Epidemiological aspects of bovine trypanosomosis in an endemic focus of eastern Zambia: The role of trypanosome strain variability in disease pattern

Bovine trypanosomosis displays various epidemiological aspects in various areas. In some instances the disease has a high prevalence in animals with high impact on production whereas in other cases the disease has a low impact on production despite a high level of infection in animals. In addition epidemiological changes are frequently observed in various areas and are related to many factors including the vectors, the host, the parasites, the environment as well as the livestock management. However the implication of these factors in these changes is not fully elucidated. In eastern Zambia, factors predicting the establishment of severe infection in cattle are all present. However trypanosomosis occurring in cattle in this area has a low impact on livestock production. Several studies on the characterisation of trypanosome strains circulating in domestic and wild animals have been conducted in order to clarify the epidemiology of this disease in this area. These studies aimed at evaluating genetic and biological characteristics of these strains including their virulence profiles, their transmissibility by tsetse flies, their resistance to drugs and interference between different strains. In this review these findings are analysed in order to elucidate the implication of trypanosome strain variability in the distribution and the expression of this disease in the study area. The evolutionary trends of the situation occurring in this study area are also explained. Use of these findings is the context of disease control in the study area is further discussed

Comparison of the survival on ice of thawed <i>Theileria parva</i> sporozoites of different stocks cryoprotected by glycerol or sucrose

Stabilates of Theileria parva sporozoites are mostly delivered in liquid nitrogen tanks to the East Coast fever immunization points. Using an in vitro titration model, we assessed the loss of infectivity of several stabilates when they are stored in ice baths for up to 24 h. Comparisons, with respect to rates of loss of infectivity, were made between T. parva stocks (Chitongo and Katete), cryoprotectants (sucrose and glycerol) and method of assessment (in vivo and in vitro techniques). Chitongo and Katete stabilates showed similar loss dynamics. The losses were 1-4 % (depending on parasite stock) and 3 % per hour of storage for glycerol and sucrose stabilates respectively, and the loss rates were not significantly different. The results suggest that Chitongo stabilates and sucrose cryoprotected suspensions can be delivered on ice as is done for Katete. A graphical relationship of in vitro effective dose at 50 % infectivity (ED50) and in vivo protection rate was made. The relationship showed a 35 % loss of protection for a relatively low corresponding increase of ED50 from 0.006 to 0.007 tick equivalent

Comparison of the survival on ice of thawed Theileria parva sporozoites of different stocks cryoprotected by glycerol or sucrose

Coast fever immunization points. Using an in vitro titration model, we assessed the loss of infectivity of several stabilates when they are stored in ice baths for up to 24 h. Comparisons, with respect to rates of loss of infectivity, were made between T. parva stocks (Chitongo and Katete), cryoprotectants (sucrose and glycerol) and method of assessment (in vivo and in vitro techniques). Chitongo and Katete stabilates showed similar loss dynamics. The losses were 1-4% (depending on parasite stock) and 3% per hour of storage for glycerol and sucrose stabilates respectively, and the loss rates were not significantly different. The results suggest that Chitongo stabilates and sucrose cryoprotected suspensions can be delivered on ice as is done for Katete. A graphical relationship of in vitro effective dose at 50% infectivity (ED50) and in vivo protection rate was made. The relationship showed a 35% loss of protection for a relatively low corresponding increase of ED50 from 0.006 to 0.007 tick equivalent

Theileria parva seroprevalence in traditionally kept cattle in southern Zambia and El Nino

Sero-epidemiological surveys involving 27,526 cattle over a period of 8 years show that Theileria part,a, the parasite causing East Coast fever (ECF) is found throughout southern Zambia. Higher values of T. parva scro-prevalence were observed in the plateau districts of Monze, Choma and Mazabuka than in the valley districts of Siavonga and Sinazongwe. Our results reveal a strong association between high T. parva sero-prevalence and the presence of the periodic climatic phenomenon known as the El Nino Southern Oscillation. More T. pan,a seropositive samples were recorded during El Nino years (1997/98) (P < 0.001) than other years in the study period. From this association, we conclude that Multiple El Nino Southern Oscillation Indices can be used to predict years with high or low ECF infection prevalence thereby contributing to the improved control of ECF in the area. (c) 2005 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved

Questing activity of Rhipicephalus appendiculatus (Acari: Ixodidae) nymphs: a random process?

In Zambia, an experiment under quasi-natural conditions indicated that Rhipicephalus appendiculatus nymphs react to prevailing climatic conditions. Higher temperatures and higher vapour pressure deficits lead to decreased activity. The majority of nymphs (>75%) were recorded at ground level. Simulations showed that larval phenology and temperature during the nymphal premoulting period largely explain the seasonal abundance patterns of nymphs, as observed on cattle, given the absence of a behavioural diapause. Consequently, the effect of climate, as observed in our studies, is masked. However, the results of the present study indicate that daily climatic conditions probably have a much larger effect on the transmission dynamics of Theileria parva. The vertical distribution of questing instars is a function of temperature and humidity. In years of unfavourable conditions, nymphs might feed mainly on hosts other than cattle, and this could govern the infection prevalence in the adult population. This suggestion is supported by previous epidemiological studies

Theileria parva seroprevalence in traditionally kept cattle in southern Zambia and El Niño

