Rocky Mountain spotted fever

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Rocky Mountain spotted fever
SynonymsBlue disease, [1] Brazilian spotted fever, Tobia fever, new world spotted fever, tick- borne typhus fever, Sao Paulo fever [2]
Rocky mountian spotted fever.jpg
Petechial rash on the arm caused by Rocky Mountain spotted fever
Specialty Infectious disease
SymptomsEarly: Fever, headache [3]
Later: Rash [3]
Complications Hearing loss, loss of limbs [3]
Usual onset2 to 14 days after infection [2]
Duration2 weeks [2]
Causes Rickettsia rickettsii spread ticks [4]
Diagnostic method Based on symptoms [5]
Differential diagnosis Zika fever, dengue, chikungunya, Rickettsia parkeri rickettsiosis, Pacific Coast tick fever, rickettsialpox [6] [7]
Treatment Doxycycline [8]
Prognosis0.5% risk of death [6]
Frequency< 5,000 cases per year (USA) [6]

Rocky Mountain spotted fever (RMSF) is a bacterial disease spread by ticks. [9] It typically begins with a fever and headache, which is followed a few days later with the development of a rash. [3] The rash is generally made up of small spots of bleeding and starts on the wrists and ankles. [10] Other symptoms may include muscle pains and vomiting. [3] Long-term complications following recovery may include hearing loss or loss of part of an arm or leg. [3]

Fever common medical sign characterized by elevated body temperature

Fever, also known as pyrexia and febrile response, is defined as having a temperature above the normal range due to an increase in the body's temperature set point. There is not a single agreed-upon upper limit for normal temperature with sources using values between 37.5 and 38.3 °C. The increase in set point triggers increased muscle contractions and causes a feeling of cold. This results in greater heat production and efforts to conserve heat. When the set point temperature returns to normal, a person feels hot, becomes flushed, and may begin to sweat. Rarely a fever may trigger a febrile seizure. This is more common in young children. Fevers do not typically go higher than 41 to 42 °C.

Headache pain in the head or neck

Headache is the symptom of pain anywhere in the region of the head or neck. It occurs in migraines, tension-type headaches, and cluster headaches. Frequent headaches can affect relationships and employment. There is also an increased risk of depression in those with severe headaches.


A rash is a change of the human skin which affects its color, appearance, or texture.


The disease is caused by Rickettsia rickettsii , a type of bacterium that is primarily spread to humans by American dog ticks, Rocky Mountain wood ticks, and brown dog ticks. [4] Rarely the disease is spread by blood transfusions. [4] Diagnosis in the early stages is difficult. [5] A number of laboratory tests can confirm the diagnosis but treatment should be begun based on symptoms. [5] It is within a group known as spotted fever rickettsiosis, together with Rickettsia parkeri rickettsiosis, Pacific Coast tick fever, and rickettsialpox. [6]

<i>Rickettsia rickettsii</i> species of prokaryote

Rickettsia rickettsii is a gram-negative, intracellular, coccobacillus bacterium that is around 0.8 to 2.0 micrometers long. R. rickettsi is the causative agent of Rocky Mountain spotted fever. R. rickettsii is one of the most pathogenic Rickettsia strains. It affects a large majority of the Western Hemisphere and small portions of the Eastern Hemisphere.

Blood transfusion generally the process of receiving blood or blood products into ones circulation intravenously

Blood transfusion is the process of transferring blood or blood products into one's circulation intravenously. Transfusions are used for various medical conditions to replace lost components of the blood. Early transfusions used whole blood, but modern medical practice commonly uses only components of the blood, such as red blood cells, white blood cells, plasma, clotting factors, and platelets.

Spotted fever rickettsiosis

Spotted fever rickettsiosis, also known as spotted fever group rickettsia (SFGR), is a group of infections that include Rocky Mountain spotted fever, Rickettsia parkeri rickettsiosis, Pacific Coast tick fever, and rickettsialpox. The group of infections was created in 2010 as they are difficult to tell apart.

Treatment of RMSF is with the antibiotic doxycycline. [8] It works best when started early and is recommended in all age groups as well as during pregnancy. [8] Antibiotics are not recommended for prevention. [8] Approximately 0.5% of people who are infected die as a result. [6] Before the discovery of tetracycline in the 1940s, more than 10% of those with RMSF died. [6]

Doxycycline chemical compound

Doxycycline is an antibiotic that is used in the treatment of infections caused by bacteria and certain other parasites. It is useful for bacterial pneumonia, acne, chlamydia infections, early Lyme disease, cholera and syphilis. It is also useful for the treatment of malaria when used with quinine and for the prevention of malaria. Doxycycline can be used either by mouth or intravenously.

