What is the relationship between cats and infectious disease?

Definition

Feline-to-human infections are zoonotic diseases that are transmitted
through bites and scratches, through contact with shared vectors (such as ticks, fleas, or mosquitoes), through shared environments (such as
contaminated soil), and through direct contact with infected skin.

Bites and scratches. About 1 percent of emergency room visits are
attributed to injuries caused by animal bites. Out of those cases, the majority
(85 to 90 percent) involves dog bites and a small minority (5 to 10 percent)
involves cat bites. Despite the disparities, few dog-related bites result in
infectious complications; 50 to 80 percent of cat bites (depending on the source)
become infected. Although a dog can exert 450 pounds of pressure per inch when
biting, canine teeth are relatively dull. A feline’s long and sharp teeth, in
contrast, can penetrate human skin, create deep puncture wounds, and penetrate
tissue surrounding bones. Consequently, a cat-related bite wound is more likely to
result in an infection.

Pasteurella

multocida is a gram-negative bacteria found in the mouths of most
cats. The bacteria are very common and can be transmitted through cat scratches,
bites, or saliva (by licking). The first signs of infection (pain, swelling, and
redness) usually occur within two to twelve hours of being bitten.
Pasteurellosis, the disease caused by the bite, can spread quickly through the body
from the wound site, so one should seek medical attention immediately. Bites to
the hand require special attention. If left untreated, the infection can cause
complications, such as upper respiratory problems, pneumonia, prosthetic-valve
endocarditis, and, less often, meningitis and brain abscesses.

Shared vectors. Cat scratch fever (CSF), or bartonellosis, is transmitted through cat scratches and
bites. Between twenty thousand and twenty-five thousand people in the United
States are diagnosed with this infection every year, but the disease is most
prevalent in warm, humid climates where fleas thrive. Although 30 to 40 percent of
healthy looking cats may be carriers, kittens most often transmit
CSF. When fleas bite an infected cat, the bacteria are spread through flea
excretions onto the cat’s skin and, ultimately, to the cat’s claws or saliva.

CSF is more common among persons with suppressed immune systems (persons with HIV or who are undergoing chemotherapy) and with children because their immunity is less developed and because they are more likely to roughhouse with cats. Symptoms include a rash or blister at the wound site; swollen lymph nodes around the head, neck, and upper limbs; fever; headache; and sore muscles and joints. The infection usually disappears in four to eight weeks. In immunosuppressed persons, however, complications, often severe, include high fever, sweats, chills, vomiting, and weight loss. Flea control is the key to preventing this disease, so one should consult a veterinarian.

Shared environment. Salmonellosis is a common bacterial disease of the
intestinal tract of many animals. It usually is contracted by eating undercooked
meat and eggs or contaminated vegetables. When cats eat raw meat or wild prey,
they are more likely to contract this bacteria and transmit it through
contaminated stools. Salmonellosis is one of the few infections that can be passed
from humans to cats and back to humans.

Following a twelve- to thirty-six-hour incubation period, symptoms include headache, fever, diarrhea, nausea, and dehydration. The best prevention is to feed cats processed foods and to wash hands thoroughly after cleaning litter boxes. Also, a person who has a cat as a pet should be extra vigilant if the cat has diarrhea.

Another form of transmission in a shared environment is contact with cat feces
contaminated with
Toxoplasma gondii, a single-celled protozoal organism that
infects animals and birds. Only in the cat, however, does this organism find an
ideal host to reproduce and complete its life cycle. Cats become targets when they
ingest contaminated prey or raw meat, or infected soil. Once ingested, the
bacteria burrow into the cat’s intestine, and early-stage cells, called oocytes,
are eliminated in cat feces. The bacteria can also foul soil, water, gardens, sand
boxes, or any location where an infected cat defecates. Because toxoplasma oocysts
require one to four days to incubate to become infective, it is important to empty
litter daily and dispose of waste properly to prevent this serious
parasitic
disease.

Typically, symptoms include body aches, swollen lymph nodes, headaches, fever,
fatigue, and eye infections. However, in immunosuppressed persons or in pregnant
women, complications can be serious. Pregnant women who contract toxoplasmosis
have a 30 percent chance of passing this infection to their fetus, which can
result in stillborn births or miscarriage. Even children who survive may develop
complications, such as seizures, an enlarged spleen, jaundice, and eye infections.
Additionally, research has linked toxoplasma to mental illness such as
schizophrenia and bipolar disorder in adults.

Pregnant or immunocompromised persons should ask another person to change a litter box daily, and those who clean the litter box should wear gloves and wash hands thoroughly afterward. Cat owners can limit exposure by keeping cats indoors.

Direct contact. Ringworm is a fungal infection, whose manifestation in cats includes, most
commonly, Microsporum canis; Trichophyton,
through rodent contact; and M. gypseum, through contact with
contaminated soil. Ringworm is highly contagious and is spread through direct
contact with an infected animal or through spores shed in carpets, furniture,
bedding, and air filters. Spores can last eighteen months, so treatment must
include thorough house cleaning. Most common among kittens, the resulting ringworm
lesions consist of localized hair loss, scaling, and crusting, although some cats
are asymptomatic carriers. Treating cats with medication is highly recommended. To
reduce environmental contamination, infected cats should be confined to one room
until they are ringworm free and until the household can be disinfected.

Lacasse, Alexandre, et al. “Pasteurella multocida Infection.” Available at http://emedicine.medscape.com/article/224920-overview. Discusses the frequency, mortality rates, and clinical assessments of pasteurellosis.

Lamps, L. W., and M. A. Scott. “Cat-Scratch Disease: Historic, Clinical, and Pathologic Perspectives.” American Journal of Clinical Pathology 121, suppl. (2004): S71-S80. A multidisciplinary look at cat scratch fever.

Regnery, Russell, and John Tappero. “Unraveling Mysteries Associated with Cat-Scratch Disease, Bacillary Angiomatosis, and Related Syndromes.” Atlanta: Centers for Disease Control and Prevention, January-March, 1995. Discusses the transmission of Bartonella henselae infection.

Reynolds, M. G., et al. “Epidemiology of Cat-Scratch Disease Hospitalizations Among Children in the United States.” Pediatric Infectious Disease Journal24, no. 8 (August, 2005): 700-704. A study of cat scratch disease incidence rates and patterns in children.

Talan, D. A., et al. “Bacteriologic Analysis of Infected Dog and Cat Bites.” New England Journal of Medicine 340 (1999): 85-92. Discusses the particular dangers of cat bites and dog bites.