Wing length of tsetse caught by stationary and mobile sampling methods.

INTRODUCTION: A variety of techniques have been used to control tsetse with varying degrees of success. In a study on the population structure of Glossina fuscipes fuscipes that recovered after a previous vector control trial on two Kenyan islands, it was reported that the average fly size on the intervention islands was significantly smaller than on the none intervention islands and also compared to the size before the intervention. The conclusion was that vector control using tiny targets exerted size selection pressure on the population. The study recommended for further studies and suggested that this phenomenon could be among the reasons why targets used as a sole control method have rare reports of successful elimination of tsetse populations. Therefore, in this paper we report on a study of body size of tsetse flies caught in epsilon traps (as a stationary device) and black screen fly rounds (as a mobile trapping device). MATERIALS AND METHODS: The study was carried out in eastern Zambia to test the hypothesis that the body size (measured as wing length) of G. m. morsitans males or females, captured by epsilon traps and fly rounds is the same. RESULTS: A total of 1442 (489 females and 953 males) wing length measurements of G. m. morsitans were used in the analysis. It was established that tsetse flies caught by epsilon traps are on average larger than those caught by fly rounds. The likelihood of a large female or male fly being caught by traps, relative to a small one, significantly increased by 5.088 times (95% CI: 3.138-8.429) and by 2.563 times (95% CI: 1.584-4.148), respectively, p < 0.0001, compared with being caught by fly rounds. The hypothesis was rejected. CONCLUSION: This study showed that epsilon traps capture significantly larger G. m. morsitans than fly rounds do. Therefore, further research is recommended to verify i) whether the predilection of traps to capture larger flies has an effect on the process of tsetse elimination when targets are used e.g. targets may take longer to reach elimination than if the predilection was not there, ii) whether different results can be obtained on ecogeographic distribution of different sizes of the species if fly rounds are used for sampling instead of epsilon traps. The results from such studies could influence the strategies used in future control operations.

Longitudinal monitoring of Culicoides in Belgium between 2007 and 2011: local variation in population dynamics parameters warrant cautious use of monitoring data.

BACKGROUND: Several European countries suffered important economic losses during the past decade due to the emergence of bluetongue and Schmallenberg viruses. Both are viruses of veterinary importance and are spread by Culicoides spp. This triggered many European countries to start Culicoides population monitoring. Recently a one year monitoring study at 16 sites in Belgium revealed that important variation existed in Culicoides abundance and species diversity between collection sites. In order to analyze whether this variation is consistent over years, a detailed analysis of monitoring data collected at seven locations in Belgium between 2007 and 2011 was performed in this study. At all locations, biting midges were collected with OVI black light traps set-up in close proximity to livestock. RESULTS: In total, 42 different Culicoides species were morphologically identified. Species of the subgenus Avaritia represented 83% of all collected midges. Nevertheless, important differences in species composition were found between sites. Furthermore, statistical differences between sites were found for the total and maximum annual abundance, showing that a consistent higher or lower number of Culicoides could be collected depending on the selected collection site. Yearly, up to 16 and 30-fold differences in total and maximum annual abundances between sites, respectively, were found. Also the month in which most Culicoides were collected varied greatly between years, both at local (from May to October) and country level [May (2008), June (2010), July (2009), August (2011), October (2007)]. Finally, the average vector-free period over all sites and years was 173 days and could roughly be defined between November and the end of April. Interestingly, important yearly variations of up to two months in the duration of the vector-free period were found between the studied collection sites. In contrast to the abundance parameters, no specific sites could however be identified where monitoring consistently showed shorter or longer vector-free periods. CONCLUSIONS: In conclusion, our results show that the selection of collection sites for Culicoides monitoring, even in a small country such as Belgium, strongly influences abundance parameters and that yearly variation in seasonality occurs. This emphasizes that care should be taken when using such parameters in risk assessments for transmission of Culicoides-borne diseases and that more clear and strict guidelines for Culicoides monitoring should be considered when monitoring data are used for legislative purposes.

Impact of habitat fragmentation on tsetse populations and trypanosomosis risk in Eastern Zambia.

