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Rocky Mountain spotted fever
Ronald D. Warner, DVM, MPVM, PhD, DACVPM, and Wallace W. Marsh, MD, FAAP Rocky Mountain spotted fever (RMSF), a classic SFG rickettsiae are transmitted by arthropods and cause
metazoonosis that involves both vertebrate and non- various illnesses worldwide, R rickettsii is the only one vertebrate reservoir hosts, is a seasonal disease of dogs known to be pathogenic for both animals and humans and humans in the Americas. The clinical illness was first described among Native Americans, soldiers, andsettlers in the Bitterroot River and Snake River valleys of Cycle of the Organism in Nature
Montana and Idaho during the late 1890s, but remained and the Vectors
unrecognized in dogs until the late 1970s. The causative Rickettsia rickettsii are maintained in nature by organism, Rickettsia rickettsii, was first described by transstadial passage within, and transovarial (vertical) Howard T. Ricketts in 1909 and is maintained in nature transmission between, generations of ixodid ticks. These by ixodid (hard-bodied) ticks via transmission to-and- ticks also vector R rickettsii to and from various rodent from various rodent reservoirs. As primary reservoir reservoirs and other small mammals. Naïve larval and hosts, the ticks vector R rickettsii to larger mammals; nymphal ticks become infected while feeding on small however, dogs and humans are the only ones that dis- rodents (eg, mice, voles, squirrels, or chipmunks) with play clinically recognizable illnesses. Rickettsia rickettsii acute rickettsemia.2,5 To enable transovarial transmission, are not naturally transmitted dog-to-dog, dog-to- female ticks need to ingest numerous rickettsiae or be human, or human-to-human. Public health surveillance, infected transstadially. Male ticks can transfer R rickettsii since the 1930s, has revealed RMSF to be the most fre- to females during the mating process via spermatozoa or quently reported and most severe human rickettsial ill- other body fluids, thus contributing to the maintenance ness in the United States and, probably, in the Western of the organism from one generation to another. Ticks Hemisphere. Reducing exposure to ticks, prompt can remain infective for life (possibly 2 to 5 years), espe- removal of ticks, and early diagnosis with appropriate cially if there are long periods between blood meals.2,3,6 antibiotic treatment are the most important factors in Ticks transmit R rickettsii to a vertebrate principal- reducing morbidity and mortality from RMSF.
ly during their feeding behavior. However, humaninfection has occurred much less often following trans- The Causative Organism
dermal or inhalation exposure to tick fluids Rickettsia rickettsii are small (0.2 X 0.5 µm to 0.3 X (hemolymph), tick feces, or crushed tick tissues. In the 2.0 µm) coccobacillary, gram-negative, obligate intra- natural history of R rickettsii transmission, human and cellular parasites in the family Rickettsiaceae. Like most domestic dog infections are considered incidental other spotted fever group (SFG) rickettsiae, R rickettsii
events (Fig 1). Even in areas where RMSF is most
are conveyed to vertebrate hosts by tick vectors.1,2 Once endemic, only 1 to 5% of ticks (in a particular eco- they infect dogs or humans, R rickettsii multiply withinvascular endothelium and vascular smooth muscle,inducing vasculitis and thrombosis in many organs,notably those with an abundant endarterial circulation(eg, brain, dermis, gastrointestinal organs, heart, lungs,kidneys, and skeletal muscles).2-4 These organisms aregenerally susceptible to doxycycline, tetracycline, andchloramphenicol. Special stains (ie, Giemsa, Gimenez,or immunohistochemical) are required to demonstrateR rickettsii in histologic sections.1,2,4 Although other From the Department of Family and Community Medicine, School of Medicine, Texas Tech University Health Sciences Center,Lubbock, TX 79430-0001 (Warner); and the Department ofPediatrics, School of Medicine, Texas Tech University Health Figure 1—Pathways of natural transmission for Rickettsia rick- Sciences Center, Lubbock, TX 79430-0001 (Marsh).
ettsii. Large open arrows are between stages of tick hosts, The authors thank Susan B. Warner, MLS; Traci English; Dustin E.
solid-line arrows are between tick vectors and vertebrates, and Hawley; and Ronald L. Cook, MS, DO for technical assistance.
dashed-line arrows are unlikely or very rare routes of natural Address correspondence to Dr. Warner.
