Understanding the effects of time on collaborative learning processes in problem based learning: a mixed methods study.

Little is known how time influences collaborative learning groups in medical education. Therefore a thorough exploration of the development of learning processes over time was undertaken in an undergraduate PBL curriculum over 18 months. A mixed-methods triangulation design was used. First, the quantitative study measured how various learning processes developed within and over three periods in the first 1,5 study years of an undergraduate curriculum. Next, a qualitative study using semi-structured individual interviews focused on detailed development of group processes driving collaborative learning during one period in seven tutorial groups. The hierarchic multilevel analyses of the quantitative data showed that a varying combination of group processes developed within and over the three observed periods. The qualitative study illustrated development in psychological safety, interdependence, potency, group learning behaviour, social and task cohesion. Two new processes emerged: 'transactive memory' and 'convergence in mental models'. The results indicate that groups are dynamic social systems with numerous contextual influences. Future research should thus include time as an important influence on collaborative learning. Practical implications are discussed.

Virulence in Trypanosoma congolense Savannah subgroup. A comparison between strains and transmission cycles.

Trypanosoma congolense strains have been shown to differ in their virulence both between subgroups and within the Savannah subgroup between strains. This review revisits these findings and complements them with information on the virulence of T. congolense Savannah subgroup strains isolated from cattle (domestic transmission cycle) in different geographical areas and of strains isolated in protected areas where trypanotolerant wildlife species are the reservoir of the trypanosomes (sylvatic transmission cycle). The virulence of a total of 62 T. congolense Savannah subgroup strains (50 domestic and 12 sylvatic), determined using a standard protocol in mice, was compared. Virulence varied substantially between strains with, depending on the strain, the median survival time of infected mice varying from five to more than sixty days. The proportion of highly virulent strains (median survival time <10 days) was significantly (P = 0·005) higher in strains from the sylvatic transmission cycle. The analysis highlights repercussions of the domestication of the trypanosomiasis transmission cycle that may have to be taken in consideration in the development of trypanosomiasis control strategies.

Occurrence of Theileria parva and other haemoprotozoa in cattle at the edge of Hluhluwe-iMfolozi Park, KwaZulu-Natal, South Africa.

Theileria parva, the most important bovine theilerial species in sub-Saharan Africa, causes widespread mortality and morbidity in endemic areas. A survey was conducted using buffy-coat specimens from 60 apparently healthy adult communally herded Nguni-type cattle at the northeastern edge of the Hluhluwe-iMfolozi Park to determine, by means of PCR and Reverse Line Blot (RLB) hybridisation, the occurrence of Theileria and Babesia species. The presence of Trypanosoma species was determined using PCR-RFLP. Results showed that 6.7 % of the specimens were positive for Theileria parva. This significant finding suggests that cattle in South Africa, and not only African buffaloes (Syncerus caffer), may be subclinical carriers of T. parva. Other species identified were T. mutans (83.3%), T. velifera (70.0%), Theileria sp. (sable) (46.8%) and T taurotragi (1.7%). Two specimens (3.3%) were positive for Babesia bovis and single specimens (1.7%) positive for B. bigemina and B. rossi, respectively. Mixed infections, of up to 4 species, were common (65.0%). Only 1 specimen was found to be positive for Trypanosoma vivax, and 2 for T theileri, of which only the first species is pathogenic.

Maturation of a Trypanosoma brucei infection to the infectious metacyclic stage is enhanced in nutritionally stressed tsetse flies.

We report on the effect of tsetse fly starvation on the maturation of an established Trypanosoma brucei brucei midgut infection, i.e., the development of procyclic infection into the infectious metacyclic parasites in the tsetse fly salivary glands. Glossina morsitans morsitans flies were nutritionally stressed 10 d after the uptake of a T. b. brucei-infected bloodmeal by depriving these flies from feeding for seven consecutive days, whereas the control fly group (nonstarved group) continued to be fed three times a week. After this period, both fly groups were again fed three times per week on uninfected rabbit. Thirty days after the infected bloodmeal, all surviving flies were dissected and examined for the presence of an immature midgut and a mature salivary gland trypanosome infections. Results showed a significantly increased proportion of flies with salivary gland infection in the nutritionally stressed fly group suggesting an enhanced maturation of the trypanosome infection. These data suggest that environmental factors that cause nutritional stress in a tsetse population do not only make tsetse flies significantly more susceptible to establish a midgut infection as was shown previously but also boost the maturation of these midgut infections.

Nutritional stress affects the tsetse fly's immune gene expression.

