Rickettsia en Latinoamérica
Rickettsia in Latin America)
Las garrapatas son ectoparásitos hematófagos causantes de perjuicios por el parasitismo per se o por la transmisión de agentes patógenos que pueden provocar enfermedades en animales y humanos. Dentro de este grupo de parásitos, tres de las especies con mayor importancia sanitaria son Rhipicephalus sanguineus sensu lato, Amblyomma cajennense y Amblyomma triste. Estudios recientes han demostrado que los taxones R. sanguineus s.s y A. cajennense en realidad constituyen complejos de especies. Particularmente en Sudamérica, existen evidencias que indican que el complejo R. sanguineus está formado por al menos dos especies, mientras que A. cajennense es un complejo de la menos seis especies. Amblyomma cajennense ha sido incriminada como una de las especies con mayor relevancia sanitaria no solo por el efecto deletéreo causado por el parasitismo per se, sino también por su capacidad para transmitir agentes patógenos a los humanos. Una de las enfermedades en la que las garrapatas del complejo A. cajenense se constituyen en el principal vector es la fiebre manchada por Rickettsia rickettsii. Esta es la rickettsiosis humana transmitida por garrapatas más importante de Latinoamérica. Ha sido reportada en México, Panamá, Costa Rica, Colombia, Brasil y Argentina, con casos fatales en la mayoría de estos países. Hasta el momento, todos los casos fatales por rickettsiosis en humanos reportados en Latinoamérica fueron provocados por R. rickettsii. Las garrapatas del complejo R. sanguineus pueden actuar como vectores y reservorios de Ehrlichia canis, el agente causal de la erlichiosis canina, y son también vectores potenciales de otros agentes rickettsiales como R. rickettsii, R. massiliae y Anaplasma platys. Este nuevo escenario taxonómico referido a A. cajennense s.s y R. sanguineus s.s conlleva implicancias ecológicas y epidemiológicas relacionadas a diferencias en la dinámica estacional, distribución y capacidad vectorial entre las especies que forman los dos complejos. Amblyomma triste es una garrapata filogenéticamente también presenta una amplia distribución, desde el sur de Estados Unidos al sur de Uruguay y centro de Argentina. Sin embargo, las poblaciones de A. triste involucradas en la transmisión de Rickettsia parkeri a humanos están restringidas a localidades de la Cuenca del Plata, en Argentina, Brasil y Uruguay. Estudios publicados recientemente y en curso han mostrado que A. tristepresenta una distribución más amplia que la usualmente reconocida. Asimismo, se han establecido diferencias morfológicas asociadas a poblaciones con distinto origen geográfico. En esta presentación se detallan y discuten los avances mencionados sobre sistemática y ecología de estas tres garrapatas con importancia sanitaria en la región Neotropical.
Brazil. It is caused by infection with the bacterial organism Rickettsiarickettsii. In the last 10 years, approximately 80 cases of BSF have been reported annually and over 50% lethality. In the last ten years, several other Rickettsia species have been detected infecting ticks in South America, for most of them the potential threat to human being is yet to be confirmed. The disease epidemiology is strongly associated with the life cycle and ecology of the tick vectors, and therefore with the behavior of their hosts.
Rickettsia antibodies through Indirect Immunofluorescence Assay (IFA), this technique depends on glass slides prepared with cell cultured Rickettsia. IFA test shows a cross reaction among all Rickettsia species from the spotted fever group. It is possible to determine the likely homologous reaction if each individual serum is tested against different Rickettsia species, if the title obtained against one species is four times higher than the other tested species, it is highly probable that it is an homologous reaction, whereas if just one or few species of Rickettsia is tested the positive outcome may only be informative to Spotted Fever Group Rickettsia.
Rhipicephalus sanguineus, because this species is extremely anthropophilic and population of this tick can rise very fast and be suitable to have rickettsial agent introduced in by hosts that are also fed on by native tick species, such as hunting dogs that go into forests and dwell nearby or in human houses, which may cause an epizootic profile and eventually human infection, but this situation is not natural and especially different from the expected behavior of New World endemic tick species.
Brazil have shown a seroprevalence higher than 40% for endemic areas and smaller than 5% for non-endemic areas.
The parameters of a surveillance program must be determined specifically for each Country and ought to be an important research focus for the forthcoming years.
