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

gram-negative Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelope consists ...

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 180th meridian.- The other half is called the Eastern Hemisphere. Geopolitically, ...

and is transmitted via the bite of hard ticks of the genus '' Amblyomma''. ''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 a ...

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

eschar Eschar (; ; ; or ''an'' eschar) is a slough or piece of necrosis, dead tissue that is cast off from the surface of the skin, particularly after a Burn, burn injury, but also seen in gangrene, Ulcer (dermatology), ulcer, mycosis, fungal infection ...

at the site of tick attachment, rash, headache, and muscle aches.

Doxycycline Doxycycline is a Broad-spectrum antibiotic, broad-spectrum antibiotic of the Tetracycline antibiotics, tetracycline class used in the treatment of infections caused by bacteria and certain parasites. It is used to treat pneumonia, bacterial p ...

should be given after any tick bite especially those occurring on children.

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 genus was n ...

''. 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 in the eastern United States; and "''Rickettsia parkeri'' rickettsiosis" 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 institutes, national public health agency of the United States. It is a Federal agencies of the United States, United States federal agency under the United S ...

(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 make millions to billions of copies of a specific DNA sample rapidly, allowing scientists to amplify a very small sample of DNA (or a part of it) sufficiently to enable detailed st ...

(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 Immunofluorescence (IF) is a light microscopy-based technique that allows detection and localization of a wide variety of target biomolecules within a cell or tissue at a quantitative level. The technique utilizes the binding specificity of anti ...

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 Petechial rash, made up of small s ...

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 A systematic review is a scholarly synthesis of the evidence on a clearly presented topic using critical methods to identify, define and assess research on the topic. A systematic review extracts and interprets data from published studies on ...

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 Myalgia or muscle pain is a painful sensation evolving from muscle tissue. It is a symptom of many diseases. The most common cause of acute myalgia is the overuse of a muscle or group of muscles; another likely cause is viral infection, espec ...

, 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 antibiotic in the tetracyclines family of medications, used to treat a number of infections, including acne, cholera, brucellosis, plague, malaria, and syphilis. It is available in oral an ...

. 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, 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