BACKGROUND: Fragmentation of tsetse habitat in eastern Zambia is largely due to encroachments by subsistence farmers into new areas in search of new agricultural land. The impact of habitat fragmentation on tsetse populations is not clearly understood. This study was aimed at establishing the impact of habitat fragmentation on physiological and demographic parameters of tsetse flies in order to enhance the understanding of the relationship between fragmentation and African animal trypanosomosis (AAT) risk. METHODS: A longitudinal study was conducted to establish the age structure, abundance, proportion of females and trypanosome infection rate of Glossina morsitans morsitans Westwood (Diptera: Glossinidae) in areas of varying degrees of habitat fragmentation in Eastern Zambia. Black screen fly rounds were used to sample tsetse populations monthly for 1 year. Logistic regression was used to analyse age, proportion of females and infection rate data. RESULTS: Flies got significantly older as fragmentation increased (p < 0.004). The proportion of old flies, i.e. above ovarian category four, increased significantly (P < 0.001) from 25.9% (CI 21.4-31.1) at the least fragmented site (Lusandwa) to 74.2% (CI 56.8-86.3) at the highly fragmented site (Chisulo). In the most fragmented area (Kasamanda), tsetse flies had almost disappeared. In the highly fragmented area a significantly higher trypanosome infection rate in tsetse (P < 0.001) than in areas with lower fragmentation was observed. Consequently a comparatively high trypanosomosis incidence rate in livestock was observed there despite lower tsetse density (p < 0.001). The overall proportion of captured female flies increased significantly (P < 0.005) as fragmentation reduced. The proportion increased from 0.135 (CI 0.10-0.18) to 0.285 (CI 0.26-0.31) at the highly and least fragmented sites, respectively. CONCLUSIONS: Habitat fragmentation creates conditions to which tsetse populations respond physiologically and demographically thereby affecting tsetse-trypanosome interactions and hence influencing trypanosomosis risk. Temperature rise due to fragmentation coupled with dominance of old flies in populations increases infection rate in tsetse and hence creates high risk of trypanosomosis in fragmented areas. Possibilities of how correlations between biological characteristics of populations and the degree of fragmentation can be used to structure populations based on their well-being, using integrated GIS and remote sensing techniques are discussed.

Serological responses and biomarker evaluation in mice and pigs exposed to tsetse fly bites.

BACKGROUND: Tsetse flies are obligate blood-feeding insects that transmit African trypanosomes responsible for human sleeping sickness and nagana in livestock. The tsetse salivary proteome contains a highly immunogenic family of the endonuclease-like Tsal proteins. In this study, a recombinant version of Tsal1 (rTsal1) was evaluated in an indirect ELISA to quantify the contact with total Glossina morsitans morsitans saliva, and thus the tsetse fly bite exposure. METHODOLOGY/PRINCIPAL FINDINGS: Mice and pigs were experimentally exposed to different G. m. morsitans exposure regimens, followed by a long-term follow-up of the specific antibody responses against total tsetse fly saliva and rTsal1. In mice, a single tsetse fly bite was sufficient to induce detectable IgG antibody responses with an estimated half-life of 36-40 days. Specific antibody responses could be detected for more than a year after initial exposure, and a single bite was sufficient to boost anti-saliva immunity. Also, plasmas collected from tsetse-exposed pigs displayed increased anti-rTsal1 and anti-saliva IgG levels that correlated with the exposure intensity. A strong correlation between the detection of anti-rTsal1 and anti-saliva responses was recorded. The ELISA test performance and intra-laboratory repeatability was adequate in the two tested animal models. Cross-reactivity of the mouse IgGs induced by exposure to different Glossina species (G. m. morsitans, G. pallidipes, G. palpalis gambiensis and G. fuscipes) and other hematophagous insects (Stomoxys calcitrans and Tabanus yao) was evaluated. CONCLUSION: This study illustrates the potential use of rTsal1 from G. m. morsitans as a sensitive biomarker of exposure to a broad range of Glossina species. We propose that the detection of anti-rTsal1 IgGs could be a promising serological indicator of tsetse fly presence that will be a valuable tool to monitor the impact of tsetse control efforts on the African continent.

Seroprevalence and potential risk factors for Brucella spp. infection in traditional cattle, sheep and goats reared in urban, periurban and rural areas of Niger.

