Volume 24, Number 2—February 2018
Rickettsia africae and Novel Rickettsial Strain in Amblyomma spp. Ticks, Nicaragua, 2013
We report molecular detection of Rickettsia africae in Amblyomma ovale ticks from Nicaragua and a novel rickettsial strain in an A. triste tick. Of 146 ticks from dogs, 16.4% were Rickettsia PCR positive. The presence of Rickettsia spp. in human-biting ticks in Nicaragua may pose a public health concern.
Obligately intracellular Rickettsia spp., typically transmitted by ticks, cause a multitude of mild to severe rickettsial diseases in humans and other animals. Novel Rickettsia species have been identified through molecular techniques (1). Rickettsiae in Central America have primarily been reported in ticks, dogs, and humans, with limited data on tick species and rickettsial prevalence in Nicaragua (1). In an earlier study, 87% of 77 dogs in the Bosawás Biosphere Reserve were seropositive for rickettsiae (2); the ticks in that study were collected from 40 of those dogs.
The Bosawás Reserve in remote northern Nicaragua, part of the second largest tropical rainforest in the Western Hemisphere, is inhabited by 2 rapidly growing populations of indigenous people: the Miskito and the Mayangna. These subsistence-based communities use dogs for hunting in the reserve. Increasing connectivity with outside areas, population growth, and interference of dogs with wildlife pose an increased risk for the emergence of zoonotic rickettsioses. We planned to expand information on zoonotic Rickettsia spp. in Nicaragua by surveying ticks from hunting dogs for diversity, number, and presence of rickettsiae.
We collected ticks in 2013 from villages at similar latitude and longitude measured by using global positioning system (GPS): Arang Dak (14.51583, −84.99944), Amak (14.06542, −85.142233), and Raiti (14.59464, −85.02772) (Table). Arang Dak is the smallest of the 3 villages and closest to the densest part of the rainforest; Raiti is the largest and most developed village of the 3 and is situated on a heavily traveled route through the reserve. We obtained owner consent before physical examination and sampling of ticks from dogs and stored ticks in 70% ethanol. In the laboratory, we identified ticks for sex, life stage, and species by using a key (3) and screened tick DNA for Rickettsia spp. by real-time PCR (4). Rickettsia-positive samples were further tested by conventional PCR targeting the outer membrane protein A gene (ompA) (5). We also amplified the rpmB and 17kDa genes of the rickettsia in the Amblyomma triste ticks we recovered (4). We sequenced each amplicon by using the forward primer at University of California Davis Sequencing (Davis, CA, USA) and compared sequences to those in the GenBank database by using the BLAST algorithm (https://blast.ncbi.nlm.nih.gov).
Of 146 ticks from 40 dogs, 126 (86%) were A. ovale, 12 were A. mixtum, and 7 were A. triste. We detected rickettsial DNA in 24 (16.4%, 95% CI 11.0%–23.7%) of the 146 ticks: 18 A. ovale, 5 A. mixtum, and 1 A. triste. We deposited rickettsial sequences from these ticks into GenBank (accession no. KX530472, KX576685, and KX576686).
By location, the PCR prevalence was 25.5% (95% CI 15.1%–39.3%) in Raiti, 16.0% (95% CI 5.25%–36.9%) in Amak, and 9.09% (95% CI 3.75%–19.4%) in Arang Dak. These differences were statistically significant (p = 0.05 by Fisher exact test). The finding of highest prevalence in the most populated community is consistent with peridomestic animals maintaining the infection, and the rainforest and remote wildlife not being significant sources.
For the 576-bp ompA sequence, all from A. ovale ticks were identical and were 99.6% homologous with sequences from GenBank identified as R. africae. R. africae has not been reported in A. ovale ticks or in North, Central, or South America. R. africae causes a mild rickettsiosis known as African tick-bite fever and was first described in a patient in the Western Hemisphere in 1998 (1). R. africae has been detected in A. variegatum ticks by using PCR and in humans in Guadeloupe by using serology (6) and more recently in A. loculosum ticks from New Caledonia (7). In Brazil, adult A. ovale ticks bite humans most frequently and are present from the borders of Mexico to those of Argentina (8). A. ovale is a common human-biting tick in Central and South America and poses a public health concern.