Pregnancy time when children develop inside the mothers body before birth

Pregnancy, also known as gestation, is the time during which one or more offspring develops inside a woman. A multiple pregnancy involves more than one offspring, such as with twins. Pregnancy can occur by sexual intercourse or assisted reproductive technology. Childbirth typically occurs around 40 weeks from the last menstrual period (LMP). This is just over nine months, where each month averages 31 days. When measured from fertilization it is about 38 weeks. An embryo is the developing offspring during the first eight weeks following fertilization, after which, the term fetus is used until birth. Symptoms of early pregnancy may include missed periods, tender breasts, nausea and vomiting, hunger, and frequent urination. Pregnancy may be confirmed with a pregnancy test.

Tetracycline chemical compound

Tetracycline, sold under the brand name Sumycin among others, is an antibiotic used to treat a number of infections. This includes acne, cholera, brucellosis, plague, malaria, and syphilis. It is taken by mouth.

Less than 5,000 cases are reported a year in the United States, most often in June and July. [6] It has been diagnosed throughout the contiguous United States, Western Canada, and parts of Central and South America. [10] [2] Rocky Mountain spotted fever was first identified in the 1800s in the Rocky Mountains. [10]

Contiguous United States 48 states of the United States apart from Alaska and Hawaii

The contiguous United States or officially the conterminous United States consists of the 48 adjoining U.S. states on the continent of North America. The terms exclude the non-contiguous states of Alaska and Hawaii, and all other off-shore insular areas. These differ from the related term continental United States which includes Alaska but excludes Hawaii and insular territories.

Western Canada geographical region of Canada

Western Canada, also referred to as the Western provinces and more commonly known as the West, is a region of Canada that includes the four provinces of Alberta, British Columbia, Manitoba and Saskatchewan. British Columbia is culturally, economically, geographically, and politically distinct from the other parts of Western Canada and is often referred to as the "west coast" or "Pacific Canada", while Alberta, Saskatchewan, and Manitoba are grouped together as the Prairie Provinces and most commonly known as "The Prairies".

Central America Place

Central America is located on the southern tip of North America, or is sometimes defined as a subcontinent of the Americas, bordered by Mexico to the north, Colombia to the southeast, the Caribbean Sea to the east, and the Pacific Ocean to the west and south. Central America consists of seven countries: Belize, Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua, and Panama. The combined population of Central America has been estimated to be 41,739,000 and 42,688,190.

Signs and symptoms

Spotted fever can be very difficult to diagnose in its early stages, due to the similarity of symptoms with many different diseases.

People infected with R. rickettsii usually notice symptoms following an incubation period of one to two weeks after a tick bite. The early clinical presentation of Rocky Mountain spotted fever is nonspecific and may resemble a variety of other infectious and non-infectious diseases.

Initial symptoms:

Nausea medical symptom or condition

Nausea is an unpleasant, diffuse sensation of unease and discomfort, often perceived as an urge to vomit. While not painful, it can be a debilitating symptom if prolonged, and has been described as placing discomfort on the chest, upper abdomen, or back of the throat.

Vomiting involuntary, forceful expulsion of stomach contents, typically via the mouth

Vomiting is the involuntary, forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose.

Myalgia, or muscle pain, is a symptom of many diseases and disorders. The most common causes are the overuse or over-stretching of a muscle or group of muscles. Myalgia without a traumatic history is often due to viral infections. Longer-term myalgias may be indicative of a metabolic myopathy, some nutritional deficiencies or chronic fatigue syndrome.

Later signs and symptoms:

A maculopapular rash is a type of rash characterized by a flat, red area on the skin that is covered with small confluent bumps. It may only appear red in lighter-skinned people. The term "maculopapular" is a compound: macules are small, flat discolored spots on the surface of the skin; and papules are small, raised bumps. It is also described as erythematous, or red.

Abdominal pain Stomach aches

Abdominal pain, also known as a stomach ache, is a symptom associated with both non-serious and serious medical issues.

