Feline Viral Diseases: Need To Be Aware
With the modernization, the trend of rearing cats in metropolitan and cities is increasing remarkably. Most of the owners rear them but do not have enough knowledge and awareness to various infectious diseases, their clinical signs, causing agents and methods of prevention and control of occurrences of diseases. Infectious diseases may be of bacterial, viral and mycotic etiology. There is a long list of infectious diseases. In this communication only the viral diseases are being discussed to make cat owners aware of infectious diseases of viral origin, as these are of prime importance due to lack of antiviral drugs, cost of treatment and high mortality rate, in spite of treatment, particularly in kittens. Most common viral infections of cats are:
- Feline Panleukopenia Virus (FPV)
- Feline Rabies Virus
- Feline Leukemia Virus (Felv)
- Feline Infectious Peritonitis (FIP) or Feline Corona Virus
- Feline Immunodeficiency Virus (FIV)
- Feline Calci Virus
- Feline Rhino trachitis Virus
- Feline Panleukopenia Virus (FPV)
A single-stranded DNA virus of Parvoviridae family is responsible for disease in all felids mainly during the first year of life and are responsible for high mortality in week, debilitated, malnourished and immunosuppresed kittens, however survivors attain a long-lasting and strong protective immune response.
1.1 Transmission: It is transmitted from all the secretions and excretions of affected animals and even up to 6 weeks of post-recovery by direct contact or indirectly by contaminated objects as these are extremely resistant to inactivation and can survive for up to one year in some environments.
1.2 Pathogenesis: FPV infects and destroys rapidly dividing cells in the bone marrow, lymphoid tissues and intestinal epithelium whereas cerebellum and retina are affected severely in young ones. The transplacental transmission of virus in pregnant queens to their kittens may result in embryonic resorption, fetal mummification, abortion, still birth or birth defects.
1.3 Clinical signs: Infection mainly occurs in young ones in peracute and acute form. Adults have either mild infection or subclinical form of infection. The incubation period for acute cases is 2-7 days however in peracute cases kittens die without showing clinical signs. In acute cases fever, anorexia, depression and vomition along with diarrhea lead to severe dehydration. Generally infected animal do not drink water but used to sit near the water source looking at the water. In terminal cases, the patients develop hypothermia and septic shock. Incoordination and tremors are observed in the conditions of cerebellar hypoplasia whereas grey foci are found as retinal lesions.
1.4 Prognosis: The mortality rate in young kittens may go up to 90%, however infection is subclinical and self-limiting in adult animals. Transplacental transmissions lead to abortion or reabsorption of kittens in uterus. Those that survive pregnancy often appear normal at birth, but develop a lack of coordination and balance with otherwise normal brain functions and are incurables.
1.5 Treatment: Kittens infected with clinical disease are treated with intravenous fluids for rehydration along with broad spectrum antibiotics to prevent secondary bacterial infection. Antidiarrheal and drug to reduce vomiting are also recommended if diarrhea and vomition occurs.
1.6 Prevention: The best way to avoid infection with this virus is routine vaccination. Inactivated modified live virus vaccines that produce long lasting immunity are available for the prevention of feline panleukopenia infection. These vaccines should not be given to pregnant, sick or immunosuppressed cats and kitten less than one month of age.
- Feline Rabies Virus
Primarily an acute encephalomyelitis of carnivores is caused by lyssaviruses of family Rhabdoviridae. There are many reservoir species for the rabies virus as raccoons, bats and foxes. The cats are affected mainly from rabid dogs.
2.1 Transmission: The transmission of the rabies virus is mostly in two ways; either through saliva or through bite of rabid animals. Aerosol transmission is rare.
2.2 Pathogenesis: After infection virus remains to the site of infection for a variable period. Then travels through peripheral nerves to the spinal cord, and from the spinal cord to the brain. After reaching the brain, the virus descends peripheral nerves to reach the salivary glands. Once the virus is established in the salivary glands, it can be transmitted via the saliva, and will be detectable in the brain.
2.3 Clinical Signs: The clinical signs are sudden and unexplainable behavioral changes and a rapid onset of a progressive paralysis. The behavioral changes include anorexia, irritability, anxiety, apprehension, hyperexcitability, unexplained aggressiveness and the animals may seek out solitude.
The clinical disease can be divided into three phases:
- Prodromal Period
- Excitative Period
The prodromal phase is characterized by vague CNS signs and typically lasts 1-3 days then in excitative period behavioral changes become apparent. The endstage is fatal stage due to progressive paralysis of nervous system. All phases do not occur in all affected animals and some animals die acutely with minimal clinical signs. Other than these phases some animals also show the stage of aggression “Furious Form” in which animal often chew on bars, fences and attempt to bite moving objects. They often swallow foreign objects, and are easily provoked to viciously attack other animals or people. The disease will progress to incoordination and seizures and finally the animal will succumb to paralysis and death.