Latin America)
Spottedfever rickettsioses are causedby bacteria of the genusRickettsia, whichareprimarily transmittedtohumans throughthe bite of infected ticks. These bacteria belong to the so called spotted fever group (SFG), currently composed by over 20 valid species distributed through the world. While some SFG species are agents of human illness (SFGrickettsioses), others have been described only from ticks, and are considered non-pathogenic or of unknownpathogenicity. InLatin America, at least four tick-borne SFGrickettsiaehave been reported to cause illness in humans:Rickettsia rickettsii,Rickettsia parkeri,Rickettsia massiliae,and strain Atlantic rainforest (aR. parkeri-like agent).Rickettsia rickettsiiis the agent of Rocky Mountain spotted fever, a severe, acute disease caused by the bacteriumRickettsia rickettsii, which has been reported in Canada, the United States, Mexico,Costa Rica, Panama, Colombia,Argentina, and Brazil. In this later country, the disease was named as Brazilian spotted fever (BSF). Current fatality rates of BSF are between 30-40% inBrazil. In the state ofSão Paulo, southeasternBrazil,R. rickettsiiis transmitted mainly by Amblyommacajennense in the country side, and byAmblyomma aureolatumin the Metropolitan area. For both ticks under natural conditions,R. rickettsii-infection rates are usually very low, below 1%. Interestingly, laboratory studies have shown that whileA. aureolatum ticks are highly susceptible to R.rickettsii (usually 100% of the ticks become infected after feeding onrickettsemic guinea pigs), A.cajennense are partially refractory (only ≈20% of the ticks become infected after feeding onrickettsemicguinea pigs). In addition,transovarialtransmission ofR. rickettsii is highly efficient inA. aureolatum, and very low inA. cajennense.Thus, populations of A. cajennensemight not be capable to sustainR. rickettsiiinfection though successive generations, unless new cohorts of infected ticks are frequently created through the feeding onrickettsemicamplifier hosts, such as capybaras (Hydrochoerushydrochoeris), a common host of A. cajennense in BSF-endemic areas in the country side of the state ofSão Paulo. In fact, experimental studies have shown that capybaras are competent amplifier hosts ofR. rickettsii for A.cajennense ticks. Despite of the high susceptibility ofA. aureolatum to R. rickettsiiinfection, this tick also might not be able to sustain rickettsialinfection for a long term due to the deleterious effect thatR. rickettsii elicits to engorged females. In this case, the participation of amplifier hosts (yet to be determined) might also be needed for maintenance of infection amongstA. aureolatumpopulations in the metropolitan area of São Paulo, although in a lesser extent. Anyhow, BSF has occurred with similar incidences, always low, in both the country side and the metropolitan areas. In this case, low number of cases in the metropolitan area might occur because the highly competent vector (A.aureolatum) only rarely bites human; on the other side, even thatA. cajennense frequently bites humans, the low incidence of the disease in the country side might be a result of the low vector competence of this tick, since it is partially refractory toR.rickettsii infection. Finally, a recent study showed thatR. rickettsii infectionamongA. aureolatum populations in the São Paulometropolitan area was significantly associated with degraded Atlantic forest fragments, especially in the southern part of the metropolitan area. The agentRickettsia parkeri has been reported infecting ticks in theUnited States, Peru,Bolivia, Brazil, Argentina, andUruguay. In South America, human cases ofR. parkeri-causedrickettsioses have been reported only in Uruguay and Argentina, where the agent is transmitted byAmblyomma triste ticks. In the Atlantic coast of Brazil,Rickettsia sp. strain Atlantic rainforest (SARF) causes a disease very similar toR. parkeri.In fact, this strain is genetically very similar to R. parkeri, raising the possibility that both agents could be strains of a single species. SARF is primarily transmitted by the tickAmblyomma ovale, although A. aureolatummight also be important in some areas where both tick species coexist. While bothR.parkeri and SARF are usually found infecting around 10% of the ticks in nature, nothing is known abouttransovarialandtransstadialtransmission of these agents in ticks, and neither if there is any amplifier vertebrate host for the bacteria in nature. Finally, recent studies have reported the presence ofR.massiliae infecting Rhipicephalussanguineus ticks in Argentina, from where at least one case ofR. massiliae-caused rickettsioses was reported. Since R. massiliaeis considered a pathogenic species in Eurupe, where it is transmitted by ticks of theR. sanguineusgroup, it is possible that the presence of this agent in the south cone ofSouth Americais much broader than currently recognized.
References
Publication Dates
-
Publication in this collection
09 Nov 2015 -
Date of issue
July 2013