Tsetse-transmitted trypanosomiasis poses a serious threat to human and animal health in sub-Saharan Africa. The majority of tsetse flies (Glossina spp.) in a natural population will not develop a mature infection of either Trypanosoma congolense or Trypanosoma brucei sp. because of refractoriness, a phenomenon that is affected by different factors, including the tsetse fly's immune defence. Starvation of tsetse flies significantly increases their susceptibility to the establishment of a trypanosome infection. This paper reports the effects of nutritional stress (starvation) on (a) uninduced baseline levels of gene expression of the antimicrobial peptides attacin, defensin and cecropin in the tsetse fly, and (b) levels of expression induced in response to bacterial (Escherichia coli) or trypanosomal challenge. In newly emerged, unfed tsetse flies, starvation significantly lowers baseline levels of antimicrobial peptide gene expression, especially for attacin and cecropin. In response to trypanosome challenge, only non-starved older flies showed a significant increase in antimicrobial peptide gene expression within 5 days of ingestion of a trypanosome-containing bloodmeal, especially with T. brucei bloodstream forms. These data suggest that a decreased expression of immune genes in newly hatched flies or a lack of immune responsiveness to trypanosomes in older flies, both occurring as a result of fly starvation, may be among the factors contributing to the increased susceptibility of nutritionally stressed tsetse flies to trypanosome infection.

Zoonotic tuberculosis and brucellosis in Africa: neglected zoonoses or minor public-health issues? The outcomes of a multi-disciplinary workshop.

Late in 2007, veterinary, medical and anthropological professionals from Europe and Africa met in a 2-day workshop in Pretoria, South Africa, to evaluate the burden, surveillance and control of zoonotic tuberculosis and brucellosis in sub-Saharan Africa. Keynote presentations reviewed the burden of these diseases on human and livestock health, the existing diagnostic tools, and the available control methods. These presentations were followed by group discussions and the formulation of recommendations. The presence of Mycobacterium bovis and Brucella spp. in livestock was considered to be a serious threat to public health, since livestock and animal products are the only source of such infections in human beings. The impact of these pathogens on human health appears to be relatively marginal, however, when compared with Mycobacterium tuberculosis infections and drug resistance, HIV and malaria. Appropriate diagnostic tools are needed to improve the detection of M. bovis and Brucella spp. in humans. In livestock, the 'test-and-slaughter' approach and the pasteurization of milk, which have been used successfully in industrialized countries, might not be the optimal control tools in Africa. Control strategies should fit the needs and perceptions of local communities. Improved intersectoral and international collaboration in surveillance, diagnosis and control, and in the education of medical and veterinary personnel, are advocated.

Cross-protection between Trypanosoma congolense strains of low and high virulence.

The aim of this study was to assess the existence of possible cross-protection between Trypanosoma congolense strains of low and extreme virulence circulating in the same trypanosomiasis focus. Groups of six mice were infected using one of three strains of low virulence and challenged with one of three strains of extreme virulence. A group of six mice was used as control for each strain of low and extreme virulence. The results showed that mice infected with one of the strains of extreme virulence developed high parasitaemia and a significant drop of the PCV compared to mice infected with a strain of low virulence and challenged with one of the strains of extreme virulence. With an exception of one strain of extreme virulence (strain F), the survival time of mice infected with the strains of extreme virulence was shorter compared to mice infected with strains of low virulence and subsequently challenged with a strain of extreme virulence. These results suggest that in an area where trypanosomes of various virulence profiles circulate, livestock infected with T. congolense strains of low virulence can be protected against the adverse effects of extremely virulent T. congolense strains.

Investigations on the transmissibility of Trypanosoma congolense by the tsetse fly Glossina morsitans morsitans during its development in a mammalian host.

Experiments were conducted to investigate the effect of the developmental stage of a monomorphic T. congolense IL1180 strain, in a vertebrate host, on its transmissibility by the tsetse fly Glossina morsitans morsitans Westwood (Diptera: Glossinidae). Batches of 160 male teneral tsetse flies were given a single bloodmeal on mice infected with this T. congolense strain 4, 5, 6, 7 or 10 days post-infection. The proportion of infected flies in each of those batches showed that the stage of development of the trypanosome does affect the proportion of flies that develop a mature or immature infection with immature and mature infection rates of flies infected on days 5 or 10 significantly higher. The proportion of infected flies was not affected by the parasitaemia at the moment of infection. Results show that tsetse flies can become infected at any phase of the development of the T. congolense IL 1180 strain but the ease with which trypanosomes develop in the fly depends on the phase in the parasite's development in the host. Those observations suggest that in analogy with the pleomorphic T. brucei s.l. adaptation of the monomorphic T. congolense to development in the fly may also determine the parasite's transmissibility. Moreover, the findings stress the importance of standardising experiments in which the vectorial capacity of tsetse flies is determined and compared.

Evaluating the use of packed cell volume as an indicator of trypanosomal infections in cattle in eastern Zambia.

