A collection of infectious diseases in cats (Proceedings)


Infectious diseases can often be insidious in their clinical presentation. Case studies will be used to highlight some interesting infectious diseases that can affect the feline patient.

Infectious diseases can often be insidious in their clinical presentation. Case studies will be used to highlight some interesting infectious diseases that can affect the feline patient.

Lungworm infection

     • Causative agent: Aelurostrongylus abstrusus

     • Transmission: Predation of paratenic hosts (mice, voles and possibly birds) that ingest infected snails or slugs (intermediate hosts); Cats are the principle hosts.

     • Geographic distribution: Worldwide

     • Pathogenesis: Cats are the principle hosts of this worm. Adult worms live in the bronchioles. Larvae are deposited in the bronchioles and coughed up, swallowed and shed in the feces. Snails and slugs are the intermediate hosts.

     • Risk factors: Outdoor cats with exposure to snails and slugs and paratenic hosts

     • Clinical findings: Related to inflammatory reactions to the parasites. "Asthma"- like signs – coughing, wheezing, overt respiratory distress. Thoracic radiographs may show diffuse interstitial nodules; peribronchial and alveolar patterns may also be present.

     • Diagnosis: Detection of larvae in airway washes or lung aspirates or Baermann fecal

     • Treatment: Fenbendazole 25-50 mg/kg PO q 24 hours for 10-14 days; Ivermectin 400 ug/kg SQ; bronchodilators and glucocorticoids may be needed to address the inflammation.

     • Public health considerations: None.

     • Things to remember: A treatable cause of "asthma"

Mycoplasma polyarthritis

     • Causative agent: Mycoplasma spp. (M. gatae, M. felis)

     • Transmission: Cat to cat - suspect initial respiratory, conjunctival or urogenital infection with systemic spread.

     • Geographic distribution: Worldwide

     • Risk factors: Large cat population (cattery), exposure to other cats, immunosuppression, stress

     • Clinical findings: Fever, hyperesthesia, difficulty walking, joint effusion, joint pain.

     • Diagnosis: Identification of the organism by culture or PCR in joint fluid; suppurative joint effusion

     • Treatment: Doxycycline 5 mg/kg PO q 12h; Prednisolone may also be needed due to the polyarthritis (2.5 – 5 mg/ cat every 12-24h). Must treat for an extended period of time.

     • Public health considerations: Not considered to be a major public health risk.

     • Things to remember: The organisms may become intracellular, resulting in chronic persistent infection. These organisms may also stimulate chronic immune-mediated disease.

Toxoplasma gondii -neurologic involvement

     • Causative agent:Toxoplasma gondii, an obligate intracellular coccidian protozoan parasite

     • Transmission: Infection acquired by ingestion of infective oocysts or tissue cysts.

     • Geographic distribution: Worldwide; higher seroprevalence in warm, moist, or tropical climates.

     • Risk factors: Immunosuppression from infections such as FeLV, FIV, or FIP; Glucocorticoid therapy or antitumor chemotherapy; post renal transplantation; ingestion of raw meat; outdoor cats hunting prey (birds, rodents).

     • Clinical findings: Anorexia, lethargy, fever, weight loss, vomiting, diarrhea, respiratory difficulties, icterus, abdominal effusion, ocular inflammation, blindness, anisocoria, seizures, behavioral changes, incoordination, circling, twitching, tremors, ataxia, paresis, paralysis, muscle pain/weakness, tetraparesis. Clinical signs may be sudden or slow in onset.

     • Diagnosis: Serology – IgM, IgG titers on serum and CSF; CSF analysis – high leukocyte count (mononuclear cells and neutrophils), elevated protein; organism detection rare.

     • Treatment: Clindamycin 25-50 mg/kg PO or IM divided q. 12h; Trimethoprim-sulfonamide 15 mg/kg PO q 12h; long-term antibiotic administration may be required.

     • Public health considerations: Immunocompromised people and pregnant women should avoid contact with raw meat and litter boxes.

     • Things to remember: Oocysts need at least 24 hours to become infective, so risk of exposure/infection is minimized if litter boxes are cleaned daily.


     • Causative agent:Histoplasma capsulatum, a soil-borne, dimorphic fungus. This organism grows best in soil with nitrogen-rich organic material like bat and bird excrement.

     • Transmission: The source of infection is usually inhalation of microconidia, but oral exposure may also be possible.

     • Geographic distribution: Endemic areas – Ohio, Missouri, Mississippi, Tennessee, and St. Lawrence River basins; also seen in Texas, southeastern US and the Great Lakes region

     • Risk factors: Exposure to bird or bat droppings, especially in roosting areas; exposure to airborne dust contaminated with fungal spores

     • Clinical findings: This disease can affect young and old cats (age range 4-14 years) but younger cats are more commonly affected. There is no breed predilection. Females seem to be more commonly affected than males. Clinical signs include anorexia, weight loss, coughing, respiratory difficulties, lameness, ocular discharges, fever and diarrhea.

