science

Rickettsia parkeri

Rickettsia parkeri is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Rickettsia parkeri rather than just read about it. In short: Rickettsia parkeri (abbreviated R. parkeri) is a gram-negative intracellular bacterium. The organism is found in the Western Hemisphere and is transmitted via the bite of hard ticks of the genus Amblyomma.

Key takeaways

Rickettsia parkeri belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Rickettsia parkeri to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Rickettsia parkeri from memory before moving on to harder problems.

Reference excerpt

Rickettsia parkeri (abbreviated R. parkeri) is a gram-negative intracellular bacterium. The organism is found in the Western Hemisphere and is transmitted via the bite of hard ticks of the genus Amblyomma. R. parkeri causes mild spotted fever disease in humans, whose most common signs and symptoms are fever, an eschar at the site of tick attachment, rash, headache, and muscle aches. Doxycycline 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. 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 (CDC) as of 2016 became infected between the months of July and September.

Diagnosis The CDC recommends polymerase chain reaction (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 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. 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 "Rickettsia parkeri rickettsiosis". Centers for Disease Control and Prevention. January 10, 2019.

Illustrations

Worked examples

Example 1 — a first encounter with Rickettsia parkeri

Start with the simplest possible case. Write down what Rickettsia parkeri claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Rickettsia parkeri before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Rickettsia parkeri ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Rickettsia parkeri

In research: Rickettsia parkeri appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Rickettsia parkeri in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Rickettsia parkeri is common in secondary-school and first-year university syllabi. It links to neighbouring topics Bacteria described in 1939, Gram-negative bacteria, Rickettsiaceae, so understanding it makes those chapters shorter.
In everyday life: Look for Rickettsia parkeri outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Rickettsia parkeri in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Rickettsia parkeri means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Rickettsia parkeri out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Rickettsia parkeri in simple terms?

Why does Rickettsia parkeri matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Rickettsia parkeri?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Rickettsia parkeri.