JAVMA, Vol 221, No. 10, November 15, 2002 niche) harbor R rickettsii.2,7,8 It usually requires several Dogs have been reported to experience a higher inci- (6 to 20) hours of tick attachment and feeding before dence of illness, and English Springer Spaniels with sus- the rickettsiae are transferred to a vertebrate, depend- pected phosphofructokinase deficiency are reported to ing on the developmental stage and species of tick.2,5,7 have a more severe and fulminant form of the disease.2 Consequently, the risk of exposure to R rickettsii fol-lowing an individual tick bite is considered to be low.
Clinical RMSF in Dogs
In southeastern and mid-Atlantic regions of the An early and usually consistent finding is fever United States, the most common vector of R rickettsii is (39.2oC [102.6oF] to 40.5oC [104.9oF]), occurring 4 or Dermacentor variabilis (American dog tick); in the 5 days following a tick bite. If present, petechiae and northwestern United States and southwestern Canada, ecchymoses tend to be in oral, ocular, and genital the common vector is D andersoni (Rocky Mountain mucous membranes, and there may be focal retinal wood tick). Dermacentor variabilis is a 3-host tick hemorrhages. Edema of extremities is often noticed in found in southern Oregon, California, and from the dogs and may involve the lips, pinna of ears, penile Great Plains to the Atlantic coast of the United States, sheath, and scrotum.2 In late-stage disease or during and in southeastern Canada. The 3-host D andersoni is recovery, necrosis (acryl gangrene) of the extremities found from the Cascade and Sierra Nevada mountains can develop in dogs. One of the authors (RDW) noted through the Rocky Mountains, to western Nebraska this on the planum nasale of a military working dog and South Dakota, and into southwestern Canada. In that had recovered from RMSF in central Alabama in Latin America, Amblyomma cajennense (Cayenne tick) the early 1980s. Other findings in dogs may include is reported to be the primary vector of R rickettsii.2,3,6 evidence of abdominal pain, anorexia, or both; altered Dermacentor variabilis larvae and nymphs feed on mental status (signs of depression, stupor); myalgia, various small mammals, particularly rodents, after polyarthritis, or both; vestibular deficits (circling, head which they drop off and develop to the next stage.
tilt, or nystagmus); and dyspnea or cough.2 Such signs Unfed larvae may live up to 15 months; unfed nymphs, indicate more disseminated lesions, substantial organ up to 20 months. Adults of this tick prefer medium- sized mammals (eg, raccoon, skunk, and canid species, The most likely abnormal clinical laboratory find- especially the domestic dog), but will readily feed on ings are hypoalbuminemia, moderate leukocytosis humans. Unfed adults can live up to 30 months.
(minimal left shift), and thrombocytopenia. Platelet Following a blood meal, adults drop off, lay from 4,000 counts usually range from 25,000 to 250,000/µL.2 If to 6,500 eggs, and die. Unfed larvae of D andersoni can hypoalbuminemia develops, it probably results from live up to 4 months; unfed nymphs, up to 10 months.
widespread damage to the vascular endothelium and Adults of this tick prefer large mammals (eg, deer, subsequent intercellular leakage. In dogs that are bison, sheep, or cattle), including humans. Unfed examined primarily because of cough or dyspnea, tho- adults may live up to 14 months or longer. Following a racic radiography typically reveals diffuse interstitial blood meal, they drop off, lay approximately 4,000 densities (pneumonitis).2 Criteria for laboratory confir- In the United States, 3 other tick species have been suggested to vector R rickettsii. Amblyomma ameri- Treatment of RMSF in Dogs
canum (Lone Star tick), a 3-host tick, is found from The antibiotics of choice for treating RMSF in dogs central Texas to the Gulf of Mexico and Atlantic coasts, are tetracycline (25 to 30 mg/kg [11.3 to 13.6 mg/lb]), as far north as Iowa, and New Jersey. Rhipicephalus san- doxycycline (10 to 20 mg/kg [4.5 to 9.1 mg/lb]), or guineus (brown dog tick), found from southern Canada chloramphenicol (15 to 30 mg/kg [6.8 to 13.6 mg/lb]).