Conjunctivitis inflammation of the outermost layer of the eye and the inner surface of the eyelids

Conjunctivitis, also known as pink eye, is inflammation of the outermost layer of the white part of the eye and the inner surface of the eyelid. It makes the eye appear pink or reddish. Pain, burning, scratchiness, or itchiness may occur. The affected eye may have increased tears or be "stuck shut" in the morning. Swelling of the white part of the eye may also occur. Itching is more common in cases due to allergies. Conjunctivitis can affect one or both eyes.

The classic triad of findings for this disease are fever, rash, and history of tick bite. However, this combination is often not identified when the people initially presents for care. The rash has a centripetal, or "inward" pattern of spread, meaning it begins at the extremities and courses towards the trunk.


The rash first appears two to five days after the onset of fever, and it is often quite subtle. Younger patients usually develop the rash earlier than older patients. Most often the rash begins as small, flat, pink, non-itchy spots (macules) on the wrists, forearms, and ankles. These spots turn pale when pressure is applied and eventually become raised on the skin. The characteristic red, spotted (petechial) rash of Rocky Mountain spotted fever is usually not seen until the sixth day or later after onset of symptoms, but this type of rash occurs in only 35 to 60% of patients with Rocky Mountain spotted fever. The rash involves the palms or soles in as many as 80% of people. However, this distribution may not occur until later on in the course of the disease. As many as 15 percent of patients may never develop a rash. [11]


People can develop permanent disabilities including "cognitive deficits, ataxia, hemiparesis, blindness, deafness, or amputation following gangrene". [7]


The life cycle of Dermacentor variabilis and Dermacentor andersoni ticks (Family Ixodidae) Life cycle of ticks family ixodidae.PNG
The life cycle of Dermacentor variabilis and Dermacentor andersoni ticks (Family Ixodidae)
American dog tick (Dermacentor variabilis) range Dermacentor variabilis range map.svg
American dog tick (Dermacentor variabilis) range
Rocky Mountain wood tick (Dermacentor andersoni) range Dermacentor andersoni range map.svg
Rocky Mountain wood tick (Dermacentor andersoni) range

Ticks are the natural hosts of the disease, serving as both reservoirs and vectors of R. rickettsii . Ticks transmit the bacteria primarily by their bites. Less commonly, infections may occur following exposure to crushed tick tissues, fluids, or tick feces.

A female tick can transmit R. rickettsii to her eggs in a process called transovarial transmission. Ticks can also become infected with R. rickettsii while feeding on blood from the host in either the larval or nymphal stage. After the tick develops into the next stage, the R. rickettsii may be transmitted to the second host during the feeding process. Furthermore, male ticks may transfer R. rickettsii to female ticks through body fluids or spermatozoa during the mating process. These types of transmission represent how generations or life stages of infected ticks are maintained. Once infected, the tick can carry the pathogen for life.

Rickettsiae are transmitted to through saliva injected while a tick is feeding. Unlike Lyme disease and other tick-borne pathogens that require a prolonged attachment period to establish infection, a person can become infected with R. rickettsii in a feeding time as short as 2 hours. [12] In general, about one to three percent of the tick population carries R. rickettsii, even in areas where the majority of human cases are reported. Therefore, the risk of exposure to a tick carrying R. rickettsii is low.

The disease is spread by the American dog tick (Dermacentor variabilis), Rocky Mountain wood tick (Dermacentor andersoni), brown dog tick (Rhipicephalus sanguineus), and Amblyomma sculptum . [13] [14] Not all of these are of equal importance, and most are restricted to certain geographic areas.

The two major vectors of R. rickettsii in the United States are the American dog tick and the Rocky Mountain wood tick. American dog ticks are widely distributed east of the Rocky Mountains and they also occur in limited areas along the Pacific Coast. Dogs and medium-sized mammals are the preferred hosts of an adult American dog ticks, although it feeds readily on other large mammals, including human beings. This tick is the most commonly identified species responsible for transmitting R. rickettsii to humans. Rocky Mountain wood ticks (Dermacentor andersoni) are found in the Rocky Mountain states and in southwestern Canada. The life cycle of this tick may require up to three years for its completion. The adult ticks feed primarily on large mammals. The larvae and nymphs feed on small rodents.

Other tick species have been shown to be naturally infected with R. rickettsii or serve as experimental vectors in the laboratory. These species are likely to play only a minor role in the ecology of R. rickettsii.


