What is Rickettsiosis?
Ticks have become synonymous with Lyme disease. However, the same ticks that transmit Lyme disease are also carriers of pathogens that cause a number of other tick-borne diseases, such as Rickettsiosis. Rickettsiosis, also known as Rickettsial diseases, is a group of diseases classified by two main biogroups: the spotted fever group (SFG) and the typhus group (TG). In 1909, the causative organism and mode of transmission of these diseases were discovered by American pathologist Howard T. Ricketts. These antigenic Rickettsial diseases are caused by species of the genus Rickettsia, which falls under the family Rickettsiaceae. The family Rickettsiaceae consists of three genera, two of which are closely related – Rickettsia and Orientia – that once belonged to the same genus.
How is Rickettsiosis transmitted?
Rickettsia features a large group of obligate, intracellular, Gram-negative bacteria that can present as cocci, rods, or thread-like, ranging from 0.1 μm to 2.0 μm. Rickettsiae are typically maintained in nature through arthropod vectors such as ticks, fleas, lice, and mites. They infect a wide variety of mammals, including humans, which serve as hosts for the organisms and ensure the survival of the parasitic vectors that feed on them. The rickettsiae reside in the cytoplasm or within the nucleus of the cell they invade.
Rocky Mountain Spotted Fever & Ticks
Rocky Mountain spotted fever (RMSF) is the deadliest tick-borne disease in the world, according to the Centers for Disease Control and Prevention (CDC). Anyone bitten by an infected tick can get RMSF, and it can cause death even in young or previously healthy people.
In fact, without prompt treatment, the illness can cause serious damage to internal organs, such as your kidneys and heart. Before the use of antibiotics, RMSF in certain locations had a mortality rate of 70 percent. RMSF is now easier to treat and has a mortality rate of 0.3 percent following treatment.
Rocky Mountain Spotted Fever (RMSF) is caused by Rickettsia rickettsii, which is primarily transmitted to mammals via three major vectors: the American Dog tick, Dermacentor variabilis, in the eastern United States, the Rocky Mountain Wood tick, Dermacentor andersoni, in the western United States, and the Brown Dog tick, Rhipicephalus sanguineus, found throughout the United States. R. sanguineus transmits RMSF rickettsia to dogs and on rare occasions to humans. In addition to these three vectors, there has been significant evidence to suggest the transmission of R. rickettsii by the Lone Star tick, Amblyomma americanum, as well.
Note: RMSF spreads quickly!
If an infected tick attaches itself to your skin and feeds on your blood for six to 10 hours, you may pick up the infection, according to the Mayo Clinic.
Other Rickettsia types
Spotted fever Rickettsial diseases
The spotted fever group of Rickettsial diseases consists of diseases closely related to RMSF, such as Boutonneuse Fever caused by R. conorii, and Cat flea rickettsiosis caused by R. felis, as well as several others. Rickettsia felis, causing flea-borne spotted fever, was previously classified under the typhus group.
Typhus group: Louse- and flea-borne Rickettsial diseases
Epidemic Typhus is one of the most notable diseases of the typhus group of Rickettsiosis, having caused millions of deaths in previous centuries, major outbreaks occurring during World Wars I and II, the Napoleonic Wars, and the Irish Potato Famine. Also known as camp fever, jail fever, or war fever, this louse-borne disease caused by R. prowezekii is associated with people living in overcrowded unhygienic conditions. The disease is spread to humans via the infected feces of the human body louse, Pediculus humanus humanus.
The typhus group of Rickettsiosis includes other forms of typhus, such as the endemic typhus, also known as murine typhus. Murine typhus is caused by the bacterium R. typhi, and is transmitted to humans by contact with infected fleas found on rodents, thus earning the name flea-borne typhus. Domestic cats and opossums are also known carriers of fleas infected with R. typhi. Both human body lice and fleas defecate as they feed, spreading infected feces by scratching into the bite site or other skin lesions.
