Tick bites are a growing public health concern as ticks act as vectors for various pathogens. Accurate tick species identification is vital to assess disease exposure and determine prophylactic measures. MALDI–TOF MS has emerged as a promising tool for precise tick identification. This study evaluates the performance of MALDI–TOF MS in clinical tick identification, focusing on how the number of peaks present in the reference and sample spectra influences the accuracy of the identification process.
MethodsBetween April 2022 and March 2024, 42 tick specimens sent to our hospital were identified using MALDI–TOF MS. The reference spectrum was created with 70 peaks and expanded to include versions with 40, 100, and 130 peaks using Compass Biotyper Explorer v4.1.1. Spectra were analyzed with Flex Analysis v3.4 software. Identification was performed by querying sample spectra against these libraries, with a log score value (LSV)≥1.70 considered accurate for species identification.
ResultsLibraries with 40, 100, and 130 peaks improved identification scores for several species, though the degree varied. The highest scores were achieved in 64.3% of specimens. Combining all libraries as a single database yielded LSVs above the 1.70 threshold for all specimens.
ConclusionsThe study highlights the species-specific nature of peak importance in spectra and underscores the potential of MALDI–TOF MS as a rapid and accurate tool for tick identification in clinical settings. Enhanced spectral libraries could further improve this technique, aiding timely clinical decisions and effective management of tick bites.
Las picaduras de garrapatas son una preocupación en salud pública, ya que las garrapatas son vectores de diversos patógenos. La identificación precisa de especies es esencial para evaluar la exposición a enfermedades y determinar medidas profilácticas. MALDI-TOF MS es una herramienta prometedora para la identificación de garrapatas. Evaluamos el rendimiento de MALDI-TOF MS en la identificación clínica de garrapatas, determinando la influencia del número de picos en los espectros de referencia y de las muestras en la precisión del proceso de identificación.
MétodosEntre abril de 2022 y marzo de 2024 se identificaron mediante MALDI-TOF MS 42 especímenes de garrapatas enviadas a nuestro hospital. El espectro de referencia se creó con 70 picos y se amplió para incluir versiones con 40, 100 y 130picos utilizando el software Compass Biotyper Explorer v4.1.1. Los espectros se analizaron con el software Flex Analysis v3.4. La identificación se realizó comparando los espectros de las muestras con estas bibliotecas, considerando un valor de puntuación logarítmica (LSV) ≥1,70 como identificación precisa de especie.
ResultadosBibliotecas con 40, 100 y 130picos mejoraron las puntuaciones en varias especies, aunque el grado de mejora varió. En el 64,3% de los especímenes se lograron las puntuaciones más altas. Combinando todas las bibliotecas en una única, todos los especímenes obtuvieron valores de LSV por encima del umbral de 1,70.
ConclusionesLa naturaleza específica de la especie es importante en los picos espectrales. MALDI-TOF MS es una herramienta rápida y precisa para la identificación de garrapatas en entornos clínicos. Las bibliotecas espectrales mejoradas podrían optimizar más esta técnica, facilitando decisiones clínicas y el manejo de las picaduras de garrapatas.
Tick bites are an increasing public health concern, particularly due to their vector capacity.1–3 A critical aspect of tick-borne diseases is the specificity between microorganism and vector, where each pathogenic microorganism species can be transmitted by a limited number of tick species, often just one. Identifying a tick at species level removed from a patient helps both to determine the potential exposure to pathogens and the possibility of antibiotic prophylaxis.4,5
Classically, the method of tick identification has relied on morphological characterization. In recent years, molecular techniques have been used, but are only available in reference centers. However, morphological identification of ticks at the species level is challenging, even when performed by qualified experts.6,7 Molecular identification methods also present difficulties, including incomplete or missing DNA sequence information for many arthropod families, the lack of a consensus sequence for identifying all tick species, as well as the high cost and time required.8 In recent years, several studies have demonstrated the capability of mass spectrometry to identify medically and veterinary important ticks, with an excellent degree of agreement with morphological and molecular methods. The correlation rates have varied between 13.3% and 100%.9–21 Tick-protein extraction has not been standardized, which explains the diversity of published protocols. This suggests that enhancing the precision and inter-center reproducibility of the mass spectrometry technique is feasible by optimizing certain parameters in the analytical or post-analytical processes.
