Low effective population sizes in Amblyomma variegatum, the tropical bont tick.

Effective population sizes have rarely been estimated in ticks despite the importance of this parameter for evaluating the evolutionary and adaptive potential of tick populations. The present study was aimed at evaluating the effective population sizes of Amblyomma variegatum, the tropical bont tick, in three villages in Burkina Faso. For this purpose, microsatellites markers were developed. Eight out of 19 assessed markers provided good amplification results with 4 to 24 alleles recorded per marker on 216 genotyped ticks. The within-samples polymorphism was congruent with Hardy-Weinberg expectations at four markers while sex linkage and/or null alleles were observed at the others. As sampling involved two tick generations, effective population sizes were independently estimated by two methods insensitive to heterozygosity: the first one is based on linkage disequilibrium analysis within a single cohort while the second uses the changes in allele frequencies across generations. Both methods estimated the number of reproducing ticks ranging from two to a few tens reproductive adults per village and cohort. Such small estimates are congruent with the rarity of records of acaricide resistance in A. variegatum.

Seroprevalence of West Nile and Usutu viruses in military working horses and dogs, Morocco, 2012: dog as an alternative WNV sentinel species?

A serosurvey of 349 military working horses and 231 military working dogs was conducted in ten sites in Morocco in 2012. This survey revealed a high level of exposure of these animals to flaviviruses: seroprevalence rates of 60% in horses and of 62% in dogs were observed using a competitive West Nile virus (WNV) enzyme-linked immunosorbent assay (cELISA). Seroneutralization test results showed that the majority of cELISA-positive results were due to exposure to WNV. Further assays conducted in vaccinated horses with a DIVA (Differentiating Infected from Vaccinated Animals) test indicated that anti-WNV antibodies had been stimulated through WNV natural infection. Moreover, in both species, seroneutralization tests suggested an exposure to Usutu virus (USUV). Data analysis did not show any significant difference of cELISA seropositivity risk between horses and dogs. Dogs may thus represent an interesting alternative to equines for the serological surveillance of WNV or USUV circulation, especially in areas where equine vaccination precludes passive surveillance (based on the detection of West Nile fever cases) in horses.

Opportunities in diagnostic and vaccine approaches to mitigate potential heartwater spreading and impact on the American mainland.

Heartwater, caused by the Rickettsiales Ehrlichia ruminantium (ER), is a tropical tick-borne disease of wild and domestic ruminants, transmitted by Amblyomma ticks. It causes significant economic losses due to high mortality and the high cost of antibiotic treatment of affected animals, limiting herd productivity. It is present in sub-Saharan Africa, islands in the Indian Ocean and two Caribbean islands (Guadeloupe and Antigua) from where it threatens the American mainland due to risk of the spread of infected A. variegatum by migratory birds or by uncontrolled movement of animals. If an accidental introduction of a tick-free ER carrier animal occurs, autochthonous A. maculatum has proven to be a good experimental vector for heartwater. Modeling A. variegatum population dynamics has been developed, but further work is needed to predict favourable habitats and allow targeted surveillance. We overview here the advances in diagnostics, vaccines and epidemiology of heartwater and analyze the research gaps and needs to mitigate potential ER introduction and spread on the American mainland. Effective serologic ELISA tests allow prevalence studies, and several PCR-based diagnostic tests are currently available to detect ER in sick animals. However, the development of rapid assays, including multi-pathogen tests, would enhance the efficacy and cost-effectiveness of heartwater diagnosis. Several experimental vaccines (inactivated, attenuated and recombinant) are under development. Attenuated and inactivated vaccines are effective against homologous strains but their efficacy in the field is decreased due to broad antigenic diversity of ER. New molecular typing assays are now being used to study the genetic structure of ER populations worldwide, but the linking of genotyping to cross-protection is still not straightforward. Currently an inactivated vaccine would be the most appropriate vaccine for the American mainland due to its safety, the availability of a fully controlled bioprocess allowing ER mass production and the possibility to design "regional cocktail vaccines". This would require the selection and isolation of Caribbean ER strains supported by data of molecular epidemiology studies in this region. Development of an universal recombinant vaccine requires increased knowledge of ERbiology, including virulence mechanisms. Comparison of virulent and attenuated strains using"omic approaches" is on-going and will be crucial to understand these mechanisms and to develop improved vaccines.

Surveillance of avian influenza in the Caribbean through the Caribbean Animal Health Network: surveillance tools and epidemiologic studies.

