Human Rickettsiosis Caused by Rickettsia parkeri Strain Atlantic Rainforest, Urabá, Colombia

We describe the clinical, serologic, and molecular findings of a new human rickettsiosis in Colombia. Antibodies against Rickettsia spp. were detected. PCR showed amplification of genes for R. parkeri strain Atlantic Rainforest. This new rickettsiosis of minor virulence could explain some of the undifferentiated acute febrile diseases in Colombia.


DISPATCHES
We describe the clinical, serologic, and molecular findings of a new human rickettsiosis in Colombia. Antibodies against Rickettsia spp. were detected. PCR showed amplification of genes for R. parkeri strain Atlantic Rainforest. This new rickettsiosis of minor virulence could explain some of the undifferentiated acute febrile diseases in Colombia. eschar biopsy, and scrapings with the DNeasy Blood and Tissue kit (QIAGEN, https://www.qiagen. com), according to the manufacturer's instructions. The samples were processed by PCR for gltA, sca0, sca4, and sca5 genes of Rickettsia using previously described primers and methods (8). The amplification products were sent for sequencing to Macrogen, and the sequences were analyzed with BLASTn (https:// blast.ncbi.nlm.nih.gov), MEGA 7.0 (https://www. megasoftware.net), and MrBayes 3.2.6 (https:// www.geneious.com). The human protocol was approved by the Bioethical Committee at the University of Antioquia (act 001/2016).
Indirect fluorescent antibody testing demonstrated seroconversion to all 6 Rickettsia antigens. Acute serum samples showed reactivity with none of the antigens at a titer of 64, whereas seroconversion to each of the antigens was observed by reactivity with R. parkeri (titer 1,024); R. rickettsii (titer 512); R. bellii (titer 256); and R. amblyommatis, Candidatus R. colombianensi, and R. rhipicephali (titer 128), without a quadruple difference between the different antigens.
Amplicons were obtained for all genes tested and all samples analyzed. All the sequences demonstrated 100% identity with R. parkeri strain Atlantic Rainforest and were submitted to GenBank (accession nos. MK860199-202).
Previous patients with rickettsial infections in the Department of Antioquia were gravely ill with rapid deterioration and respiratory and renal compromise, hepatic injury, and case-fatality rates of 28%-35% (4). In contrast, R. parkeri infections are mild or moderate acute febrile illnesses with fever, chills, headache, arthromyalgia, inoculation eschar, maculopapular or vesicular rash, and painful lymphadenopathy at lymphatic drainage sites of the entry lesion. Some patients do not manifest lymphadenopathy or, as in this patient, a rash (9).
In 2004, a new SFG human infection attributed to R. parkeri sensu stricto was described in the United States (10); later, Spolidorio et al. described a patient in Brazil with a clinically identical moderate febrile condition, with myalgia, arthralgia, and eschar, caused by a strain of R. parkeri designated Atlantic Rainforest (11). Human infections with similar signs and symptoms caused by R. parkeri sensu stricto and R. parkeri strain Atlantic Rainforest have been documented in the United States, Brazil, Uruguay, Argentina, and now in Colombia; meanwhile, these bacteria have also been demonstrated in ticks (in the absence of recognized human infections) in Bolivia, Peru, Nicaragua, Belize, and Mexico. Amblyomma maculatum, A. triste, and A. tigrinum ticks have been found infected with R. parkeri sensu stricto in nature; R. parkeri strain Atlantic Rainforest has been reported in A. ovale, A. aureolatum, and Dermacentor parumapertus ticks (12,13). R. parkeri strain Atlantic Rainforest was previously identified in A. ovale ticks in Colombia, where dogs are suspected of bringing the ticks into homes (6).

Conclusions
There may be a substantial unrecognized occurrence of R. parkeri infections in South and Central America. Increased awareness and knowledge by primary care physicians and establishment of effective national surveillance programs and guidelines, including empiric treatment with doxycycline, would lead to improved patient outcomes. Enhanced research to identify the range of vectors, vertebrate hosts, and risk factors to predict human exposure to this and other agents that may be causing similar diseases would contribute to the elucidation of the causes of acute febrile illnesses in Latin America.