Tick-Borne Rickettsioses around the World: Emerging Diseases Challenging Old Concepts

Abstract

SUMMARY During most of the 20th century, the epidemiology of tick-borne rickettsioses could be summarized as the occurrence of a single pathogenic rickettsia on each continent. An element of this paradigm suggested that the many other characterized and noncharacterized rickettsiae isolated from ticks were not pathogenic to humans. In this context, it was considered that relatively few tick-borne rickettsiae caused human disease. This concept was modified extensively from 1984 through 2005 by the identification of at least 11 additional rickettsial species or subspecies that cause tick-borne rickettsioses around the world. Of these agents, seven were initially isolated from ticks, often years or decades before a definitive association with human disease was established. We present here the tick-borne rickettsioses described through 2005 and focus on the epidemiological circumstances that have played a role in the emergence of the newly recognized diseases.

Update on tick-borne bacterial diseases in Europe

“…T ick-borne rickettsioses are caused by obligate intracellular bacteria belonging to the spotted fever group (SFG) of the genus Rickettsia within the family Rickettsiaceae in the order Rickettsiales (Parola et al, 2005;Merhej et al, 2009). These bacteria infect and colonize the organs of ticks, particularly the salivary glands and ovaries of adult females.…”

“…MSF cases are still being identified in new locations within this region, and have recently been described in Turkey, Bulgaria, Ukraine, Slovenia, Croatia, Albania, Malta and Georgia (Rovery & Raoult, 2008;Tonna et al, 2006). In Italy, around 1,000 cases are reported each year (Parola et al, 2005). The annual MSF incidence rate in southern France is approximately 50 cases per year per 100,000 persons.…”

“…A few cases have been reported sporadically across northern and central Europe, including Belgium, Switzerland, the Netherlands, Germany and the northern region of France, where Rh. sanguineus ticks have been imported (Parola et al, 2005;Peter et al, 1984;Rovery & Raoult, 2008;Dobler & Wolfel, 2009). In Europe, most MSF cases are encountered in late spring and summer, when the tick vectors are most active.…”

“…During the 1970s, an increase in MSF cases was observed in France, Italy, Spain, and Portugal. The increase was correlated with higher temperatures and lower rainfall in Spain and with a decrease in the number of days of frost during the preceding year in France Parola et al, 2005). In Portugal, the number of positive cases of MSF doubled in [2004][2005], and the authors speculated that it was probably associated with climate change, particularly low precipitation .…”

“…After an incubation of around six days, the onset of MSF is abrupt. Typical patients have a high fever, flulike symptoms, a local necrotic inflammation with a black crust called an eschar (the "tache noire") at the tick bite site and a maculopapular rash (Rovery & Raoult, 2008;Parola et al, 2005). Occasionally, the eschar is not found, and it is seen rarely in multiples (Rovery & Raoult, 2008).…”