Colonization of the Mediterranean Basin by the vector biting midge species Culicoides imicola: an old story

Understanding the demographic history and genetic make-up of colonizing species is critical for inferring population sources and colonization routes. This is of main interest for designing accurate control measures in areas newly colonized by vector species of economically important pathogens. The biting midge Culicoides imicola is a major vector of Orbiviruses to livestock. Historically, the distribution of this species was limited to the Afrotropical region. Entomological surveys first revealed the presence of C. imicola in the south of the Mediterranean basin by the 1970's. Following recurrent reports of massive bluetongue outbreaks since the 1990s, the presence of the species was confirmed in northern areas. In this study, we addressed the chronology and processes of C. imicola colonization in the Mediterranean basin. We characterized the genetic structure of its populations across Mediterranean and African regions using both mitochondrial and nuclear markers, and combined phylogeographical analyses with population genetics and approximate Bayesian computation. We found a west/east genetic differentiation between populations, occurring both within Africa and within the Mediterranean basin. We demonstrated that three of these groups had experienced demographic expansions in the Pleistocene, probably because of climate changes during this period. Finally, we showed that C. imicola could have colonized the Mediterranean basin in the late Pleistocene or early Holocene through a single event of introduction; however we cannot exclude the hypothesis involving two routes of colonization. Thus, the recent bluetongue outbreaks are not linked to C. imicola colonization event, but rather to biological changes in the vector or the virus

Estimation of canine Leishmania infection prevalence in six cities of the Algerian littoral zone using a Bayesian approach

A large-scale study on canine Leishmania infection (CanL) was conducted in six localities along a west-east transect in the Algerian littoral zone (Tlemcen, Mostaganem, Tipaza, Boumerdes, Bejaia, Jijel) and covering two sampling periods. In total 2,184 dogs were tested with an indirect fluorescent antibody test (IFAT) and a direct agglutination test (DAT). Combined multiple-testing and several statistical methods were compared to estimate the CanL true prevalence and tests characteristics (sensitivity and specificity). The Bayesian full model showed the best fit and yielded prevalence estimates between 11% (Mostaganem, first period) and 38% (Bejaia, second period). Sensitivity of IFAT varied (in function of locality) between 86% and 88% while its specificity varied between 65% and 87%. DAT was less sensitive than IFAT but showed a higher specificity (between 80% and 95% in function of locality or/and season). A general increasing trend of the CanL prevalence was noted from west to east. A concordance between the present results and the incidence of human cases of visceral leishmaniasis was observed, where also a maximum was recorded for Bejaia. The results of the present study highlight the dangers when using IFAT as a gold standard

Canine <i>Leishmania</i> infection prevalence estimates according to full conditional test dependence model.

<p>Top prevalence is for first sampling period, bottom for second.</p

Canine <i>Leishmania</i> infection prevalence estimates according to the Hui-Walter model.

<p>Top prevalence is for first sampling period, bottom for second.</p

Apparent prevalence per locality.

<p>From top to bottom: only IFAT, only DAT, serial interpretation of the two test results and parallel interpretation of the two test results.</p

Estimates from the Hui-Walter model.

<p>Pr₁ = prevalence first period; Pr₂ = prevalence second period; Se_IFAT = sensitivity IFAT; Sp_IFAT = specificity IFAT; Se_DAT = sensitivity DAT; Sp_DAT = specificity DAT; <i>p_D</i>, <i>DIC</i> top line = values calculated from posterior values of variable nodes resp. for first period and second period, (bottom line) = values calculated from posterior probabilities</p><p>Estimates from the Hui-Walter model.</p

Apparent prevalence per test per sampling period per locality.

<p>From top to bottom: IFAT first period; IFAT second period; DAT first period; DAT second period.</p

Canine <i>Leishmania</i> infection true prevalence and diagnostic test characteristics estimated from the full conditional dependence model.

<p>^†lines with the same letter are not different from one another</p><p>Canine <i>Leishmania</i> infection true prevalence and diagnostic test characteristics estimated from the full conditional dependence model.</p

Range expansion of the Bluetongue vector, Culicoides imicola, in continental France likely due to rare wind-transport events

The role of the northward expansion of Culicoides imicola Kieffer in recent and unprecedented outbreaks of Culicoides-borne arboviruses in southern Europe has been a significant point of contention. We combined entomological surveys, movement simulations of air-borne particles, and population genetics to reconstruct the chain of events that led to a newly colonized French area nestled at the northern foot of the Pyrenees. Simulating the movement of air-borne particles evidenced frequent wind-transport events allowing, within at most 36 hours, the immigration of midges from north-eastern Spain and Balearic Islands, and, as rare events, their immigration from Corsica. Completing the puzzle, population genetic analyses discriminated Corsica as the origin of the new population and identified two successive colonization events within west-Mediterranean basin. Our findings are of considerable importance when trying to understand the invasion of new territories by expanding species

Jacquet_C.imicola_Cytb_alignment

Jacquet_C.imicola_Cytb_alignmen