     • Diagnosis: Demonstration of organisms from tissue sampling (cytology, histopathology, or culture)

     • Treatment: Itraconazole - 5-10 mg/kg orally once daily or divided q 12h; Fluconazole -100 mg per cat divided q 12h (may be better for ocular and CNS infections); Amphotericin B lipid complex - 1 mg/kg three times weekly for a total of 12 treatments.

     • Public health considerations: Direct transmission of this disease from animal to animal or animal to human has not been reported. Humans residing in areas where the disease has been diagnosed are at increased risk of exposure due to environmental factors. Fungal cultures of this organism are considered to be highly infectious.

     • Things to remember: The disease can be insidious in onset. Travel history can be very helpful in making the diagnosis.

Songbird fever (salmonellosis)

     • Causative agent: Salmonella typhimurium

     • Transmission: Ingestion of a songbird

     • Geographic distribution: Worldwide

     • Risk factors: Bird-hunting activity

     • Clinical findings: Diarrhea (often hemorrhagic), vomiting, fever, anorexia, lethargy, septicemia

     • Diagnosis: Cytology – fecal leukocytes; fecal culture

     • Treatment: Amoxicillin 22 mg/kg PO q 12h; Enrofloxacin 5 mg/kg PO q 12h. Supportive care – rehydration.

     • Public health considerations: High zoonotic potential. Acutely ill cats shed large numbers of organisms in stool. Reportable disease.

     • Things to remember: Spread of infection in the household (humans and other animals) is common.

Latent felv infections

     • Causative agent: Feline leukemia virus (retrovirus)

     • Transmission: Cat-to-cat transmission through bites, close casual contact over time, shared dishes or litter boxes.

     • Geographic distribution: Worldwide

     • Risk factors: Free-roaming, multicat household/cattery, unneutered male behavior

     • Clinical findings: Nonregenerative anemia, often severe; may also have neutropenia, lymphopenia, and/or thrombocytopenia.

     • Diagnosis: Hypocellular bone marrow; bone marrow sample IFA positive for FeLV; ELISA serum tests negative for FeLV. Can also document with virus isolation or PCR on bone marrow cells.

     • Treatment: Supportive care, blood transfusions, treatment of secondary diseases.

     • Public health considerations: Probably low, but controversial

     • Things to remember: Cats that are exposed to feline leukemia virus (FeLV) can clear the viremia but may develop persistent infection of the bone marrow. These cats will test FeLV negative on peripheral blood tests, but are positive for the virus at the bone marrow level.

Feline plague

     • Causative agent:Yersinia pestis, gram-negative, bipolar staining rod

     • Reservoirs: wild rodents, ground squirrels, prairie dogs, rabbits, bobcats, coyotes

     • Geographic distribution: Occurs worldwide; U.S. reported cases in New Mexico, Arizona, California, Colorado, Idaho, Nevada, Oregon, Texas, Utah, Washington, Wyoming, and Hawaii

     • Vector: Fleas

     • Risk factors: Outdoor cats who hunt, travel to endemic areas, environment with heavy flea infestation or large rodent populations

     • Clinical findings: Bubonic form – marked lymphadenopathy, especially around head and neck, abscessed/draining lymph nodes, fever, lethargy, anorexia, vomiting, diarrhea, dehydration, ocular discharge, weight loss, oral ulcers, ataxia, and coma. Septicemic form – septicemia without lymphadenopathy or abscess formation, signs as for bubonic form.

     • Diagnosis: Demonstration of organism microscopically, fluorescent antibody test, culture isolation

     • Treatment: Treat early and aggressively. IV fluids to rehydrate. Antibiotics - Tetracycline 25 mg/kg PO q 8h for 10 days or 7.5 mg/kg IV q 12h; Doxycycline 5-10 mg/kg PO q 12h; Chloramphenicol 30-50 mg/kg PO q 8h. Treat patient for fleas.

     • Public health considerations: Highly zoonotic; risk of exposure through flea bites or contact with infected animal (blood, tissue). Seek medical advice from physician for all exposed people. Reportable disease (Category A – highest priority agents).

     • Things to remember: Treat all suspect cases empirically until lab confirmation is obtained.


     • Causative agent:Cytauxzoon felis, a protozoal organism

     • Reservoirs: Bobcats

     • Geographic distribution: Occurs in the southcentral and southeastern US extending into east and north.

