Rickettsialpox: Symptoms, Causes and Treatment

February 28, 2025

Rickettsialpox is a rare, self-limiting bacterial infection caused by the bacteria Rickettsia Akari and transmitted to humans via house mouse mites (Liponyssoides sanguineus family) bites. The zoonotic illness is known to cause fever (and chills), eschars (dead crusty skin tissues), body aches, and vesicular rash (which resembles chickenpox). The disease was initially reported in New York City (and some other towns in the US) but now there have been reported cases from all subcontinents including Africa, South America, Asia, and Europe. It was previously grouped under the spotted-fever group rickettsioses (a group of bacterial diseases spread via ticks/mites) but is now placed in a transitional group. According to reports, the average national incidence of spotted fever cases in the US is 12.77 per 1 million persons per year.¹ The disease usually resolves itself, but doctors may prescribe antibiotics like doxycycline to speed up recovery.

Rickettsialpox Symptoms

In general, symptoms appear 7-14 days after the bite (the incubation period of the bacteria). The following symptoms are most commonly seen in rickettsialpox:

Fever & Chills:

Fever (with chills) and dermatological presentations are highly prevalent in individuals suffering from rickettsialpox. Reports suggest that fever is present in almost every patient. Other symptoms that may accompany the raised body temperature include joint pain, headache, lymphadenopathy, etc.² Initial symptoms of rickettsialpox (fever and skin presentations) resemble chickenpox. Most patients explain the fever to be irregular and fluctuating, which is accompanied by the development of vesicular rash on the bite site.

Skin Symptoms:

The two highlighting dermatological features of rickettsialpox are vesicular rash and eschar. Fever, rash, and eschar (the triad of rickettsialpox) are present in almost 92% of patients.³

Vesicular Rash

Patients note the development of a papular skin lesion at the location of the bite around 10 days (6-15 days) after the bite. The vesicular rash is characterized by small, fluid-filled blisters which are sharply demarcated and slightly raised. The lesions can reach up to a width of 1 inch and gradually become vesicular and surrounded by an area of erythema. The most common sites of the lumps include the arms, legs, face, and the trunk. However, the lesions do not develop on the soles of the feet and palms of the hand. The papulovesicular rash is frequently seen in old patients and resembles chickenpox.⁴Young patients experience similar symptoms of rash, fever, eschar, and headache, etc. According to one case report, a 4-year-old boy developed erythematous papules on his thigh after a tick bite. The papules then turned to a mildly pruritic diffuse rash that spread to the whole body. The papulovesicular rash was caused by an underlying Rickettsia Akari infection.⁵

Eschar

Eschar formation is a salient feature of rickettsialpox and is characterized by a black, crusty lesion on the site of the bite. An eschar is composed of dead skin tissues that shed/fall off. It’s an important hallmark of this particular zoonotic illness that typically develops a few days after a bite. An eschar initially appears as a papule, which turns into a vesicle (at the center). The vesicle then dries leading to a brown-black eschar.⁶
Black pinpoint eschars are frequently seen along with maculopapular rash in rickettsialpox patients.⁷While symptoms of rash, fever, and malaise are similar, the presence of eschars helps differentiate between chickenpox and rickettsialpox.⁸

Muscle & Joint Pain:

Many patients report muscle and joint pains in conjunction with headaches and fluctuating fever. In the study conducted by Shivnitwar and colleagues, it was found that body aches are present in 72.5% of patients while joint pains were experienced by 62.5% of the study participants.

Headache:

There are multiple cases of infection in which patients report persistent headaches associated with other symptoms like malaise, fever, and fatigue. The symptoms arise after a bug bite⁹

Enlarged Lymph Nodes:

Lymph node swelling is a presentation of several infectious conditions. Tick bites leading to rickettsialpox can also lead to lymphadenopathy, i.e., swelling of the lymph nodes. The disease can cause generalized or localized (regional) lymphadenopathy. One patient suffering from acquired rickettsialpox reported experiencing lymphadenopathy in the right groin. Swelling of the lymph nodes sets 2-3 days after the onset of initial symptoms.¹⁰

Other symptoms of rickettsialpox include:

Photophobia (hypersensitivity and discomfort on exposure to bright lights)
Sore throat, cough, and runny nose
Nausea and vomiting
Loss of appetite
Sweating

Rickettsialpox Causes

The Rickettsia Akari bacteria live in their hosts, i.e., the house mouse mite. The bacteria pathogen transfers to humans via an infected mite’s bite. Once inside the body, the bacteria target the CD68 macrophages (which is a unique feature of this bacteria).

The pathogen also targets the vascular endothelial cells. Activation of the macrophages induces self-phagocytosis (similar to rickettsiae) which leads to symptoms. As tick bites are painless, most people do not notice them until symptoms develop.

Rickettsialpox Transmission:

Transmission to humans occurs via mites that live on mice. Only vertical transmission from mites to humans is noted. You can acquire the disease if the bacteria comes in contact with skin abrasions. Rickettsialpox may also develop if you inhale the bacteria. This is why laboratory technicians take extra precautions when dealing with blood samples/specimens.

Rickettsialpox Diagnosis

History & Examination:

There are no quick tests available to diagnose rickettsialpox. Therefore, doctors rely on the history and physical examination of the rash and several detailed tests. Your physician will look at the skin rash, and black eschar, and correlate it with other symptoms like lymphadenopathy, fever, myalgia, headache, etc.