Entry into host

Rickettsia rickettsii can be transmitted to human hosts through the bite of an infected tick. As with other bacterium transmitted via ticks, the process generally requires a period of attachment of 4 to 6 hours. However, in some cases a Rickettsia rickettsii infection has been contracted by contact with tick tissues or fluids. [15] Then, the bacteria induce their internalization into host cells via a receptor-mediated invasion mechanism.

Researchers believe that this mechanism is similar to that of Rickettsia conorii. This species of Rickettsia uses an abundant cell surface protein called OmpB to attach to a host cell membrane protein called Ku70. It has previously been reported that Ku70 migrates to the host cell surface in the presence of "Rickettsia". [16] Then, Ku70 is ubiquitinated by c-Cbl, an E3 ubiquitin ligase. This triggers a cascade of signal transduction events resulting in the recruitment of Arp2/3 complex. CDC42, protein tyrosine kinase, phosphoinositide 3-kinase, and Src-family kinases then activate Arp2/3. This causes the alteration of local host cytoskeletal actin at the entry site as part of a zipper mechanism. [17] Then, the bacteria is phagocytosized by the host cell and enveloped by a phagosome. [16]

Studies have suggested that rOmpB is involved in this process of adhesion and invasion. Both rOmpA and rOmpB are members of a family of surface cell antigens (Sca) which are autotransporter proteins; they act as ligands for the Omp proteins and are found throughout the rickettsiae. [18]

Exit from host cell

The cytosol of the host cell contains nutrients, adenosine triphosphate, amino acids, and nucleotides which are used by the bacteria for growth. For this reason, as well as to avoid phagolysosomal fusion and death, rickettsiae must escape from the phagosome. To escape from the phagosome, the bacteria secrete phospholipase D and hemolysin C. This causes disruption of the phagosomal membrane and allows the bacteria to escape. Following generation time in the cytoplasm of the host cells, the bacteria utilizes actin based motility to move through the cytosol. [16]

RickA, expressed on the rickettsial surface, activates Arp2/3 and causes actin polymerization. The rickettsiae use the actin to propel themselves throughout the cytosol to the surface of the host cell. This causes the host cell membrane to protrude outward and invaginate the membrane of an adjacent cell. [17] The bacteria are then taken up by the neighboring cell in a double membrane vacuole that the bacteria can subsequently lyse, enabling spread from cell to cell without exposure to the extracellular environment.

Consequences of infection

Rickettsia rickettsii initially infect blood vessel endothelial cells, but eventually migrate to vital organs such as the brain, skin, and the heart via the blood stream. Bacterial replication in host cells causes endothelial cell proliferation and inflammation, resulting in mononuclear cell infiltration into blood vessels and subsequent red blood cell leakage into surrounding tissues. The characteristic rash observed in Rocky Mountain spotted fever is the direct result of this localized replication of rickettsia in blood vessel endothelial cells. [10]


Even doctors who are familiar with the disease find it hard to diagnose early during infection.

Abnormal laboratory findings seen in patients with Rocky Mountain spotted fever may include a low platelet count, low blood sodium concentration, or elevated liver enzyme levels. Serology testing and skin biopsy are considered to be the best methods of diagnosis. Although immunofluorescent antibody assays are considered some of the best serology tests available, most antibodies that fight against R. rickettsii are undetectable on serology tests the first seven days after infection. [19]

Differential diagnosis includes dengue, leptospirosis, chikungunya, and Zika fever. [7]


Appropriate antibiotic treatment should be started immediately when there is a suspicion of Rocky Mountain spotted fever. [10] Early treatment of Rocky Mountain spotted fever prevents further damage to internal organs. Treatment should not be delayed for laboratory confirmation. Failure to respond to a tetracycline argues against a diagnosis of Rocky Mountain spotted fever. Severely ill people may require longer periods before their fever resolves, especially if they have experienced damage to multiple organ systems. Preventive therapy in healthy people who have had recent tick bites is not recommended and may only delay the onset of disease. [20]