East Coast fever (ECF), a tick-borne disease of cattle, is a major constraint to livestock development in Africa in general and southern Zambia in particular. Understanding the transmission patterns of this disease complex is very difficult as shown by previous studies in southern and eastern Zambia due to the interplay of risk factors. In this long-term study, we investigated whether global weather changes had any influence on disease transmission in traditionally kept cattle in southern Zambia. The results from this study show a strong association between increased Theileria parva contacts in cattle and the presence of El Niño, clearly linking a simple climatic index to disease outbreaks. We therefore propose that in southern Zambia, the simple and readily available multiple El Niño Southern oscillation index (MEI) ranks be used in planning ECF control programmes and early warning

Infectivity of Theileria parva sporozoites following cryopreservation in four suspension media and multiple refreezing: Evaluation by in vitro titration

Theileria parva sporozoite stabilates are used for immunizing cattle against East Coast fever and in in vitro sporozoite neutralization assays. In this study, we attempted to identify a cheaper freezing medium and quantified the infectivity loss of sporozoites due to refreezing of stabilates, using an in vitro technique. Pools of stabilates prepared using Minimum Essential Medium (MEM), Roswell Park Memorial Institute (RPMI 1640), foetal calf serum (FCS) and phosphate-buffered saline (PBS) were compared. All were supplemented with bovine serum albumin except the FCS. RPMI 1640 was as effective as MEM in maintaining sporozoite infectivity while the infectivity in PBS and FCS reached only 59% and 67%, respectively. In a second experiment, a stabilate based on MEM was subjected to several freeze-thaw cycles including various holding times on ice between thawing and refreezing. Refrozen stabilate gave an average sporozoite infectivity loss of 35% per cycle. The results indicate that RPM I can be used as a cheaper freezing medium for T. parva stabilates and that refrozen stabilate doses need to be adjusted for the 35% loss of infectivity

Comparison of manual and homogenizer methods for preparation of tick-derived stabilates of Theileria parva: equivalence testing using an in vitro titration model

Theileria parva sporozoite stabilates are used in the infection and treatment method of immunization, a widely accepted control option for East Coast fever in cattle. T. parva sporozoites are extracted from infected adult Rhipicephalus appendiculatus ticks either manually, using a pestle and a mortar, or by use of an electric homogenizer. A comparison of the two methods as a function of stabilate infectivity has never been documented. This study was designed to provide a quantitative comparison of stabilates produced by the two methods. The approach was to prepare batches of stabilate by both methods and then subject them to in vitro titration. Equivalence testing was then performed on the average effective doses (ED). The ratio of infective sporozoites yielded by the two methods was found to be 1.14 in favour of the manually ground stabilate with an upper limit of the 95% confidence interval equal to 1.3. We conclude that the choice of method rests more on costs, available infrastructure and standardization than on which method produces a richer sporozoite stabilate

Participatory assessment of paid vaccination campaigns for village chickens against Newcastle disease in Kongo Central province

In the Democratic Republic of Congo (DRC), where state-driven animal vaccination campaigns are organized only in response to epidemics, the organization of a permanent animal vaccination service is urgently needed. A non-governmental organization has set up an experimental paid vaccination service for village chickens against Newcastle Disease (ND) in the Kongo Central province. This mixed-method study presents a participatory assessment of this experiment, identifying socio-economic factors that influence the decision of chicken keepers to adopt vaccination. The study was conducted in four territories of the province. Qualitative and quantitative data were collected through 12 focus group discussions (FGDs) with professionals of animal health and chicken keepers and 160 semi-structured interviews with chicken keepers, sampled by snowball technique. This participatory process has resulted in the design of a grid for assessing animal vaccination service's performance. Here translating the narratives into a preliminary structured assessment, this grid is an output of the study, to be mobilized for future rapid assessments of the vaccination service in a quantitative prospect. The grid consisted of nine criteria, further composed by 16 items, translated into questions to be asked to chicken keepers and vaccinators. In our study area, fieldworkers enumerated four animal vaccination campaigns during a period of 21 years (except those subject to the present assessment). Around 13% of chicken keepers of our sample had participated in ND vaccination programs. Almost 96% of interviewed chicken keepers expressed their willingness to pay for ND vaccination, and 87% of chicken keepers that vaccinated their chickens perceived the vaccine as effective. Vaccinators estimated that 56% of the chicken keepers who were contacted had actually paid for the vaccination of their chickens. The assessment grid highlighted four points in favor of the sustainability of this service, i.e. the general interest of chickens keepers, vaccine efficacy, vaccine availability and ease of use of the vaccine. Two weak points were identified, viz. the poor access of chicken keepers to information and the weak motivation of vaccinators. The vaccine coverage was calculated within the sample at 13.1%. Paid vaccination campaign for village chicken in Kongo Central obtained a performance score of 62.8%, with the highest score in Kwilu-Ngongo (73.1%) and the lowest in Kasangulu (52.4%). Two factors of adoption of vaccination were identified as statistically significant, i.e. chicken housing and territory. Significant differences appeared between territories in access to information for chicken keepers and in vaccinators motivation. The priorities for the improvement of this service appear to be awareness raising among chicken keepers and increasing vaccinators’ motivation. © 2019 Elsevier B.V