Hidoc Bulletin

A genus of vector-borne organisms known as Rickettsia cause acute febrile diseases throughout the world. Although rickettsial infections have a similar clinical description, the causal organisms and epidemiology can differ depending on the area. Since these diseases can potentially cause morbidity and mortality, it is crucial to identify the symptoms and the epidemiology of a region to efficiently diagnose and treat them as soon as possible.

Etiology:

There are several obligatory intracellular bacteria in the genus Rickettsia that cause rickettsial infections, and they can fall into one of four groups – spotted fever groups, typhus groups, ancestral groups, and transitional groups. The most common rickettsial infection in North America is Rocky Mountain spotted fever and it is caused by Rickettsia rickettsii. Similarly, other species are common in other regions – 
 • Rickettsia africae is found in Saharan Africa and causes African  tick bite fever.
 • Rickettsia conorii is found in Europe and North Africa and  causes Mediterranean spotted fever.
 • Rickettsia prowazekii and Rickettsia typhi present as typhus syndrome.

Epidemiology:

Rickettsia is typically transmitted by carriers such as ticks, body lice, mites, and fleas. Humans are usually considered unintentional hosts in these situations. The majority of cases of Rocky Mountain spotted fever in the United States are caused by the American dog tick (Dermacentor variabilis), the Rocky Mountain wood tick (Dermacentor andersoni), and the Lone Star tick (Amblyomma americanum). All age groups are at risk for Rickettsial infections, especially the Population exposed to outdoor activities are at a high risk of Rickettsial infections. The spread of Rickettsial infections is more among tourists.

Pathophysiology:

Rickettsia attacks the vascular endothelial cells that make up the small and medium blood arteries throughout the body, resulting in systemic symptoms and mortality rates associated with these infections. 
Endothelial cell infection causes an increase in vascular permeability,widespread inflammation, and loss of barrier function throughout the body

Symptoms:

Fever, headache, muscle aches, swollen lymph glands, cough, and rash. 

Diagnosis:

The diagnosis of Rickettsial fever is done by Culture, nucleic acid amplification (NAA), and serology which further three methods.

 • Rapid diagnostic tests (RDTs)
 • Indirect immunofluorescence assays (IFAs)
 • Enzyme-linked immunosorbent assay

Differential diagnosis includes – Dengue, Leptospirosis, Measles, pediatric rubella, pediatric syphilis, and Meningococcal infection.

Prognosis:

Rickettsial infections range in severity depending upon the host characteristics, such as the level of immunocompetence, and the severity of the Rickettsia species. If the infection is not identified at an early stage, then it shows high mortality rates as R rickettsii and R prowazekii are one of the most fatal species.

Treatment:

The treatment choice is made keeping in mind the prompt treatment due to the high mortality rates of Rickettsial infection.

 • Doxycycline from the class of tetracycline antibiotics is the preferred medication for treating rickettsial infections. The dosage and duration of treatment depend on the particular causal organism.
 • Chloramphenicol is a treatment option for allergies and serious illnesses. 
 • Clarithromycin and other macrolides can be used to treat moderate infections.