Other vector-borne parasitic diseases: animal helminthiases, bovine besnoitiosis and malaria.

The parasitic diseases discussed elsewhere in this issue of the Scientific and Technical Review are not the only ones to make use of biological vectors (such as mosquitoes or ticks) or mechanical vectors (such as horse flies or Stomoxys flies). The authors discuss two major groups of vector-borne parasitic diseases: firstly, helminthiasis, along with animal filariasis and onchocerciasis, which are parasitic diseases that often take a heavytoll on artiodactylsthroughoutthe world; secondly, parasitic diseases caused by vector-borne protists, foremost of which is bovine besnoitiosis (or anasarca of cattle), which has recently spread through Europe by a dual mode of transmission (direct and by vector). Other protists, such as Plasmodium and Hepatozoon, are also described briefly.

Spatio-temporal variation of biting flies, Stomoxys spp. (Diptera: Muscidae), along a man-made disturbance gradient, from primary forest to the city of Makokou (North-East, Gabon).

Understanding the pattern of abundance of vector populations is important to control the potential of transmission of associated pathogens. The pattern of abundance of Stomoxys Geoffroy, an ubiquitous blood-sucking fly, is poorly known in tropical Africa. In this study, we investigated the spatio-temporal pattern of abundance of the Stomoxys genus along a gradient of man-made disturbance in north-eastern Gabon. Three sites (one in primary forest, one in secondary forest and one in a man-made environment) were monitored during 13 months using Vavoua traps. Seven species and subspecies were found to live in sympatry, but with distinct patterns of abundance with respect to space and time. The most abundant species was Stomoxys transvittatus Villeneuve, whereas the rarest species was S. xanthomelas Roubaud. Stomoxys calcitrans Linné was preferentially found in man-made environments, whereas S. xanthomelas was preferentially found in primary forest. Stomoxys abundance was the greatest in secondary forest, then in man-made environments and finally in primary forest. A seasonal variation in Stomoxys abundance was also found. In conclusion, forest degradation and deforestation are likely both to favour the concentration of populations of Stomoxys, and to change the specific composition of the Stomoxys community.

Assessment of geraniol-incorporated polymers to control Aedes albopictus (Diptera: Culicidae).

Effective control of mosquito borne diseases has proven extremely difficult with both vector and pathogen remaining entrenched and expanding in many disease endemic areas. When lacking an effective vaccine, vector control methods targeting both larval habitats and adult mosquito populations remain the primary strategy for reducing risk. Aedes albopictus from Thailand was used as a reference baseline for evaluation of natural insecticides incorporated in polymer disks and pellets and tested both in laboratory and field conditions. In laboratory and field tests, the highest larval mortality was obtained with disks or pellets containing IKHC (Insect Killer Highly Concentrate) from Fulltec AG Company. This product is reputed to contain geraniol as an active ingredient. With pellets, high mortality of Ae. albopictus larvae (92%) was observed in presence of 1 g of pellets per 500 ml of water at day 1st, and the mortality was 100% at day 1st for larvae in presence of 5 or 10 g of pellets. Fulltec AG Company has not accepted to give us the exact composition of their IKHC product. Therefore, we cannot recommend it, but the principle of using monoterpenes like geraniol, incorporated into polymer disks or pellets as natural larvicide needs more attention as it could be considered as a powerful alternative in mosquito vector control.

Diversity of Stomoxys spp. (Diptera: Muscidae) and diurnal variations of activity of Stomoxys indicus and S. calcitrans in a farm, in Wang Nam Khiao District, Nakhon Ratchasima Province, Thailand.

A study of species diversity of Stomoxys spp. and diurnal variations of activity of the most abundant was performed during a one year period at a local dairy cattle farm in Wang Nam Khiao District, Nakhon Ratchasima Province, Thailand. Four species of stomoxyine flies were morphologically identified, including Stomoxys indicus Picard 1908, S. calcitrans (Linnaeus 1758), S. sitiens Rondani 1873 and S. uruma Shinonaga and Kanao 1966. The most common species were S. indicus (50.2%) and S. calcitrans (49.5%). S. sitiens and S. uruma were found in small proportions (< 1%). The number of flies captured was significantly different among the three seasons with the greatest number in the rainy season (mean = 66%; df = 2, P < 0.05). The variations of diurnal activity were observed during different period of times (06:00 to 18:00) during three seasons. Both sexes of S. indicus and males of S. calcitrans showed unimodal activity pattern in cool and summer seasons. But a bimodal activity pattern was recorded in rainy season. For females S. calcitrans, a unimodal peak of activity was observed in cool season and a constant variation of activity all along the day in summer and rainy seasons, with an increase from the morning to the evening. A better understanding of stomoxyine fly behavior, especially the daily flight activity, can assist in prioritization and design of appropriate vector prevention and control strategies.

