemiology

Prevalence

The serologic prevalence of FIV infection has been surveyed in many countries, regions, and cat populations. FIV has been found worldwide.

• The prevalence in indoor pet cats in single-cat households is less than 1%.
• The prevalence in well-controlled purebred catteries is less than 2%.
• The prevalence in free-roaming stray and feral cats in the United States is 2% to 4%.
• The prevalence in a 1991 IDEXX survey of 27,976 sick and high-risk cats in the United States presenting to veterinarians was 7.4%. This included sick cats that had a prevalence of 11.6% and asymptomatic high-risk cats (defined as outdoor pet cats, cats exposed to outdoor cats, or cats in large multicat households) that had a prevalence of 4%.
• The prevalence in some countries in areas with a high density of free-roaming cats, such as Japan and Italy, may reach 25% to 30%.

Age and Gender Distribution

• FIV affects cats of all ages (reported range is 2 months to 18 years); however, the incidence increases with age, and FIV is most prevalent in cats 6 years of age and older.

Key Point

Because of a prolonged asymptomatic latent period, most FIV-infected cats with clinical signs are older than 6 years of age.

• Adult male cats outnumber females 3 or 4 to 1 (see “Transmission”).

High-Risk Factors

• Adult, male cats living outdoors or exposed to free-roaming outdoor cats.
• Sexually intact males are at increased risk for fighting behavior that can lead to bite-wound transmission.
• Cats in high-density habitats are at increased risk for territorial fighting that can lead to bite-wound transmission.
• Cats living in large multicat households (>6 cats) that frequently introduce new cats.

Public Health Risks

• FIV is a feline host-specific virus, and there is no evidence that it causes human infection. People who have had intimate contact with infected cats or direct exposure to FIV through cat bites or lab accidents do not develop antibodies, illness, or any other evidence of infection.
• Because of their immunosuppressed state, FIV-infected cats may harbor a variety of other opportunistic pathogens that can infect humans who are immunocompromised.

Transmission

• FIV is shed in saliva and transmitted primarily through direct bite-wound inoculation during territorial fights (hence the higher prevalence in males). Experimentally, a single-tooth puncture wound from a FIV-infected cat is an efficient method of transmitting FIV.

Key Point

Direct inoculation of saliva through biting is the principal mode of FIV transmission. The highest risk for FIV is associated with territorial fighting and biting behavior in sexually intact, adult male cats living outdoors.

• Transmission through intimate contact during cohabitation is unlikely but not impossible. In a study that confined FIV-positive and FIV-negative cats together in the same cages for 2 years, only 1 of 20 negative sentinel cats became infected. Contact transmission has been suspected in rare cases in catteries, but the mode of transmission in most of these cases is undetermined. Fomite transmission is highly unlikely.
• Transmucosal transmission of FIV can occur experimentally through direct atraumatic contact of FIV with oral, vaginal, or rectal mucosa and through artificial insemination; however, these routes are unlikely to be important under natural conditions.
• Experimentally, acute and chronically infected queens may transmit FIV vertically to their kittens in utero or during passage through the birth canal (congenital infection) or postnatally through ingestion of infected milk (lactogenic infection). However, transmission from mother to offspring in these ways is infrequent under natural conditions. More commonly, infected queens pass colostral FIV antibodies to their nursing kittens, causing a false-positive FIV antibody test (e.g., ELISA or Western blot) for up to 6 months (see “Diagnosis”).
• Transmission of FIV can readily occur through intravenous transfusion of contaminated blood.

Pathogenesis

• FIV has a primary tropism for lymphocytes but also infects macrophages, salivary glands, and the central nervous system.
• FIV primarily infects and gradually destroys subpopulations of T lymphocytes. This cytopathic effect causes a progressive loss of CD4+ lymphocytes, inversion of the CD4/CD8 ratio, and eventual loss of CD8+ lymphocytes in the late stages of infection. Cell-mediated immunity is impaired to a greater extent than antibody-mediated immunity.
• In addition, impaired production and dysregulation of various cytokines plays a role in the pathogenesis of disease.
• After a prolonged, clinically silent latent period that can extend for years, the progressive loss of T lymphocytes results in an immunodeficiency syndrome characterized by chronic and recurrent infections. FIV infection is lifelong and eventually fatal. The natural incubation period for FIV averages 5 years, corresponding to this lengthy latency.
• FIV has various mechanisms for evading the host immune response so that it can persist and replicate for life.

CLINICAL SIGNS

The clinical disease caused by FIV is influenced by the age and health of the cat, the strain of the virus, the dose and route of exposure, and the interaction with concurrent infectious agents.

Key Point

The most common clinical signs associated with FIV infection are stomatitis-gingivitis (50% of cases), recurrent rhinitis-conjunctivitis, progressive weight loss (“wasting”), diarrhea, and fever.

Acute Primary Infection

This initial phase begins within 4 to 6 weeks after exposure associated with initial viremia. The effects are mild and transient, and usually go unnoticed.

• Transient fever
• Neutropenia and lymphopenia
• Generalized lymphadenopathy characterized by follicular hyperplasia and plasmacytic infiltration
• Infrequent complications: sepsis, cellulitis, pustular facial dermatitis, anemia, diarrhea, and stomatitis

Asymptomatic Latent Infection

This is a prolonged latency period following seroconversion that usually persists several years before signs of immunodeficiency occur. Persistent lymphadenomegaly sometimes is seen during this stage.

Key Point

It is typical for FIV-infected cats to remain clinically healthy for several years before developing clinical signs of disease.

Chronic Disease Syndromes

Advanced FIV infection causes an acquired immunodeficiency syndrome and predisposes the cat to chronic or recurrent opportunistic infections and chronic inflammatory conditions that wax and wane and progressively worsen over months or years. This may involve any combination of the following manifestations.

General Manifestations

• Progressive weight loss and debilitation (“chronic wasting”)
• Chronic recurrent bacterial infections that may resolve partially with antibiotics but recur
• Recurrent fevers of unknown origin
• Generalized lymphadenopathy
• Polyclonal hypergammaglobulinemia
• Persistent or recurrent anemia, leukopenia (neutropenia, lymphopenia), or thrombocytopenia

Chronic or Recurrent Bacterial Infections

• Oral cavity (most common)—Stomatitis, gingivitis, periodontitis (suppurative or plasmacytic)
• Respiratory—Purulent rhinitis and conjunctivitis; pneumonia; pyothorax
• Intestinal—Acute or chronic diarrhea due to enterocolitis that can be ulcerative, necrotizing, or pyogranulomatous
• Cutaneous—Pustular dermatitis, abscesses, purulent otitis

Related posts:

  1. Feline Infectious Respiratory Disease
  2. Mammary Gland Neoplasia
  3. Keratinization Defects
  4. Canine and Feline Demodicosis

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Aug 27, 2016 | Posted by in SMALL ANIMAL | Comments Off on Feline Immunodeficiency Virus

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