Doxycycline (a tetracycline) is the drug of choice for patients with Rocky Mountain spotted fever, being one of the only instances doxycycline is used in children. [21] Treatment typically consists of 100 milligrams every 12 hours, or for children under 45 kg (99 lb) at 4 mg/kg of body weight per day in two divided doses. Treatment should be continued for at least three days after the fever subsides, and until there is unequivocal evidence of clinical improvement. This will be generally for a minimum time of five to ten days. [10] Severe or complicated outbreaks may require longer treatment courses. Doxycycline/ tetracycline is also the preferred drug for patients with ehrlichiosis, another tick-transmitted infection with signs and symptoms that may resemble those of Rocky Mountain spotted fever. Chloramphenicol is an alternative drug that can be used to treat Rocky Mountain spotted fever, specifically in pregnancy. However, this drug may be associated with a wide range of side effects, and careful monitoring of blood levels is required. [10]


Rocky Mountain spotted fever can be a very severe illness and patients often require hospitalization. Because R. rickettsii infects the cells lining blood vessels throughout the body, severe manifestations of this disease may involve the respiratory system, central nervous system, gastrointestinal system, or kidneys.

Long-term health problems following acute Rocky Mountain spotted fever infection include partial paralysis of the lower extremities, gangrene requiring amputation of fingers, toes, or arms or legs, hearing loss, loss of bowel or bladder control, movement disorders, and language disorders. These complications are most frequent in persons recovering from severe, life-threatening disease, often following lengthy hospitalizations.


US distribution of spotted fever rickettsiosis, of which RMSF is a type, in 2014 Rickettsiosis-incidence-map.jpg
US distribution of spotted fever rickettsiosis, of which RMSF is a type, in 2014

There are between 500 and 2500 cases of Rocky Mountain spotted fever reported in the United States per year, [22] and in only about 20% can the tick be found.[ citation needed ]

Host factors associated with severe or fatal Rocky Mountain spotted fever include advanced age, male sex, African or Caribbean background, chronic alcohol abuse, and glucose-6-phosphate dehydrogenase (G6PD) deficiency. Deficiency of G6PD is a genetic condition affecting about 12 percent of the Afro-American male population. Deficiency in this enzyme is associated with a high proportion of severe cases of Rocky Mountain spotted fever. [23] This is a rare clinical complication that is often fatal within five days of the onset of the disease.

In the early 1940s, outbreaks were described in the Mexican states of Sinaloa, Sonora, Durango, and Coahuila driven by dogs andRhipicephalus sanguineus sensu lato, the brown dog tick. [7] Over the ensuing 100 years case fatality rates were 30%–80%. In 2015, there was an abrupt rise in Sonora cases with 80 fatal cases. From 2003 to 2016, cases increased to 1394 with 247 deaths. [7]

History and culture

Rocky Mountain spotted fever (or "black measles" because of its characteristic rash) was recognized in the early 1800s, and in the last 10 years of the 1800s (1890–1900) it became very common, especially in the Bitterroot Valley of Montana. The disease was originally noted to be concentrated on the west-side of the Bitterroot river. [24] Though it would be decades before scientists discovered the tick as the carrier of the disease, in as early as 1866, Doctor John B. Buker (establishing a practice in Missoula, MT) noticed a tick embedded in the skin of one of his patients. His notes were later studied as part of later research. [25]

In 1901, Dr. A. F. Longeway was appointed to solve "the black measles problem" in Montana. He in turn enlisted his friend, Dr. Earl Strain to help him. Strain suspected that the illness was from ticks. In 1906, Howard T. Ricketts, a pathologist recruited from the University of Chicago, was the first to establish the identity of the infectious organism (the organism smaller than a bacterium and larger than a virus) that causes this disease. He and others characterized the basic epidemiological features of the disease, including the role of tick vectors. Their studies found that Rocky Mountain spotted fever is caused by Rickettsia rickettsii, named in Howard Ricketts honor. Ricketts died of typhus (another rickettsial disease) in Mexico in 1910, shortly after completing his studies on Rocky Mountain spotted fever.

Prior to 1922, Doctors McCray and McClintic both died while doing research on Rocky Mountain spotted fever, as did an aide of Noguchi Hideyo at the Rockefeller Institute. McCalla and Brerton also did early research into Rocky Mountain spotted fever.