Efficacy of 1% geraniol (Fulltec) as a tick repellent.

A field trial on the efficacy of 1% geraniol (Fulltec) spray against ticks has been carried out in two farms near Rabat (Morocco). Results clearly revealed that 1% geraniol has a preventive effect against Hyalomma ticks. Comparison of geraniol sprayed cows with control herd showed a reduction of mean number of ticks per animal of 98.4%, 97.3% and 91.3% at respectively day 7, 14 and 21 post-spraying. These data give evidence that the geraniol, natural product extracted from plants, could be an alternative to limit use of chemical acaricides, which efficacy is compromised by development of resistance.

Toxicity of geraniol solution in vitro to the poultry red mite, Dermanyssus galinae.

Geraniol is a bioactive component found in Palmarosa essential oil which has previously demonstrated good repellence to cattle ticks, mosquitoes and sand flies. The toxicity of geraniol to Dermanyssus gallinae, the most economically deleterious ectoparasite of laying hens in Europe, was studied in vitro in the laboratory. Exposure of D. gallinae to 0.5, 1 and 2% concentrations of geraniol (equating approximately to 0.02, 0.04 and 0.07 mg/cm2 geraniol, respectively) over a period of 24 hours resulted in 100% mortality of D. gallinae at all doses used.

Landscape, population structure and genetic diversity of Stomoxys calcitrans.

To investigate whether different landscapes could affect genetic diversity and structure of the cosmopolitan diptera Stomoxys calcitrans, populations from Gabon and southern France were studied using dominant amplified fragment length polymorphism (AFLP) markers. Gabon is characterized by a forested closed landscape, and southern France by an open Mediterranean landscape. The genetic diversity between Gabon and France populations did not differ significantly (P > 0.05). Contrary to our expectation, this study shows a moderate level of genetic differentiation between these two distant countries (Fst = 0.0979) and a low genetic structure among Gabonese and French populations (Fst = 0.0291 and 0.0275 respectively). This result could indicate the capacities of S. calcitrans populations to sustain a high level of gene flow, despite geographic distance and isolation.

Sleeping sickness in West Africa (1906-2006): changes in spatial repartition and lessons from the past.

OBJECTIVE: To review the geography and history of sleeping sickness (Human African trypanosomiasis; HAT) over the past 100 years in West Africa, to identify priority areas for sleeping sickness surveillance and areas where HAT no longer seems active. METHOD: History and geography of HAT were summarized based on a review of old reports and recent publications and on recent results obtained from medical surveys conducted in West Africa up to 2006. RESULTS/CONCLUSIONS: Active HAT foci seem to have moved from the North to the South. Endemic HAT presently appears to be limited to areas where annual rainfall exceeds 1200 mm, although the reasons for this remain unknown. There has also been a shift towards the south of the isohyets and of the northern distribution limit of tsetse. Currently, the most severely affected countries are Guinea and Ivory Coast, whereas the northern countries seem less affected. However, many parts of West Africa still lack information on HAT and remain to be investigated. Of particular interest are the consequences of the recent political crisis in Ivory Coast and the resulting massive population movements, given the possible consequences on HAT in neighbouring countries.

[Ecology of stomoxyine fulies (Diptera: Muscidae) in Gabon. II. Blood meals analysis a nd epidemiologic consequences]. / Ecologie des stomoxes (Diptera: Muscidae) au Gabon. II. Origine des repas de sang et conséquences epidémiologiques.

