Formation of the Panama Isthmus, that had global oceanographic and biotic effects in the Neogene, is generally associated with tectonic uplift during collision of the Panama volcanic arc with South America. However, new field, geochemical and geochronological data from the Culebra Cut of the Panama Canal suggest that volcanism also contributed to the Isthmus emergence in the Early Miocene. This volcanism is recorded in a newly-recognised Central Panama volcanic field that includes several phases of development. Early activity of this field along the Panama Canal was associated with proximal effusive to explosive felsic products during formation of subaerial stratovolcanoes and possible domes ca. 21 Ma. This was followed by a period of marine transgression ca. 21–18 Ma, with more distal volcanism documented by tuffs that deposited in marine to terrestrial environments. Finally, proximal mafic volcanism formed tephra cones in a monogenetic field ca. 18(-?) Ma. This was associated with phreatomagmatic processes in a coastal environment, with remarkable kilometre-wide subvolcanic peperitic intrusions. We propose based on these observations that formation of the Central Panama volcanic field was critical in shaping regional topography, and that this could have actively contributed to obstruction and closure of an interoceanic strait in Central Panama.
Tick-borne rickettsiosis is an important emerging disease in Panama; to date, there have been 12 confirmed cases, including eight fatalities. To evaluate the distribution of rickettsiae in Panamanian ticks, we collected questing and on-host ticks in urban and rural towns in elevations varying between 0 and 2300 m. A total of 63 sites (13 urban and 50 rural towns) were used to develop models of spatial distributions. We found the following tick species: Rhipicephalus sanguineus s.l. (present in 54 of 63 towns and cities), Amblyomma mixtum (45/63), Dermacentor nitens (40/63), A. ovale (37/63), Rhipicephalus microplus (33/63), A. oblongoguttatum (33/63), Ixodes affinis (3/63), and Ixodes boliviensis (2/63). Rhipicephalus sanguineus s.l. was present in urban and rural towns, and other species were present only in rural towns. DNA was extracted from 408 R. sanguineus s.l., 387 A. mixtum, 103 A. ovale, and 11 A. oblongoguttatum and later tested for rickettsiae genes using PCR. Rickettsia DNA was detected in ticks from 21 of 63 localities. Rickettsia rickettsii was detected in five A. mixtum (1.29%), and Candidatus "Rickettsia amblyommii" was found in 138 A. mixtum (35%), 14 R. sanguineus (3.4%), and one A. ovale (0.9%). These results suggest that much of rural Panama is suitable for the expansion of tick populations and could favor the appearance of new tick-borne rickettsiosis outbreaks.
From January 2010 to December 2011, a total of 138 cases of ticks feeding on humans were reported from 11 locations in central Panama. Five of these locations were situated in forest environments, three in rural landscapes and three in urban areas. The ticks were submitted to the Gorgas Memorial Institute, where nine species were identified among 65 specimens: Amblyomma cajennense s.l., A. dissimile, A. naponense, A. oblongoguttatum, A. ovale, A. sabanerae, A. tapirellum, Haemaphysalis juxtakochi and Rhipicephalus sanguineus s.l. The remaining 73 specimens consisted of unidentified immature ticks, all belonging to the genus of Amblyomma. Rhipicephalus sanguineus s.l. was the species most frequently associated with humans, particularly in urban environments. In rural landscapes, tick bites were most often caused by A. cajennense s.l., whereas A. tapirellum was the species most often found parasitizing humans in forest environments. These data provide information on the tick species most commonly associated with humans in forested environments, rural areas and cities around the Panama Canal.
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