Excerpt from Boutonneuse Fever

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Background

Boutonneuse fever (BF) is usually a mild rickettsial disease caused by Rickettsia conorii (endemic in the Mediterranean basin); however, severe complications can occur in about 6-10% of patients. Complications are more common in patients with underlying disease or in elderly persons (so-called malignant form of BF). Mild forms are usually observed in children.

The major clinical features are fever, exanthem, and tache noire (eschar, necrotic plaque). In some patients, the eruption is papulovesicular; this form is more common in adults in Africa. In other patients, the only symptom is an isolated lymphadenopathy. Consider R conorii infection in patients with lymphadenopathy who live in or have traveled to an endemic area even when other more specific features are not present.

Pathophysiology

The pathogen is introduced through the bite of a tick. The organism, R conorii, invades and proliferates in the endothelial cells of small vessels, destroying them. Activation of the acute-phase response with changes in the coagulation state follows. Patients have an alteration in cell-mediated immunity together with a reduction in CD4 cells and a considerable alteration in the cytokine profile. The incubation time of BF is usually 4-15 days, but it can be longer (reportedly 5-28 d in German travelers).

Fractalkine (CX3CL1) is a chemokine expressed mainly by endothelial cells, which are the major cellular targets of rickettsiae. The peak of expression of CX3CL1 on day 3 of infection reportedly coincided with the time of infiltration of macrophages into infected tissues and preceded the peak of rickettsial content in tissues.

Induction of the endothelial cyclooxygenase-2 system and the ensuing release of vasoactive prostaglandins) may contribute to the regulation of inflammatory responses and vascular permeability changes.

Frequency

United States

The disease is unrecognized in most cases. About 50 imported cases of BF have been reported and confirmed by the US Centers for Disease Control and Prevention (CDC).

International

The true incidence of BF is unknown. In many endemic areas, mild infection is common, underdiagnosed, and underreported.

• In the Mediterranean region, the incidence of BF is estimated at 50 cases per 100,000 inhabitants per year.
• In Croatia, 51.6% of a studied population with a recent history of a tick bite had antibodies to R conorii.
• In the Leon province of Spain, antibodies to R conorii were discovered in 1% of humans and in 14% of dogs.
• In the Valles Occidental in Spain, a population without a previous history of BF, antibodies against R conorii were detected in 4.6-13.5% (mean, 8%) of humans and in 26.1% of dogs.
• In southern Portugal, 7.6% of the population have antibodies to R conorii, and nationally as many as 20,000 cases are estimated to occur each year, but only about 5% are reported.
• In the Mediterranean coast of Turkey, immunoglobulin G (IgG) antibodies against R conorii were detected in 13.3% of the healthy population.
• In Zambia, the seroprevalence of antibodies against R conorii is estimated to be 16.7% in the human population and higher in cattle-breeding areas.
• In Germany, Norway, and the Netherlands, sporadic cases of so-called imported (eg, via infected dogs, as a holiday souvenir) BF are described.

Mortality/Morbidity

Mortality is generally estimated to be less than 5%.

• In one series, 2.5% of patients died from the malignant form.
• In another series, 33% of patients with underlying disease (eg, chronic liver disease, alcoholism, diabetes mellitus, glucose-6-phosphate dehydrogenase deficiency end stage kidney disease, cardiac disease) died because of malignant BF.
• Death from malignant (severe) BF has been associated with delay in diagnosis (>5 d) and treatment (>10 d).

Race

BF affects all races.

Sex

The male-to-female ratio is 1.7:1.

Age

People of all ages are susceptible to infection. In published reports, most patients present at the mean age of about 50 years if a cohort of adult patients is examined.

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