To determine the origin of stomoxyine fly bloodmeals (Diptera: Muscidae) in Gabon, 1,021 flies belonging to seven different species of Stomoxys were captured and dissected in the area of Makokou. In total, 798 were not blood-fed and 223 bloodmeals could be gathered on filter paper. The identification of the origin of these meals was made by amplification of mitochondrial Cytb gene, then heteroduplex technique by using the Gambian rat (Cricetomys gambianus) as driver. Samples of fauna, collected on the local market, consisted of 24 mammal and two reptile blood and muscle samples, to which it is necessary to add human samples (27 potential hosts). 19 meals could not be amplified for technical reasons, 65 were amplified, but the acquired patterns corresponded to none of the tested potential hosts. On the 139 identified meals, 55% were taken on the black-fronted duiker (Cephalophus nigrifrons) and 19% on pig. Stomoxys transvittatus, the most abundant species in Makokou, is very opportunistic: 68 % of meals were taken on six different hosts, among whom 48% on the black-fronted duiker and 32% were not identified using the panel of tested hosts. S. xanthomelas took 50% of its meals on the moustached monkey (Cercopithecus cephus) and 7% on human beings. S. calcitrans, species of anthropised areas, took 33% of its meals on human beings. These three species can therefore take bloodmeals on wild fauna and human beings. They could potentially play an important role in the emergence of zoonotic diseases. The four other species took their bloodmeals only on wild fauna and pig, the only example of domestic fauna in this study. This preliminary study must be followed up using a larger number of specimens and by increasing the diversity of the tested potential hosts.

[Ecology of Stomoxys flies (Diptera: Muscidae) in Gabon. I. First survey in different ecological areas]. / Ecologie des stomoxes (Diptera: Muscidae) au Gabon. I--Premier inventaire dans différentes zones ecologiques.

The stomoxyine flies are hematophagous diptera and potential vectors of various pathogenic agents. Like those of the Afrotropical Region, the stomoxyine flies of Gabon remain nearly unknown. For these reasons, an entomological survey was conducted in a transverse way in eight localities representative of the various ecological zones of Gabon. The survey was based on the use of Vavoua traps. Various environmental factors able to influence the captures were noticed and included into a canonical correspondence analysis. In total, 15,966 Stomoxys spp., belonging to seven species or subspecies, were captured. The apparent densities (DAP) expressed as the number of flies per trap and per day, were highest in Franceville (41), Bakoumba (40), Makokou (25) and Mouila (21). The most abundant species were S. n niger (33.4%), S. transvittatus (33%), then S. calcitrans (17%). The principal factors that could explain the variability of the captures were the degree of anthropisation, the botanical facies (savanna or forest), the presence of wild and domestic fauna and the nature of the vegetal cover of the ground. S. calcitrans, S. niger niger were abundant in the areas where human presence was manifest. S. xanthomelas was present in forest belts. S. transvittatus, S. omega, S. inornatus were ubiquitous species. S. niger bilineatus was found in savannas areas.

[One century of "sleeping sickness" in West Africa]. / Un siècle de "trypano" en Afrique de l'Ouest. Communication affichée lors des journées du centenaire de la SPE.

This paper summarizes the geography of sleeping sickness disease (or Human African Trypanosomiasis, HAT) over the last 100 years in West Africa, with the objective of identifying today's priority areas for the sleeping sickness surveillance. The history and geography of the disease are based on a bibliographic review of old reports and recent publications on recent results obtained from medical surveys conducted in West Africa up to 2007. This allowed us to situate the historical geography of HAT from the beginning of the 20th century to nowadays. For instance, active HAT foci seem to have moved from the North (savannah area) to the South (forest area) in the last century. Taking into account the limited nature of the information available, endemic HAT presently appears to be limited to areas where annual rainfall is higher than 1,200 mm, although the reasons for this remain unknown. During this period of time there has also been a shift towards the south of the isohyets and of the northern distribution limit of tsetse. Currently the most severely affected countries are Guinea and Ivory Coast, whereas the northern countries seem less affected, but many parts of West Africa still lack information on HAT and remain to be investigated. These observations, put back in the current context of demographic growth and climatic global change, responsible for landscape evolution, political instability and population movements, raise the question of HAT becoming.

First survey of seasonal abundance and daily activity of Stomoxys spp. (Diptera: Muscidae) in Kamphaengsaen Campus, Nakornpathom province, Thailand.

