Rocky mountain spotted fever

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University of Oklahoma Study Abroad Microbiology in Arezzo, Italy[1]
Transmission electron Microscope image of Rickettsia rickettsii[2]

Classification

Taxonomy

Bacteria; Proteobacteria; Alpha Proteobacteria; Rickettsiales; Rickettsiaceae; Spotted fever group

NCBI: Taxonomy

Rickettsia rickettsii

Description

Rocky Mountain Spotted Fever is the disease associated with infection by Rickettsia rickettsii. The organism Rickettsia rickettsii was first discovered by Dr. Howard Rickets. R. rickettsii is a small rod shaped bacterium that lives within the cytoplasm of a host cell. It requires an arthropod for transmission to a human host typically through bite and is known to be caused primarily by tick bites. Rocky Mountain Spotted Fever can also infect other mammals, particularly dogs. The disease is characterized by a skin rash called purpura or petechiae, though the rash can occur up to five days after the onset of the other symptoms including fever, nausea, vomiting, headache, muscle pain, and depression.[6]

Genetic Makeup

The entire genome has an average length of 1.269 mB that codes for approximately 1225 proteins. [7]

Pathology

Early Stage Rash in RMSF patient.[3]
Late Stage rash in RMSF patient.[4]

Symptoms

Symptoms of RMSF include rash, fever, depression, nausea, vomiting, and muscle pains. The rash appears in 90% of patients, though fever and other symptoms often proceed the rash by 2-5 days. After the 6th day of infection, a petechial (red to purple spotted rash) occurs in 35-60% of patients and is indicative of severe disease progression. RMSF can be fatal within 8 days if not properly treated. [8]

Treatment

The primary treatment for RMSF in adults is 100 mg of the antibiotic Doxycycline every 12 hours for 7-14 days. The standard treatment for children is 45kg of Doxycycline every 12 hours for 7-14 days. Doxycycline is the treatment of choice because it is associated with the lowest fatatily of treatments used for RMSF. Alternate treatments include other antibiotics, but are not recommended by the CDC due to higher risk of patient death. [9]

Transmission

Rocky Mountain Spotted Fever is most often spread through the bite of a tick. The most common ticks to carry Ricketsia ricketsii are the American dog tick (Dermacentor variabilis), Rocky Mountain wood tick (Dermacentor andersoni), and brown dog tick (Rhipicephalus sanguineus). An infected tick can infect multiple hosts with Ricketsia ricketsii. [10]

Damage Response Framework

Rocky Mountain Spotted Fever has a 2-14 day incubation period before the first symptom, typically fever, shows. The fever, accompanied by headache, is typically sudden onset. 2-5 days after fever, headache, nausea, and other symptoms begin, approximately 90% of patients show the typical small, flat, non-itchy pink rash. After approximately 6 days of symptoms, the rash turns to a darker red or purple rash (petechial rash) in 30-65% of patients.
After 8 days of infection, RMSF can become fatal. Because the disease effects epithelial cells a long term infection can lead to acute damage of the blood vessels, bleeding or clotting in the brain or other major organs, and organ failure. Patients who are not treated by day 8 of infection run a high risk of long term effects from the acute symptoms. [11]

Epidemiology

Graph describing incidence of RMSF in North America over time, comparing fatality and incidence changes.[5]

Socioeconomic Effects

Rocky Mountain Spotted Fever is a very costly disease when epidemics arise, especially in small communities. A recent outbreak in 2002 caused 20 deaths on an American Indian reservation and an estimated $13.2 million in total loss when accounting for immediate productivity loss (~$181,000) and extended productivity loss due to permanent disability and death. [12]

Demographics

The nature of tick bourne disease is that cultures and demographics that spend more time in the outdoors are most prominently effected. In north and south America, native groups such as American Indian reservations and other tribes are the most likely to face high numbers of tick born illness including Rocky Mountain Spotted Fever, which occurs at a rate of 37.4 case per million in American Indian populations vs. 21.6 cases per million in the general Oklahoma population. [13]

Prevention

Instructions for preventing tick born illnesses by preventing tick bites can be seen at http://www.cdc.gov/ticks/avoid/on_people.html. It is important to follow tick prevention protocol. Rocky Mountain Spotted Fever is completely preventable, as are other tick born diseases. [14] Risk factors for contracting a tick born disease include demographics but are also largely correlated with the prevalence of roaming dogs. Animal control is an important part of preventing epidemics of tick born diseases. Dogs should be properly treated for ticks and kept away from roaming animals. [15]

References

Centers for Disease Control and Prevention. (2013). Retrieved July 28, 2015, from http://www.cdc.gov/rmsf/?rf=
Centers for Disease Control and Prevention. (2013, May). Retrieved July 28, 2015, from http://www.cdc.gov/rmsf/symptoms/index.html
Centers for Disease Control and Prevention. (2013, May). Retrieved July 28, 2015, from http://www.cdc.gov/rmsf/stats/index.html
Centers for Disease Control and Prevention. (2014). Retrieved July 28, 2015, from http://www.cdc.gov/ticks/avoid/on_people.html
CDC: Costly Epidemic of Rocky Mountain Spotted Fever in AZ. Retrieved July 28, 2015, from http://www.doctorslounge.com/index.php/news/pb/56116 Rocky Mountain spotted fever. Retrieved July 28, 2015, from http://www.mayoclinic.org/diseases-conditions/rocky-mountain-spotted-fever/basics/risk-factors/con-20032780
Summary. Retrieved July 28, 2015, from http://www.ncbi.nlm.nih.gov/genome/?term=rickettsia+rickettsii
http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Tree&id=2&lvl=3&lin=f&keep=1&srchmode=1&unlock Taxonomy
http://www.researchgate.net/publication/12095919_Incidence_of_Rocky_Mountain_spotted_fever_among_American_Indians_in_Oklahoma

Page by Cassandra Long, student of Tyrrell Conway