Challenges Posed by Tick-Borne Rickettsiae: Eco-Epidemiology and Public Health Implications

Abstract

Rickettsiae are obligately intracellular bacteria that are transmitted to vertebrates by a variety of arthropod vectors, primarily by fleas and ticks. Once transmitted or experimentally inoculated into susceptible mammals, some rickettsiae may cause febrile illness of different morbidity and mortality, and which can manifest with different types of exhanthems in humans. However, most rickettsiae circulate in diverse sylvatic or peridomestic reservoirs without having obvious impacts on their vertebrate hosts or affecting humans. We have analyzed the key features of tick-borne maintenance of rickettsiae, which may provide a deeper basis for understanding those complex invertebrate interactions and strategies that have permitted survival and circulation of divergent rickettsiae in nature. Rickettsiae are found in association with a wide range of hard and soft ticks, which feed on very different species of large and small animals. Maintenance of rickettsiae in these vector systems is driven by both vertical and horizontal transmission strategies, but some species of Rickettsia are also known to cause detrimental effects on their arthropod vectors. Contrary to common belief, the role of vertebrate animal hosts in maintenance of rickettsiae is very incompletely understood. Some clearly play only the essential role of providing a blood meal to the tick while other hosts may supply crucial supplemental functions for effective agent transmission by the vectors. This review summarizes the importance of some recent findings with known and new vectors that afford an improved understanding of the eco-epidemiology of rickettsiae; the public health implications of that information for rickettsial diseases are also described. Special attention is paid to the co-circulation of different species and genotypes of rickettsiae within the same endemic areas and how these observations may influence, correctly or incorrectly, trends, and conclusions drawn from the surveillance of rickettsial diseases in humans.

Avian Migrants Facilitate Invasions of Neotropical Ticks and Tick-Borne Pathogens into the United States

“…An increasing number of spotted fever group Rickettsia species are recognized to cause disease in humans (13,57), including R. parkeri, which we detected in ticks on northward migrants. R. parkeri was first described in 1939 in A. maculatum ticks from Texas, and it has only recently been implicated in human disease in the southern United States (58), where cross-reaction with R. rickettsii (an agent of Rocky Mountain spotted fever) occurs and the human burden of disease is therefore difficult to discern.…”

“…Rickettsia species of bacteria are transmitted to vertebrates by arthropod vectors, including Amblyomma ticks. The pathogenicity of many tick-borne Rickettsia species is unknown, but there are Ͼ25 recognized species in the zoonotic spotted fever group, including those that cause Rocky Mountain spotted fever, Mediterranean spotted fever, North Asian tick typhus, and Queensland tick typhus (13). Wild birds have been implicated as hosts of Amblyomma ticks and Rickettsia pathogens in South and Central America (8)(9)(10)(11); however, the significance of wild birds in the epidemiology of these vectors and pathogens remains poorly understood (13).…”

Do Tick Attachment Times Vary between Different Tick-Pathogen Systems?

“…Tick-borne diseases are an important health threat that continues to impact public health worldwide. The impact of tick-borne pathogens may be more extensive than currently understood due to factors such as nonspecific symptoms experienced during other illnesses, lack of adequate surveillance systems, and climatic variables impacting tick and animal behaviors [95,96]. Furthermore, emerging and re-emerging tick-borne pathogens necessitate the push for further research in this area to protect public health.…”

Caso fulminante de rickettsiosis (Rickettsia rickettsii) en una lactante del sureste de México

“…11 De acuerdo con la literatura, las garrapatas R. sanguineus son los vectores responsables de la transmisión de R. rickettsii y, aunque se ha sugerido que las zarigüeyas funcionan como reservorio, diversos estudios indican que las garrapatas mismas son el reservorio principal de esta bacteria, puesto que la transmisión vertical es el mecanismo más importante para su circulación. 12,13 Los perros no juegan un papel importante en el ciclo de estas bacterias, pero al ser sensibles a la enfermedad, actúan como centinelas y permiten prevenir la aparición de brotes en poblaciones humanas. 1 De acuerdo con las guías internacionales actuales, para la confirmación serológica, se considera la IFI como el estándar de oro, a partir del título 1:64, que tiene validez diagnóstica IFI: inmunofluorescencia indirecta; PCR: reacción en cadena de la polimerasa.…”