into tropical South America, is a 1-host tick; all 3 Of course, adequate supportive care must be provided developmental stages prefer to feed and develop on the if the dog has evidence of dehydration, kidney failure, same dog or other canid. This tick is most often found shock, or a hemorrhagic diathesis.2 In dogs, mortality in and around the homes of dog owners (seldom found from RMSF is directly related to incorrect treatment, near woodlots or uninhabited buildings), and some delayed diagnosis, or both. Appropriate antibiotics evidence suggests it may be becoming more anthro- promptly reduce the severity of illness only if they are pophilic.2,3,6 Haemaphysalis leporispalustris (rabbit given before tissue necrosis (thrombotic lesions) or tick), found throughout the Western Hemisphere, has coagulation disorders develop.2 Naturally acquired yielded rickettsiae that are antigenically similar to R immunity most likely plays a role in limiting or pro- rickettsii; however, these are not known to cause clini- tecting against clinical illness. Healthy dogs from cal illness in humans or laboratory mammals, includ- endemic areas often possess anti-SFG antibodies, pos- sibly a result of prior R rickettsii infection or exposureto nonpathogenic SFG rickettsiae.2 Epidemiology of RMSF in Dogs
Rocky Mountain spotted fever tends to be more Epidemiology of RMSF in Humans
common in young (≤ 3 years old ) dogs, and > 80% of In the United States, a seasonal pattern of RMSF in clinical cases occur in dogs that are frequently out- humans parallels what is seen in dogs. Although many doors. Incubation ranges from 2 to 14 days, following clinical cases were likely not reported, the Centers for
infection via tick transmission. In the United States, Disease Control and Prevention (CDC) has received
most dogs with RMSF are presented to veterinarians 200 to 1,120 human case reports annually during the during March through October.2 German Shepherd past 50 years.9-11 Cases have been reported from all con- JAVMA, Vol 221, No. 10, November 15, 2002 tiguous states except Vermont and Maine. To encour- headache, fatigue, muscle pain, nausea or vomiting, and age consistency among state reports, the CDC has loss of appetite.3,10,14 If a rash develops, it appears 2 to 5 advised using a standard clinical definition for human days after the fever begins. The rash begins as small, flat, cases: an acute febrile illness, usually accompanied by blanching macules on the wrists, arms, and ankles. The myalgia, headache, and petechial rash (visible on typical red rash (viz, “spotted” fever) is not seen until 6 palms, soles, or both in two-thirds of those who have or more days following the nonspecific symptoms. This the rash).12 Criteria for laboratory confirmation are rash will involve the palms, soles, or both in 50 to 80% of patients and eventually becomes petechial. 3,7,10 A rash Oklahoma, North Carolina, South Carolina, may never develop in 10 to 15% of patients.
Tennessee, and Arkansas reported the highest incidences Six or more days after initial clinical onset, espe- (per million) of RMSF in humans from 1981 through cially without definitive treatment, more severe signs 1992. Wyoming replaced South Carolina from 1993 and symptoms develop, which include crampy abdom- through 1996.9 North Carolina and Oklahoma reported inal pains, joint pain, diarrhea, and a more severe 35% of total US cases from 1993 through 1996. Rocky headache. At this point, the rash is generally macu- Mountain states reported < 3% (Fig 2).11 Nearly 95% of
lopapular with central petechiae. The eruptions usual- humans with RMSF are infected during April through ly spread centripetally with relative sparing of the September, the same period that gives rise to the great- face.7,10 One of the authors (RDW) investigated a point- est number of nymphal and adult Dermacentor ticks.6,9,11 source outbreak of RMSF that occurred in Arkansas The gender, ethnicity, and age profile of most reported among 44 young, otherwise healthy, military security human cases is male, Caucasian, child (5 to 9 years police personnel. Other than fever, the 4 most common old).3,9,11 Approximately 66% of human cases of RMSF signs and symptoms reported from the 10 serologically confirmed cases were extreme fatigue (100%), severe Exposure to tick-infested habitats or a history of headache (82%), skin rash (73%), and myalgia, tick bite(s) is reported for nearly 60% of all human cases.3,13,14 People who live near wooded lots or have Most patients have normal total WBC counts, frequent exposure to dogs may also be at some with normal differentials; however, thrombocytopenia increased risk of R rickettsii infection, compared with is a common finding, even in early or mild cases of urban or nondog-owning populations. Approximately disease. In the early phase of the disease, serum bio- 10% of humans with RMSF report only a known expo- chemical analyses usually reveal hyponatremia and sure to dogs or a dog’s ticks. Common exposure to the high hepatic enzyme activities. Later, anemia and high same population of ticks (in surrounding environ- sedimentation rates are frequently detected; high BUN ment) is the likely source of these human infections.2,3 and creatinine concentrations indicate renal fail- Although RMSF is primarily a rural and suburban dis- ure.3,10,17 Results of other routine laboratory tests are ease, microecologic niches have also been found in often nonspecific. In the acute stage of illness, a diag- nosis of RMSF should be made largely on the basis ofpatient history, examination findings, and epidemio- Clinical RMSF in Humans
The incubation period in humans generally varies Because R rickettsii induce substantial multi-sys- from 3 to 12 (median, 7) days after an infective tick bite.
