Rickettsialpox is a common condition in the Northeast Region of the United States that affects males and females in approximately equal numbers. Find out more about this disorder including its symptoms, causes, diagnosis and treatment.

Rickettsialpox Definition

It is a subtle form of a bacterial infection that clinically mimics the highly contagious chicken pox. The condition is popularly referred to as Kew Gardens Spotted Fever.

Rickettsialpox Symptoms

There is a delay of about 10 to 20 days prior to the onset of the symptoms of this disease. The condition is initially manifested by a small bump or swelling on the skin that measures 1-1.5 cm in diameter. It rapidly vesiculates to form a tiny, fluid-filled sac. The vesicle gradually develops into an eschar – a painless, dry thickened black scab or scar that occurs when a piece of dead tissue gets cast off from the surface of the skin. A week later, affected patients begin to experience symptoms like:

Picture 1 – Rickettsialpox

  • High fever
  • Sore throat
  • Swollen lymph glands
  • Chills
  • Profuse sweating
  • Headaches
  • Muscle pain
  • Weakness
  • Loss of appetite
  • Excessive sensitivity to light
  • Nausea
  • Cough
  • Conjunctivitis
  • Persistent nasal discharge
  • Neck stiffness

Approximately 2-3 days after the commencement of the systemic symptoms, there is a sudden outbreak of raised, blistering rashes that spread all over the body – except the soles and palms. This is typically a maculopapular rash, represented by a flat, red area on the skin and covered with minute lumps. In some cases, the vesicular rash may involve the oral mucosa and throat. The inflammatory condition of the skin usually lasts for about a week.

Rickettsialpox History

In 1946, the first case of the infection was reported in the Regency Park complex, which had 69 apartment units, situated in Kew Gardens in the New York City borough of Queens. The condition was initially suspected as chickenpox, since it had similar symptoms like rash, fever and chills. The number of cases began to go up, and reached a peak of more than 20 cases. Individuals of all age groups were infected, irrespective of the gender. The residents of the complex had noticed numerous mice in and around the apartments. Both living and dead mice were found in the basement of the buildings near the sewage, and incinerators where garbage was disposed and burnt. The waste matter however, was not burnt regularly due to labor shortage. The abundant waste products were sufficient to feed the rodents. When these mice were sent for pathological investigation, antibodies for the bacteria were found in their blood. The presence of mites in the complex was also suspected as the probable cause of the infection. When rickettsial strains were found in the mites, the exact cause of the illness was then identified. Robert Huebner, an American physician and Charles Pomerantz, a renowned self-trained entomologist, had major contributions in the identification of the disorder.

Rickettsialpox Causes

The infection is caused by bacteria of the Rickettsia genus called Rickettsia akari found in house mice. The bacterium belongs to the spotted fever group of rickettsiae that comprises of infectious disorders caused by various species of Rickettsia. Mites have been implicated as vectors of these bacterial agents that infest the house mice. These rodents are usually available in significant numbers in certain human-inhabited areas. The transmission of the infection occurs when an infected mite originally found in the mice (carrying Rickettsia akari) bites a human. The bacterial infection, however, is not contagious.

Rickettsialpox Diagnosis

The diagnosis of the disorder is usually made clinically when the problems of an infected patient include frequent episodes of undulant fever and a bumpy skin rash that occurs a few days after a mite bite. A history of mite exposure could be helpful to health practitioners. However, most house mites do not carry the causative bacteria. A simple blood test cannot be used alone to make the diagnosis as an increased WBC count as well as an elevated platelet count do not provide any specific information about the disorder. The other laboratory methods that could be used for detecting the underlying cause of the rash include:

Serology blood test

The blood can be examined for antibodies produced against the bacteria using techniques like immunofluorescence and enzyme immunoassays. If a high concentration of antibodies is found, the disease can be presumed to be present. It may take a week for antibodies to appear in the blood, so a negative result does not completely rule out the condition. The test can also be done at the onset of illness and again several weeks later in order to observe any deviation from the previous result.

Skin biopsy

A small piece of the inflamed skin with raised bumps can be removed and mixed with a special dye that facilitates the identification of the bacteria under a microscope.

Rickettsialpox Treatment

Doxycycline, a commonly used tetracycline antibiotic can be used in the treatment of the infection. A widely-used over-the-counter pain reliever drug, such as Acetaminophen or Paracetamol, is administered to the patients for fever and muscle ache. Chloramphenicol and Azithromycin are the other recommended medications for this condition. However, these are generally not used on a routine basis (owing to their substantial toxicity).

Rickettsialpox Prognosis

The infection is normally mild and self-limited. Infected patients recuperate well, even in the absence of antibiotic treatment, and do not suffer from any complications. The rashes normally clear within 2-3 weeks without scarring the skin. The overall prognosis of patients with the condition is excellent and no deaths have been reported so far.

Rickettsialpox Prevention

The risk of the infection can be reduced by avoiding areas where mites are common. If an individual visits such an area, protective clothing, including socks, long pants, and long sleeves must be worn in order to prevent the mites from having a blood meal. Insect repellents containing DEET can eradicate the mites. Proper sanitary measures must be taken to prevent the mice from inhabiting the human residential places. Mice can easily live and thrive under a variety of conditions in and around the houses.

Picture 2 – Rickettsialpox Image

Extermination is the only way to extirpate these animals. To reduce the risk of infection, a quick shower or bath is advisable for individuals who return from an infected site. A full body check-up is also essential to spot any mite crawling. The clothes must be thoroughly washed with warm water to kill the heat-sensitive mites. It is generally advisable to reduce heavy rodent infestation as well as avoid traveling to places, where outbreaks of the infection have occurred, to prevent transmission of the condition.

Although rashes appear late in the course of infection, the possibility of Rickettsialpox should be considered even in the absence of this distinctive symptom. Proper hygiene maintenance and exclusion of the disease-causing mice from human dwellings can decline the number of sporadic outbreaks.

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