''Rickettsia parkeri'' (abbreviated ''R. parkeri'') is a

gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wa ...

intracellular bacterium. The organism is found in the

Western Hemisphere The Western Hemisphere is the half of the planet Earth that lies west of the prime meridian (which crosses Greenwich, London, United Kingdom) and east of the antimeridian. The other half is called the Eastern Hemisphere. Politically, the te ...

and is transmitted via the bite of hard ticks of the genus ''

Amblyomma ''Amblyomma'' is a genus of hard ticks. Some are disease vectors, for example the Rocky Mountain spotted fever in Brazil or ehrlichiosis in the United States. This genus is the third largest in the family Ixodidae, with its species primarily o ...

''. ''R. parkeri'' causes mild

spotted fever A spotted fever is a type of tick-borne disease which presents on the skin. They are all caused by bacteria of the genus '' Rickettsia''. Typhus is a group of similar diseases also caused by ''Rickettsia'' bacteria, but spotted fevers and typhus ...

disease in humans, whose most common signs and symptoms are fever, an

eschar An eschar (; Greek: ''ἐσχάρᾱ'', ''eskhara''; Latin: ''eschara'') is a slough or piece of dead tissue that is cast off from the surface of the skin, particularly after a burn injury, but also seen in gangrene, ulcer, fungal infections, ...

at the site of tick attachment, rash, headache, and muscle aches. Doxycycline is the most common drug used to reduce the symptoms associated with disease.

Biology

''R. parkeri'' is classified in the spotted fever group of the genus ''

Rickettsia ''Rickettsia'' is a genus of nonmotile, gram-negative, nonspore-forming, highly pleomorphic bacteria that may occur in the forms of cocci (0.1 μm in diameter), bacilli (1–4 μm long), or threads (up to about 10 μm long). The term "ricke ...

''. Genetically, its close relatives include '' R. africae'', '' R. sibirica'', '' R. conorii'', '' R. rickettsii'', '' R. peacockii'', and '' R. honei''. The organism has been isolated from numerous species of ticks in the genus ''Amblyomma'': '' A. americanum'' in the United States; ''A. aureolatum'' in Brazil; '' A. maculatum'' in Mexico, Peru, and the United States; '' A. nodosum'' in Brazil; ''A. ovale'' in Brazil and Mexico; ''A. parvitarsum'' in Argentina and Chile; ''A. tigrinum'' in Argentina, Bolivia, Brazil, and Uruguay; and ''A. triste'' in Argentina, Brazil, the United States, and Uruguay. Different ticks may carry different strains of the organism. ''R. parkeri'' sensu stricto ("in the strict sense") is found in ''A. maculatum'' and ''A. triste''; ''R. parkeri'' strain NOD, in ''A. nodosum''; ''R. parkeri'' strain Parvitarsum, in ''A. parvitarsum''; and ''R. parkeri'' strain Atlantic rainforest, in ''A. aureolatum'' and ''A. ovale''.

Human infections

The first report of a confirmed human case of infection with ''R. parkeri'' was published in 2004. The person was infected in the state of Virginia in the United States. Other confirmed or probable human cases have been reported to have acquired infection elsewhere in the United States (e.g., Arizona, Georgia, and Mississippi), as well as in Argentina, Brazil, Colombia, Mexico, and Uruguay. Terms used to describe human infection with ''R. parkeri'' include "American boutonneuse fever" because of its similarity to boutonneuse fever caused by '' Rickettsia conorii''; " American tick bite fever" because of its similarity to African tick bite fever caused by '' Rickettsia africae''; "Tidewater spotted fever," after the

Tidewater region Tidewater refers to the north Atlantic coastal plain region of the United States of America. Definition Culturally, the Tidewater region usually includes the low-lying plains of southeast Virginia, northeastern North Carolina, southern Mary ...

in the eastern United States; and "''Rickettsia parkeri''

rickettsiosis A rickettsiosis is a disease caused by intracellular bacteria. Cause Rickettsioses can be divided into a spotted fever group (SPG) and typhus group (TG). In the past, rickettsioses were considered to be caused by species of Rickettsia. However, s ...

" or "''R. parkeri'' rickettsiosis."

Epidemiology

Of all human cases documented in the medical literature, 87% were 18-64 years of age, and most cases were male. Brazil, Argentina, and the United States accounted for the majority of cases in the medical literature. In the United States, most of the 40 cases reported to the

Centers for Disease Control and Prevention The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georgi ...

(CDC) as of 2016 became infected between the months of July and September.

Diagnosis

The CDC recommends

polymerase chain reaction The polymerase chain reaction (PCR) is a method widely used to rapidly make millions to billions of copies (complete or partial) of a specific DNA sample, allowing scientists to take a very small sample of DNA and amplify it (or a part of it) ...

(PCR) of a biopsy or swab of an eschar, or PCR of a biopsy of a rash, for diagnosis of ''R. parkeri'' infection. In addition, indirect immunofluorescence antibody (IFA) assays using paired acute and convalescent sera can be used.

Clinical manifestations

A 2008 study compared 12 ''R. parkeri'' cases with 208

Rocky Mountain spotted fever Rocky Mountain spotted fever (RMSF) is a bacterial disease spread by ticks. It typically begins with a fever and headache, which is followed a few days later with the development of a rash. The rash is generally made up of small spots of bleedin ...

cases caused by ''R. rickettsii''. Although both ''R. parkeri'' and ''R. rickettsii'' caused fever, rash, myalgia, and headache, ''R. parkeri'' caused eschars and ''R. rickettsii'' did not. Furthermore, the percentage of patients hospitalized was lower for ''R. parkeri'' than for ''R. rickettsii'' (33% vs 78%), and ''R. parkeri'' led to no deaths while ''R. rickettsii'' led to death in 7% of cases. A 2021 systematic review of 32 confirmed and 45 probable cases of human infection with ''R. parkeri'' determined that 94% of the confirmed cases had fever, 91% an eschar, 72% a rash, 56% headache, and 56% myalgia, with similar percentages among the probable cases. The rash was most frequently described as papular or macular. Among the confirmed and probable cases, the most common treatment was doxycycline, followed by

tetracycline Tetracycline, sold under various brand names, is an oral antibiotic in the tetracyclines family of medications, used to treat a number of infections, including acne, cholera, brucellosis, plague, malaria, and syphilis. Common side effects in ...

. Although 9% of all the cases were hospitalized, there was a "100% rate of clinical recovery."

History

In 1939, Ralph R. Parker, director of the

Rocky Mountain Laboratory Rocky Mountain Laboratories (RML) is part of the NIH Intramural Research Program and is located in Hamilton, Montana. Operated by the National Institute of Allergy and Infectious Diseases, RML conducts research on maximum containment pathogens s ...

, and others published a paper on "a rickettsia-like infectious agent." The agent, found in '' Amblyomma maculatum'' ticks collected from cows in Texas, produced mild disease in guinea pigs. In 1965, Lackman and others named the rickettsial organism ''R. parkeri'' after Parker.

References

External links

* {{Taxonbar, from=Q62889344 Bacteria described in 1939 Gram-negative bacteria Rickettsiaceae Zoonoses