     • Vector: Spread by tick bites, American dog tick (Dermacentor variabilis) implicated

     • Risk factors: Young, outdoor cats who hunt, travel to endemic areas, environment where tick bites are possible. More common in the months of April through September. "Hot spots" of infection may exist with other cats in the household or neighborhood infected.

     • Clinical findings: Fever, with or without jaundice. May be hypothermic if moribund on presentation. Decreases in one or more cell lines. Lymphadenopathy and splenomegaly possible. May be dyspnic. Laboratory abnormalities may include nonregenerative anemia, leukopenia, thrombocytopenia, hyperbilirubinemia and bilirubinuria, liver enzyme elevations (not as severe considering degree of total bilirubin elevation), hyperglycemia, and hypoalbuminemia. Coagulation profiles may be abnormal. The course of the disease is short, and most cats die within 5 days after clinical signs begin.

     • Diagnosis: Piroplasms evident on cytology of blood smear. Sometimes a second blood smear is needed a few days later. Can be mistaken for Mycoplasma haemofelis. Schizonts can be found is body tissues – fine needle aspirates of the liver, spleen, and lymph nodes. PCR testing can be sensitive and specific.

     • Treatment: Treat early and aggressively. IV fluids to rehydrate and anticoagulant therapy (unfractionated heparin 200-300 U/kg SQ every 8 hours or 600-900 U/kg IV as a constant rate infusion).

     • Anti-protozoal therapy – variable success. Imidocarb diproprionate (Imizol) 2-4 mg/kg IM once, repeat dose in 2 weeks. Anti-protozoal drug (atovaquone) and antibiotic (azithromycin) combination may be useful (clinical trials show survival rates of 60% or greater). Response to any treatment is not immediate and may take 4-7 days to see improvement. Blood work should return to normal in 2-3 weeks. If cats survive, they will have a persistent infection with the red blood cell form of the parasite. Unknown if they serve as reservoir for the infection.

     • Public health considerations: None.

     • Things to remember: The most effective prevention is to keep cats indoors to avoid tick exposure.

Selected readings

Bennett D: Immune-mediated and Infective Arthritis. In Ettinger SJ, Feldman EC (eds): Textbook of Veterinary Internal Medicine, 6th ed. St. Louis, Elsevier Saunders, 2005, p 1960.

Birkenheuer AJ, Levy MG, Breitschwerdt EB. Efficacy of Combined Atovaquone and Azithromycin for Therapy of Chronic Babesia gibsoni (Asian Genotype) Infections in Dogs. J Vet Intern Med, 18:494-498, 2004.

Dubey JP, Lappin MR: Toxoplasmosis and Neosporosis. In Greene CE (ed): Infectious Diseases of the Dog and Cat, 3rd ed. St. Louis, Elsevier Inc., 2006, pp 754-775.

Georgi JR, Georgi ME: Helminths. In Georgi JR, Georgi ME (eds): Parasitology for Veterinarians, 5th ed. St. Louis, Elsevier Inc., 2006, p 181.

Greene CE: Cytauxzoonis. In Greene CE (ed): Infectious Diseases of the Dog and Cat, 3rd ed. St. Louis, Elsevier Inc., 2006, pp 716-722.

Greene CE: Histoplasmosis. In Greene CE (ed): Infectious Diseases of theDog and Cat, 3rd ed. St. Louis, Elsevier Inc., 2006, pp 577-584.

Greene CE: Salmonellosis. In Greene CE (ed): Infectious Diseases of the Dog and Cat, 3rd ed. St. Louis, Elsevier Inc., 2006, pp 355-360.

Grooters AM, Taboada J: Update on antifungal therapy. Vet Clin North Am 33:749-758, 2003.

Kerl ME: Update on canine and feline fungal diseases. Vet Clin North Am 33:721-747, 2003.

Legendre AM: Histoplasmosis. In Tilley LP, Smith Jr. FWK (ed): The 5-minute Veterinary Consult: Canine Feline, 3rd ed. Philadelphia, Lippincott Williams and Wilkins, 2004, pp 590-591.

Macy DW: Plague. In Greene CE (ed): Infectious Diseases of the Dog and Cat, 3rd ed. St. Louis, Elsevier Inc., 2006, pp 439-446.

McDonough PL: Plague. In Tilley LP, Smith Jr. FWK (ed): The 5-minute Veterinary Consult: Canine Feline, 3rd ed. Philadelphia, Lippincott Williams and Wilkins, 2004, p 1017.

McDonough PL: Salmonellosis. In Tilley LP, Smith Jr. FWK (ed): The 5-minute Veterinary Consult: Canine Feline, 3rd ed. Philadelphia, Lippincott Williams and Wilkins, 2004, pp 1158-1159.

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