Rickettsiosis - An Overview

What Is Rickettsiosis?

Rickettsia organisms are found all over the world and are spread by a variety of hematophagous arthropod vectors such as ticks, lice, mites, and fleas. Despite their prevalence in nature, these organisms are frequently overlooked as a significant cause of illness around the world. This is due, in part, to their undifferentiated clinical manifestations, which are often indistinguishable from other acute febrile infectious diseases found in tropical and subtropical locations. Rickettsioses are also challenging to diagnose because there are no rapid point-of-care tests available to establish the diagnosis during acute infection. Confirmation of the diagnosis is usually sought retrospectively through serologic techniques.

Recognizing these diseases as a cause of acute febrile illness is critical because symptoms can be quickly alleviated with proper treatment. When highly pathogenic species are involved, treatment delays are linked to poor outcomes and death. It is challenging to know the full societal impact of rickettsioses because clinicians frequently fail to recognize them as a potential cause of illness. Still, it has been demonstrated that these illnesses can impact the productivity of those afflicted and cost a great deal to the health care system if not promptly recognized. These pathogens continue to emerge and reappear as causes of illness worldwide. Tick-borne infections, such as spotted fever group (SFG) rickettsioses, have increased even in the United States.

Furthermore, as the world becomes more mobile, there is a risk of contracting these diseases while traveling. Indeed, SFG rickettsioses are becoming more common in travelers, particularly those visiting Sub-Saharan Africa, and murine typhus is becoming more common in Europeans visiting Southeast Asia and the United States. The names of diseases associated with an agent frequently reflect their discovery region, but they often fail to encompass their entire geographic range. For example, Rocky Mountain spotted fever (RMSF), despite being first described in Idaho and attributed to ticks in Montana, is a disease that affects the entire Americas. In the United States, RMSF is found in the southeast and south-central states, where Dermacentor variabilis transmits it, and in the western mountainous states, where D. Andersoni transmits it.

There are numerous rickettsial species, but these three organisms are responsible for the majority of human rickettsial infections:

• R. rickettsii.

• R. typhi.

• R. prowazekii.

What Are the Symptoms of Rickettsiosis?

Rickettsiae proliferate at the site of arthropod attachment and frequently cause a local lesion known as eschar. Some organisms like R. rickettsii multiply in the endothelial cells of small blood vessels, causing vasculitis. In contrast, other organisms like Ehrlichia species replicate in monocytes, and Anaplasma species reproduce in granulocytes. When infected with Orientia species or members of the spotted fever group, regional lymphadenopathy is common (except for R. rickettsii). R. rickettsii endovasculitis causes a petechial rash due to focal areas of hemorrhage, encephalitic signs, and skin and tissue gangrene.

Patients with typhus or spotted fever may develop:

• Ecchymotic skin necrosis

• Edema (due to increased vascular permeability).

• Circulatory collapse.

• Digital gangrene.

• Oliguria.

• Shock.

• Azotemia.

• Anuria.

• Hyponatremia.

• Anemia.

• Delirium.

• Hypochloremia.

• Coma.

How Is Rickettsiosis Diagnosed?

• Based on clinical characteristics.

• To detect organisms, a rash biopsy is performed using fluorescent antibody staining.

• Serologic testing in the acute and convalescent states (In acute cases, serologic testing is not useful).

• Using polymerase chain reaction (PCR).

What Is the Treatment of Rickettsiosis?

Clinical recognition is the most crucial aspect of timely and effective rickettsial illness treatment. When a rickettsial infection is suspected or considered appropriate, prompt empiric treatment with an effective antibiotic should be administered. Many commonly prescribed antibiotics, such as penicillins, cephalosporins, and sulfonamides, do not affect rickettsiae. Sulfonamides, such as trimethoprim-sulfamethoxazole, have been linked to adverse outcomes.

Tetracyclines are the drug of choice for all SFG and typhus group rickettsioses. Doxycycline is the preferred agent in this class due to its improved tolerability and twice-daily dosing. Minocycline is also helpful. Unlike their prototype congeners, such as tetracycline hydrochloride, doxycycline and minocycline are bioavailable in food, reducing the gastrointestinal discomfort associated with this class of agents. When a critical illness or nausea and vomiting make oral administration impossible, doxycycline should be administered parenterally.

In pregnant women, tetracycline has been linked to fatal hepatotoxicity and pancreatitis. It also accumulates in the fetal skeleton, inhibiting bone growth. These events do not appear to be associated with doxycycline. As a result, in the case of RMSF and other rickettsioses with severe manifestations during pregnancy, the benefits outweigh the risks. Short and infrequent courses of tetracyclines, particularly doxycycline, do not significantly stain children's developing permanent teeth. Doxycycline is advised for the treatment of children of all ages who are suspected of having RMSF or another severe rickettsiosis. Although true doxycycline hypersensitivity appears to be uncommon, desensitization protocols are available in closely supervised settings such as the intensive care unit.

How Can Rickettsiosis Be Prevented?

• There are no vaccines available to prevent SFG and typhus group rickettsioses.

• It is recommended to avoid vectors by using repellents and protective clothing, such as long socks, to cover exposed skin.

• Permethrin-treated clothing is adequate for tick bite prevention and lasts for at least a year on treated garments.

• The use of DDT (dichloro-diphenyl-trichloroethane) on rat harborages in the mid-1940s significantly impacted the incidence of murine typhus in the United States, demonstrating the efficacy of vector control techniques in disease control. On a smaller scale, vector control may help to control local outbreaks.

• During louse-borne typhus epidemics, when conditions encourage the spread of the body louse, washing blankets and clothing in hot water kills lice and their eggs. This is frequently not possible in the midst of a typhus epidemic. In such cases, the World Health Organization recommends mass treatment with permethrin dusting on clothing using compressed air.

• Treatment of animals and the environment with acaricides have been shown to reduce the number of ticks. They promise to reduce the burden of local disease in Arizona, Mexico, Brazil, and Sonora, where there is a relatively high incidence of RMSF.

Conclusion:

Rickettsial diseases are found all over the world and are transmitted by a variety of hematophagous arthropod vectors. They continue to emerge and reappear as significant causes of febrile illness. Their clinical manifestations are largely undifferentiated, ranging from relatively mild illness to severe illnesses. Most rickettsial diseases cause mild illness, but some, such as Rocky Mountain and Brazilian spotted fevers, Mediterranean spotted fever, scrub typhus, and epidemic typhus, can be fatal in 20 % to 60 % of untreated cases. Prompt treatment is critical and results in better outcomes.