2.4 Prognosis: After onset of clinical signs prognosis is grave as the end course of disease is death.
2.5 Treatment: No treatment is available after the onset of clinical signs.
2.6 Prevention: Annual vaccination of the domestic animals is recommended. However, pre-exposure vaccination is only recommended in humans with high risk groups such as veterinary staff, animal control officers and people living in regions where canine rabies is endemic or epizootic
- Feline Leukemia Virus (FeLV)
FeLV is a lethal retrovirus of cats which is sensitive to environmental conditions and could not survive longer outside the host. Mainly young ones under 4 months of age are more severely affected.
3.1 Transmission: Usually transmitted by the transfer of saliva or nasal secretions through bite, wound, during grooming and sometimes even through the shared use of litter boxes and feeding dishes. It may also be shed in feces and milk. It is not transmissible to either humans or dogs.
3.2 Pathogenesis: FeLV causes immunosuppression in pet cats and its pathogenesis of virus can be classified in various phases designated as phase Ito VI.
- Phase I: Virus enters through pharynx and replicate in epithelial cells and infects the tonsil immune cells. These white blood cells then filter down to the lymph nodes and begin to replicate producing new virus infected cells.
- Phase II: In second phase virus begins to distribute throughout the body through blood.
- Phase III: Phase three starts when the infection of lymphoid tissues and dissemination of virus throughout the body.
- Phase IV: Dissemination of virus during this phase to circulatory system and intestines, spleen, lymph nodes, epithelial cells of the intestine and bladder, salivary glands and bone marrow.
- Phase V: In this phase virus stay with the cat for the rest of its life.
- Phase VI: During this phase virus infect mucosal and glandular epithelial cells. The virus replicates in epithelial tissues including salivary glands, stomach, esophagus, intestines, trachea, pharynx, kidney tubules, bladder, pancreas and glandular ducts.
3.3 Clinical Signs: Development of cancers including lymphoma and leukemia, immunosuppression and profound anemia are common symptoms. Inflammation involving the veins, joints and kidney due to Immune complexes are also observed. Infertility, abortions, gastro intestinal inflammations and neurologic disorders are also reported.
3.4 Prognosis: Virus produces mortality due to development of cancers like leukemia or lymphoma or anemia. There is no known cure for the virus infection.
3.5 Treatment: FeLV-positive cats can live without major diseases for many years even than specific antiviral treatments are costly but successful if the diagnosis is made early. Stress and secondary infection should be avoided for fast recovery.
3.6 Prevention: Different types of vaccines are available as killed whole virus, subunit and genetically engineered vaccines. Vaccines are recommended only for uninfected cats which are not at risk of exposure to FeLV positive cats. FeLV vaccines are intended to protect cats against FeLV infection, particularly persistent infection.
- Feline Infectious Peritonitis (FIP)
Primarily a disease of domestic cats is caused by enveloped feline coronavirus. The two forms of disease are reported; first localized form causes GI infections and second generalized form causes FIP. These viruses are relatively stable in environment and if dried, can survive for 4-6 wk but are sensitive to common disinfectants.
4.1 Transmission: The virus is transmitted by close contact with an infected cat or its excreta, most likely feces and saliva. The main route of transmission is aerosol transmission. Trans-placental transmission is also reported. All the ages and both the sexes are equally susceptible but disease mainly affects young ones and older animals.
4.2 Pathogenesis: Virus replicates in tonsil or intestinal epithelium after entry to host and then from here it is transported through white blood cells to liver, spleen, and visceral lymph nodes and also leads to development of persistent viremia depending upon the immune status and stress conditions.
4.3 Clinical Signs: Appearance of clinical signs depends upon the immune response of infected animals to virus and only few infected cats develop clinical FIP. The disease is progressive and generally manifested in two different forms as wet and dry. The wet and dry forms are also known as effusive and non effusive forms, respectively. In wet form immune complexes are deposited in blood vessels leading to inflammation, vessel damage, leakage of blood serum and protein into body cavities leading to fluid accumulation in abdomen owing to distended abdomen and difficulties in breathing due to fluid accumulation in the chest, depression, weight and appetite loss and fever. In dry form granulomatous lesions are formed in abdominal viscera, lungs, eyes and brain.
4.4 Prognosis: In the clinical cases of FIP prognosis is poor and generally the mortality rate is observed about 100%. The wet form is rapid in comparison to dry form and cats may survive years with clinical signs.
4.5 Treatment: No treatment is effective after appearance of clinical signs; only supportive therapy is given to sub side clinical signs and to provide comfort to infected cat.
