Feline leukemia – what is it really?

This disease, often mistakenly referred to as feline leukemia, is caused by the feline leukemia virus. However, since the virus causes many other serious symptoms in addition to malignant tumors of the lymphatic tissue, the name is somewhat misleading

INHALT
Cause, transmission, and development Symptoms Diagnosis Treatment Forecast Prophylaxis
Cause, transmission, and development

The feline leukemia virus is the pathogen responsible for feline leukemia. It can be divided into different subtypes, which are involved in the infection in different ways. The virus is only transmitted through direct contact between animals, as it is not very resistant and can only survive in the environment for a few seconds or minutes. Infected animals excrete the virus via saliva, nasal secretions, tears, but also via feces, urine, and breast milk. Mutual grooming by licking is the most common route of transmission. Young cats that are allowed to roam freely are particularly susceptible to the FeLV virus, with resistance to the virus increasing with age. There is generally a higher risk of FeLV infection in households with multiple cats.

The virus is usually absorbed through the nasopharyngeal cavity, where it multiplies and enters the lymph nodes and immune cells of the blood. Approximately 20 to 30% of all FeLV-infected cats can completely eliminate the virus from their bodies during this phase through an effective immune response, so that only high antibody levels but no viruses can be detected in the blood of these animals. This is referred to as an abortive infection. Affected cats are protected against reinfection with FeLV for the rest of their lives.

In 30 to 40% of infected cats, viraemia develops in the further course of the disease, which means that the virus spreads throughout the body via the blood. Only in this phase can these cats prevent the virus from spreading and multiplying by producing sufficient antibodies. In such cases, the virus can be detected in the blood in the first stage of the disease and is also excreted in the saliva. However, as the disease progresses, a kind of copy of the virus is incorporated into the body's cells and the actual virus is no longer replicated, so that it is no longer detectable in the blood but has not been completely eliminated from the body. In this phase, no more virus is excreted, meaning that these cats no longer pose a risk of infection. A so-called regressive infection develops, which in very rare cases can be reactivated in the event of a weakened immune system. However, affected animals can also develop FeLV-associated diseases and the risk of developing a tumor is higher than in cats that have never had contact with FeLV. In most cases, however, these tumors only develop at an advanced age. These cats are immune to reinfection with FeLV due to their high antibody levels.

In a further 30 to 40% of cases, the virus reaches the bone marrow approximately three weeks after the initial viremia, where it finds ideal conditions for further reproduction. In the vast majority of cases, these are young cats under 16 weeks of age whose immune systems are unable to neutralize the virus, resulting in persistent viremia (the presence of the virus in the blood), which leads to the continuous infection of other cells in the body. This is a progressive infection. Affected cats continuously excrete infectious viral material and are therefore a major source of infection for other cats. Large amounts of viral protein can be detected in the blood of these cats at any time, and they have a significantly higher risk of developing FeLV-associated diseases.

The incubation period can last for months in the case of progressive infection and even several years in the case of regressive infection, meaning that infected cats may appear healthy for a long time.

Symptoms

Depending on the severity and progression of the infection, the signs of the disease can be very unspecific and varied. The infection of white blood cells leads to a weakened immune system, which can trigger a wide variety of secondary infections. No other single pathogen causes as many different clinical symptoms and clinical pictures in cats as the FeLV virus.

The symptoms that occur depend on the type of virus and the immune response of the infected animal. Cats with a progressive infection are more likely to show clinical symptoms. The disease is named after the tumors that often develop in the white blood cells in a specific type of virus, known as leukemia. Another type of virus leads to anemia (low blood count). The most common clinical symptoms of FeLV infection are swollen lymph nodes, anemia, and apathy. Due to the immune deficiency described above, affected cats often also have gum inflammation. Depending on the location, tumor formation can lead to breathing difficulties, vomiting, diarrhea, and liver or kidney problems.

Diagnosis

In addition to their clinical examination, your veterinarian will of course also receive important information about the presence of a FeLV infection from a detailed preliminary report. However, as the symptoms can be so varied, a definitive diagnosis can only be made with an additional blood test. Various test procedures are available for this purpose.

In practice, a rapid test (often in combination with the FIV test) is usually used, which detects the virus directly in the blood and is 98% accurate. It should be noted that in a newly infected cat, viral protein can usually only be detected in the blood after three weeks. In order to correctly assess the status and progression of a FeLV infection, several tests are often carried out at intervals of several weeks. The FeLV vaccination has no influence on the test result.

Furthermore, various other test methods can be used to detect viral DNA or antibodies. In general, the different forms of the disease must always be taken into account when evaluating the test results, as viral DNA can also be detected temporarily in cats with a regressive infection, for example.

Treatment

According to current knowledge, there is no cure for this viral infection. Cats that are unable to fight off the virus themselves remain infected for life. Treatment therefore focuses primarily on the accompanying or secondary diseases and on alleviating the symptoms.

Management and care also play an important role in protecting the weakened immune system of infected cats. Since otherwise harmless pathogens can be particularly dangerous for these cats and in order to protect other cats from infection, they should be kept indoors at all times.

Cat with IV
Only the symptoms of FeLV can be treated
Forecast

The prognosis depends largely on the course of the disease. Cats with progressive infection generally have a poorer prognosis and significantly lower life expectancy than cats with regressive or abortive infection. The majority of permanently infected animals die three to five years after infection. However, some permanently infected animals can live with the infection for years. A stress-free environment, successful treatment of concomitant diseases, and good management are all beneficial factors.

Prophylaxis

Unlike FIV, vaccines are available for FeLV. Although vaccination cannot completely prevent infection, it effectively protects against the virus entering the bloodstream and developing FeLV-associated diseases. Vaccination is recommended for cats at increased risk of infection. These include outdoor cats, breeding and show cats, and cats in shelters. Cats are generally particularly susceptible to progressive FeLV infection in the first few years of life and should be especially well protected during this time. The minimum vaccination age for most vaccines is eight weeks. Two injections are required at intervals of three to four weeks. After that, a vaccination should be given after one year to complete the basic immunization. Booster vaccinations are then necessary every three years. The risk of progressive infection is very low in cats over seven years of age. In these cats, the need for vaccination can be decided on an individual basis. Your vet can send you a personalized vaccination schedule for your cat via petsXL, and you will automatically receive notifications when it is time to make your next appointment.

Cats whose infection status is unknown should be tested for FeLV before their first vaccination, as the vaccination is not effective in infected cats.

To prevent infection as far as possible, the following additional preventive measures should be taken:

  • Strict separation of progressively infected animals from uninfected animals
  • Neutering of all progressively infected animals to reduce virus transmission through mating or fights
  • Keep new additions to FeLV-free groups (e.g., in animal shelters or multi-cat households) in quarantine for at least three weeks before introducing them to the group and test them for FeLV

Since the virus is not very resistant in the environment and can be killed with commercially available disinfectants, indirect transmission via contaminated objects can be effectively prevented with general cleaning and hygiene measures.