Rocky Mountain spotted fever (RMSF) is a disease caused by infection with bacterium Rickettsia rickettsia which is transmitted by a bite from infected ticks.
Three (3) species of ticks have been identified to be carriers of this bacterium:
Rocky mountain wood tick (Dermacentor andersoni), American dog tick (Dermacentor variabilis), and the Brown dog tick (Rhipicephalus sanguineus).
These are a female (left) and male (right) Rocky Mountain Wood Tick (Dermacentor andersoni).
Female (left) and male (right) American dog tick (Dermacentor variabilis)
Brown dog tick (Rhipicephalus sanguineus) (female on left, male on right).
Below is a link to a website dedicated to Rocky Mountain Fever:
http://www.aldf.com/rocky-mountain-spotted-fever
Below is some information from that website regarding this illness.
What is Rocky Mountain Spotted Fever?
Rocky Mountain spotted fever (RMSF) is most serious tick-borne disease in US & is caused by Rickettsia rickettsii, a type of bacteria known as rickettsia. These bacteria are transmitted to humans by bite of certain hard ticks.The 2 most important species of ticks that can transmit R. rickettsii in United States are Dermacentor variabilis (American dog tick) & Dermacentor andersoni (Rocky Mountain wood tick).
A third species, Rhipicephalus sanguineus (brown dog tick) has been implicated as a vector.
Dogs are susceptible to RMSF, & sometimes household members of infected dogs may also be at risk for acquiring disease. In countries south of US, cayenne tick (Amblyomma cajennense) has also been shown to act as a vector of RMSF.
More recently another rickettsie has been identified as cause of a spotted fever-like disease. Theis species, called Rickettsia parkeri, was first identified more than 60 years ago in Amblyomma maculatum ticks (Gulf coast ticks).
Confirmation of R. parkeri as a causative agent of human disease occurred in 2002 when serological (blood) tests, immunohistochemical staining, cell culture isolation & other molecular tests positively verified infection in a patient.
The classic symptoms of RMSF include fever & a spotted (petechial) rash, although they aren't always present. RMSF can be a fatal disease & patients often require hospitalization.
Severe illness is seen more often in patients who delay seeking care from a physician because such patients don't receive antibiotic treatment as soon as they should.
RMSF is considered an acute infection & infection with Rickettsia rickettsii is thought to provide long-lasting immunity against re-infection, however this shouldn't deter those who feel they suffer symptoms from seeking care.
RMSF is typically treated with a course of tetracycline antibiotics (CDC).
Where is Rocky Mountain Spotted Fever Prevalent?
Although first recognized in late 19th century in Rocky Mountain region, by 1930s this disease was found to be present in eastern portion of country as well.The wood tick (Dermacentor andersoni), one of main tick vectors is found in Rocky Mountain states& southwestern Canada. The second major vector is American dog tick (Dermacentor variabilis).
This tick is distributed east of Rocky Mountains & in some regions along Pacific Coast.
The cayenne tick (Amblyomma cajennense) is found in South & Central America; however its range also extends into some southern states including Texas.
The most recently implicated vector of R. parkeri is lone star tick (Amblyomma americanum). It is found in southern states as well as along East coast up to Maine.
There has been a marked drop in incidence of RMSF in Rocky Mountain States since 1940s. Today over half of cases of RMSF occur in South Atlantic states (Delaware through Florida).
Rocky Mountain spotted fever is a seasonal disease with majority of cases occurring between months of April & September. Clustered cases of RMSF have occurred among families in states including Kentucky, Arizona & Oklahoma.
Rocky Mountain spotted fever is a nationally notifiable disease to CDC, & cases are reported via 2 national surveillance systems, standardized case report forms & National Electronic Telecommunications System for Surveillance (NETSS).
Cases are considered confirmed or probable based on results of lab tests. Over last 50 years approximately 250 to 1200 cases have been reported annually.
Image obtained from CDC MMWR Report
Symptoms
Symptoms of Rocky Mountain spotted fever usually appear 2 to 14 days (average of 7 days) after being bitten by infected tick.Fever is often first symptom experienced by patients. The classic triad of fever, rash & tick bite is present among many but not all cases at initial visit to physician.
Nausea, vomiting, severe headache, muscle pain & lack of appetite are also sometimes reported by patients in early stage of disease.
Other clinical symptoms include abnormal platelet count (thrombocytopenia), elevated liver enzymes, & electrolyte abnormalities.
The initial rash tends to appear 2 or 3 days after onset of illness as small pink non-itchy spots (macules) on skin that later become characteristic spotted red rash (petechiae).
The rash is most often found on ankles& wrists & then appears on trunk, palms & soles. The characteristic petechial rash occurs in only 35 to 60% of patients, & as many as 10 to 15% of patients may never develop a rash. Other late stage symptoms associated with RMSF include abdominal pain, joint pain, & diarrhea.
Long term consequences of RMSF include paralysis of lower extremities, hearing loss, loss of bowel or bladder control, loss of limbs through amputation, movement disorders, & language disorders.
If left untreated RMSF can be fatal.
Symptoms of spotted fever like disease caused by most recently implicated rickettsia, R. parkeri, are very similar to those caused by R. rickettsii.
However, while lesions (called eschars) at site of tick bite rarely occur in R. rickettsii-associated RMSF, they do occur in infections caused by R. parkeri.
Diagnosis
Clinical diagnosis of RMSF is based on serological tests including detection of antibody titers via IFA, detection of bacterial agent via culture or immunohistochemical staining of biopsies, & by detection of bacterial DNA in a clinical specimen via PCR.However, treatment decisions shouldn't be delayed while waiting for confirmation with lab results. Patients with a relevant history & symptomology should be treated with appropriate antibiotic regimen immediately.
Since R. rickettsii & R. parkeri bacterial species are so closely related, cross-reactivity between these 2 agents may make it difficult to distinguish between them using less specific serological or immunohistochemical assays.
Treatment
Upon suspicion of Rocky Mountain spotted fever, treatment should begin immediately. Delay of treatment has been associated with fatal outcomes.Treatment with tetracycline or chloramphenicol antibiotics can be used to treat RMSF. Doxycycline (a tetrycycline) antibiotic is treatment of choice for both adults & children. However doxycycline isn't recommended for use by pregnant women.
Current recommendations from Centers for Disease Control & Prevention (CDC) include doxycycline therapy for 5 to 10 days. Complicated disease cases may require longer treatment. Patients usually see an improvement in fever 24 to 72 hours after starting antibiotics.
No comments:
Post a Comment