4.6 Prevention: FIV infection can be prevented by using a live intranasal vaccine; however the immunity produced is thought to be of short duration. Vaccination alone is not sufficient to prevent further infection and must be accompanied by other practices to prevent transmission.
- Feline Immunodeficency Virus (FIV)
FIV is lentivirus of family reteroviridae family and mainly affects domestic cats and is endemic throughout the world. It attacks and weakens the immune system, making the animal susceptible to infections and diseases.
5.1 Transmission: Viruses are shed in saliva of infected cats main route of transmission is through deep bite wounds therefore freely roaming aged and male cats are more commonly infected.
5.2 Pathogenesis: FIV infects white blood cell types including T lymphocytes, B lymphocytes and macrophages and produce immunodeficiency to infected cats.
5.3 Clinical Signs: Transient fever, swelling of the lymph nodes and reduction in circulating white blood cell numbers are commonly recorded. Chronic secondary and opportunistic infections affect all body systems as respiratory, gastrointestinal, urinary tracts and skin. A minority of affected cats develop neurologic signs including behavioural abnormalities, psychomotor disturbances, dementia or convulsions.
5.4 Prognosis: The life span of FIV infected cats is highly variable but once the disease progresses to producing immunodeficiency many cats die or are euthanized within one year. Cats once infected remain infected for life.
5.5 Treatment: No treatment is available. Confirmed cats are euthanized.
5.6 Prevention: Vaccination is not recommended for use in cats housed exclusively indoors but cats on high risk are vaccinated with recently developed vaccine.
- Feline Calicivirus (FCV)
It is a non–enveloped RNA virus from the family Caliciviridae. It is quite resistant to many disinfectants. FCV is one of two major causes of Feline Respiratory Disease Complex. and produces clinical disease similar to that observed with Feline Rhinotracheitis.
6.1 Transmission: The main route of transmission is aerosol route and main source of contamination is discharges of nose, mouth or the eye.
6.2 Pathogenesis: Oral ulcerations, formation of vesicles on the margin of the tongue and development of interstitial pneumonia, rarely lameness and swelling and in severe cases lesions forming in many areas of the body, edema, pneumonia and multiple organ damage are also found.
6.3 Clinical Signs: Conjunctivitis, coughing, difficult breathing, nasal discharge along with formation of vesicles and ulcers on oral mucosa are major clinical signs. Sometimes fever, anorexia, weakness and debility along with lameness are also observed.
6.4 Prognosis: Disease has high morbidity rate and low mortality rate thus it rarely causes death in adult cats but they remain carrier for longer periods. In young kittens, the mortality rate may be as high as 30%.
6.5 Treatment: There are no specific anti-viral treatments available for calici-virus
and animals are treated with supportive therapy which includes fluids, antibiotics to prevent secondary bacterial infections and symptomatic treatment for other lesions.
6.6 Prevention: Control of feline calici virus is best achieved through routine vaccination.
- Feline Rhinotracheitis
It is caused by species specific double stranded DNA virus Feline Herpes Virus-1 (FHV1) of family Herpesviridae. This virus is a member of infectious agents responsible for Feline Respiratory Disease Complex producing around 50-70 % of respiratory diseases of cats.
7.1 Transmission: Virus can be transmitted directly through contact with nasal or respiratory secretions of infected animals or indirectly via contaminated fomites. The virus does not survive longer in the environment and can be easily inactivated by common disinfectants.
7.2 Pathogenesis: Virus enters through epithelial cells or mucous membranes. Then replicate in the nucleus of cells leading to cell death. Lesions are formed in the form of blisters on epithelial surfaces and ulcers or erosions on mucous membranes. Infected animals remain as carrier and continue to shed the viruses.
7.3 Clinical Signs: Like other viral infection of upper respiratory tract sneezing, coughing, nasal, ocular discharge with frothing salivation, trouble breathing, corneal ulcers and tongue ulcers are common signs. Pregnant queens may abort their kittens.
7.4 Prognosis: The recovery time of the disease is 10-21 days. However, many cats will remain latent carriers of the disease and may spread the virus to other cats. In rare cases in which very young kittens are infected and develop pneumonia, the disease may be fatal.
7.5 Treatment: Antimicrobial drugs may be administered to reduce the risk of a secondary bacterial infection. In cases with severe corneal ulceration, anti-viral medicated drops may be prescribed.
7.6 Prevention: Both inactivated virus and attenuated virus vaccines are available and are used for control, but not prevention of this disease.
Viral diseases are mostly acute and fatal in nature. There specific treatment is not available and symptomatic treatment with antiviral agents is costly and not very effective particularly in young ones which are most severely affected. Therefore, it is essential, economic and effective to vaccinate against viral infections during early stage of life.