Rocky Mountain Spotted Fever

AUTHORS:
Michael Weipert, MD • Sean O’Mara, MD

AFFILIATIONS:
US Navy Aerospace Medicine, Naval Hospital Pensacola, Florida

CITATION:
Weipert M, O’Mara S. Rocky Mountain spotted fever. Consultant. Published online July 30, 2020. doi:10.25270/con.2020.07.00008

Received April 8, 2020. Accepted June 19, 2020.

DISCLOSURES:
The authors report no relevant financial relationships.

DISCLAIMER:
The views expressed in this article are those of the authors and do not necessarily reflect the official position of the institution, the Department of the Navy, the Department of Defense, or the United States Government.

CORRESPONDENCE:
Michael Weipert, MD, Naval Hospital Pensacola, 6000 US-98, Pensacola, FL 32512 (michael.j.weipert.mil@mail.mil)

A 26-year-old man presented to his primary care physician (PCP) in Pensacola, Florida, with fever, headache, and myalgia. He was worried because he had already been to an urgent care clinic twice within a week with the same concern, and his symptoms appeared to be worsening.

The patient explained to the PCP that a week ago, he had been healthy and had traveled to Tennessee to visit family and to hunt; 2 days after having returned to the Pensacola area, he had awoken with a fever and myalgia and had decided to stay home from work. The patient learned that his father back in Tennessee simultaneously had been experiencing the same symptoms; both men assumed that they had been exposed to the same sick contact and had contracted influenza, since neither had received a recent flu shot. As the day progressed, however, the patient’s fever continued to rise. He became extremely fatigued and experienced abnormally intense myalgia, prompting him to have a friend take him to an urgent care clinic late in the evening.

At the urgent care clinic, test results for influenza and streptococcal infection were both negative. He was diagnosed with “a flulike illness” and was given acetaminophen. He returned home and decided to stay home from work for a few days to rest. The patient’s fever and fatigue did not abate, and his myalgia and nausea continued to worsen; 48 hours after his initial visit to the urgent care clinic, he returned to the same clinic for imaging and additional laboratory testing.

Chest radiography findings were unremarkable, and test results for influenza A and B viruses, streptococcus, and Epstein-Barr virus were negative. The results of a comprehensive metabolic panel showed an elevated alanine aminotransferase (ALT) level of 67 U/L, an elevated aspartate aminotransferase (AST) level of 80 U/L, an elevated creatinine level of 1.4 mg/dL, and thrombocytopenia (platelet count, 125 × 10³/µL). Complete blood cell count results showed leukopenia (white blood cell [WBC] count, 2390/µL), and urinalysis revealed elevated levels of WBCs (11/high-power field), red blood cells (5/high-power field), hyaline casts (8/low-power field), protein (100 mg/dL), ketones (10 mg/dL), hemoglobin (1+), and urobilinogen (>12 mg/dL).

The patient was again diagnosed with “a flulike illness” and was given ibuprofen and ondansetron. He was told not to return to the urgent care clinic, given that the clinical workup had not revealed any serious illness, but instead to follow up with his PCP in 48 hours if symptoms persisted.

The patient’s symptoms did not improve, so he presented to his PCP’s office, 5 days after onset of symptoms. Because the patient had only returned from a trip to Tennessee 6 days previously, the PCP began looking for information that would be useful in determining the etiology of the man’s symptoms in relation to his recent activity while on vacation. The patient reviewed physical activities, sexual contacts, food consumption, and locations visited. Noting that the patient’s father had been experiencing the same symptoms, the PCP pressed further about where the two had been together; the patient stated that they had been hunting in a swamp in Tennessee. His father had shot a deer, and the patient had helped field-dress the deer (ie, remove the internal organs).

He recalled noticing that the deer had evidently been in the swamp for some time, because it was covered in ticks. Despite that, neither hunter found any ticks or noticed any tick bites upon their return from hunting. The patient had worn boots, long pants, a long-sleeved shirt, and a hat while hunting; however, he had not used any insecticide spray, nor had he worn gloves while field-dressing the deer. The PCP asked repeatedly whether the patient had noticed any cuts, abrasions, or other skin abnormalities on his hands or elsewhere, but the patient insisted that there had been none.

Physical examination findings showed a patient in obvious discomfort but were otherwise unremarkable, with no rash present anywhere on his body. Based on the findings of the history and physical examination, laboratory tests were performed, the results of which are summarized in the accompanying Table.

The laboratory test results returned within 36 hours and were positive for Rocky Mountain spotted fever (RMSF). At that time, the patient was sent to a local emergency department (ED) for further treatment. He received intravenous doxycycline and was released from the hospital 8 hours after having arrived at the ED.