The quality of a reference spectrum depends on numerous factors, including the number of peaks.22 It has been demonstrated that only a subset of the spectrum's peaks significantly influence identification. In a spectrum of hundreds of peaks, spectra with just 18 peaks allowed for 97% of identifications compared to the complete spectrum.23 Our group recently published a simple protocol for identifying medically significant ticks. This publication showed that the number of peaks in the spectra was highly variable and dependent on the tick species.21 In April 2022, the Lozano Blesa University Clinical Hospital (HCULB) in Zaragoza, Spain, implemented MALDI–TOF MS for tick identification using the protocol detailed in this publication.
The objective of this research was to demonstrate the performance of MALDI–TOF MS technology in the clinical practice and to investigate the effect of the number of peaks in reference and sample spectra on the accuracy of tick identification using MALDI–TOF MS.
Materials and methodsThe samples included in the present study included all tick specimens sent to HCULB for identification between April 2022 and March 2024. Upon receipt of the tick in the laboratory, visual inspection of the specimen was conducted to determine its stage and gender, assess the degree of engorgement, and make a preliminary identification at the genus level. Subsequently, identification was performed using mass spectrometry. The protein extraction procedure has been previously published21: first, the tick legs were dissected in a Petri dish and then transferred to an eppendorf tube, where they were mechanically fragmented with a dispensable micro pestle in the presence of formic acid. Initial mechanical fragmentation was performed with 5μl of formic acid, followed by the addition of 25μl of formic acid to complete the process. After fragmentation, the eppendorf tube was vortexed and centrifuged at 13,000rpm for 2min. Next, the MALDI–TOF metal plate was preheated to 45°C, and 1μl of the supernatant was added to each of four wells. Once dry, 1μl of matrix solution was added, and after drying, the sample was read with the MALDI–TOF device.
MALDI–TOF MS (Bruker-Daltonics, Germany) identification was performed on all tick specimens submitted to the laboratory. The reference mass spectra had been previously built and includes 15 tick species as well as different types of arthropods.21 Reference spectra were initially created following the manufacturer's instructions, with a maximum of 70 peaks. This library was designated as the original library (OL). From the tick specimens originally used to create the reference library, raw, unprocessed data files were generated and preserved at the time of their creation. For each original raw file corresponding to a tick sample, three alternative reference spectrum versions were created. These alternative versions were nearly identical to the original files, differing only in the maximum number of peaks included in the reference spectrum. Consequently, for each tick specimen used in the original library, three additional versions were generated: the 40-peak, 100-peak, and 130-peak spectra. These newly generated reference spectra were incorporated into three supplementary reference libraries, designated as the 40-peak library, 100-peak library, and 130-peak library, respectively. These processed versions were referred to as extended library (EL). For library creation, Compass Biotyper Explorer v4.1.1 was used through “Edit: Method: MSP creation” and “Maximum desired Peak number for the MSP”. Hence, all tick samples were identified by matching the sample spectrum against each of the four reference libraries. For peak count calculation, Flex Analysis v3.4 software (method MBT_Standard.fams) was used, applying smoothing and baseline subtraction methods. For peak count analysis, only spectra with more than 10 peaks were considered. A log score value (LSV) of 1.70 for correct species-level identification had been previously established by our group as species threshold value.
The presumptive identification by MALDI–TOF MS was validated using molecular techniques at the reference laboratory for three specimens.24,25 This confirmation was performed only in cases where the mass spectrometry results were uncertain or when the specimen held particular clinical significance, such as in suspected cases of tick-borne diseases.
For the comparison between the mean LSV of both libraries (OL and EL), we used the paired t-test in the R program (version 4.2.1).
