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Feline Leukemia Virus: Allogenic PRP for Hematological Disorders

The Virus

The Feline Leukemia Virus (FeLV) is a retrovirus that affects cats, and has the ability to insert its genetic material into the infected cells, which technically allows it to take over the cell’s natural replication mechanisms and use them to make copies of itself. This particular “viral intelligence” is what makes it so much more difficult to treat than other virus infections; the FeLV belongs to a category of viruses similar to the Human Immunodeficiency Virus (HIV) and the Feline Immunodeficiency Virus (FIV), and it possesses some of the same characteristics, one of them being an especially difficult or impossible elimination of the virus, and its likely permanent persistence and infection inside the affected individual.

Transmission

The virus can be transmitted rather easily through bite wounds, mutual grooming, and mother-to-kitten during pregnancy or nursing. Since the virus is eliminated through saliva, feces, urine, nasal secretions and milk, transmission through close contact and sharing food dishes and litter boxes is rare, but possible.

Without a doubt, cats living on the streets or outdoors, and non-neutered cats are more prone to catch the virus because of the classic reproductive catfight. However, this does not mean that indoor cats are exempt, since the virus can be transmitted from their mother’s milk as kittens, and in many occasions there is no knowledge of a cat being infected until clinical signs appear (which can take from weeks to years), or the cat does show unspecific clinical signs that may lead to diagnose other infectious diseases, therefore missing the FeLV infection.

Clinical Signs

Symptomatology in FeLV infection can be a little tricky, since most of the early symptoms are not pathognomonic or specific. Weight loss, anorexia, hirsute coat, diarrhea, halitosis (bad breath), corneal ulcers, recurrent bladder, respiratory and skin infections, abortions, seizures are commonly reported by cat owners.

Other signs that can be detected in consult by the veterinarian are fever, enlarged lymph nodes, pale mucous membranes, abnormal neurological exam and stomatitis. The individual may be extremely susceptible to other viral, bacterial or parasitic infections. Between the most common secondary viral infections one can find the Feline Panleukopenia Virus (FPV) and the Feline Respiratory Complex caused by calicivirus. All of the previously mentioned signs are seen during the primary viremia stage, where the patient still stands a chance to eliminate the virus.

When the disease progresses to secondary viremia, the infection starts attacking the bone marrow, generating a number of hematological abnormalities, and the patient is categorically considered as infected for the rest of its life.  In this case scenario, the clinical signs above may still be present, but other complications will start to appear, such as immune deficiency, cancer development (frequently lymphoma and fibrosarcoma), and even death.

Diagnosis

The timing of the diagnosis is essential for the prognosis of the feline. If it is achieved during the primary viremia, there are much better treatment options than if diagnosed during secondary viremia.

In the process of ruling-out other infections, the routine blood panels must be ran, where significant alterations in blood count may be observed:

  • Anemia. Normochromic, regenerative or nonregenerative. Nonregenerative usually indicates bone marrow suppression.
  • Leukemia. Neoplastic proliferation of hematopietic cells.
  • Thrombocytopenia.
  • Macrothrombocytosis.
  • Neutropenia.

The integration of clinical signs and blood work leading to suspect of FeLV infection should lead to specific tests. FeLV is most frequently diagnosed through ELISA tests (enzyme-linked immunosorbet assay). There are different commercial brands of ELISA kits that can be performed in the veterinary clinic, and that offer incredibly quick results. ELISA has the benefit of detecting primary and secondary viremia, which is why it is the first diagnostic option when suspecting FeLV infection.

IFA (indirect immunofluorescent antibody assay) is another commonly used test, but this one has to be done in a diagnostic laboratory. The limitation of the IFA diagnosis—which can be an advantage or a disadvantage, depending on the case— is that it only detects secondary viremia. This explains why ELISA is almost always done first, and then IFA helps determine the staging of the infection. Positive individuals to IFA will be infected for life.

PCR and virus isolation are even more diagnostically relevant, but not as affordable and practical for the daily veterinary practice.

Once a cat has tested positive to FeLV, all the other cohabitant cats should be also tested.   

Prevention

FeLV can be prevented by following an adequate vaccination protocol of cats as kittens, and annual revaccination depending on the lifestyle of the adult cat in question.  Neutering both males and females is also important to prevent outdoor lifestyle and reproductive fighting.

If a cat in a shelter or household tests positive for FeLV, all the other cats should be tested and the positives separated from the healthy cats.

Treatment

Since FeLV is a virus that persists inside the cells of the bloodstream, there is no definitive cure. The treatment management is merely reduced to control the viremia as far as possible, and to prevent and manage the secondary pathologies that might derive from the viral infection.

  • Control of viremia and immunological status

Many virus-supressing drugs are currently under investigation to see if they have the same effect on feline patients than the one they have shown in human patients with HIV. A few examples of them are tenofovir, decitabine, gemcitabine, among others. However, the treatment that has shown better results in controlling viremia and reactivating the immunological system so far is the use of recombinant feline omega interferon. It is applied at 1MU/kg subcutaneously on Day 0 to 4, and then on Day 14, when a follow-up revision should be made, accompanied with blood work to assess if symptoms and blood alterations are normalized and if treatment can be suspended.

  • Prevention and management of secondary pathologies
  1. When treating lymphomas, the most commonly used drugs are combinations of vincristine, cyclophosphamide and prednisolone, and then switching to doxorubicin through different cycles. There are many different schedules for this drug protocol, which should be selected individually, according to the specific symptomatology and status of the patient under treatment.
  2. Secondary infections should be prevented by avoiding stress, separating sick and healthy cats, thorough hygiene and constant veterinary monitoring. Each complication should be attacked accordingly: bacterial infections, gingivitis, diarrhea, prevention of parasitic infestations, etc.

What PRP can do

One of the most common blood alterations in cats with FeLV infection is thrombocytopenia (low platelet counts) and macrothrombocytosis (abnormal, larger sized platelets). These two abnormalities happen because the FeLV virus infects the bone marrow, thereby the megakariocytes and platelets; this leads to platelet destruction, stressed hematopoietic stimulus, immature platelet release (hence, the macrothrombocytosis), and decreased platelet lifespan.

The consequences of this can go in two different ways—or both:

  1. The lack of platelets may lead to bleeding disorders, where small injuries, gastric ulcers, or even chronic gingivitis or stomatitis could result in serious blood loss.
  1. The low platelet levels, high rates of destruction, and platelet malfunctioning generate a hematopoietic stimulus, in an attempt to stress the bone marrow to produce more cells and compensate the losses in the bloodstream. This continuous overpressure of the bone marrow can accelerate the process of cancer development and difficult the clinical picture and treatment, and put the patient’s life at risk.

An excellent way to manage this situation is by administering allogenic PRP whenever the blood work reveals alterations in platelet count and/or function. Allogenic PRP is platelet-rich plasma obtained from a healthy donor cat, which when applied intravenously immediately improves the platelet function, releases stimuli on the bone marrow tissue, temporarily compensates platelet count, and provides growth factors from healthy platelets that help regenerate damaged tissue (including bone marrow).

It is important to remember that the effect will be temporary, especially when the patient is at secondary viremia stage, so this is a procedure that should be repeated in accordance with the constant monitoring and blood work.

To know how to obtain PRP, please go to our GET STARTED Section, so you can begin to provide a better quality of life for your FeLV infected cat patients!

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