Research began in 1922 in western Montana, in the Bitterroot Valley around Hamilton, Montana, after the Governor's daughter and his son-in-law died of the fever. However, prior to that, in 1917, Dr. Lumford Fricks introduced herds of sheep into the Bitterroot Valley. His hypothesis was that the sheep would eat the tall grasses where ticks lived and bred. [26] Past Assistant Surgeon R.R. Spencer of the Hygienic Laboratory of the U.S. Public Health Service was ordered to the region, and he led a research team at an abandoned schoolhouse through about 1924. [27] [28] Spencer was assisted by R. R. Parker, Bill Gettinger, Henry Cowan, Henry Greenup, Elmer Greenup, Gene Hughes, Salsbury, Kerlee, and others, of whom Gettinger, Cowan and Kerlee died of Rocky Mountain spotted fever. [28] Through a series of discoveries, the team found that a previous blood meal was necessary to make the tick deadly to its hosts, as well as other facets of the disease. [28] On May 19, 1924, Spencer put a large dose of mashed wood ticks, from lot 2351B, and some weak carbolic acid into his arm by injection. This vaccine worked, and for some years after it was used by people in that region to convert the illness from one with high fatality rate (albeit low incidence) to one that could be either prevented entirely (for many of them) or modified to a non-deadly form (for the rest). [28] Today there is no commercially available vaccine for RMSF [21] because, unlike in the 1920s when Spencer and colleagues developed one, antibiotics are now available to treat the disease, so prevention by vaccination is no longer the sole defense against likely death.

Much of the early research was conducted at Rocky Mountain Laboratories [29] [30] a part of the National Institute of Allergy and Infectious Diseases. The schoolhouse laboratory of 1922-1924, filled with ticks in various phases of the life cycle, is identifiable in retrospect as a biohazard, although the team did not fully appreciate it at first. The deaths of Gettinger and Cowan, and the near death of the janitor's son, were the results of inadequate biocontainment, but in the 1920s, the elaborate biocontainment systems of today had not been invented yet.

Research into this disease in Montana is a sub-plot of the film Green Light (1937 film) starring Errol Flynn. Some of the researchers who perished are mentioned by name and their photographs are shown.

Rocky Mountain spotted fever is a big part of the 1947 Republic Pictures movie "Driftwood", starring Walter Brennan, James Bell, Dean Jagger, Natalie Wood, and Hobart Cavanaugh.

In December 2013, hockey player Shane Doan was diagnosed with Rocky Mountain spotted fever, and returned to play in January 2014. [31]

Other names

Some synonyms for Rocky Mountain spotted fever in other countries include “tick typhus,” “Tobia fever” (Colombia), “São Paulo fever” or “febre maculosa” (Brazil), and “fiebre manchada” (Mexico).

Related Research Articles

Q fever disease caused by infection with Coxiella burnetii, a bacterium that affects humans and other animals; the most common manifestation is flu-like symptoms; the name Q stands for “query”, so named when the pathogen was unknown

Q fever is a disease caused by infection with Coxiella burnetii, a bacterium that affects humans and other animals. This organism is uncommon, but may be found in cattle, sheep, goats, and other domestic mammals, including cats and dogs. The infection results from inhalation of a spore-like small-cell variant, and from contact with the milk, urine, feces, vaginal mucus, or semen of infected animals. Rarely, the disease is tick-borne. The incubation period is 9–40 days. Humans are vulnerable to Q fever, and infection can result from even a few organisms. The bacterium is an obligate intracellular pathogenic parasite.

Colorado tick fever (CTF) is a viral infection (Coltivirus) transmitted from the bite of an infected Rocky Mountain wood tick. It should not be confused with the bacterial tick-borne infection, Rocky Mountain spotted fever.

Boutonneuse fever Human disease

Boutonneuse fever is a fever as a result of a rickettsial infection caused by the bacterium Rickettsia conorii and transmitted by the dog tick Rhipicephalus sanguineus. Boutonneuse fever can be seen in many places around the world, although it is endemic in countries surrounding the Mediterranean Sea. This disease was first described in Tunisia in 1910 by Conor and Bruch and was named boutonneuse due to its papular skin rash characteristics.

<i>Coxiella burnetii</i> species of prokaryote

Coxiella burnetii is an obligate intracellular bacterial pathogen, and is the causative agent of Q fever. The genus Coxiella is morphologically similar to Rickettsia, but with a variety of genetic and physiological differences. C. burnetii is a small Gram-negative, coccobacillary bacterium that is highly resistant to environmental stresses such as high temperature, osmotic pressure, and ultraviolet light. These characteristics are attributed to a small cell variant form of the organism that is part of a biphasic developmental cycle, including a more metabolically and replicatively active large cell variant form. It can survive standard disinfectants, and is resistant to many other environmental changes like those presented in the phagolysosome.

