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tvpjournal.com | July/August 2015 | TodAy's VeTerinAry PrAcTice PArAsiTology eXPerTise FroM THe ncVP Peer reviewed 59 Presentation. dogs with disease due to H americanum usually present with fever, myalgia, muscle atrophy, and poor body condition. Profound neutrophilia is often present, and periosteal bone proliferation may occur. 18 Without treatment, body condition continues to deteriorate and many affected dogs die or are euthanized. Diagnosis. disease is most commonly diagnosed by whole blood Pcr, although gamonts are occasionally found on blood smears (Figure 3). Histologic examination of muscle biopsy specimens is more sensitive than whole blood Pcr for diagnosing infection, but less commonly pursued due to the invasive nature of sample collection. serologic assays to confrm Hepatozoon infection are not available. NOVEL TICK-BORNE DISEASE AGENTS A variety of novel pathogens transmitted by ticks have been described in north America in recent years: • canine, human, and tick infections with novel Ehrlichia species have been described 9,10 • canine and human infections with spotted fever group Rickettsia species other than R rickettsii have been reported 14,20 • canine infections with previously unrecognized Babesia and Hepatozoon species have been identified 17,21 • s ome data suggest that ticks may transmit other organisms, such as Bartonella species. 22,23 in addition, viral tick-borne pathogens have been increasingly identifed in humans. 24,25 Heartland virus and Bourbon virus are 2 examples of recently identifed, apparently tick-transmitted pathogens in humans, although neither has yet been described in dogs. TREATMENT OF TICK-BORNE DISEASES When treating dogs suspected of having tick- borne disease: 1. Base the decision to treat primarily on your clinical judgment. 2. Use diagnostic results as an adjunct to clinical judgment, but not as the basis for administering or withholding treatment. 3. in dogs with moderate to severe clinical illness, do not: » delay treatment while waiting for diagnostic test results » Withhold treatment if fndings on serologic testing or P cr are negative. 4. do not delay treatment in dogs with clinical disease, particularly rickettsial infections; these patients may be serologically negative at initial presentation and Pcr may fail to identify a novel disease agent, but delaying treatment can result in death. Bacterial Disease Treatment of choice for common bacterial tick-borne disease agents is doxycycline. recommended regimens vary according to the specifc target agents, but doxycycline at 10 mg/ kg Po Q 24 H for 28 days is effective against B burgdorferi , Anaplasma species, Ehrlichia species, and R rickettsii. 5,6,8 clinical improvement is typically evident within the frst week of therapy. 6,26 dogs that do not respond to doxycycline should be carefully re-evaluated for additional etiologic agents. co-infection with bacterial and protozoal agents is frequent and can be responsible for apparent doxycycline treatment failure in some patients. Protozoal Disease Treatment recommendations for canine babesiosis and hepatozoonosis vary depending on the specifc agent responsible. • infections with large Babesia species, such as B vogeli, can be treated with imidocarb dipropionate, 6 mg/kg iM, with the dose repeated in 14 days. • infections with small Babesia species, such as B gibsoni, are generally more difficult to treat; a combination of atovaquone, 13 mg/kg Po Q 8 H for 10 days, and azithromycin, 10 mg/kg Po Q 24 H for 10 days, is recommended. 27 Hepatozoonosis due to H americanum is particularly challenging to treat and requires either: 18 • Ponazuril, 10 mg/kg Po Q 12 H for 14 days or Figure 3. gamont of Hepatozoon americanum (arrow) within a leukocyte. Wright-Giemsa stain, magnifcation, 1000×. Courtesy National Center for Veterinary Parasitology