Panleukopenia is a very serious disease, especially in the young cat. The virus may infect any susceptible animal, but kittens between 3 and 5 mouths of age are at higher risk. Adult cats tend to get a sub-clinical disease, and recover rapidly.
The virus is highly contagious and is transmitted through direct contact and secretions (saliva, vomitus, stool, and urine). Cats can also become infected when in contact with a contaminated environment. The virus is resistant in the environment and, under ideal conditions, may remain infectious for one year. Susceptible animals become ill between 2 and 7 days after exposure to the virus.
The panleukopenia virus replicates in rapidly multiplying cells and causes cellular death after replication. The most common areas affected by the virus include the intestinal tract, the bone marrow, and the lymphatic tissue.
As the cells lining the inner surface of the intestines become infected, they are destroyed, and vomiting and diarrhea ensue. The loss of fluid from the bowel leads to severe dehydration, and possibly to shock.
When the virus replicates in the bone marrow, the circulating white blood cells, which are produced in the bone marrow, are dramatically decreased in number, resulting in a leukopenia (low white blood cell count); the name "panleukopenia" reflects this decrease in all white blood cell lines. Since white blood cells are vital in fighting infections, their decrease in numbers prevents the cat from initially mounting an effective immune response.
As the virus continues to damage the intestinal lining, the normal bacteria in the bowel penetrate the intestinal barrier, enter the blood stream, and cause a secondary bacterial infection of the blood (sepsis). This combination of events leads to a critically ill patient, and to the clinical signs that are observed.
If a queen is infected while pregnant, the rapidly growing cells of the fetus are affected and fetal or neonatal death may occur. Occasionally, intrauterine infection of the fetus will cause more specific damage to the central nervous system, and especially to the cerebellum (the part of the brain controlling balance and coordination), resulting in a condition known as cerebellar hypoplasia. These kittens may be born alive, but have balance problems as they mature. This can also occur if a pregnant queen is vaccinated with a modified live virus panleukopenia vaccine.
Other conditionsOther conditions may produce clinical signs similar to panleukopenia. These include:
Feline leukemia virus infection. This virus typically infects young cats, and kittens may also have low white blood cell counts and gastrointestinal signs. However, this tends to be a more chronic disease than panleukopenia.
Salmonella and campylobacter are bacterial infections that cause severe vomiting and diarrhea. They may be contracted via contact with infected stool or by eating contaminated food.
Feline coronavirus is another viral infection that infects the gastrointestinal tract. It generally causes much less severe disease than panleukopenia, and is more prevalent in cats over two years of age.
Severe gastrointestinal parasitic infections may cause young kittens to become quite ill and have signs that include vomiting and diarrhea.
Other causes of sepsis can also occur in kittens. Bacteria can invade the bloodstream via wounds, infected umbilical cords, perforating gastrointestinal foreign bodies, or from lung infections.
Intussusception. An intussusception is a condition in which one segment of the intestine telescopes into an adjacent segment of the intestine. This condition usually occurs in young animals and will cause vomiting and diarrhea.
Intestinal foreign bodies may cause an intestinal obstruction, resulting in a critically ill kitten.
Dietary indiscretion is a term used to describe eating inappropriate food items. Kittens eating rancid food or getting into garbage may become quite ill, and will present with signs referable to the gastrointestinal tract.