The seasonal changes and the daily activity of Stomoxyine species (Diptera: Muscidae) were examined, using Vavoua traps, in a dairy and a beef cattle farm in Nakhonpathom province, Thailand during July 2004 to June 2005. Over this period, Stomoxys calcitrans was the most commonly trapped species, followed by S. sitiens and S. indica. For the later species, this is the first report of its presence in Thailand. A total of 80 % of flies were captured during the rainy season from May to October and 20 % during the dry season from November to April. No major difference of fly density was observed between the dairy and the beef cattle farm. The activity pattern of S. calcitrans was diurnal with a peak between 08:00 am to 10:00 am and another less marked one in the afternoon. The activity pattern of S. sitiens and S. indica was mainly crepuscular with 2 peaks, early in the morning (06:00 a.m.) and late in the afternoon (6:00 p.m.). Those species are important pests of livestock in Thailand, where they are known as a mechanical vector of trypanosomes. A better knowledge of their ecology is a prerequisite for more efficient control measures.

Microsatellite markers for genetic population studies in Glossina palpalis gambiensis (Diptera: Glossinidae).

Little is known about intraspecific variability in tsetse flies and its consequences for vectorial capacity. Microsatellite markers have been developed for Glossina palpalis gambiensis. Three loci have been identified and showed size polymorphisms for insectarium samples. G. palpalis gambiensis from Burkina Faso were also subjected to PCR to investigate then genetic variability. Amplifications were observed in different species belonging to the palpalis group. These molecular markers will be useful to estimate gene flow within G. palpalis gambiensis populations and analysis could be extended to related species.

[Experimental trypanosomiasis caused by Trypanosoma brucei brucei in domestic cattle. Antigenic diversity and trypanotolerance]. / Trypanosomose expérimentale à Trypanosoma brucei brucie chez les bovins domestiques. Variation antigénique et trypanotolérance.

The antigenic repertoire expressed in four trypanosensitive Zebu cattle after cyclic infection by a late variant of the repertoire DiTAR 1 was studied using agglutinating antibodies. The repertoire expressed appeared similar to that found previously following syringe infection or cyclic infection by an early variant in trypanosensitive and trypanoresistant bovids. The late variant used to infect the Glossina, however, appeared earlier, immediately after the dominant variants. These results also confirm that the sensitivity of certain bovids to trypanosomiasis is not due to the expression of different antigenic variants.

Microsatellite markers for genetic population studies in Glossina palpalis (Diptera: Glossinidae).

Little is known about tsetse intraspecific variability and its consequences on vectorial capacity. Since isoenzyme analyses revealed little polymorphism, microsatellite markers have been developed for Glossina palpalis gambiensis species. Three loci have been identified and showed size polymorphisms for insectarium samples. Moreover, amplifications were observed in different species belonging to palpalis group. These molecular markers will be useful to estimate gene flow within G. p. gambiensis populations and analyses could be extended to related species.

Identification of trypanosomes isolated by KIVI from wild mammals in Côte d'Ivoire: diagnostic, taxonomic and epidemiological considerations.

In Côte d'Ivoire, a comparative study was carried out on 122 wild mammals by parasitological and serological examination and by in vitro isolation of trypanosomes from fresh blood (KIVI). Thirteen isolated stocks were studied by isoenzymes and compared with Trypanosoma congolense and T. brucei bouaflé group reference stocks. Of the 122 animals, only 22 were positive on blood smears while 88 were KIVI positive and 92 were CATT/T. b. gambiense positive. For six stocks identified by isoenzymes as T. congolense, the agreement between ELISA and CATT was good (75%). As compared with CATT, antigen detection ELISA was not satisfactory for T. brucei (20%). Out of 18, 16 stocks represented a separate zymodeme (seven T. congolense and nine T. brucei) and a high genetic heterogeneity was observed. For T. congolense, savanna, kilifi and forest groups were represented by one zymodeme each. The four remaining zymodemes while put into this T. congolense group, were strongly independent of each other. Morphology indicated that those new zymodemes correspond to T. congolense. In the other hand, five new zymodemes fit into T. brucei classification.

Polymerase chain reaction characterization of trypanosomes in Glossina morsitans submorsitans and G. tachinoides collected on the game ranch of Nazinga, Burkina Faso.