The next day, he continued to take oral doxycycline and stated he felt “90% better” within 18 hours of the initial dose of intravenous doxycycline. The patient noted that for a few days after treatment, he experienced decreased libido and genital discomfort, but 7 days after starting doxycycline, all of his symptoms had completely resolved with no complications or sequelae.

In this case, the patient never developed the classic rash of RMSF or any other skin abnormality. He contacted his father and explained the situation and diagnosis, after which his father was also treated with doxycycline and made a full recovery.

DISCUSSION

RMSF is a tickborne disease caused by Rickettsia species that produces vascular injury to an infected patient. The Gram-negative bacteria species is an intracellular type that brings about vascular permeability through the production of prostaglandins that are created by the endothelial cells.¹ While RMSF has been identified in every state in the contiguous United States (Figure 1), more than 50% of cases are reported in 5 states (Arkansas, Missouri, North Carolina, Tennessee, and Virginia).²

The seasonal distribution of RMSF skews toward spring and early summer, which correlates to both the activity of the transmitting ticks and when people are most active outdoors.³

The vector for RMSF east of the Mississippi River is the American dog tick (Dermacentor variabilis) (Figure 2), while the vector for RMSF west of the Mississippi River is the Rocky Mountain wood tick (Dermacentor andersoni). The tick bites and attaches itself to the host, and after 6 to 10 hours, the rickettsia are released from the salivary glands of the tick. Because tick bites are painless, up to one-third of patients with RMSF do not report a tick bite.⁴ The incubation period from the tick bite to the development of symptoms is usually from 5 to 7 days.

RMSF presents with nonspecific symptoms of fever, headache, myalgia, and arthralgia. The classic sign of RMSF is a maculopapular rash that appears from 2 to 6 days after the onset of the original fever (Figures 3 and 4). The patient in this case presented with the other classic RSMF symptoms but did not have a rash. This is an uncommon presentation, given that the rash is present in most patients who test positive for RMSF, with only 12% of RMSF-positive patients never developing a rash.⁵ The rash typically begins on the wrists and ankles, but as the disease progresses, the rash can invade the trunk, palms, and soles.

A rash-less patient makes the initial diagnosis of RMSF much more difficult, since most of the symptoms are not unique to any single disease. Laboratory test results can show thrombocytopenia due to the vascular injury, which will become more pronounced with the degree of vascular injury. Azotemia can occur, but it is usually a result of systemic hypotension, which can also lead to acute tubular necrosis.

The preferred treatment for RMSF is doxycycline for adults (men, nonpregnant women, and pregnant women) and children. If a patient has a severe reaction to doxycycline, then chloramphenicol is an option. In almost all cases, however, preventing the tick bite is easier than treating the disease. When undertaking outdoor activities, especially in the spring and early summer, the Centers for Disease Control and Prevention recommends wearing boots, long pants, long sleeves, and gloves that have been treated with 0.5% permethrin.⁶

REFERENCES:

1. Rydkina E, Sahni A, Baggs RB, Silverman DJ, Sahni SK. Infection of human endothelial cells with spotted fever group rickettsiae stimulates cyclooxygenase 2 expression and release of vasoactive prostaglandins. Infect Immun. 2006;74(9):5067-5074. doi:10.1128/IAI.00182-06
2. Centers for Disease Control and Prevention. Rocky Mountain spotted fever: epidemiology and statistics. Last reviewed April 7, 2020. Accessed July 1, 2020. https://www.cdc.gov/rmsf/stats/index.html
3. Spach DH, Liles WC, Campbell GL, Quick RE, Anderson DE Jr, Fritsche TR. Tick-borne diseases in the United States. N Engl J Med. 1993;329(13):936-947. doi:10.1056/NEJM199309233291308
4. Treadwell TA, Holman RC, Clarke MJ, Krebs JW, Paddock CD, Childs JE. Rocky Mountain spotted fever in the United States, 1993-1996. Am J Trop Med Hyg. 2000;63(1-2):21-26. doi:10.4269/ajtmh.2000.63.21
5. Helmick CG, Bernard KW, D’Angelo LJ. Rocky Mountain spotted fever: clinical, laboratory, and epidemiological features of 262 cases. J Infect Dis. 1984;150(4):480-488. doi:10.1093/infdis/150.4.480
6. Centers for Disease Control and Prevention. Preventing tick bites. Last reviewed September 30, 2019. Accessed July 1, 2020. https://www.cdc.gov/ticks/avoid/on_people.html