INTRODUCTION: In Niamey, Niger, interactions within the interface between animals, humans and the environment induce a potential risk of brucellosis transmission between animals and from animals to humans. Currently, little is known about the transmission of Brucella in this context. RESULTS: 5,192 animals from 681 herds were included in the study. Serum samples and hygroma fluids were collected. A household survey enabled to identify the risk factors for transmission of brucellosis. The true adjusted herd-level prevalence of brucellosis ranged between 11.2% and 17.2% and the true adjusted animal-population level prevalence was 1.3% (95% CI: 0.9-1.8%) based on indirect ELISA test for Brucella antibodies. Animals aged of 1-4 years were found to be more susceptible than animals less than 1 year old (Odds ratio [OR] of 2.7; 95% CI: 1.43-5.28). For cattle, the odds of brucellosis seropositivity were higher in rural compared to the periurban areas (OR of 2.8; 95% CI: 1.48-5.17) whereas for small ruminants the risk of seropositivity appeared to be higher in urban compared to periurban areas (OR of 5.5; 95% CI: 1.48-20.38). At herd level, the risk of transmission was increased by transhumance (OR of 5.4; 95% CI: 2.84-10.41), the occurrence of abortions (OR of 3.0; 95% CI: 1.40-6.41), and for herds having more than 50 animals (OR of 11.0; 95% CI: 3.75-32.46). Brucella abortus biovar 3 was isolated from the hygromas. CONCLUSION: brucellosis in Niger is a serious problem among cattle especially in the rural areas around Niamey and among sheep in the urban areas of Niamey. The seroprevalence varies across strata and animal species with important risk factors including herd size, abortion and transhumance at herd level and age at animal population level. For effective control of brucellosis, an integrated approach seems appropriate involving all stakeholders working in public and animal health.

Shifting from wild to domestic hosts: the effect on the transmission of Trypanosoma congolense to tsetse flies.

The epidemiology and impact of animal African trypanosomosis are influenced by the transmissibility and the pathogenicity of the circulating trypanosome strains in a particular biotope. The transmissibility of 22 Trypanosoma congolense strains isolated from domestic and wild animals was evaluated in a total of 1213 flies. Multivariate mixed models were used to compare infection and maturation rates in function of trypanosome origin (domestic or sylvatic) and pathogenicity. Both trypanosome pathogenicity and origin significantly affected the ability to establish a midgut infection in tsetse flies but not the maturation rates. The interaction between pathogenicity and origin was not significant. Since being pathogenic and having a domestic origin both increased transmissibility, dominant lowly pathogenic trypanosomes from domestic environments and highly pathogenic trypanosomes from sylvatic environments presented similar levels of transmissibility: 12% and 15%, respectively. Blood meals with parasite concentration ranging from 0.05 to 50trypanosomes/µl blood for 3 strains of T. congolense were provided to different batches of tsetse flies to evaluate the relationship between the parasite load in blood meals and the likelihood for a fly to become infected. A linear relationship between parasite load and transmissibility was observed at low parasitaemia and a plateau was observed for meals containing more than 5trypanosomes/µl. Maximum transmission was reached with 12.5trypanosomes/µl blood. About 50% of the flies were refractory to T. congolense, whatever their concentration in the blood meal. The results suggest that the dose-transmissibility relationship presents a similar profile for different T. congolense isolates.

Identification of different trypanosome species in the mid-guts of tsetse flies of the Malanga (Kimpese) sleeping sickness focus of the Democratic Republic of Congo.

BACKGROUND: The Malanga sleeping sickness focus of the Democratic Republic of Congo has shown an epidemic evolution of disease during the last century. However, following case detection and treatment, the prevalence of the disease decreased considerably. No active survey has been undertaken in this focus for a couple of years. To understand the current epidemiological status of sleeping sickness as well as the animal African trypanosomiasis in the Malanga focus, we undertook the identification of tsetse blood meals as well as different trypanosome species in flies trapped in this focus. METHODS: Pyramidal traps were use to trap tsetse flies. All flies caught were identified and live flies were dissected and their mid-guts collected. Fly mid-gut was used for the molecular identification of the blood meal source, as well as for the presence of different trypanosome species. RESULTS: About 949 Glossina palpalis palpalis were trapped; 296 (31.2%) of which were dissected, 60 (20.3%) blood meals collected and 57 (19.3%) trypanosome infections identified. The infection rates were 13.4%, 5.1%, 3.5% and 0.4% for Trypanosoma congolense savannah type, Trypanosoma brucei s.l., Trypanosoma congolense forest type and Trypanosoma vivax, respectively. Three mixed infections including Trypanosoma brucei s.l. and Trypanosoma congolense savannah type, and one mixed infection of Trypanosoma vivax and Trypanosoma congolense savannah type were identified. Eleven Trypanosoma brucei gambiense infections were identified; indicating an active circulation of this trypanosome subspecies. Of all the identified blood meals, about 58.3% were identified as being taken on pigs, while 33.3% and 8.3% were from man and other mammals, respectively. CONCLUSION: The presence of Trypanosoma brucei in tsetse mid-guts associated with human blood meals is indicative of an active transmission of this parasite between tsetse and man. The considerable number of pig blood meals combined with the circulation of Trypanosoma brucei gambiense in this focus suggests a transmission cycle involving humans and domestic animals and could hamper eradication strategies. The various species of trypanosomes identified in the Malanga sleeping sickness focus indicates the coexistence of animal and human African Trypanosomiasis. The development of new strategies integrating control measures for human and animal trypanosomiasis may enable the reduction of the control costs in this locality.

