Today's Veterinary Practice

JUL-AUG 2015

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TodAy's VeTerinAry PrAcTice | July/August 2015 | tvpjournal.com PArAsiTology eXPerTise FroM THe ncVP Peer reviewed 58 Rocky Mountain Spotted Fever Transmission. rocky Mountain spotted fever— caused by Rickettsia rickettsii—is considered one of the most serious tick-borne diseases in the Americas due to its high fatality rate and rapid onset. infection with R rickettsii is most commonly transmitted by Dermacentor variabilis in eastern north America and D andersoni in the rocky Mountain states, but other tick species, including R sanguineus and Amblyomma species, have been confrmed to also transmit infections in north, central, and south America. 12 Presentation. clinical signs include rapid onset of fever, lethargy, and anorexia. Thrombocytopenia is often present, and some dogs may develop bleeding diatheses. neurologic complications occur frequently. clinical disease, although relatively uncommon, is associated with high fatality rates in both humans and dogs, particularly when treatment is delayed or withheld. 13 Prompt, aggressive treatment can result in a rapid response, with resolution of clinical signs within a few days. Diagnosis. diagnosis can be confrmed with serologic testing, but treatment should be initiated upon suspicion of infection rather than upon diagnostic confrmation because: 8 • Many patients with acute infection and disease have not yet seroconverted • Pcr of whole blood is less likely to identify infection with R rickettsii than with Anaplasma or Ehrlichia species. When presenting and convalescent titers are compared, demonstration of a rising titer can be diagnostic. serologic assays for R rickettsii are not specifc, and when tick infestations are common, many dogs will have antibodies reactive to R rickettsii due to past infection with other, nonpathogenic Rickettsia species. results of any diagnostic tests should always be interpreted together with clinical presentation. 14 TICK-BORNE PROTOZOAL DISEASES Babesiosis Transmission. Many Babesia species cause disease in dogs worldwide. However, the 2 most commonly identifed in north American dogs are: • B vogeli (formerly B canis vogeli), transmitted by R sanguineus (Figure 2) • B gibsoni, usually transmitted between dogs through contaminated blood during dog fighting; also transmitted by ticks (Haemaphysalis species) in other parts of the world, with R sanguineus suspected, but not confirmed, to be involved in transmission. 15 infection with B vogeli appears particularly common in the southern U.s., where R sanguineus populations are intense; infections are often identifed in kennels harboring infestations with brown dog ticks. 16 Presentation. dogs with clinical babesiosis present with anorexia, fever, and depression; hemolytic anemia and pale mucous membranes are common. disease is considered more common following splenectomy. 17 infection with B gibsoni is most commonly reported in American staffordshire and American pit bull terriers. 16 Diagnosis. infection is usually diagnosed by careful examination of stained blood smears for characteristic large (B vogeli) or small (B gibsoni) piroplasms within red blood cells. 15 s erologic testing and P cr are also widely available and can be helpful in identifying chronic and acute infections, respectively. Hepatozoonosis Transmission. The most common and severe cause of canine hepatozoonosis in the U. s . is Hepatozoon americanum, transmitted by Amblyomma maculatum primarily in southern states. 18 in recent years, H canis has also been identifed in the U. s ., although this R sanguineus – transmitted pathogen is more common in dogs in s outh America, europe, Africa, and Asia. rather than transmission by tick bite, hepatozoonosis agents infect dogs when they ingest a tick containing infective sporozoites during grooming, predation or, in the case of H americanum, when cystozoites are ingested from tissues of rodents or rabbits that have ingested infected ticks. 19 Figure 2. Piroplasms of Babesia vogeli within erythrocytes. Wright-giemsa stain, magnifcation, 1000×. Courtesy National Center for Veterinary Parasitology

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