Rocky Mountain spotted fever natural history

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Ilan Dock, B.S.

Overview

Rocky Mountain spotted fever, like all rickettsial infections, is classified as a zoonosis. Zoonoses are diseases of animals that can be transmitted to humans. Many zoonotic diseases require a vector (e.g., a mosquito, tick, or mite) in order to be transmitted from the animal host to the human host. In the case of Rocky Mountain spotted fever, ticks are the natural hosts, serving as both reservoirs and vectors of R. rickettsii. Ticks transmit the organism to vertebrates primarily by their bite. Less commonly, infections may occur following exposure to crushed tick tissues, fluids, or tick feces.

A female tick can transmit R. rickettsii to her eggs in a process called transovarial transmission. Ticks can also become infected with R. rickettsii while feeding on blood from the host in either the larval or nymphal stage. After the tick develops into the next stage, the R. rickettsii may be transmitted to the second host during the feeding process. Male ticks may transfer R. rickettsii to female ticks through body fluids or spermatozoa during the mating process. These types of transmission represent how generations or life stages of infected ticks are maintained. Once infected, the tick can carry the pathogen for life.

Natural history

Early Onset Symptoms (2-14 days after infected tick bite):

Late Stage:

Untreated or Improperly Diagnosed:


Complications

Possible complications include:

Long term complications:

  • Paralysis of lower extremities
  • Impaired bladder function
  • Impaired bowel function
  • Amputation
  • Hearing impairment
  • Speech Disorders[1]

Prognosis

  • Treatment usually cures the infection.
  • Complications can include paralysis, hearing loss, nerve damage, and, if left untreated or treated but less commonly occurring, death.
  • Rocky Mountain spotted fever can be a severe illness, and the majority of patients are hospitalized.
  • Prior to the development of tetracycline and chloramphenicol, antibiotics, Rocky mountain spotted fever's mortality rate was as high as 87%. Now, with new medical practices including the implementation of antibiotic therapies, the mortality rate is approximately 20% if untreated and 5% if treated properly. [3]
  • Infection with R. rickettsii may provide long lasting immunity against re-infection.
  • Previous infection with Rocky Mountain spotted fever should not deter persons from practicing good tick-preventive measures or visiting a physician if signs and symptoms consistent with Rocky Mountain spotted fever occur, especially following a tick bite, as other diseases may also be transmitted by ticks. [4]

Illness Severity

Epidemiology Graph 3 - Comparison between RMSF cases and their fatality.
Epidemiology Graph 3 - Comparison between RMSF cases and their fatality.

Initial health problems

  • Rocky Mountain spotted fever can be a very severe illness and patients often require hospitalization. Because R. rickettsii infects the cells lining blood vessels throughout the body, severe manifestations of this disease may involve the respiratory system, central nervous system, gastrointestinal system, or renal system.
  • Host factors associated with severe or fatal Rocky Mountain spotted fever include advanced age, male sex, African-American race, chronic alcohol abuse, and

glucose-6-phosphate dehydrogenase (G6PD) deficiency.

  • Deficiency of G6PD is a sex-linked genetic condition affecting approximately 12% of the U.S.
  • African-American male population; deficiency of this enzyme is associated with a high proportion of severe cases of Rocky Mountain spotted fever. This is a rare clinical course that is often fatal within 5 days of onset of illness. [5]
  • Long-term health problems following acute Rocky Mountain spotted fever infection include partial paralysis of the lower extremities, gangrene requiring amputation of fingers, toes, or arms or legs, hearing loss, loss of bowel or bladder control, movement disorders, and language disorders.
  • These complications are most frequent in persons recovering from severe, life-threatening disease, often following lengthy hospitalizations. [5]

Long term health problems

References

  1. 1.0 1.1 Rocky Mountain Spotted Fever general information. American Lyme Disease Foundation (2016). Accessed on January 11, 2016
  2. Rocky Mountain Spotted Fever Symptoms. Centers for Disease Control and Prevention (2015). http://www.cdc.gov/rmsf/symptoms/index.html Accessed on December 30, 2015
  3. Dantas-Torres, Filipe. Lancet Infect Disease 2007;7:724-32. Department of Immunology, Center of Research Aggeu Magalhaes, Oswaldo Cruz Foundation. Recife Pernambuco, Brazil. Volume 7, November 2007. Accessed on January 11, 2016
  4. Rocky Moutnain Spotted Fever. Department of Health. Idaho Health District 4. http://www.cdhd.idaho.gov/CD/public/factsheets/rockymtnspottedfever.htm Accessed on January 11, 2016
  5. 5.0 5.1 5.2 Rocky Mountain Spotted Fever Symptoms. Centers for Disease Control and Prevention (2015). http://www.cdc.gov/rmsf/symptoms/index.html Accessed on December 30, 2015