ResultsDuring the study period, 42 tick specimens were submitted for identification (Table 1). These specimens corresponded to seven species, as determined by MALDI–TOF MS or molecular techniques (see below): Dermacentor marginatus (n=3), Hyalomma lusitanicum (n=4), Hyalomma marginatum (n=12), Ixodes ricinus (n=12), Rhipicephalus bursa (n=2), Rhipicephalus pusillus (n=1), and Rhipicephalus sanguineus sensu lato (n=8). In three instances, two tick specimens were removed from the same patient: H. marginatum (one male, one female), I. ricinus (two nymphs) and R. sanguineus s.l. (one male, one female). In some instances (e.g., due to the reduced size of the specimen), it was necessary to use half of the idiosoma instead of four legs, as established in our protocol.
Identification by MALDI–TOF MS of tick specimens submitted to the Lozano Blesa University Hospital from April 2022 to March 2024.
| Id. | Molecular identification | Stage/Gender | Top-scoring id. MALDI–TOF MS (OL) | Average LSV value (range) (OL) | Top-scoring id. MALDI–TOF MS (EL) | Average LSV value (range) (EL) | Absolute and relative increase in top-scoring LSV values | Number of peaks of best scoring database | Number of peaks, average; range (number of peaks from highest scoring spectra) | Relative position and quartile according to top-down number of peaks for best-scoring spectra |
|---|---|---|---|---|---|---|---|---|---|---|
| 1 | – | F | D. marginatus | 1.91 (1.74–2.06) | D. marginatus | 1.94 (1.83–2.06) | 0 (0%) | 70 | 57.94; 24–125 (34) | 32/36; Q4 |
| 2 | – | F | D. marginatus | 2.06 (1.90–2.20) | D. marginatus | 2.07 (1.95–2.20) | 0 (0%) | 70 | 96.1; 100–144 (123) | 6/20; Q2 |
| 3 | – | M | D. marginatus | 2.17 (2.01–2.26) | D. marginatus | 2.17 (2.01–2.26) | 0 (0%) | 70 | 96.5; 37–159 (133) | 6/24; Q1 |
| 4 | H. lusitanicum | F | H. lusitanicum | 1.65 (1.47–1.78) | H. lusitanicum | 1.65 (1.47–1.78) | 0 (0%) | 70 | 58.6; 41–74 (48) | 33/36; Q4 |
| 5 | – | F | H. lusitanicum | 1.77 (1.62–1.92) | H. lusitanicum | 1.89 (1.74–2.06) | 0.12 (7.3%) | 100 | 80.8; 26–135 (98) | 15/36; Q2 |
| 6 | – | F | H. lusitanicum | 1.85 (1.68–1.94) | H. lusitanicum | 1.86 (1.68–1.97) | 0.03 (1.5%) | 130 | 73.5; 13–111 (13) | 36/36; Q4 |
| 7 | – | F | H. lusitanicum | 1.93 (1.77–2.08) | H. lusitanicum | 1.93 (1.70–2.08) | 0 (0%) | 70 | 81.9; 58–110 (83) | 17/36; Q2 |
| 8 | – | F | H. marginatum | 1.87 (1.68–2.05) | H. marginatum | 1.87 (1.75–2.07) | 0.02 (0.98%) | 100 | 36.95; 10–99 (55) | 3/22; Q1 |
| 9A | – | F | H. marginatum | 2.12 (1.86–2.23) | H. marginatum | 2.19 (2.03–2.27) | 0.04 (1.79%) | 40 | 122.96; 49–185 (182) | 4/24; Q1 |
