Ecology, biology and distribution of spotted-fever tick vectors in Brazil

Abstract

Spotted-fever-caused Rickettsia rickettsii infection is in Brazil the major tick-borne zoonotic disease. Recently, a second and milder human rickettsiosis caused by an agent genetically related to R. parkeri was discovered in the country (Atlantic rainforest strain). Both diseases clearly have an ecological background linked to a few tick species and their environment. Capybaras (Hydrochoerus hydrochaeris) and Amblyomma cajennense ticks in urban and rural areas close to water sources are the main and long-known epidemiological feature behind R. rickettsii-caused spotted-fever. Unfortunately, this ecological background seems to be increasing in the country and disease spreading may be foreseen. Metropolitan area of São Paulo, the most populous of the country, is embedded in Atlantic rainforest that harbors another important R. rickettsii vector, the tick Amblyomma aureolatum. Thus, at the city-forest interface, dogs carry infected ticks to human dwellings and human infection occurs. A role for R. rickettsii vectoring to humans of a third tick species, Rhipicephalus sanguineus in Brazil, has not been proven; however, there is circumstantial evidence for that. A R. parkeri-like strain was found in A. ovale ticks from Atlantic rainforest and was shown to be responsible for a milder febrile human disease. Rickettsia-infected A. ovale ticks are known to be spread over large areas along the Atlantic coast of the country, and diagnosis of human infection is increasing with awareness and proper diagnostic tools. In this review, ecological features of the tick species mentioned, and that are important for Rickettsia transmission to humans, are updated and discussed. Specific knowledge gaps in the epidemiology of such diseases are highlighted to guide forthcoming research.

Keywords: Brazil; Rickettsia; ecology; human spotted-fever; tick species.

Figure 1

Locations of spotted-fever vector ticks in Brazil. Light gray: States from Brazil where A. cajennense is proven or suspected vector of R. rickettsii to humans. Dark gray: areas where Atlantic rainforest Rickettsia-infected A. ovale were already found. Black: area with A. aureolatum transmission of R. rickettsii to humans.

Figure 2

Environmental backgrounds and ticks associated with Brazilian spotted-fever caused by human infection with R. rickettsii in Brazil. Capybaras in anthropized area (A). Tick-infested capybara (B). Male and female adults of Amblyomma cajennense (Ac) and Amblyomma dubitatum (Ad). Endemic human settlement at the border of the Atlantic rainforest and metropolitan area of São Paulo (C). Dog ear with an attached Amblyomma aureolatum (D). Adult couple of Amblyomma aureolatum (Aa).

Figure 3

Environments with potential for dog and human infestation with ticks associated to spotted-fever in Brazil. Dog restrained to its house providing conditions for the maintenance of Rhipicephalus sanguineus infestation but with potential for infestation with Amblyomma ovale or Amblyomma aureolatum in the nearby forest (A). Rhipicephalus sanguineus bite of a human leg (B). Adult couple of Rhipicephalus sanguineus (Rs). Atlantic rainforest with high Amblyomma ovale prevalence (C). Dog infestation with Amblyomma ovale ticks at the same area (D). Adult couple of Amblyomma ovale (Ao).