Widespread occurrence of Trypanosoma vivax in bovines of tsetse- as well as non-tsetse-infested regions of Ethiopia: a reason for concern?

A cross-sectional study was undertaken to assess the prevalence of bovine trypanosomosis in some tsetse-infested and tsetse-free areas of Ethiopia. From August 2010 till April 2011, a total of 1524 animals were parasitologically examined and compared by the haematocrit centrifugation technique (Woo test) and polymerase chain reaction (ITS-1 PCR). The ITS-1 PCR was more sensitive and more accurate in species identification than the Woo test. In ITS-1 PCR, an overall trypanosome prevalence of 31.0% was observed that is significantly (P<0.001) higher than in the Woo test (5.3%). Trypanosoma vivax was the predominant taxon (24.9%), followed by T. theileri (6.0%), T. congolense (2.9%) and Trypanozoon (1.6%). Mixed infections were quite common (14% of all infections). The overall prevalence of trypanosome infections in tsetse area (32.4%) was not different from non-tsetse area (30.5%) neither were the prevalences of T. vivax in both areas (respectively 22.6% and 25.7%). With these high prevalences, bovine trypanosomosis continues to hinder animal production and productivity in Ethiopia, both in tsetse-infested and non-infested parts of the country. Attempts to control African trypanosomosis should also pay attention to mechanically transmitted pathogenic trypanosomes and should adopt the most advanced molecular tests for species identification.

Taenia solium Infections in a rural area of Eastern Zambia-a community based study.

BACKGROUND: Taenia solium taeniosis/cysticercosis is a parasitic infection occurring in many developing countries. Data on the status of human infections in Zambia is largely lacking. We conducted a community-based study in Eastern Zambia to determine the prevalence of human taeniosis and cysticercosis in a rural community. METHODS AND FINDINGS: Stool and serum samples were collected from willing participants. Geographical references of the participants' households were determined and household questionnaires administered. Taeniosis was diagnosed in stool samples by coprology and by the polyclonal antibody-based copro-antigen enzyme-linked immunosorbent assay (copro-Ag ELISA), while cysticercosis was diagnosed in serum by the B158/B60 monoclonal antibody-based antigen ELISA (sero-Ag ELISA). Identification of the collected tapeworm after niclosamide treatment and purgation was done using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). A total of 255 households from 20 villages participated in the study, 718 stool and 708 serum samples were collected and examined. Forty-five faecal samples (6.3%) were found positive for taeniosis on copro-Ag ELISA while circulating cysticercus antigen was detected in 5.8% (41/708) individuals. The tapeworm recovered from one of the cases was confirmed to be T. solium on PCR-RFLP. Seropositivity (cysticercosis) was significantly positively related to age (p = 0.00) and to copro-Ag positivity (taeniosis) (p = 0.03) but not to gender. Change point analysis revealed that the frequency of cysticercus antigens increased significantly in individuals above the age of 30. Copro-Ag positivity was not related to age or gender. The following risk factors were noted to be present in the study community: free-range pig husbandry system and poor sanitation with 47.8% of the households visited lacking latrines. CONCLUSIONS: This study has recorded high taeniosis and cysticercosis prevalences and identified the need for further studies on transmission dynamics and impact of the disease on the local people.

Economic burden of bovine trypanosomosis in three villages of Metekel zone, northwest Ethiopia.

The study was carried out to assess the economic burden of trypanosomosis in three villages of the Metekel zone in 2009. The disease was found to cause substantial economic losses through cattle mortality, drug purchase, and draft power loss of infected oxen. The farmers in the area were spending a significantly (p < 0.05) higher amount of money for the treatment of trypanosomosis than all other diseases combined. The overall mortality rate of cattle due to trypanosomosis was 4.4%. The mortality was significantly higher (p < 0.05) in an area where trypanosomosis prevalence was also higher. Many of the farmers prioritized losses of draft power as the most important impact of the disease. The overall prevalence of the disease was 12.1%. The disease burden was significantly (p < 0.05) higher in the rainy season than at other times of the year. In general, farmers had good knowledge on the signs and seasonality of trypanosomosis. Thus, tsetse suppression activities that involve the local community can be an important tool towards minimizing the economic burden of the disease in the area.