Involvement of roe deer as source of Anaplasma phagocytophilum infection for Ixodes ricinus in a heterogeneous landscape

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1 Involvement of roe deer as source of Anaplasma phagocytophilum infection for Ixodes ricinus in a heterogeneous landscape Extract of the PhD thesis of Amélie Chastagner A m é l i e C h a s tagner 1*, A n g é l i q u e P i o n 1*, H é l è n e Ve r h e y d e n 2, B r u n o L o u r t e t 2, B r u n o C a r g n e l u t i 2, D e n i s P i c o t 2, G w e n a ë l Vo u r c h 1, X a v i e r B a i l l y 1 ( 1 ) I N R A U R E p i A C l e r m o n t - F e r r a n d, F r a n c e ( * ex- m e m b e r s ) ( 2 ) I N R A U R C E F S T o u l o u s e, F r a n c e

2 Context Impact of fragmented landscapes: Creates geographical barriers and/or modifies species distribution Promotes contact between wild and domestic animal populations Increased ecotones favorable to ticks Increasing and emerging of multi-host tick-borne diseases Source : AMÉLIE CHASTAGNER - TMT

3 Context Multi-host pathogen spread by I. ricinus : no totally generalist! Ixodes ricinus feed in a wilde range of host (mammals, birds et reptiles) Allows the spread of multi-host pathogens However, in multi-host pathogens we observed: High intraspecific genetic variability + Presence of genetic groups link to different ecotypes = specialization to a host group Ex. Borrelia afzelii rodents & B. garinii birds AMÉLIE CHASTAGNER - TMT

4 Context Why study the genetic diversity in the vector? Study genetic diversity - in host allows to define ecotypes - in ticks allows to caracterize all diversity of circulating strains Frequency of strains in the vector population reflects the contribution of each host AMÉLIE CHASTAGNER - TMT

5 Problematic Anaplasma phagocytophilum : Intracellular bacterium causing granulocytic anaplasmosis, Tick-borne pathogen, Infects wilde range of mammals, High strain diversity-> several ecotypes -> several cycles What is the contribution of each host species in the different epidemiological cycles (reservoir host, accidental host)? Roe deer : high prevalence (up to 80% infected) -> reservoir host? What is the contribution of roe deer in the Ixodes ricinus infection by A.phagocytophilum in fragmented landscapes? AMÉLIE CHASTAGNER - TMT

6 Material & Methods 1 site in south-western of Toulouse, France A. phagocytophilum prevalence 35/ 1837 I. ricinus nymphs (1,9 %) 56/75 roe deer (75 %) 0/ 263 small rodents 21 ticks and 56 roe deer selected for 454 sequencing 3 loci sequenced: groel, anka and msp4 AMÉLIE CHASTAGNER - TMT

7 Nb of ticks (n = 21) Nb of roe deer (n = 56) Results: sequencing and co-infection Nb of alleles by roe deer Average number of sequences by sample: for groel, for msp4, for anka Nb of alleles by nymph No correlation between number of sequences and number of alleles by individuals ( R² = 0,208) ~ 20 % of anka and msp4 alleles non sequenced and 8 % of groel alleles 41.1 % of roe deer & 52.4 % of ticks were coinfected in at least 1 locus AMÉLIE CHASTAGNER - TMT

8 Results : alleles distribution Hôtes : Roe deer VG (n=56) Ticks VG (n=21) Cattle ref. France (n=40) anka Ticks were distributed in anka I & anka IV already described in livestock (Scharf et al 2011) Roe deer principaly distributed in anka II (a specific deer group), and also anka IV => Few strains shared by roe deer and ticks AMÉLIE CHASTAGNER - TMT

9 groel Résultats : répartition des allèles Hôtes : Roe deer VG (n=56) Ticks VG (n=21) Cattle ref. France (n=40) msp4 Similar to anka : Ticks shared few strains of roe deer > 70 % of ticks carried strains described in livestock AMÉLIE CHASTAGNER - TMT

10 Questions raised Q1: How to explain the maintenance of the epidemic cycle and the high prevalence in roe deer? Q2: How to explain the presence of genotypes usually associated with livestock in some roe deer? -> Is this related to their exploitation of the landscape or proximity of cattle? Q3: What factors might explain the uneven distribution of A. phagocytophilum in I. ricinus nymphs in the landscape? AMÉLIE CHASTAGNER - TMT

11 Q1: How to explain the maintenance of the epidemic cycle and the high prevalence in roe deer? < 0,3 % of questing nymphs were infected by strains associated with roe deer Cycle maintenance? Hypothesis 1: Another tick species maintains the roe deer cycle (i.e. Dermacentor sp present in the study site) Hypothesis 2: I. ricinus adults only could maintain the cycle Maintenance with a high prevalence? Hypothesis 1: Long persistence of strains? => 3 individuals captured twice: differente strains between t and t+1 Hypothèse 2: constant re-infection due to the high tick infestation rate Source: AMÉLIE CHASTAGNER - TMT

12 Q2: How to explain the presence of genotypes usually associated with livestock in some roe deer? anka genotypes carried by roe deer & composition of their home range (K=95%) Reminder: anka 1 & anka 4 are associated to livestock, while anka 2 is assocaited to deer No relation between use of pasture and the infection by genotypes associated with livestock => Reservoir host of livestock strains could live in forest? AMÉLIE CHASTAGNER - TMT

13 Q3: What factors might explain the uneven distribution of A.phagocytophilum in I. ricinus nymphs in the landscape? Positive nymphs seemed often in the interface between wood and pasture? -> No significant, p-value= 0,64 Presence of positive nymphs is correlated with the abundance of ticks (p-value < ) => Presence of host favorable to ticks and Anaplasma AMÉLIE CHASTAGNER - TMT

14 General conclusion Roe deer contribute little to the infection of Ixodes ricinus during their first blood meal -> Involvement at the next meal remains to study through questing adult ticks A favorable host for ticks seems reservoir of Anaplasma in VCG - Suspects removed: roe deer and small mammals - Possible suspects: wild boars, mustelidae, hares... Other tick species might be involved in maintenance of A. phagocytophilum in roe deer AMÉLIE CHASTAGNER - TMT

15 Thanks Thanks you to research teams: - CEFS (INRA Toulouse) - BioEpAR (INRA-ONIRIS Nantes) - EpiA (INRA Clermont-Ferrand) - MIVEGEC (IRD Montpellier) - EcoBio (CNRS Rennes) And thank you to all the volunteers who aids sampling roe deer each winter. Research funding by: AMÉLIE CHASTAGNER - TMT