| 9B | – | M | H. marginatum | 2.26 (1.98–2.40) | H. marginatum | 2.29 (1.96–2.41) | 0.01 (0.42%) | 40 | 92.58; 34–139 (121) | 7/24; Q2 |
| 10 | – | M | H. marginatum | 2.08 (1.94–2.24) | H. marginatum | 2.12 (1.99–2.24) | 0 (0%) | 40/100 | 99.53; 20–157 (120) | 14/36; Q2 |
| 11 | – | M | H. marginatum | 2.01 (1.86–2.12) | H. marginatum | 2.04 (1.91–2.18) | 0.06 (2.83%) | 100 | 138.38; 112–169 (133) | 16/24; Q3 |
| 12 | – | F | H. marginatum | 2.07 (1.90–2.17) | H. marginatum | 2.08 (1.94–2.17) | 0 (0%) | 70 | 80.04; 11–158 (104) | 8/22; Q2 |
| 13 | – | M | H. marginatum | 2.03 (1.91–2.16) | H. marginatum | 2.04 (1.92–2.16) | 0 (0%) | 40 | 91.83; 22–151 (43) | 33/36; Q4 |
| 14 | – | M | H. marginatum | 2.31 (2.22–2.39) | H. marginatum | 2.33 (2.25–2.43) | 0.04 (1.67%) | 100 | 73.49; 29–116 (65) | 24/35; Q3 |
| 15 | – | M | H. marginatum | 2.03 (1.89–2.24) | H. marginatum | 2.05 (1.92–2.24) | 0.02 (0.89%) | 70 | 105.61 (60–153) (125) | 11/36: Q2 |
| 16 | – | M | H. marginatum | 2.17 (2.05–2.24) | H. marginatum | 2.20 (2.06–2.30) | 0.06 (2.7%) | 100 | 99.86 (60–138) (89) | 25/36: Q3 |
| 17 | – | M | H. marginatum | 2.22 (2.09–2.34) | H. marginatum | 2.23 (2.09–2.34) | 0 (0%) | 70 | 76.03 (21–125) (71, 78) | NA |
| 18 | – | M | H. marginatum | 2.21 (2.10–2.29) | H. marginatum | 2.21 (2.09–2.29) | 0 (0%) | 70 | 111.33 (66–137) (86, 125) | NA |
| 19 | – | N | I. ricinus | 1.52 (1.30–1.71) | I. ricinus | 1.63 (1.36–1.84) | 0.13 (7.60%) | 40 | 91.96; 37–140 (75) | 15/24; Q3 |
| 20 | – | N | I. ricinus | 1.80 (1.52–1.96) | I. ricinus | 1.86 (1.67–2.01) | 0.05 (2.56%) | 40 | 101.08; 51–158 (98) | 11/24; Q2 |
| 21A* | – | N | I. ricinus | 1.66 (1.48–1.82) | I. ricinus | 1.74 (1.58–1.93) | 0.11 (6.04%) | 40 | 99.27; 40–168 (148) | 3/33; Q2 |
| 21B* | – | N | I. ricinus | 1.79 (1.55–1.97) | I. ricinus | 1.84 (1.38–2.04) | 0.07 (3.56%) | 40 | 75.91; 28–181 (38) | 17/23; Q3 |
| 22* | – | N | I. ricinus | 1.46 (1.35–1.63) | I. ricinus | 1.53 (1.19–1.78) | 0.15 (9.20%) | 40 | 84.83; 28–148 (117) | 8/36; Q1 |
| 23* | – | F | I. ricinus | 1.75 (1.61–1.96) | I. ricinus | 1.82 (1.59–1.99) | 0.03 (1.53%) | 130 | 115.76; 68–141 (116) | 14/24; Q2 |
| 24 | – | F | I. ricinus | 1.87 (1.67–2.04) | I. ricinus | 1.94 (1.77–2.10) | 0.06 (2.86%) | 40 | 99.22; 61–142 (105) | 11/36; Q2 |
| 25 | – | N | I. ricinus | 1.36 (0.91–1.61) | I. ricinus | 1.51 (1.16–1.72) | 0.11 (6.39%) | 130 | 66.27; 16–153 (142) | 2/36: Q1 |
| 26 | – | F | I. ricinus | 2.00 (1.55–2.21) | I. ricinus | 2.07 (1.72–2.21) | 0 (0%) | 70 | 92.89; 36–149 (104) | 15/36; Q2 |