tem vasculitis, septic shock can develop and lead to Early signs and symptoms are nonspecific and usually acute respiratory distress. Dark feces may indicate gas- consist of fever (37.8oC [100.0oF] to 39.0oC [102.2oF]), trointestinal hemorrhage. Central nervous system vas-culitis will often present as aseptic meningitis and maylead to thrombotic stroke. Occlusion of other smallarteries may lead to renal failure and gangrene of thefingers or toes.4,17 Other than delayed treatment or mis-diagnosis, there are specific risk factors for more severedisease or fatal outcome. These include male gender,history of alcohol abuse, advanced age, glucose-6-phosphate dehydrogenase deficiency, and non-Caucasian ethnicity. Unless it appears on the palms orsoles, the typical rash of RMSF can be difficult to rec-ognize on dark-skinned individuals.3,10,13 Treatment of RMSF in Humans
Doxycycline is the antibiotic of choice: 4 mg/kg (1.8 mg/lb) for children, divided in 2 doses (every 12hours) orally or IV, to a maximum of 200 mg/day; foradults, 100 mg orally or IV every 12 hours.3,10 If the Figure 2—Average annual human incidence per million popula- patient is treated within 4 to 5 days of disease onset, tion of Rocky Mountain spotted fever by county in the United the fever usually subsides within 24 to 48 hours, and States, 1993 through 1996, based on cases reported to the improvement is rapid. Doxycycline should be con- National Electronic Telecommunications System for Surveillance.
tinued for at least 3 days after the fever subsides and Reprinted with permission from the American Journal of TropicalMedicine and Hygiene.11 until there is unequivocal evidence of disease resolu- JAVMA, Vol 221, No. 10, November 15, 2002 tion, generally 5 to 10 days of treatment.3,10 People diagnostic.12 However, these may not be as practical, with severe or complicated disease may require timely, or widely available.7,10,21 Because there is no longer courses of treatment. In people with mild or widely available rapid laboratory assay to provide early early stages of disease (ie, without significant co- confirmation of RMSF, specific antibiotic treatment morbidity), failure to respond to adequate doses of decisions should be made on the basis of epidemiolog- doxycycline argues against a diagnosis of RMSF.
ic and clinical clues rather than awaiting laboratory Chloramphenicol is an alternate antibiotic for treat- confirmation. An acutely ill 9-year-old human who is ing RMSF in humans, especially if renal failure, preg- presented for care in late May through late August, has nancy, or allergy to doxycycline is documented.
not responded to treatment for a viral syndrome, and However, this drug is associated with a range of has a history of camping in a RMSF-endemic area 10 adverse effects and requires careful monitoring of days prior to disease onset should prompt the inclu- sion of RMSF in the differential diagnosis.3,10,17 Similar signs and symptoms often result from ehrlichiosis and borreliosis (Lyme disease), and both Preventing RMSF
are tickborne zoonoses that occur in some locations Preventing or limiting exposure to ticks, applying that overlap RMSF-endemic areas. Therefore, doxycy- repellants to skin and outer clothing, and rapid and cline should be initially prescribed if either is suspect- safe removal of attached ticks are effective ways to ed. In the Arkansas RMSF outbreak mentioned, the ini- reduce the risk of RMSF in humans.3,10,14 For dog own- tial clinical diagnosis was Lyme disease, but none of ers, the best methods of keeping ticks off the pets may the people who met the case definition, or the controls, be topical or systemic tick-control treatments such as seroconverted to Borrelia burgdorferi. One person who permethrin, fipronil,22 or seasonal dips, along with lim- met the case definition, but did not have a rash, sero- iting access to tick-infested areas. Alternatively, these converted (IgM) to Ehrlichia chaffeensis but not to SFG efforts could include the use of impregnated collars (eg, containing amitraz)23 or regular applications of an Only Maryland appears on both lists of the top 10 acaricidal treatment to kennels. Obviously, the best states for incidence of human RMSF or Lyme disease approach will depend on the geographic region where (1992–1998).9,11,18 However, Lyme disease has received the dog resides, the habit of the dog (most time spent more publicity during the past 25 years, likely result- indoors vs outdoors), and what the dog does (house ing in overdiagnosis and inappropriate prophylaxis pet vs field-trial or hunting). In addition, any ticks with doxycycline for those with a history of tick bite.3,10 attached to dogs should be promptly and carefully Several studies estimate that 38 to 60% of Lyme diag- removed.2 There are no antirickettsial vaccines avail- noses in the northeastern United States may be incor- rect.19,20 Fortunately, as yet, this has not resulted in any For humans, the following personal protective clinical evidence that the agents of RMSF or the other measures ensure the most effective risk reduction 2 diseases are developing resistance to the appropriate when tick-infested areas cannot be avoided3,10,14,24: ' Apply tick repellants to exposed skin. The most effective is DEET (N, n-diethyl-m-toluamide); 20 Criteria for Confirmation
to 35% active ingredient for adults, and 6 to 10% of RMSF Diagnoses in Dogs and Humans
for children ≤ 12 years old. If skin becomes wet Comparing acute and convalescent titers is the from perspiration or water, reapply DEET to dry most practical means of confirming a clinical diagno- skin. Now known as N, n-diethyl-3-methyl-benza- sis. Investigators and clinicians consider the indirect
mide, concentrations of ≥ 35% DEET may be immunofluorescence assay (IFA), which can detect
appropriate for those adults who work for many either IgM or IgG antibodies, to be the serologic stan- hours in tick-infested areas (brush and tall grass; dard for a diagnosis of RMSF.21 A 4-fold or greater woodlots, powerline rights-of-way, etc).25 increase in IgM titers to SFG antigens, from acute to ' Spray permethrin-containing products on outer convalescent (≥ 3 weeks apart) sera, is considered diag- nostic for recent infection.12 Serum samples should be ' Wear long-sleeved shirts and long pants. Tuck pant assayed in parallel after collection of the convalescent sample. Most infected individuals develop increasing ' Wear light-colored clothing to facilitate seeing IgM titers by the seventh day of infection; however, peaks may be delayed in those who promptly receive a ' Conduct body checks immediately after returning correct antibiotic.10,16 A clinically probable, epidemio- from outdoor activities in tick-infested areas; use logically compatible case with a single IFA titer of ≥ 64 mirrors to view all body areas. Remove all ticks for IgM antibodies may be considered diagnostic.10,12 A single IgG titer is more problematic because SFG IgG ' Check children returning from infested areas, may remain high several years after an infection.10,21 especially behind the ears, back of the neck, Other current serologic procedures are considered less around the waist, and in and along the hairline.
' Remove attached ticks by using fine-tipped tweezers.
A positive polymerase chain reaction for R rick- Alternatively, shield fingers with tissue paper, a ettsii antigen, positive immunofluoresence from a skin foil-covered gum wrapper, or plastic sandwich bag lesion biopsy or autopsy specimen, or the isolation of and grasp the tick as close to the skin as possible, R rickettsii from a clinical specimen are also considered pulling upward with steady, even pressure. Do not JAVMA, Vol 221, No. 10, November 15, 2002 twist the tick or cause tick’s mouthparts to remain 4. Paddock CD, Greer PW, Ferebee TL, et al. Hidden mortali- in the skin. Do not burn, puncture, squeeze, or ty attributable to Rocky Mountain spotted fever: immunohistochem- crush the tick’s body because its fluids may be ical detection of fatal, serologically unconfirmed disease. J Infect Dis1999;179:1469–1476.
infectious. Wash the affected area with soap and 5. Goddard J. Basic tick biology and ecology. In: Ticks and water, and disinfect the bite site and your hands.
tickborne diseases affecting military personnel. San Antonio, Tex: Ordinary household brands of 70% isopropyl USAF School of Aerospace Medicine, 1989;13–19.
(rubbing) alcohol or 2% tincture of iodine are ade- 6. Goddard J. Ixodidae (hard ticks). In: Ticks and tickborne dis- eases affecting military personnel. San Antonio, Tex: USAF School ofAerospace Medicine, 1989;70–75, 92–95, 104–106, 123–125.
7. Walker DH. Rocky Mountain spotted fever: a seasonal alert.
Remember that SFG rickettsiae are obligate intra- Clin Infect Dis 1995;20:1111–1117.
cellular parasites and will not survive long once out- 8. Burgdorfer W. A review of Rocky Mountain spotted fever, its agent, and its tick vectors in the United States. J Med Entomol 1975;12:269–278.
