Rocky Mountain Spotted Fever (RMSF)

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Rocky Mountain Spotted Fever (RMSF)

By: Dr. Anne Marie Manning

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Section: Veterinary Care In-depth

Diagnosis In-depth

In addition to taking an extensive medical history including questions regarding travel and exposure to ticks, your veterinarian will perform a thorough physical exam and may recommend the following diagnostic tests.

Complete blood count (CBC) to evaluate red blood cells, white blood cells and platelets. Platelets are often decreased and anemia may be present although this is relatively uncommon. White blood cell counts are often decreased initially and then rise later in the course of infection. A shift toward immature white cells may also be observed.

The biochemistry profile for showing increases in liver enzymes, blood sugar and cholesterol levels as well as a decrease in the blood protein albumin. Occasionally, decreases are seen in blood sodium and chloride levels due to vomiting and diarrhea.

Evidence of kidney insufficiency such as elevations in creatinine and blood urea nitrogen (BUN) levels may be present.

A urinalysis to show proteinuria (protein in the urine) or hematuria (blood in the urine).

A coagulation profile to identify potential bleeding or coagulation problems that may occur as a result of low platelets or vasculitis. Tests included in a coagulation panel are the prothrombin time (PT), activated partial thromboplastin time (APTT), fibrinogen levels, fibrin degradation products (FDPs), and a platelet count.

A Coomb's test or ANA (antinuclear antibody test) to rule out the presence of an immune mediated disorder that could produce symptoms similar to those of RMSF.

An indirect fluorescent antibody (IFA) test to measure antibody levels or titers to RMSF. This is the most important test for identification and diagnosis of RMSF. A blood sample is drawn during suspected infection and a convalescent sample is drawn 4 weeks later to confirm infection. Titers greater than 1:128 suggest recent infection. In the eastern United States a single titer greater than 1:512 is required to confirm active infection.

Treatment In-depth

Most pets with RMSF require hospitalization for initial treatment although length of hospitalization depends on the severity of infection and clinical symptoms and may vary from 24 hours to several days.

An intravenous catheter is placed in pets that are dehydrated or debilitated, or in pets that are unable to take medications orally due to vomiting.

Intravenous fluids are administered to pets that are dehydrated, vomiting, or are showing signs of kidney insufficiency. The presence of a fever greater than 104 F also warrants the administration of intravenous fluids. Anti-emetics, or anti-vomiting medications, may be added to IV fluids to control vomiting.

Antibiotics such as oxytetracycline, doxycycline or chloramphenicol are administered to treat infection with RMSF. [ART|1519|Doxycycline]] is the preferred antibiotic and is usually administered orally but may be administered intravenously if the pet is vomiting. A favorable response to antibiotic administration is usually seen within 24 to 48 hours of their initiation.

Colloids such as hydroxyethyl starch (hetastarch) or dextrans may be administered to pets with low protein levels. Colloids are solutions that mimic proteins and help prevent edema formation due to low proteins.

Blood products such as plasma may be administered to pets that have evidence of bleeding disorders or exceptionally low protein levels.

Rocky Mountain spotted fever can cause rapid weight loss so nutritional support is important, particularly in those pets that have not eaten for several days or have protracted vomiting. Nutrition may be administered intravenously, called parenteral nutrition, to those pets that are vomiting or via a feeding tube that reaches the stomach in those pets that are not vomiting but refuse to eat despite encouragement.

Follow-up

At home, administer all medication prescribed by your veterinarian. Treatment of RMSF often requires a two to three week course of doxycycline. Do not stop medication before instructed or infection may reoccur.

Doxycycline may cause stomach upset in some pets. If you have trouble administering the medication or your pet is nauseated or vomiting as a result of the doxycycline, call your veterinarian as soon as possible.

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