Supportive care for dehydration and hemorrhagic diathesis may be necessary. Because of alterations in vascular integrity, conservative rates of fluid administration are advised. Animals with neurologic dysfunction may have residual deficits. Immunity appears to be lifelong after natural infection. (Foley et. al., 2024) Prevention Tick prevention is the best method to prevent infection. Because products that kill ticks after they attach can take longer than 20 hours to be effective, a product that repels ticks and prevents bites is a better option. (Kidd, 2020) Currently there are no vaccines available to prevent RMSF in either dogs or people. Vaccine development against RMSF is complicated due to the limited understanding of the protective host response and the R. rickettsii antigens involved in stimulating protective immunity. (Foley, 2020) Because dogs are reservoirs for the pathogen and keystone hosts for the tick, canine-focused management is an efficient strategy to manage RMSF epidemics. (Coile, 2023) Veterinarians and shelter staff should be aware that Ehrlichia or Anaplasma infection may co-occur with Rocky Mountain spotted fever, which is a human health risk. (Mylonakis et. al., 2019) gauged by a fourfold antibody titer increase over a 1-2 week period. Therefore, using quantitative or semi-quantitative serological assays is considered more useful compared to purely qualitative serological assays. (Krämer et. al., 2020) Bleeding diathesis may occur in both the acute and chronic phases of CME but is more common and severe in the chronic phase and is manifested as cutaneous and mucosal petechiae and ecchymoses, epistaxis, hematuria, melena and prolonged bleeding from venipuncture sites. (Australian Government, 2023) The acute phase of illness typically lasts for 2–4 weeks. Concurrent infection with other tick fever organisms ( Anaplasma platys and Babesia canis ) is common and worsens the prognosis. (Waner, 2022) During the acute or the subclinical phase of CME, immunocompetent dogs may eliminate the infection or, alternatively, diminish ehrlichiaemia and tissue bacterial loads to levels not amenable to molecular detection by polymerase chain reaction (PCR) amplification. Occasionally, myelosuppression may develop without any premonitory signs indicative of the acute and subclinical phases of CME. Therefore, the terms “non-myelosuppressive” and “myelosuppressive” CME may better reflect disease severity in a clinical context, regardless of illness onset or the presumed phase of CME. (Waner, 2022) During the subclinical phase, no clinical signs are evident but platelet counts may be subnormal. Dogs in this phase may remain persistent carriers of E. canis for months and even years. For reasons still unclear, certain dogs will progress to the chronic severe pancytopenic form of CME, which bears a poor prognosis. (Krämer et. al., 2020) In chronic CME, blood tests often show severely low platelets, low white blood cells, and anaemia, progressing to non-regenerative pancytopenia. (Waner, 2022) Chronic pancytopenic CME develops only in some infected dogs. The presence of severe pancytopenia characterizes the severe chronic form of ehrlichiosis and is a consequence of hypoplasia of all bone marrow cell lines. Clinical signs at this stage are usually severe and include lethargy, inappetence, bleeding tendencies, mucosal pallor, fever or hypothermia, weight loss, lymphadenomegaly,
for serologic testing. However, there is a high incidence of cross-reacting antibodies to a variety of non- and less-pathogenic spotted fever group rickettsiae, so a single seropositive test does not confirm RMSF as a cause of clinical disease. (Foley et. al., 2024) antimicrobial treatment with doxycycline must begin before the diagnosis is confirmed by laboratory testing. (Backus et. al., 2023) Enrofloxacin has been shown to be effective against Rickettsia rickettsii in experimentally infected dogs. (Kidd et. al., 2020) Case fatality rates of ~1–10% are expected. (Foley et. al., 2024) If untreated, RMSF can quickly progress into a life- threatening illness in people and dogs, with high fatality rates ranging from 30 to 80%. (Foley, 2020) Treatment Doxycycline is the treatment of choice. Appropriate Early seronegative tests should not be considered a reason to stop therapy, because antibodies may take ≥1 week to develop in acute cases. (Foley et. al., 2024) A follow-up serology is recommended 4-6 weeks after initial infection. (Kidd, 2020) Canine monocytic ehrlichiosis (CME) Canine monocytic ehrlichiosis (canine monocytotropic ehrlichiosis) is caused by Ehrlichia canis , a gram-negative, obligate intracellular bacterium. CME is a tick-borne disease of worldwide distribution. E. canis bacteria are transmitted trans-stadially and intra-stadially by the brown dog tick ( Rhipicephalus sanguineous ). (Australian Government, 2023) The tick retains the bacterium through its life stages (trans- stadial transmission) and can infect hosts in both nymph and adult stages. Around the world, the disease is known as ehrlichiosis, canine tropical pancytopenia, tracker dog disease, canine haemorrhagic fever, and canine typhus. (Waner, 2022) In addition to its role as a vector of R rickettsii and Ehrlichia canis , the brown dog tick also transmits Anaplasma platys , the cause of infectious cyclic thrombocytopenia in dogs. Ehrlichia canis and A. platys were historically regarded as strictly canine diseases, but both have now been proven to infect humans as well. (Coile, 2023) Diagnosis Clinical symptoms ● Fever (or hypothermia in profoundly pancytopenic dogs) ● Depression or lethargy ● Anorexia ● Generalized lymphadenomegaly ● Ocular abnormalities (e.g., anterior or posterior uveitis) Ulcerative stomatitis and necrotic glossitis, hind limb and/ or scrotal edema, and central nervous system signs, such as seizures, ataxia, vestibular dysfunction, and cervical pain, have been more frequently reported in the chronic disease. (Australian Government, 2023) ● Splenomegaly ● Mucosal pallor ● Bleeding tendency Generally, serology for IgG anti- E. canis antibodies is the first of the tests to be undertaken and evaluated due to the simplicity of the test and its availability. Moderate to severe thrombocytopenia is the most consistent and indicative hematological abnormality in the acute phase of CME. An immunofluorescence antibody assay (IFA) titer (IgG) against E. canis > 1:40 is indicative of previous exposure to the rickettsia but cannot be used to confirm the current disease. Acute active infection is
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