| 27 | – | N | I. ricinus | 1.89 (1.74–2.02) | I. ricinus | 1.96 (1.84–2.06) | 0.07 (3.39%) | 40/100 | 89.89; 25–154 (71,121) | NA |
| 28 | – | N | I. ricinus | 1.63 (1.43–1.79) | I. ricinus | 1.67 (1.55–1.79) | 0 (0%) | 70/130 | 123.31; 90–160 (126) | 17/36; Q2 |
| 29 | N | I. ricinus | 1.73 (1.13–1.97) | I. ricinus | 1.79 (1.13–2.09) | 0.12 (6.09%) | 40 | 95.22; 54–115 (95) | 19/36; Q3 | |
| 30 | – | F | R. bursa | 1.96 (1.77–2.11) | R. bursa | 2.09 (1.94–2.19) | 0.13 (5.94%) | 40 | 90.22; 56–134 (101) | 12/36; Q2 |
| 31 | – | F | R. bursa | 2.17 (2.04–2.26) | R. bursa | 2.19 (2.11–2.26) | 0.02 (0.89%) | 70 | 102.09; 60–132 (92) | 26/36; Q3 |
| 32 | – | M | R. pusillus | 1.56 (1.34–1.72) | R. pusillus | 1.58 (1.39–1.72) | 0 (0%) | 70 | 53.63 (32–94) (59) | 19/31; Q3 |
| 33 | – | F | R. sanguineus s.l. | 2.10 (1.98–2.26) | R. sanguineus s.l. | 2.12 (2.01–2.26) | 0 (0%) | 70 | 104.71; 79–122 (95) | 20/24; Q4 |
| 34A | R. sanguineus s.l. | F | R. pusillus | 1.75 (1.50–1.93) | R. sanguineus s.l. | 1.83 (1.59–1.99) | 0.06 (3.11%) | 40 | 75.04; 43–107 (72) | 26/48; Q3 |
| 34B | R. sanguineus s.l. | M | R. sanguineus s.l. | 1.85 (1.50–2.04) | R. sanguineus s.l. | 1.87 (1.67–2.04) | 0 (0%) | 70 | 77.88; 42–123 (83) | 10/24; Q2 |
| 35 | – | F | R. sanguineus s.l. | 1.89 (1.77–1.99) | R. sanguineus s.l. | 1.94 (1.77–2.07) | 0.08 (2.41%) | 70 | 107.42; 49–144 (101) | 22/36; Q3 |
| 36 | – | M | R. sanguineus s.l. | 1.92 (1.79–2.07) | R. sanguineus s.l. | 2.01 (1.89–2.13) | 0.06 (2.89%) | 130 | 99.71; 42–132 (117) | 9/24; Q2 |
| 37 | – | M | R. sanguineus s.l. | 2.03 (1.89–2.19) | R. sanguineus s.l. | 2.10 (1.93–2.24) | 0.05 (2.28%) | 100 | 96.46; 41–142 (110) | 9/24; Q2 |
| 38 | – | M | R. sanguineus s.l. | 2.01 (1.90–2.21) | R. sanguineus s.l. | 2.09 (1.94–2.24) | 0.03 (1.36%) | 130 | 121.11; 58–155 (153) | 2/36; Q1 |
| 39 | – | F | R. sanguineus s.l. | 1.85 (1.63–1.96) | R. sanguineus s.l. | 1.89 (1.66–1.97) | 0.04 (2.03%) | 40 | 95.39; 59–137 (88) | 22/36; Q3 |
Denotes those specimens for which half of the idiosome was used for identification by MALDI–TOF MS. Id: identification of the specimen. LSV: log score value. OL: original library (library with reference spectra containing a maximum of 70 peaks); EL: Expanded library, containing a total of four independent libraries, each one with reference spectra containing a maximum of 40, 70, 100, and 130 peaks, respectively. M: male. F: female. N.: nymph. D.: Dermacentor.H.: Hyalomma.I.: Ixodes.R.: Rhipicephalus. s.l.: sensu lato.
