title: Matrix-assisted laser desorption/ionization time of flight mass spectrometry for comprehensive indexing of East African ixodid tick species.
abstract: BACKGROUND
  The tick population of Africa includes several important genera belonging to the family Ixodidae. Many of these ticks are vectors of protozoan and rickettsial pathogens including Theileria parva that causes East Coast fever, a debilitating cattle disease endemic to eastern, central and southern Africa. Effective surveillance of tick-borne pathogens depends on accurate identification and mapping of their tick vectors. A simple and reproducible technique for rapid and reliable differentiation of large numbers of closely related field-collected ticks, which are often difficult and tedious to discriminate purely by morphology, will be an essential component of this strategy. Matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) is increasingly becoming a useful tool in arthropod identification and has the potential to overcome the limitations of classical morphology-based species identification. In this study, we applied MALDI-TOF MS to a collection of laboratory and field ticks found in Eastern Africa. The objective was to determine the utility of this proteomic tool for reliable species identification of closely related afrotropical ticks.
  
  
  METHODS
  A total of 398 ixodid ticks from laboratory maintained colonies, extracted from the hides of animals or systematically collected from vegetation in Kenya, Sudan and Zimbabwe were analyzed in the present investigation. The cytochrome c oxidase I (COI) genes from 33 specimens were sequenced to confirm the tentatively assigned specimen taxa identity on the basis of morphological analyses. Subsequently, the legs of ticks were homogenized and analyzed by MALDI-TOF MS. A collection of reference mass spectra, based on the mass profiles of four individual ticks per species, was developed and deposited in the spectral database SARAMIS™. The ability of these superspectra (SSp.) to identify and reliably validate a set of ticks was demonstrated using the remaining individual 333 ticks.
  
  
  RESULTS
  Ultimately, ten different tick species within the genera Amblyomma, Hyalomma, Rhipicephalus and Rhipicephalus (Boophilus) based on molecular COI typing and morphology were included into the study analysis. The robustness of the 12 distinct SSp. developed here proved to be very high, with 319 out of 333 ticks used for validation identified correctly at species level. Moreover, these novel SSp. allowed for diagnostic specificity of 99.7 %. The failure of species identification for 14 ticks was directly linked to low quality mass spectra, most likely due to poor specimen quality that was received in the laboratory before sample preparation.
  
  
  CONCLUSIONS
  Our results are consistent with earlier studies demonstrating the potential of MALDI-TOF MS as a reliable tool for differentiating ticks originating from the field, especially females that are difficult to identify after blood feeding. This work provides further evidence of the utility of MALDI-TOF MS to identify morphologically and genetically highly similar tick species and indicates the potential of this tool for large-scale monitoring of tick populations, species distributions and host preferences.
authors.affiliation: Department of Medical Parasitology and Infection Biology, Clinical Immunology Unit, Swiss Tropical and Public Health Institute (Swiss TPH), Socinstr. 57, CH 4002, Basel, Switzerland. julian.rothen@unibas.ch.|University of Basel, Petersplatz 1, CH 4003, Basel, Switzerland. julian.rothen@unibas.ch.
authors.forename: Julian
authors.initials: J
authors.lastname: Rothen
authors.affiliation: International Livestock Research Institute (ILRI), PO Box 30709-00100, Nairobi, Kenya.
authors.forename: Naftaly
authors.initials: N
authors.lastname: Githaka
authors.affiliation: Biosciences eastern and central Africa - International Livestock Research Institute (BecA-ILRI) Hub, PO Box 30709, 00100, Nairobi, Kenya.|Department of Biochemistry, School of Medicine, University of Nairobi, PO Box 30197, Nairobi, Kenya.
authors.forename: Esther G
authors.initials: EG
authors.lastname: Kanduma
authors.affiliation: Department of Veterinary Microbiology and Pathology, Washington State University, PO Box 647040, Pullman, WA, 99163, USA.
authors.forename: Cassandra
authors.initials: C
authors.lastname: Olds
authors.affiliation: Mabritec SA, Lörracherstrasse 50, CH 4125, Riehen, Switzerland.
authors.forename: Valentin
authors.initials: V
authors.lastname: Pflüger
authors.affiliation: International Livestock Research Institute (ILRI), PO Box 30709-00100, Nairobi, Kenya.
authors.forename: Stephen
authors.initials: S
authors.lastname: Mwaura
authors.affiliation: International Livestock Research Institute (ILRI), PO Box 30709-00100, Nairobi, Kenya.
authors.forename: Richard P
authors.initials: RP
authors.lastname: Bishop
authors.affiliation: Department of Medical Parasitology and Infection Biology, Clinical Immunology Unit, Swiss Tropical and Public Health Institute (Swiss TPH), Socinstr. 57, CH 4002, Basel, Switzerland.|University of Basel, Petersplatz 1, CH 4003, Basel, Switzerland.
authors.forename: Claudia
authors.initials: C
authors.lastname: Daubenberger
mesh_terms: D000043:Abstracting and Indexing; D000818:Animals; D004772:Entomology / Q000379:methods*; D007303:Insect Vectors; D026863:Ixodidae / Q000737:chemistry* / Q000145:classification*; D007630:Kenya; D012680:Sensitivity and Specificity; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*; D013397:Sudan; D015030:Zimbabwe
keywords: Amblyomma; Boophilus; COI; Hyalomma; MALDI-TOF MS; Rhipicephalus; Species identification; Ticks; Vector epidemiology