The Caribbean region is considered to be at risk for avian influenza (AI) due to a large backyard poultry system, an important commercial poultry production system, the presence of migratory birds, and disparities in the surveillance systems. The Caribbean Animal Health Network (CaribVET) has developed tools to implement AI surveillance in the region with the goals to have 1) a regionally harmonized surveillance protocol and specific web pages for AI surveillance on www.caribvet.net, and 2) an active and passive surveillance for AI in domestic and wild birds. A diagnostic network for the Caribbean, including technology transfer and AI virus molecular diagnostic capability in Guadeloupe (real-time reverse transcription-polymerase chain reaction for the AI virus matrix gene), was developed. Between 2006 and 2009, 627 samples from four Caribbean countries were tested for three circumstances: importation purposes, following a clinical suspicion of AI, or through an active survey of wild birds (mainly waders) during the southward and northward migration periods in Guadeloupe. None of the samples tested were positive, suggesting a limited role of these species in the AI virus ecology in the Caribbean. Following low pathogenic H5N2 outbreaks in the Dominican Republic in 2007, a questionnaire was developed to collect data for a risk analysis of AI spread in the region through fighting cocks. The infection pathway of the Martinique commercial poultry sector by AI, through introduction of infected cocks, was designed, and recommendations were provided to the Caribbean Veterinary Services to improve cock movement control and biosecurity measures. The CaribVET and its organization allowed interaction between diagnostic and surveillance tools on the one hand and epidemiologic studies on the other, both of them developed in congruence with regional strategies. Together, these CaribVET activities contribute to strengthening surveillance of avian influenza virus (AIV) in the Caribbean region and may allow the development of research studies on both AI risk analysis and on AIV ecology.

Interaction between research and diagnosis and surveillance of avian influenza within the Caribbean animal health network (CaribVET).

The Caribbean region is considered to be at risk for avian influenza (AI) because of predominance of the backyard poultry system, important commercial poultry production, migratory birds and disparities in the surveillance systems. The Caribbean animal health network (CaribVET) has developed tools to implement AI surveillance in the region: (i) a regionally harmonized surveillance protocol, (ii) specific web pages for AI surveillance on http://www.caribvet.net, and (iii) a diagnostic network for the Caribbean including AI virus molecular diagnostic capability in Guadeloupe and technology transfer. Altogether 303 samples from four Caribbean countries were tested between June 2006 and March 2009 by real time PCR either for importation purposes or following clinical suspicion. Following AI H5N2 outbreaks in the Dominican Republic in 2007, a questionnaire was developed to collect data for risk analysis of AI spread in the region through fighting cocks. The infection pathway of Martinique commercial poultry sector by AI through introduction of infected cocks was designed and recommendations were provided to the Caribbean veterinary services to improve fighting cock movement controls and biosecurity measures. Altogether, these CaribVET activities contribute to strengthen surveillance of AI in the Caribbean region and may allow the development of research studies on AI risk analysis.

Analysis of Amblyomma surveillance data in the Caribbean: lessons for future control programmes.

Amblyomma variegatum, the Tropical Bont Tick (TBT), is the principal vector of heartwater and is associated with dermatophilosis, major causes of losses in animal production and mortality in Caribbean livestock. From 1995 to 2007, the Caribbean Amblyomma Programme (CAP) supported treatment and surveillance activities in 11 islands of the Eastern Caribbean with an initial objective of eradicating TBT. In addition to control activities, surveillance data were collected between 1997 and 2006 in a unique regional database. We report the analysis of the surveillance data from four islands (Nevis, St Kitts, St Lucia, and Barbados) where control and surveillance followed the initial protocol and where enough data were collected. We describe the evolution of TBT infestation levels and the efforts carried out throughout the surveillance period. Logistic regression identified factors associated with herds found infested with TBT. Overall, treatment programmes were associated with a decrease in proportion of TBT-infested farms. High surveillance efforts were carried out throughout the 1997-2007 period for all island of interest, but inadequate level of surveillance was observed in several quarters especially for St Kitts. Third quarter of the year, as indication of adult TBT seasonality on livestock, was significantly associated with the risk of detecting TBT in Nevis and St Kitts livestock farms. Also, presence of cattle in Nevis farms was shown associated with an increasing probability of farms being declared TBT-infested. Outcomes of these analyses provide basis for recommendations to improve future national and regional control and surveillance activities. This analysis demonstrates the usefulness of long term and adequate surveillance data for control programmes and identification of factors associated with risk of having infested herds.

Risk factors for West Nile virus seropositivity of equids in Guadeloupe.

In Guadeloupe, West Nile virus (WNV) activity was first observed in equids in 2002, and a high seroprevalence was found in 2003. The objective of our study was to determine individual and environmental factors associated with the risk of WNV seropositivity during 2002-2003. Fieldwork was conducted to retrospectively determine the location of equids at the time of virus circulation and to collect information regarding environmental and individual variables. Sera were collected from 369 equids out of an estimated total population of less than 500. Thirty-four environmental and individual variables were investigated. Equids had a higher risk (p<0.001) for WNV seropositivity if they lived within the proximity "distance less than 1.5km" of marshes or swamp forests "a large freshwater formation behind mangroves" or if they remained outside after dusk. Equids living within the proximity of ouassous shrimp (Macrobrachium rosenbergii) basins or sugar cane fields had a lower risk (p<0.001) for WNV seropositivity. These results confirm that WNV circulation is more likely in the humid coastal areas of Guadeloupe. The identification of risk factors is useful for predicting future emergence sites of WNV in the archipelago and other Neotropical islands, and to better target sentinel surveillance in the region.

Analysis of Ehrlichia ruminantium-specific T1/T2 responses during vaccination with a protective killed vaccine and challenge of goats.

