UPDATE ON FELV/FIV AND

FELINE HEARTWORM DISEASE

Dr. Kari Mundschenk

Director, American Association of Feline Practitioners

Our goal at Just For Cats Veterinary Hospital is to constantly remain apprised of changes/recent research as it relates to feline medicine.  Recently, our doctors, Dr. Peter Mundschenk and Dr. Kari Mundschenk attended the spring meeting of the American Association of Feline Practitioners in Palm Springs, California.  The meeting was held the first weekend of February, 2008, and the specific focus of the meeting was diagnostics, more specifically, what does a positive test mean if there are no clinical signs of disease?  Many diseases were discussed, and in this talk, we will focus on two in particular which have the most clinical relevance to most patients in our area.

Our doctors and staff try to bring back to the practice the latest information in order to help you and your cats.  With that said, we will be discussing Feline Leukemia and Feline Immunodeficiency Viruses and Feline Heartworm Associated Respiratory Disease.  Our talk will focus on the highlights as related to the pet kitty.

FELV and FIV are associated with the illness of more cats than any other group of infectious diseases.  In the United States, seroprevalence is less than 2% of healthy cats and 6%-33% of high risk cats and cats that are tested during illness.  Risk factors for seropositivity include male sex, adulthood, and outdoor access, whereas indoor lifestyle and sterilization are associated with reduced infection rates.  This protection is likely due to the reduced risk of encountering and fighting with infected cats, events which are risk factors for transmission.  Of the total number of cats in the United States, 4-8 million are infected with one of the viruses.  Unfortunately a failure to follow proper protocols for testing results in many undiagnosed kitties which expose a higher risk to other cats.

Of a major concern to those of us in feline medicine is the fact that many people do not understand that testing for the viruses indicates the presence of the agent, NOT the presence of disease.  In a recent prevalence study conducted in 2004, FIV cat survival rates were similar to negative cats with 94% and 80% around at 3 and 6 years, respectively.  FELV numbers were less due to the fact that younger cats are more often affected and the study showed 47% and 29% around at 3 and 6 years.  There used to be some thought that there is an age resistance to FELV (older cats can't catch) but recent data is showing that to not be true.

Both FIV and FELV infected cats live many years with proper care and, in fact, may die at older age from causes completely unrelated to their retrovirus infections.  An FIV infection has little impact on a cat population and does not reduce the number of cats in a household.  Thus, a decision for treatment or for euthanasia should NEVER be based solely on the presence of a retroviral infection.

FELV is primarily spread from infected queens to their kittens, but other forms of horizontal transmission among cats that live together or that fight are also possible.  Cats typically acquire FELV via the oronasal route by mutual grooming, but also through bites.  Veremic cats shed infectious virus in ALL body fluids.  In the past, it was believed that approximately 1/3 of cats would become persistently infected, 1/3 would become latently infected and 1/3 would clear the infection.  New reseaarch suggests that most cats remain infected for life following exposure, but may revert to an aviremic state (regressive infection) in which there is no serological evidence of infection, but FELV provirus can be detected by PCR.

Cats are typically infected with FIV through biting, but mucosal infection and vertical transmission from queens to kittens is possible (but rare).  Transmission within households of cats without evidence of fighting has also been reported.  Plasma-and cell-associated viremia followed by production of circulating antibodies occurs during the first 2 months of infection.  Similar to other lentiviral infections, FIV infection is considered to be life long, with recovery from infection being extremely rare.

So when do we recommend testing?  In kittens, just because an infected queen tests positive for FELV, it does not mean that the kittens will test positive.  If testing of kittens reveals a positive result, it is recommended to retest 8 weeks later (at time of ovh/neuter).  In contract, queen to kittent transmission is very rare in FIV.  If the kittens test positive, it is usually due to the presence of maternal antibodies.  These kittens are usually not infected and retesting 12-16 weeks later is recommended.  The important thing to remember is testing kittens for FIV tells you they are negative.

There are multiple testing mistakes to avoid:

þ It is preferable to use non-hemolyzed serum/plasma over whole blood.

þ Do NOT pool blood (decreases sensitivity due to dilution).

þ Do NOT rely on "representative" cats:  queens are not representative of kittens, prevalence is low for meaningful results, infections within litters are frequently sporadic

þ Do NOT rely on a single test; seroconversion may happen over weeks to months, cats may become infected over life.

General testing guidelines:

þ All cats should be tested (@ acquisition and 60 days later)

þ Sick cats tested regardless of previous test

þ 60+ days post event (i.e. fight wound)

þ Prior to vaccination

þ Prior to blood/tissue donation, including real time PCR

þ Annually retesting for cats at continued high risk

þ Optional for single housed cats

þ Required for group housed cats (isolation and retest ideal)

þ Resident cats in foster homes

þ Prior to adoption is ideal; if not possible, recommend testing @ new vet

þ Retest annually for group-housed cats kept in long term care

þ T-N-R cats vary on situation and no clear consensus is out yet;
at this time, testing is recommended.

In 2007, a study released by the American Association of Feline Practitioners and the American Heartworm Society brought heartworm disease into focus as it relates to the cat.  It has always been thought that heartworm disease in cats does not exist.  This has been found to be inaccurate.  Instead, heartworm disease, in the cat, is not the same as the dog.  The cat is not a natural host for the heartowrm so very few heartworms make it to adulthood.

The prevalence of heartworm disease in cats can be correlated with the dog population (both domestic and wild), the feeding preference of the vectors (mosquitoes), and climate change (wet vs. dry season).  A retrospective study showed that indoor only cats made up 27% of naturally infected patients and 8-19% of antibody+ cats.

In the kitty, there are two distinct stages of disease:  infection of the arteriole (commonly misdiagnosed as asthma) and worm death (commonly presents as sudden death).  Signs of disease commonly seen with heartworm disease include anorexia, blindness, coughing, diarrhea, difficult breathing, collapse/convulsions, lethargy, vomiting, weight loss and sudden death.

The life cycle of the heartworm is shown on the accompanying slide.

Diagnosis of heartworm disease in kitties can be very frustrating.  Many times, just having the index of suspicion is the most important factor.  Current tests on the market require the presence of adult female worms, and given the low worm burdens, single-sex infections and the transient nature of feline microfilaremia, testing can be frustrating.  Testing for BOTH antigen and antibody is necessary due to the variation in when the tests will pick up infection.

As stated earlier, true heartworm disease caused by adult worms in the pulmonary arteries is rare.  Most of these kitties present with an acute cardiac crisis and/or death.  Research has shown that the more common presentation of feline heartworm disease is related to respiratory disease.  Radiographs can assist with diagnosis but findings can also match true asthma, neoplasia and other infiltrative or allergic diseases.  Lung damage due to heartworm disease may never reverse and kitties may have long-term effects of the disease.  Treatment is palliative at best and is aimed at controlling clinical signs.

An excellent summation of heartworm disease in cats would be an ounce of prevention is worth a pound of cure.  In areas of high HW prevalence in dogs (as in Northern California/foothills), approximately 3-15% of cats are found to harbor adult heartworms.  Many more can be expected to suffer from HARD (heartworm associated respiratory disease), which is particularly hard to diagnose.  This vastly exceeds the national rate of infection with FELV or FIV (each affecting approximately 2-3% of cats in the United States).  As is the case for FELV and FIV, there are few effective treatment options once cats become infected with heartworms.  However, unlike FELV and FIV, preventive measures for heartworms approach 100% (not to mention the benefit of other parasite control).  We recommend year-round prevention in ALL cats for heartworms.