FIV and FeLV Flashcards
How do cats get infected with FeLV
Vertically from queens to kittens
Horizontally through living or fighting with each other
Progressively infected cats shed infectious virus in body fluids, including saliva, nasal secretions, milk, urine and faeces.
Typically acquired through oro-nasal route
Outline the pathogenesis of FeLV
After virus exposure via the oronasal route, FeLV can be found first in the local lymphoid tissues;
it then spreads via monocytes and lymphocytes (primary viremia) into the periphery.
during this primary viremia, the virus can infect the bone marrow.
After bone marrow infection, a secondary viremia can occur, with FeLV-containing leukocytes and platelets
appearing in the blood, resulting in virus being detectable by immunofluorescent antibody (IFA) test.
What are the possible outcomes of FeLV infection?
Abortive infection
Regressive infection
Progressive infection
What is progressive FeLV infection?
FeLV infection is not contained during the early stage, and extensive virus replication occurs first in the local
lymphoid tissues, then in the bone marrow, and subsequently in mucosal and glandular epithelial tissues
associated with excretion of infectious virus, mainly in saliva but also in other secretions. Progressive infection is characterized by insufficient FeLV-specific
immunity and usually neutralizing antibodies are not detectable. Cats with progressive infection have a shorter survival time than cats with regressive FeLV infection and typically succumb to FeLV-associated diseases within several years after infection
What is regressive FeLV infection?
immune response that contains, but does not eliminate, virus replication.
Low risk of developing FeLV associated disease
Viral shedding does not occur after the first antigenemic phase is over. However, FeLV proviral dNA can be detected in the blood by some PCR assays
FeLV is incorporated into the genome, cat persistently shows high level of virus neutralising AB
Not actively infected but can transmit FeLV in blood transfusions and cause disease in recipient cat
Reactivation can occur in immunosuppressed cats and then go on to develop FeLV associated disease
Regressive infection itself can be associated with FeLV associated disease e.g. lymphoma or BM suppression
What is abortive FeLV infection?
characterized by negative test results for culturable virus, antigen, viral RNA and proviral dNA.
The only indication of FeLV infection is the presence
of antibodies.
How is FIV transmitted
Mostly through bite wounds with FIV infected saliva and white blood cells
Vertical transmission uncommon
Sexual transmission uncommon
Outline the initial phase of FIV infection
Experimental studies have shown transient fever, lymphadenopathy and lymphopenia, but this has not been reported in natural infection, perhaps because the early signs might not be noticed by cat owners. During this acute stage, FIV is detected in high concentrations in the blood by culture and PCR. Within
the first few weeks of infection, both Cd4+ (helper) and Cd8+ (cytotoxic-suppressor) T lymphocyte concentrations decline
What occurs after the inital FIV infection stage?
an immune response characterized by the production of FIV antibodies, suppression of circulating virus leading to a decreasing viral load, and an increase in Cd8+ T lymphocytes to higher than pre-infection levels.
This results in an inversion of the Cd4:Cd8 ratio that can persist for the rest of the cat’s life.
Over time, both Cd4+ and Cd8+ lymphocyte numbers continue to gradually decline
What is the longest part of an FIV infection?
After initial infection, cats enter a long asymptomatic stage that can last for many years
During this stage, progressive dysfunction of the immune system can occur. Thus, FIV-infected cats are
predisposed to chronic and recurrent infections. Neoplasia is about five times more common than in uninfected cats
Cell-mediated immunity is more profoundly affected than humoral immunity
Hyperglobulinemia, characteristic of nonspecific stimulation of humoral immunity, can also occur in cats with FIV infection.
Survival time for FIV-infected cats is highly variable among individuals, but can be similar to that of non-FIV-infected cats
how useful are POC tests for FIV and FeLV
Falsepositive results might, among other things,
arise from improperly conducted tests or test failure. Negative test results are generally reliable when highly sensitive PoC tests are used, especially in apparently healthy cats with a low-risk lifestyle.
The exception would be when the cat is in the early phase of infection before FeLV antigenemia (<30 days) or FIV antibodies (<60 days) have developed.
False positives are possible and cats should ideally have their tests confirmed prior to diagnosis, especially in low risk healthy patients
How is FeLV diagnosed
Looking for p27 antigen
Mostly from POC ELISA
If you get a +ve, ideally re-check either with a different brand POC check or send to the lab, especially in a well indoor cat
Should be +ve within 30 days of exposure
How is a regressive infection diagnosed
Regressive infections are characterized by low levels of antigen and proviral DNA. At times, concentrations of one or the other can drop below the level of detection of some tests, leading to discordant results that may change over time.
Quantitative PCR assays for proviral DNA are becoming commercially available in more countries and they provide additional information to classify a cat’s status
Outline IFA testing for FeLV
IFA tests for blood or bone marrow smears are available from some commercial laboratories for the diagnosis of FeLV infection. These tests detect secondary viremia once bone marrow infection is established. Before bone marrow infection is established, cats will test negative using IFA. Most cats with regressive infections and those that resist bone marrow infection will also test negative. The subjective
nature of IFA interpretation and differences in performance among laboratories can lead to both false-positive and false-negative results. False-negative results may also be observed in cats with leukopenia and regressive infections.
How is FIV diagnosed?
detection of FIV-specific antibodies using PoC tests performed on whole blood, serum or plasma. Infected cats usually develop high concentrations of FIV-specific antibodies, and FIV produces a persistent
infection from which cats do not recover.
Thus, detection of antibodies is generally
indicative of FIV infection
Normally detected through POC ELISAs
Most cats produce ABs within 60 days of infection
Can confirm with western blot which is considered the gold standard for detecting ABs, although it is possible some POC devices are better
