Monday, October 27, 2014

Disease Monograph: Feline Panleukopenia Virus


This little kitten was brought into our office because he had a poor appetite and a fever. Two days later, he had a severe drop in white blood cell numbers, and we suspected distemper. The next day, he started vomiting and having diarrhea and his parvo test was positive. We placed him on our isolation room on IV fluids and total parenteral nutrition (TPN) - since he wasn't eating and was severely dehydrated, we gave him all his nutrients through IV fluids - Plasmalyte (electrolytes), Procalamine (amino acids) and Intralipids (fats).

Distemper, Panleukopenia, Parvo, Infectious enteritis...whatever you call it, it's not good for cats.
For the purposes of this article, we will refer to this disease as Feline Panleukopenia Virus or FPV.

FPV is a disease that is highly contagious and almost always life-threatening. The virus that causes this disease is from the family Parvoviridae, which is the reason that one of its names is Feline Parvo. Others refer to the disease by some of its symptoms: Panleukopenia (a severe decrease in all types of white blood cells), Infectious enteritis (an inflammation of the intestinal tract that can be passed between cats), or Distemper (symptoms of Canine Distemper - a disease caused by an entirely different virus - are similar to many signs of FPV: fever, vomiting, diarrhea, seizures). The virus is a single strand of DNA inside a virus capsule that is extremely long-lived in the environment. It can survive freezing temperatures, is unaffected by alcohol, iodine, and general disinfectants, and is considered to be ubiquitous - or found everywhere in the environment. Just about the only thing that will destroy FPV is a 10 minute soak in a bleach solution.
Differences in structure in canine vs. feline Parvovirus

In the wild, the bobcat, the raccoon, and members of the Mustelid family (such as mink, skunk and otter) can carry the disease. Among other mammals, some species of monkey are susceptible to FPV. Despite the similar names and symptoms, FPV is not contagious to dogs, nor can cats contract Canine Distemper Virus or Canine Parvo Virus*. In fact, it is suspected by some scientists that Canine Parvo Virus is actually a sub-species of Feline Parvovirus - a mutation of the original, if you will - since some apparently healthy cats shed Canine Parvo Virus in their stool.


*Correction: Canine Parvo virus subtypes have been isolated from both domestic and wild felids, but does not appear to result in the same level of virulence as FPV (the cats are not nearly as sick). However, there is one published case from March 2014 that reports of a cat that was infected with CPV2c that was critically ill with symptoms mimicking FPV. The feline vaccine appears to provide adequate protection from Canine Parvo Virus, but most agree that more research should be done before this presumption is relied upon.

Transmission

Any unvaccinated cat is at risk for contracting FPV, but those at highest risk are cats that are immunocompromised, such as kittens age 2-6 months, pregnant females, cats with immune-suppressing diseases such as FIV and FeLV, and cats who are being treated with immune-suppressing drugs.

The virus is shed from the body in the stool, vomit, urine, saliva and mucus, and a cat may remain contagious and shedding the virus for at least six weeks following infection. Since the virus is so long-lived, it can be transmitted by handling contaminated items (called "fomites") such as food bowls, towels, and litterboxes, or shoes, clothing and hands that have come into contact with the virus.

Additionally, the virus can be passed from mother to developing kittens, and can be spread by fleas.

Generally, the virus enters the cat through the mouth and then affects the lymph nodes. It takes about 2-7 days for the virus to make its way to the bone marrow and the intestinal tract. In the bone marrow, the virus interferes with cell production, and in the intestinal tract, the virus causes ulceration of the lining of the gut that is in charge of absorbing nutrients and prevents damage to the intestinal wall from digestive acids and bacterial growth. Once the intestinal lining is damaged, the cat is at risk for infection from normal bacterial flora, perforation of the bowel, and may suffer from dehydration, vomiting, diarrhea, and malnutrition, eventually leading to septicemia (severe bacterial infection in the bloodstream) and shock.

Mortality in kittens is 90%, though if the kitten survives 5 days of infection, the chances or survival and recovery begin to improve. If a cat is able to recover from FPV, they maintain lifetime immunity. If a pregnant female is exposed to the virus in early to mid-pregnancy, she will abort the kittens. If exposed during the last 2-3 weeks of pregnancy, the kittens will develop a condition called cerebellar hypoplasia.


Symptoms


FPV affects the rapidly dividing cells in the body, especially the bone marrow, which produces red and white blood cells, and the lining of the gastrointestinal tract (stomach and intestines). Since a lack of white blood cells occurs (a panleukopenia), the cat develops risk for other bacterial and viral infections to occur. A decrease in red blood cells may occur (anemia) and platelet numbers may also decrease (thrombocytopenia). Severe anemia results in a lack of oxygen to the cells of the body, and a lack of platelets can result in clotting problems. If white blood cells, red blood cells and platelets are all decreased, it is called a "pancytopenia" - literally, a lack of all cells in the blood.

  • Vomiting
  • Diarrhea, especially bloody diarrhea
  • Fever
  • Weight loss
  • Depression
  • Anorexia, loss of appetite
  • Hiding
  • Rough hair coat
  • Anemia
  • Weakness
  • Neurologic signs
  • Shock
  • Abdominal discomfort, bloating, gas
  • Elevated third eyelids


Diagnosis


In-hospital Parvo test
Any time that we see a kitten with a fever, vomiting, diarrhea and poor appetite, we will recommend a complete blood count. If the kitten has a low white blood cell count, we will likely recommend a special Parvo test. This test is marketed for dogs for the detection of canine parvo virus, but the feline parvo virus is similar enough that the test is accurate in cats, as well - though vaccination within 5-12 days of the test can occasionally result in a false positive. To run this test, a small amount of fresh stool is collected from the patient.

