Three emerging vector-borne diseases in dogs and cats in the United States - Veterinary Medicine
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Three emerging vector-borne diseases in dogs and cats in the United States
Canine babesiosis, feline cytauxzoonosis, and canine bartonellosis are being diagnosed more often. Make surethat these diseases are on your differential diagnoses list and that you're current on the treatment options.


VETERINARY MEDICINE SUPPLEMENT


Treatment and prevention

Imidocarb dipropionate is the only drug approved by the FDA for treating canine babesiosis. The labeled dosage is 6.6 mg/kg given intramuscularly; the dose is repeated in two weeks for a total of two treatments. The most commonly reported side effects are pain at the injection site and cholinergic signs, such as salivation, defecation, and panting. Pretreatment with atropine (0.022 mg/kg subcutaneously 15 to 30 minutes before imidocarb administration) may reduce cholinergic signs. Imidocarb is effective for treating all subspecies of B. canis and is likely to eliminate B. canis infections completely.57-60 Imidocarb reduces morbidity and mortality when used to treat B. gibsoni infections but is not effective in eliminating the infections.5,61 No extensive reports exist on the use of imidocarb for treating infection with the western piroplasm or T. annae. Recent studies have shown that treating dogs with B. gibsoni infection with a combination therapy of atovaquone (Mepron–GlaxoSmithKline; 13.5 mg/kg orally t.i.d. given with a fatty meal for 10 days) and azithromycin (10 mg/kg orally once a day for 10 days) resulted in either elimination of infection or the suppression of parasitemia below the limit of detection.5 In my experience, early diagnosis and treatment with appropriate antiprotozoal drugs result in the highest rate of remission. The anemia and thrombocytopenia associated with babesiosis are immune-mediated, so concurrent treatment with immunosuppressive drugs is often instituted. However, in my experience, prolonged immunosuppression (weeks to months) before specific antiprotozoal therapy has resulted in a worse prognosis for remission.

Some studies have documented the prevention of babesiosis with imidocarb administration before experimental challenge infection.59 This approach is not practical in most cases. Reduced exposure to risk factors for transmission is recommended and is likely to reduce the chances of infection. These precautions include using acaricides, removing ticks daily, screening brood bitches (greyhounds and American pit bull terriers), screening blood donors, sterilizing needles and surgical equipment, and preventing dogfights.

FELINE CYTAUXZOONOSIS

Cytauxzoonosis is a tick-transmitted disease in cats caused by the protozoan parasite Cytauxzoon felis. Feline cytauxzoonosis was first described in two cats from Missouri in 1975, and since that time cytauxzoonosis has been recognized throughout much of the southeastern and midwestern United States.6,62-66 Wild felids such as bobcats (Lynx rufus) are considered to be the main reservoir for C. felis.67,68 Dermacentor variabilis has been demonstrated to transmit C. felis from bobcats to domestic cats.69 Only trans-stadial transmission of C. felis in D. variabilis has been documented.69 In domestic cats, C. felis undergoes a tissue or schizogenous phase followed by an erythrocytic phase. Clinical disease and death are attributed mainly to the tissue phase of the infection.

Clinical disease

Two distinct clinical presentations of cytauxzoonosis occur in domestic cats. Some cats have acute severe illness while others have mild or absent clinical disease.70 Cats with acute severe illness typically are presented with a one- to three-day history of anorexia and lethargy.6 Occasionally owners will notice dyspnea as the primary sign, or the cat may be found in a recumbent state. Physical examination often reveals one or more of the following: fever, icterus, lymphadenopathy, hepatomegaly, or splenomegaly.6,12,71 In end-stage disease, cats often become hypothermic.6 Some cats will vocalize as if in pain or distress.70

Pancytopenia is considered to be the classic hematologic abnormality associated with cytauxzoonosis, but cats may only present with decreases in one or two cell lines.6,70,72 Anemia and thrombocytopenia are the most commonly reported cytopenias. The anemia is often nonregenerative at the time of presentation because of the acute nature of the disease. Common serum chemistry profile abnormalities detected in these cats include hyperbilirubinemia and increased liver enzyme activity. Most clinical signs in acute cytauxzoonosis are attributed to the occlusion of small vessels by schizont-laden macrophages.6,70,72

Less commonly, cats are presented with mild clinical signs or without any signs of clinical illness. Many of these cases have been identified in the same household or area as cats that have developed severe or fatal illness. The reasons for the distinctly different manifestations of infection are unknown. Some researchers speculate that it may be due to a genetic mutation of the C. felis organisms rendering them less pathogenic, while others speculate that the immune response in some cats results in less severe clinical disease.


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