Sequences of ompA in 2 of 5 PCR-positive A. mixtum matched 99.6% to Candidatus R. amblyommii in GenBank (ompA of the other samples did not amplify, likely because they were relatively weak on real-time PCR). Candidatus R. amblyommii is common among Amblyomma spp. ticks in the New World and was reported in A. mixtum ticks in Brazil (9). Candidatus R. amblyommii has unknown pathogenicity but has been implicated in rickettsiosis cases in humans (9).
The ompA amplicon from A. triste ticks matched Rickettsia sp. ARAGAOI; sequencing of the rpmB and 17kDa genes was unsuccessful. This rickettsial species was originally described in marsupials in Brazil (10). Further monitoring of tick vectors in this remote area is needed to characterize local risk and detect possibly emerging vectorborne disease.
The authors thank members of J.F.’s laboratory for their technical assistance and feedback; and L. Schwartz, J. Liu, J. Koster, F. Diaz-Santos, and U. Coleman for assistance with field logistics. K. Thomas produced the map.
This project was funded by the One Health Institute and the Wildlife Health Center of University of California, Davis.
- Parola P, Paddock CD, Socolovschi C, Labruna MB, Mediannikov O, Kernif T, et al. Update on tick-borne rickettsioses around the world: a geographic approach. Clin Microbiol Rev. 2013;26:657–702.
- Fiorello CV, Straub MH, Schwartz LM, Liu J, Campbell A, Kownacki AK, et al. Multiple-host pathogens in domestic hunting dogs in Nicaragua’s Bosawás Biosphere Reserve. Acta Trop. 2017;167:183–90.
- Voltzit OV. A review of neotropical Amblyomma species (Acari: Ixodidae). Acarina. 2007;15:3–134 [cited 2016 Nov 23]. http://bibliotecavirtual.minam.gob.pe/biam/bitstream/handle/minam/890/BIV00727.pdf?sequence=1&isAllowed=y)
- Stephenson N, Blaney A, Clifford D, Gabriel M, Wengert G, Foley P, et al. Diversity of rickettsiae in a rural community in northern California. Ticks Tick Borne Dis. 2017;8:526–31.
- Roux V, Fournier P-E, Raoult D. Differentiation of spotted fever group rickettsiae by sequencing and analysis of restriction fragment length polymorphism of PCR-amplified DNA of the gene encoding the protein rOmpA. J Clin Microbiol. 1996;34:2058–65.
- Parola P, Vestris G, Martinez D, Brochier B, Roux V, Raoult D. Tick-borne rickettiosis in Guadeloupe, the French West Indies: isolation of Rickettsia africae from Amblyomma variegatum ticks and serosurvey in humans, cattle, and goats. Am J Trop Med Hyg. 1999;60:888–93.
- Eldin C, Mediannikov O, Davoust B, Cabre O, Barré N, Raoult D, et al. Emergence of Rickettsia africae, Oceania. Emerg Infect Dis. 2011;17:100–2.
- Labruna MB, Camargo LMA, Terrassini FA, Ferreira F, Schumaker TT, Camargo EP. Ticks (Acari: Ixodidae) from the state of Rondônia, western Amazon, Brazil. Syst Appl Acarol. 2005;10:17–32.
- Nunes EC, Vizzoni VF, Navarro DL, Iani FC, Durães LS, Daemon E, et al. Rickettsia amblyommii infecting Amblyomma sculptum in endemic spotted fever area from southeastern Brazil. Mem Inst Oswaldo Cruz. 2015;110:1058–61.
- Blanco CM, Teixeira BR, da Silva AG, de Oliveira RC, Strecht L, Ogrzewalska M, et al. Microorganisms in ticks (Acari: Ixodidae) collected on marsupials and rodents from Santa Catarina, Paraná and Mato Grosso do Sul states, Brazil. Ticks Tick Borne Dis. 2017;8:90–8.