Ehrlichia ruminantium is an obligate intracellular bacterium that causes heartwater in ruminants and for which T-cell-mediated immunity is believed to play an important role in protection. To better characterize protective cellular immunity, E. ruminantium-specific IFN-gamma and IL-4 recall responses in major T-cell subsets were analysed by flow cytometry during immunization of goats with a killed vaccine and following a virulent challenge. The killed vaccine elicited both CD8+ and CD4+ subsets to produce cytoplasmic IFN-gamma in the absence of IL-4, thus indicating a biased T1 response. The relative capacity of CD8+ T-cells to produce IFN-gamma was significantly higher than CD4+ T-cells but the final contribution of both subsets was comparable. Circulating ER-specific CD4 and CD8 effectors substantially decreased in numbers after the booster injection and could not be detected in most animals during challenge, which warrants further investigation in immune compartments other than blood. Since IFN-gamma inhibits the growth of the pathogen in target cells, the information provided in this study on E. ruminantium-specific T1 responses will be valuable to develop cellular tools for the identification of potential protective antigens.

Effect of isolation techniques, in vitro culture and IFNgamma treatment on the constitutive expression of MHC Class I and Class II molecules on goat neutrophils.

Previous studies on the ability of human neutrophils to synthesize cytokines and express MHC Class I and inducible Class II molecules have suggested a possible role of these cells as accessory or antigen presenting cells (APC). There is no information available to date concerning this aspect in ruminants. Therefore, as the first step of these investigations, we have studied the cell surface expression of MHC molecules on goat neutrophils. We show that goat neutrophils can be distinguished from eosinophils with monoclonal antibody (MoAb) ILA-24 which recognizes cattle monocytes and neutrophils. Goat neutrophils constitutively express MHC Class II molecules. However, cell surface expression of MHC Class I and Class II molecules is dramatically reduced on neutrophils purified by density gradient centrifugation in comparison to neutrophils obtained from whole blood after lysis of erythrocytes. Also, the level of expression of MHC Class I antigens is seasonal and donor-dependent and rapidly decreases after in vitro culture despite negligible necrosis and apoptosis of neutrophils. Although treatment with IFNgamma partially prevents the loss of MHC Class I molecules on neutrophils, it fails to induce MHC Class II antigens. Implications of these results for further studies on the potential role of neutrophils as APC are discussed.

Inhibitory effect of Cowdria ruminantium on the expression of MHC class I and class II molecules on bovine endothelial cells.

Bovine endothelial cells constitutively express MHC class I molecules, whereas MHC class II molecules can be induced by interferon gamma (IFN gamma) treatment. Endothelial cells may play a role as antigen presenting cells (APC), but their role in the immune response against Cowdria ruminantium is unknown. We have studied the effect of C. ruminantium infection on the expression of MHC class I and class II molecules on the surface of bovine endothelial cells. Bovine brain endothelial cells (BBEC) from the microvasculature and bovine umbilical endothelial cells (BUEC) from the macrovasculature were cultured in vitro, infected with different concentration of Cowdria, and treated or not with IFN gamma. We observed that Cowdria induced a reduction of MHC molecules expression on the surface of BUEC and BBEC. This inhibitory effect of Cowdria on MHC molecules could affect the capacity of endothelial cells to act as efficient antigen-presenting cells.

Inhibition of MHC class I and class II cell surface expression on bovine endothelial cells upon infection with Cowdria ruminantium.

Endothelial cells constitute a main target for Cowdria ruminantium (CR) and can potentially play a role as antigen presenting cells (APC). Therefore, we measured, in vitro, the effect of CR infections on the expression of MHC class I and class II molecules on bovine umbilical endothelial cells (BUEC) and on bovine brain endothelial cells (BBEC). A dramatic inhibition of the expression of IFNgamma induced MHC class II molecules was observed on BUEC and to a lesser extent on BBEC upon CR infection. This inhibitory effect was also observed on constitutively expressed MHC class I molecules. Part of the reduction of cell surface MHC molecules could be ascribed to their accumulation in intracellular compartments pinpointing a disruption in the transit of these molecules to the surface of the cells. The exact mechanisms of inhibition are not yet known but, as opposed to what is described in other models, the involvement of prostaglandin E2 can be excluded. The results obtained in this study show that endothelial cells have a decreased capacity to express both MHC class I and class II molecules on their surface upon CR infection, thus favouring the escape of this pathogen from the host immune system.

Recombinant bovine interferon gamma inhibits the growth of Cowdria ruminantium but fails to induce major histocompatibility complex class II following infection of endothelial cells.

Recombinant bovine IFN gamma is a potent inhibitor of Cowdria ruminantium growth in vitro irrespective of the rickettsial stock, or the origin of the endothelial cells. These results suggest an important role for IFN gamma in protective immune responses against C. ruminantium infections. Here we also show that IFN gamma can induce the expression of MHC class II molecules on the surface of endothelial cells. However, treatment of endothelial cells with IFN gamma following infection with Cowdria fails to induce MHC class II expression. The implications of this pathogen-specific effect on class II expression by endothelial cells with regard to its recognition by the host immune system are discussed.