Additional tests, such as PCR testing and antibody level analysis can also confirm the diagnosis of FPV.

Unfortunately, many kittens will show mild signs of illness, such as fever and depression, before the white blood cells become affected, which can delay the diagnosis of FPV if conservative treatment is chosen over full diagnostic evaluation. If a kitten dies suddenly, a necropsy (the term for an autopsy, when discussing animals), may be recommended to collect samples to test for the virus - especially if there are other kittens in the home.

Because all the symptoms of FPV do not necessarily appear at once, it may be easy to confuse FPV with other conditions, such as poisoning or the ingestion of a foreign body (kittens love to eat toys, strings, hair ties, rubber bands, ear plugs...), Salmonella, Feline Leukemia (FeLV), feline immunodeficiency virus (FIV), feline infectious peritonitis (FIP), and pancreatitis.

Additional testing, such as urinalysis or blood chemistries may be performed to help rule out other diseases and conditions, or to assess the severity of the disease. X-rays may be recommended if blood tests are inconclusive or the cat does not have a known history - such as a stray or recently adopted cat.

Treatment


There is no definitive cure for this disease, no medication that kills the virus that causes this disease. Cats affected with FPV must have immediate and intensive supportive care to help nourish and protect their bodies while the struggling immune system fights the virus. Since the lining of the intestine is being attacked, and nutrient absorption is decreased, most medications, if not all, will be given by injection - either into the vein (intravenously) or under the skin (subcutaneously). IV fluids will be necessary to protect the cat from severe dehydration due to poor nutrient absorption, lack of food and water intake and fluid loss from severe vomiting and diarrhea - TPN or total parenteral nutrition (IV fats and amino acids) will be administered this way, too, since affected cats are likely to vomit any food or water they eat or drink. Anti-vomiting medications will also likely be given.

Antibiotics may be given to aid the weakened immune system in preventing "opportunistic infections"  - exposure to bacteria that would not affect a normal, healthy cat, but that could be life-threatening to a cat with few white blood cells. In the case of FPV - the biggest concern is exposure to the normal bacteria living in the intestinal tract. As the protective lining of the gut is attacked by the virus, normally "friendly" bacteria may attack the unprotected cells and cause ulceration and eventually perforation of the intestinal wall, allowing bacteria to leak into the abdomen. In severe cases, the cat is given medication to help protect the intestinal lining from damage. Cats with severe depletion of both red and white blood cells (pancytopenia), or severely low blood proteins may require one or more blood or plasma transfusions.

Some suspect that treatment with immune-stimulation medications such as Interferon, or transfusion with antibody-containing serum may aid in fighting infection, but this therapy is not yet confirmed or considered to be routine.

An infected cat should be strictly isolated from other cats to prevent the spread of this extremely contagious disease.

Almost all recognized cases of FPV require hospitalization.

Prevention

If a cat in your home has been diagnosed with FPV, closely observe other cats in the home for signs of illness. You can use a bleach solution to clean any potentially contaminated toys, food dishes, beds, and litterboxes, but the safest way to ensure the virus has been eliminated from your home is to replace all possibly infected belongings with new ones. If your cat recovers from FPV infection, he or she will have lifelong immunity, but other cats in the home, or visiting cats (or visiting people) may come into virus contamination in the environment. If you have had a cat that has been infected with FPV in your home, any new cats should not enter the home for at least two weeks and should have a Distemper vaccination 1-2 weeks prior to entering the home.

To clean contaminated areas, use a bleach solution of 1:20 (1 part bleach in 20 parts water) and allow the solution to remain in contact with the contaminated item for 30 minutes before rinsing. Any dirt, feces, vomit or other biological fluid should be cleaned up before applying bleach. Fabric items such as carpets, rugs and cat beds or other areas that cannot be bleached, such as wood flooring, should be steam cleaned at 240-270 degrees F.

The best way to prevent your cat from contracting FPV is to have your cat vaccinated routinely every 2-4 weeks from the age of 8 weeks through the age of 16 weeks.  Maternal antibodies conflict with the vaccine's ability to help the body form immune responses. Since it is uncertain exactly when maternal antibodies no longer protect kittens after they stop nursing, routine re-vaccination until the age at which their risk factors are minimized is key to provide protection. After the first annual vaccine, a cat's future vaccination schedule should be determined based on the cat's age, health status and lifestyle by having a conversation with your trusted veterinarian, or at a minimum every three years.

References

Michigan DNR article on Canine and Feline Distemper

Isolation and characterization of feline panleukopenia virus from a diarrheic monkey 

High prevalence of non-productive FeLV infection in necropsied cats and significant association with pathological findings

Panleukopenia-like syndrome of FeLV caused by co-infection with FeLV and feline panleukopenia virus

Detection of Feline Panleukopenia Virus using a commercial ELISA for Canine Parvovurus

Evidence for recombination between Feline Panleukopenia Virus and Canine Parvovirus Type 2

Immunisation against Panleucopenia: Early Development of Immunity

Structural Comparison of Different Antibodies Interacting with Parvovirus Capsids

 Macintire DK, Smith-Carr S, Jones R, Swango L. Treatment of dogs naturally infected with canine parvovirus with lyophilized canine IgG. Proceedings of the 17th Annual Conference of the American College of Veterinary Internal Medicine. June 10–13, 1999, abstract 118, 1999: 721. 

De Mari K, Maynard L, Eun HM, Lebreux B. Treatment of canine parvoviral enteritis with interferon-omega in a placebo-controlled field trial.Vet Rec2003;152:105–8

Genetic complexity and multiple infections with more Parvovirus species in naturally infected cats


Feline Host Range of Canine parvovirus: Recent Emergence of New Antigenic Types in Cats
Isolation of canine parvovirus from a cat manifesting clinical signs of feline panleukopenia.