Blood Tests:

Your healthcare provider might order a Complete blood count (CBC), and serological tests. Blood serological tests detect antibodies (in response to the rickettsia bacteria). A reliable method of antibody detection is the Indirect fluorescent antibody (IFA) test. Generally, a four-fold rise in antibodies is seen in R. Akari infections.

PCR Test:

The Polymerase chain reaction (PCR) technique is an accurate diagnostic method for identifying R. Akari. For this technique, the doctor removes small specimens (via biopsy) from skin lesions (rash or eschars).

Swab & Culture Tests:

Eschar swabs can also provide details of the causative agents. Pathologists may also opt to culture Rickettsia Akari bacteria in a Vero cell system (using blood or eschar specimen). Immunohistological staining of skin biopsies may also be used in diagnosis.

Differential Diagnosis:

Rickettsialpox Vs Small Pox

There are multiple similarities and some differences between both conditions. Initial presentation of both rickettsialpox and smallpox, i.e., rash and fever, are the same. However, in the case of rickettsialpox, the generalized maculopapular rash mainly develops on the bite location and gradually spreads to other parts of the body. On the other hand, the aggressive skin lesions of smallpox are simultaneously present over different body parts at the same time. Rickettsialpox lesions do not develop on the palms and soles, but smallpox can. A short course of doxycycline can treat rickettsialpox but you will need strong antivirals like brincidofovir to inhibit smallpox virus growth.

Rickettsialpox Vs Chickenpox

The skin rash of rickettsialpox resembles that of chickenpox, however, eschar formation is limited to rickettsialpox and not present in chickenpox. While chickenpox is highly contagious, man-to-man transmission of rickettsialpox is not reported. Moreover, skin lesions of chickenpox are very itchy (pruritic) while R. Akari’s infection-induced rash is only slightly itchy.

Rickettsialpox Treatment

Rickettsia Akari infection only causes a mild disease that resolves itself within 7-10 days. However, sometimes, doctors prescribe antibiotics to speed up the process of recovery. The main drug of choice for R. Akari infection is doxycycline. With antibiotic therapy, the duration of symptoms shortens to 48 hours. The most commonly prescribed dosage for adults is 100mg doxycycline (oral) twice daily for 2-5 days.¹¹
Doctors do not advise treatment for children less than 8 years old and pregnant women.

Rickettsialpox Prevention & Control

As bacteria spread through the bite of a house mouse mite, controlling mice populations in living areas and offices can reduce the risk of infection.

Final Word

Rickettsialpox is a rare bacterial infection that causes mild, self-resolving disease. The causative agent Rickettsia Akari gets transmitted to humans via mouse mites. Common presentations of the infection (which arise a week after the bite) include fever, headache, generalized maculopapular rash, and black, pinpoint dead crusted skin i.e., eschars. Doctors perform PCR tests to diagnose. Generally, it doesn’t require treatment because it goes away within 10 days. When needed, antibiotic therapy with doxycycline is highly effective.

Refrences

1
Bishop, A., Borski, J., Wang, H. H., Donaldson, T. G., Michalk, A., Montgomery, A., … & Teel, P. D. (2022). Increasing incidence of spotted fever group rickettsioses in the United States, 2010–2018. Vector-Borne and Zoonotic Diseases, 22(9), 491-497
2
Shivnitwar, S., Rajput, S., Avate, A., Narayankar, A., Sujanyal, S., & Ahlawat, M. (2024). A Clinical Study of Rickettsial Fever and Factors Affecting Its Outcome. Cureus, 16(7)
3
Akram, S. M., Jamil, R. T., & Gossman, W. (2017). Rickettsia akari (Rickettsialpox).
4
Ganjuur, N., Abu Rached, N., Doerler, M., & Gambichler, T. (2020). Rickettsialpox caused by Rickettsia africae in an elderly woman. Clinical and Experimental Dermatology, 45(7), 905-907.
5
Metzger, M. C. Fever, eschar, and rash in a 4-year-old male.
6
Akram, S. M., Jamil, R. T., & Gossman, W. (2017). Rickettsia akari (Rickettsialpox)
7
Rao, M. (2021). Rickettsialpox or chickenpox?. IDCases, 25, e01138.
8
Mittal, A., Elias, M. L., Schwartz, R. A., & Kapila, R. (2021). Recognition and treatment of devastating vasculopathic systemic disorders: Coronavirus disease 2019 and rickettsioses. Dermatologic therapy, 34(4), e14984.
9
.Saini, R., Pui, J. C., & Burgin, S. (2004). Rickettsialpox: report of three cases and a review. Journal of the American Academy of Dermatology, 51(5), S137-S142.
10
A Szakacs, T., Wood, H., Russell, C. B., Nelder, M. P., & Patel, S. N. (2020). An apparent, locally acquired case of rickettsialpox (Rickettsia akari) in Ontario, Canada. Official Journal of the Association of Medical Microbiology and Infectious Disease Canada, 5(2), 115-119.
11
Paddock, C. D. (2020). Rickettsialpox. In Hunter’s Tropical Medicine and Emerging Infectious Diseases (pp. 594-598). Elsevier.

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