A total of 27 out of 42 specimens analyzed (64.3%) showed the highest identification score using one (or two) of the alternative libraries with 40, 100, and 130 peaks from the extended library (EL), compared to the original library (OL). Extended libraries improved the identification scores of five species in total: H. lusitanicum, H. marginatum, I. ricinus, R. bursa, and R. sanguineus. The 40-peak library improved the scores of 4/12 (33.3%) H. marginatum specimens, 8/12 (66.7%) I. ricinus specimens, 1/2 (50%) R. bursa specimens, and 2/8 (25%) R. sanguineus specimens. The 100- and 130-peak libraries improved the scores of 2/4 (50%) H. lusitanicum, 5/12 (41.7%) H. marginatum, 4/12 (33.3%) I. ricinus, and 3/8 (37.5%) R. sanguineus. The comparison between the averages of the LSVs of both libraries (OL and EL) using the paired t-test showed a statistically significant difference (p<0.05) in favor of the expanded library (EL). Three specimens showed identical scores using more than one library. Thus, the expanded library allowed for the identification (LSV≥1.70) of 100% of the specimens.
The absolute and relative increases in LSV values ranged from 0.01 (0.42%) (H. marginatum) to 0.15 (9.20%) (I. ricinus), again being species specific. The relative increase in scores averaged: 2.2% (H. lusitanicum), 0.94% (H. marginatum), 3.92% (I. ricinus), 3.41% (R. bursa), and 1.76% (R. sanguineus s.l.).
The improvements observed were particularly evident in three specific cases. Identification of all four specimens 21A, 21B, 22, and 23 was performed using half of the idiosome instead of legs. Specimen 22 was initially identified as I. ricinus with a score of 1.63. The addition of the 40-peak library increased the LSV value to 1.78, which is above the identification threshold of 1.70; specimen 25 corresponded to a nymph of I. ricinus, identified with a maximum LSV of 1.61 using OL, and a score of 1.72 using EL; lastly, two ticks (34A and 34B) from another patient were initially identified as a female R. pusillus (LSV: 1.93) and a male R. sanguineus s.l. (LSV: 2.04). The use of the expanded library re-classified the first specimen as R. sanguineus s.l. (LSV: 1.99). Molecular biology confirmed both specimens as R. sanguineus s.l.
The relative contribution of each of the four libraries to identification was as follows: the 70-peak library provided the highest score for 16/42 (38.09%) of the specimens; the 40-peak library, for 13/42 (30.95%); the 100-peak library, for 8/42 (19.05%); and the 130-peak library, for 6/42 (14.29%). In some cases, the highest identification score was obtained using more than one library (for example, for specimen 10 of H. marginatum and specimens 27 and 28 of I. ricinus, the libraries provided similar scores, with the highest being obtained by two of them). For each specimen, the number of peaks in the spectrum with the best identification was highly variable, ranging from 13 (H. lusitanicum, specimen 6) to 182 (H. marginatum, specimen 9A). In 24/38 (63.16%) specimens, spectra with the highest LSV values had a peak count above the median. Occasionally, the best identification was achieved with two spectra with different peak counts (H. marginatum, specimens 17 and 18; I. ricinus, specimen 27).
Apart from specimen 34A (as previously mentioned), the species with the second-highest identification scores consistently exhibited lower LSV values relative to the top-scoring species (data not shown).
Molecular techniques were applied only for three specimens: one male of H. lusitanicum (100% identitiy with H. lusitanicum public sequence with ascension number MK946449) and one male and one female of R. sanguineus s.l. (both with 100% identitiy with R. sanguineus s.l. public sequence with ascension number MZ420717). In all three cases, concordance with the identification by MALDI–TOF MS was observed.