The polymerase chain reaction was used to characterize the trypanosomes infecting Glossina morsitans submorsitans and G. tachinoides in the game ranch of Nazinga, Burkina Faso, situated near an agropastoral zone. Dissection of 435 tsetse flies, and PCR analysis of 166 infected flies were conducted to assess the epidemiological situation. Trypanosomes of the Nannomonas subgenus were the most abundant in the two tsetse species (80.4% and 73.7% of identified infections in G. m. submorsitans and G. tachinoides respectively). T. vivax and T. brucei infection rates were comparable between the two tsetse species. Mature infection pattern identified by PCR differed from overall infections, mainly because T. simiae infections did not mature, whereas T. vivax represented the predominant taxon. Parasitological and PCR results showed some discrepancies; possibly some typical Duttonella strains could not be recognized by the sets of primers used. The technologies used in this work helped to determine the high trypanosomosis risk in this area.

Molecular characterization of trypanosome isolates from naturally infected domestic animals in Burkina, Faso.

A total of 33 trypanosome cryostabilates isolated from domestic animals (bovine and dogs) were analysed using the polymerase chain reaction (PCR). The PCR was undertaken on diluted and treated buffy coat solutions according to an easy protocol of purification, using primers specific to Trypanosoma (Nannomonas) congolense of Savannah, Riverine-Forest, Kilifi and Tsavo types, T. (N) simiae, T. (Trypanozoon) brucei and T. (Duttonella) vivax. The results showed a lack of PCR sensitivity when target solutions were simply diluted, probably a reflection of the inaccuracy of the dilution procedure at very low trypanosome numbers. Nine mixed infections were found in purified samples whereas only three were detected in diluted crude solutions. T. congolense Savannah-type was present in all stabilates. Double infections involving this type with the Riverine-Forest type, T. vivax or T. brucei, were found. One stabilate was found to be infected with the three trypanosome types, namely T. congolense Savannah and Riverine-Forest genotypes and T. vivax. No infection attributable to T. congolense Kilifi and Tsavo types or T. simiae was detected in these stabilates. This work confirmed the abundance of mixed infections in the field, which could not have been detected by the classical parasitological methods. Amongst the T. congolense infections, the Savannah genotype was found to be predominant over the Riverine-Forest type; that could be a consequence of differences in genotype virulence in cattle. The detection of T. congolense Riverine-Forest type in vertebrate hosts living in wet areas could be confirmation of the suspected affinity of relationships between this taxa and the riverine forest tsetse fly species.

[A new morphological character for the identification of Stomoxys calcitrans and S. niger (Diptera: Muscidae). Comparison of La Réunion island populations]. / Un nouveau caractère morphologique pour distinguer Stomoxys calcitrans et S. niger (Diptera: Muscidae). Comparaison de populations de l'île de La Réunion.

On La Reunion Island (France), two morphological closely related species of stable flies (Diptera: Muscidae), living in the same environment, Stomoxys calcitrans and S. niger, are involved in the transmission of blood parasites to the livestock. To facilitate a rapid identification of both species in the field conditions, we highlighted a diagnostic morphological character not yet described: the length of the maxillary palpus. The study of three populations of S. calcitrans and two populations of S. niger, collected at various elevations, showed that the maxillary palpi of S. niger were significantly longer than in S. calcitrans, independent of sex. This character, easily visible in the field with a simple magnifying glass, has been confirmed on individuals of both species from West Africa.

[Evaluation of vectorial capacity of Glossina tachinoides (Diptera, Glossinidae) infected by Trypanosoma (Nannomonas) congolense: epidemiological implications]. / Evaluation de la capacité vectorielle de Glossina tachinoides (Diptera, Glossinidae) vis-à-vis de Trypanosoma (Nannomonas) congolense: implications épidémiologiques.

A total of 182 Glossina tachinoides were infected with Trypanosoma congolense savannah type. Infection rates were determined according to microscopical examination of dissected flies and PCR on proboscis. Different techniques of trypanosomes detection in the saliva of live tsetse flies were compared. Results show a high percentage of immature infection rates. PCR amplification of trypanosomes in tsetse flies proboscis confirm parasitological observations. The salivation technique showed fluctuations of the number of trypanosomes deposited with saliva. Variability between individual flies was observed in the mean number of parasites ejected, the rate of positive salivates detected by PCR and the rate of infected mice. PCR technique was as efficient as parasitological technique to detect trypanosomes in the salivates. The infectivity on mice was the less efficient method. These results improve our knowledge on G. tachinoides vectorial competence in the laboratory, and precise the role of this tsetse species in the epidemiology of this disease.