Public Health Considerations
9. Dalton MJ, Clarke MJ, Holman RC, et al. National surveillance Rocky Mountain spotted fever is important from the for Rocky Mountain spotted fever, 1981–1992: epidemiologic summary public health perspective.2,10 Based on current knowl- and evaluation of risk factors for fatal outcome. Am J Trop Med Hyg1995;52:405–413.
edge and available antibiotics, RMSF is preventable and, 10. Silber JL. Rocky Mountain spotted fever. Clin Dermatol failing that, theoretically, a nonfatal illness. Why, then, is it currently the most frequently reported and most 11. Treadwell TA, Holman RC, Clarke MJ, et al. Rocky Mountain severe human rickettsial disease in the United States? spotted fever in the United States, 1993–1996. Am J Trop Med Hyg Possibly because biologic and medical knowledge is not communicated with the public or shared between the 12. Centers for Disease Control and Prevention. Case defini- tions for infectious conditions under public health surveillance.
professions.2,3,10 Veterinarians and physicians need to MMWR Morb Mortal Wkly Rep 1997;46(RR-10):28–29.
increase their diagnostic suspicion between the months 13. McQuiston JH, Holman RC, Groom AV, et al. Incidence of of April and September. As a zoonosis, RMSF in dogs Rocky Mountain spotted fever among American Indians in can serve as a sentinel event in the community.2 Oklahoma. Public Health Rep 2000;115:469–475.
Veterinarians need to inform and encourage more 14. Rotz L, Callejas L, McKechnie D, et al. An epidemiologic pet owners about measures to prevent RMSF and share and entomologic investigation of a cluster of Rocky Mountain spot-ted fever cases in Delaware. Del Med J 1998;70:285–291.
more information about local zoonoses with physi- 15. Salgo MP, Telzak EE, Currie B, et al. A focus of Rocky cians in the community.2 Likewise, physicians need to Mountain spotted fever within New York City. N Engl J Med 1988; be more suspicious of RMSF in patients with spring or summer flu-like illness, especially in children, without 16. Warner RD, Jemelka ED, Jessen AE. An outbreak of tick- evidence of coryza, sore throat, or cough.4,17 bite associated illness among military personnel subsequent to a field Doxycycline is proven safe and effective in treating training exercise. J Am Vet Med Assoc 1996;209:78–81.
RMSF, and courses of therapy for ≤ 14 days have not 17. Centers for Disease Control and Prevention. Consequences of delayed diagnosis of Rocky Mountain spotted fever in children: resulted in staining of children’s teeth.7,10 Members of West Virginia, Michigan, Tennessee, and Oklahoma, May–July 2000.
both professions should report all RMSF cases to local MMWR Morb Mortal Wkly Rep 2000;49:885–888. 18. Centers for Disease Control and Prevention. Surveillance Everyone needs to be aware that RMSF continues for Lyme disease—United States, 1992-1998. MMWR Morb Mortal to be endemic in densely populated areas of many Wkly Rep 2000;49(SS-03):1–11.
states, least commonly in the Rocky Mountains, and 19. Rose CD, Fawcett PT, Gibney KM, et al. The overdiagnosis of Lyme disease in children residing in an endemic area. Clin Pediatr the typical rash is not often part of the clinical presen- tation.10,13-15 Community health education efforts need 20. Reid MC, Schoen RT, Evans J, et al. The consequences of to stress that age-specific incidence is high in children, overdiagnosis and overtreatment of Lyme disease: an observational there are effective preventive measures, and treatment study. Ann Intern Med 1998;128:354–362.
needs to begin as early as possible. Otherwise there can 21. Centers for Disease Control and Prevention, National be serious sequelae, with the untreated case fatality Center for Infectious Diseases, Division of Viral and Rickettsial rate ranging from 15 to 30%.4,10,11,17,24 If we all do as Diseases. Rocky Mountain spotted fever: laboratory detection.
Available at: www.cdc.gov/ncidod/dvrd/rmsf/Laboratory.htm.
much health education as possible, RMSF should be much less of a threat in our communities.
22. Endris RG, Matthewson MD, Cooke D, et al. Repellency and efficacy of 65% permethrin and 9.7% fipronil against Ixodes rici- References
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the dog and cat. 2nd ed. 1998. Philadelphia: WB Saunders Co, 1998; Available at: www.cdc.gov/ncidod/dvrd/rmsf/Prevention.htm.
3. Thorner AR, Walker DH, Petri WA Jr. Rocky Mountain 25. Pollack RJ, Kiszewski AE, Spielman A. Perspective: spotted fever. Clin Infect Dis 1998;27:1353–1359.
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JAVMA, Vol 221, No. 10, November 15, 2002

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