Tick-borne diseases, which afflict humans and other animals, are caused by infectious agents transmitted by tick bites. Tick-borne illnesses are caused by infection with a variety of pathogens, including rickettsia and other types of bacteria, viruses, and protozoa. Because individual ticks can harbor more than one disease-causing agent, patients can be infected with more than one pathogen at the same time, compounding the difficulty in diagnosis and treatment. As of 2016, 16 tick-borne diseases of humans are known.

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Howard Taylor Ricketts American pathologist

Howard Taylor Ricketts was an American pathologist after whom the Rickettsiaceae family and the Rickettsiales are named.

<i>Dermacentor variabilis</i> species of arachnid

Dermacentor variabilis, also known as the American dog tick or wood tick, is a species of tick that is known to carry bacteria responsible for several diseases in humans, including Rocky Mountain spotted fever and tularemia. It is one of the most well-known hard ticks. Diseases are spread when it sucks blood from the host, which could take several days for the host to experience some symptoms.

<i>Anaplasma phagocytophilum</i> species of prokaryote

Anaplasma phagocytophilum is a Gram-negative bacterium that is unusual in its tropism to neutrophils. It causes anaplasmosis in sheep and cattle, also known as tick-borne fever and pasture fever, and also causes the zoonotic disease human granulocytic anaplasmosis.

A rickettsiosis is a disease caused by intracellular bacteria.

<i>Orientia tsutsugamushi</i> species of prokaryote

Orientia tsutsugamushi is a mite-borne bacterium belonging to the family Rickettsiaceae and is responsible for a disease called scrub typhus in humans. It is a natural and an obligate intracellular parasite of mites belonging to the family Trombiculidae. With a genome of only 2.4–2.7 Mb, it has the most repeated DNA sequences among bacterial genomes sequenced so far. The disease, scrub typhus, occurs when infected mite larvae accidentally bite humans. Primarily indicated by undifferentiated febrile illnesses, the infection can be complicated and often fatal.

Ehrlichia chaffeensis is an obligate intracellular gram-negative species of rickettsiales bacteria. It is a zoonotic pathogen transmitted to humans by the lone star tick. It is the causative agent of human monocytic ehrlichiosis.

Human granulocytic anaplasmosis human disease

Human granulocytic anaplasmosis (HGA) is a tick-borne, infectious disease caused by Anaplasma phagocytophilum, an obligate intracellular bacterium that is typically transmitted to humans by ticks of the Ixodes ricinus species complex, including Ixodes scapularis and Ixodes pacificus in North America. These ticks also transmit Lyme disease and other tick-borne diseases.

African tick bite fever spotted fever that has material basis in Rickettsia africae, which is transmitted by ticks

African tick bite fever (ATBF) is a bacterial infection spread by the bite of a tick. Symptoms may include fever, headache, muscles pains, and a rash. At the site of the bite there is typically a red skin sore with a dark center. Onset usually occur 4–10 days after the bite. Complications are rare, however may include joint inflammation. Some people do not develop symptoms.

<i>Amblyomma cajennense</i> species of arachnid

Amblyomma cajennense or Cayenne tick is species of tick found in a range from the southern part of the United States to northern Argentina, through Central America and some of the Caribbean.

Rickettsia helvetica, previously known as the Swiss Agent, is a bacterium found in Dermacentor reticulatus and other ticks which has been implicated as a suspected but unconfirmed human pathogen. First recognized in 1979 in Ixodes ricinus ticks in Switzerland as a new member of the spotted fever group of Rickettsia, the Rickettsia helvetica bacterium was eventually isolated in 1993. Although R. helvetica was initially thought to be harmless in humans and many animal species, some individual case reports suggest that it may be capable of causing a non-specific fever in humans. In 1997 a man living in eastern France seroconverted to Rickettsia 4 weeks after onset of an unexplained febrile illness. In 2010, a case report indicated that tick-borne R. helvetica can also cause meningitis in humans.

Pacific Coast tick fever is an infection caused by Rickettsia philipii. The disease is spread by the Pacific coast ticks. Symptoms may include an eschar. It is within a group known as spotted fever rickettsiosis together with Rickettsia parkeri rickettsiosis, Rocky Mountain spotted fever, and rickettsialpox. These infections can be difficult to tell apart.


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External resources