Some common Rickettsia symptoms
Despite the diversity of Rickettsiosis, most early-stage Rickettsia symptoms are very similar.
Common Rickettsiosis symptoms include:
- fever
- headache
- rash
- nausea
- vomiting
- abdominal pain
- malaise
- myalgia
- respiratory concerns
- chills
- loss of appetite
Rickettsiosis usually requires a 5 to 14 day incubation period, and therefore, Rickettsia symptoms do not present immediately after infection.
The rash developed by patients can vary among Rickettsial diseases and during the stages of specific diseases. For example, some rashes developed during RMSF can look like red splotches, a maculopapular rash, and some like pinpoint dots, spots, a petechial rash. It can be difficult to distinguish between the different spotted fevers, as the rashes do not develop until after some of the other Rickettsia symptoms. However, those infected with spotted fevers other than RMSF usually develop eschars at the site of the tick or mite bite. Rashes brought about by both spotted fever and typhus rickettsiosis may be present on the chest, back, and stomach before spreading to the rest of the body.
Some rashes that can occur from Rickettsial diseases. Image credit: CDC
Brill-Zinsser disease can occur in people with epidemic typhus years following their infection due to weakened immune systems.
How is Rickettsiosis geographically distributed?
Variations of different spotted fever and typhus rickettsiosis can be found worldwide due to the prevalence and distribution of host animals infected with rickettsia through fleas, mites, ticks, and lice. According to a recent CDC presentation, Rickettsial diseases within the United States have a much wider geographical distribution than previously thought. What’s more, RMSF is something of a misnomer, as most cases reported for RMSF are from outside of the Rocky Mountain region of the United States – North Carolina, Oklahoma, Arkansas, Tennessee, Missouri, and Arizona account for most cases.
In the United States, Murine typhus has mainly been reported in California, Hawaii, and Texas. Epidemic typhus is rare compared to the widespread effect it has had in the past, and now occurs in regions where war, overcrowding, and poor hygiene are prevalent.
The different Rickettsial diseases are transmitted by different types of vectors, have worldwide geographic distribution, and are caused by several other species of Rickettsia, as shown in the table below:
| Rickettsial Disease Group | Disease | Species | Geographical Distribution | Vector |
| Spotted Fever Group (SFG) | Rocky Mountain Spotted Fever (RMSF) | R. rickettsii | Americas (North, Central, and South) | Ticks |
| Flea-borne spotted fever/ cat flea typhus | R. felis | Worldwide | Fleas | |
| Boutonneuse fever/ Mediterranean spotted fever | R. conorii | Europe, Asia, Africa | Ticks | |
| Typhus Group (TG) | Epidemic typhus | R. prowazekii | Worldwide | Human body lice, flying squirrel ectoparasites |
| Murine typhus/ Endemic typhus/ Flea-borne typhus | R. typhi | Worldwide | Fleas |
How is Rickettsiosis diagnosed?
Rickettsial diseases are very difficult to diagnose based on symptoms alone, as Rickettsiasymptoms are non-specific and common to several other illnesses. Additionally, the appearance of the specific diseases varies from patient to patient. Therefore, without laboratory testing, doctors are rarely able to correctly make a Rickettsia diagnosis.
A Rickettsia diagnosis should be considered in patients who have been in areas where Rickettsiosis is endemic, highly infested with ticks, and patients display symptoms concurrent with Rickettsial infections. PCR tests are useful for early detection of the disease by testing the blood or skin biopsy of the site of the lesions. In contrast, serology tests that show the body’s immune response to the diseases are recommended a few weeks after infection, once the body has developed antibodies.
Rickettsia can be treated with antibiotics. Patients should be examined by their healthcare professional. The healthcare professional will use clinical symptoms along with laboratory tests to find out whether a patient has Rickettsiosis or perhaps some other tick-borne infection.
To learn more about Rickettsia diagnosis and testing, explore the PCR and serological Rickettsia tests available from IGeneX today.