DiscussionThe aim of this study was to address the utility of MALDI–TOF MS for the identification of tick species in a clinical microbiology setting. Accurate tick identification is essential for determining the species responsible for human bites and for evaluating the associated clinical risks posed by each tick species.26 Our results highlight the accuracy of MALDI–TOF MS in the identification of ticks. But, while most studies have been conducted in controlled laboratory settings, there is a paucity of publications including ticks extracted from human patients.27,28
The influence of the number of peaks obtained in a biological sample on the quality of the mass spectrum has been emphasized,22,23,29 but this has not been previously documented for tick samples. The findings of this study indicate that the number of peaks in both the reference spectra and that from the sample plays an important role in the accuracy of tick identification. With the exception of D. marginatus (3 specimens) and R. pusillus (1 specimen), the remaining five species showed improved identification scores for at least some of their submitted specimens following the expansion of the reference library. While it appears that certain species may benefit more from reference libraries containing spectra with either a higher (H. lusitanicum, H. marginatum, R. sanguineus s.l.) or lower (I. ricinus, R. bursa) number of peaks, this observation is highly specimen-dependent. For instance, among H. marginatum, I. ricinus, and R. sanguineus s.l., individual specimens achieved better identification scores when matched against spectra from libraries containing either more or fewer peaks, depending on the specific specimen. Notably, one specimen of H. marginatum and one of I. ricinus achieved their highest identification scores using both libraries with a higher and a lower number of reference peaks. Therefore, since the tick species to be identified is not known beforehand, it is recommended to use all four libraries simultaneously (40, 70, 100 and 130 peaks) to achieve the most accurate identification. Furthermore, achieving the highest identification score typically, though not always, involved a number of peaks in the sample spectrum above the median. This suggests that only a subset of the peaks (and this could be species-specific) in the spectrum is crucial for identification, as evidenced by one sample where the highest LSV value was achieved by the spectrum with the lowest number of peaks.
The rapid and accurate information of the specimen enables clinicians to make informed clinical decisions based on unequivocal identification. Under optimal conditions, results can be delivered within less than an hour. Quick and accurate identification of the tick species allows for timely clinical decisions regarding the initiation of antibiotic chemoprophylaxis if is required. For example, in the case of Lyme disease, promptness of treatment initiation is a critical factor4 and the rapid and highly accurate results makes MALDI–TOF MS a perfectly suited technique from a clinical management perspective. In Europe there are no official recommendations. Nevertheless, a clinical trial that would allow extending this recommendation to Europe has been recently published.30 In this open-label, randomized, controlled trial, administering a single dose of 200mg doxycycline within 72h after removing an attached tick from the skin, compared to no treatment in people older than eight years resulted in a relative risk reduction of 67% (95% CI 31–84%). In the consensus of Spanish scientific societies, a prophylaxis recommendation is not made for all patients bitten by ticks, although the option is given when the tick has been manipulated, the tick is engorged or the patient has a high level of anxiety, and always in the case of I. ricinus bite.5 No other recommendations have been made about other tick-borne diseases in Europe.
Not all species of hard ticks found in Spain (just over 30) are included in the MALDI–TOF MS database. The most common biting species are included: D. marginatus, Dermacentor reticulatus, Haemaphysalis punctata, H. lusitanicum, H. marginatum, I. ricinus, R. bursa, R. pusillus, and R. sanguineus s.l., along with less common biting species such as Haemaphysalis inermis, Haemaphysalis concinna, Hyalomma scupense, Ixodes frontalis, Ixodes hexagonus, and Argas sp. If a species that bit the patient is not included in our database, it would likely yield a very low identification score and would need to be identified using molecular biology techniques.
In conclusion, MALDI–TOF MS is a robust and fast diagnostic tool for tick identification, allowing for a more effective management of tick bites. The expansion of spectral libraries has the potential for enhancing the precision of this technique and clinicians should be encouraged to refer tick specimens to the laboratory for accurate identification.
FundingThe authors declare that no funds, grants, or other support were received during the preparation of this manuscript.
Conflict of interestThe authors have no relevant financial or non-financial interests to disclose.
We thank the Center of Rickettsiosis and Arthropod-borne diseases (CRETAV) for managing samples and reporting results.