In this study, packed cell volume-values (PCV) are evaluated as indicator of trypanosomiasis infections in cattle. A total of 734 blood samples were collected in 11 different sampling sites in eastern Zambia: 84 calves (< 1 year), 52 young females and 40 young males (between 1 and 3 years), 228 cows, 317 oxen and 13 bulls (> 3 years). All samples were subjected to three diagnostic tests: parasitological examination using the buffy coat method, PCR/RFLP and PCV determination. The results were compared and analysed in a Bayesian model, which allowed the estimation of the infection prevalence and the respective test sensitivities and specificities. The presence of a trypanosomal infection significantly reduced the PCV, independently of the age and sex of the infected animal. The estimated prevalence of trypanosomal infections in the study area was 34% (95% credibility interval: 30-38%). While the specificity of both the parasitological and the PCR/RFLP tests were set to 1, the parasitological diagnosis had a low sensitivity (37%) compared to the PCR/RFLP (96%). When using a cut-off value of 24, the PCV had a high specificity (98%) but a rather low sensitivity (53%) for identifying trypanosomiasis infections. Using 26% as a cut-off increased the sensitivity to 76% without much affecting the specificity (94%). A parallel combination of the parasitological diagnosis and the PCV improved the diagnostic sensitivity (74% and 89% for PCV cut-off values of 24% or 26%, respectively) while specificity remained high (98% and 94% for PCV cut-off values of 24% or 26%, respectively). These results suggest that such a combination could advantageously be used for the diagnosis of cattle trypanosomiasis in the field: it is much more sensitive than parasitological examination alone and it is much cheaper than molecular tests. However, the value of this approach depends largely on the determination of an appropriate cut-off value to consider a sample positive, depending on the required test sensitivities and specificities.

Climate change and animal health in Africa.

Climate change is expected to have direct and indirect impacts on African livestock. Direct impacts include increased ambient temperature, floods and droughts. Indirect impacts are the result of reduced availability of water and forage and changes in the environment that promote the spread of contagious diseases through increased contact between animals, or increased survival or availability of the agent or its intermediate host. The distribution and prevalence of vector-borne diseases may be the most significant effect of climate change. The potential vulnerability of the livestock industry will depend on its ability to adapt to such changes. Enhancing this adaptive capacity presents a practical way of coping with climate change. Adaptive capacity could be increased by enabling the African livestock owner to cope better with animal health problems through appropriate policy measures and institutional support. Developing an effective and sustainable animal health service, associated surveillance and emergency preparedness systems and sustainable disease control and prevention programmes is perhaps the most important strategy for dealing with climate change in many African countries.

The transfer of East Coast fever immunisation to veterinary paraprofessionals in Zambia.

In eastern Zambia, immunisation by 'infection and treatment' is the main method used to control East Coast fever, an acute and lethal cattle disease. This service, which requires a stringent cold chain, used to be free of charge. When a minimal user fee was introduced, attendance dropped drastically. Consequently, this complex immunisation programme was transferred to veterinary paraprofessionals working on their own account, with the aim of boosting a more sustainable distribution of vaccine. Paraprofessionals were provided with a motorbike and the required specific equipment, but fuel and drugs were at their expenses. The paraprofessionals recovered their costs, with a profit margin, by charging the cattle owners for immunisation. The reasons for the successful transfer of immunisation to paraprofessionals (despite the maintenance of a fee) are attributed mainly to the absence of information asymmetry between the paraprofessional and the livestock owner, the appreciable level of effort of the paraprofessionals and the verifiable outcome of the service provided.

Heterogeneity in the trypanosomosis incidence in Zebu cattle of different ages and sex on the plateau of eastern Zambia.

On the plateau of eastern Zambia, trypanosomosis is endemic. Glossina morsitans morsitans Westwood (Diptera: Glossinidae), the only tsetse species present, is almost entirely dependent on livestock as its source of food with cattle being the most preferred host. To determine if tsetse challenge is distributed equally over the various age categories and sexes within a cattle herd, a longitudinal study of trypanosomosis incidence was conducted during the rainy season. A total of 354 head of cattle consisting of 40% oxen, 30% cows, 15% young stock, 13% calves and 2% bulls were sampled for three consecutive months and their infection statuses determined using the PCR-RFLP technique as diagnostic method. Results indicated that there were significant differences (P<0.001) in the proportion of infected animals between the various categories. In oxen, the risk of infection was 5.6 times higher than in calves. Those results suggest heterogeneity in the challenge by tsetse flies and are in line with entomological observations on the feeding preference of tsetse on cattle. The implications of these results for the control of trypanosomosis in Eastern Province and other epidemiologically related areas are discussed.

The comparative role of cattle, goats and pigs in the epidemiology of livestock trypanosomiasis on the plateau of eastern Zambia.

To determine and compare the prevalence of trypanosome infections in different livestock species (cattle, pigs and goats) in areas where game animals are scarce and livestock constitute the main food source of tsetse, a survey was conducted on the plateau of the Eastern Province of Zambia in Katete and Petauke districts where Glossina morsitans morsitans is the only tsetse species present. Blood was collected from a total of 734 cattle, 333 goats and 324 pigs originating from 59 villages in both districts and was examined using the buffy coat method and the PCR-RFLP as diagnostic tools. The prevalence of trypanosome infections differed substantially between livestock species. Using microscopic diagnostic methods, trypanosome infections were detected in 13.5% of the cattle and 0.9% of the pigs. All goats were parasitologically negative. The PCR-RFLP analyses increased the trypanosomiasis prevalence to 33.5, 6.5 and 3.3% in cattle, pigs and goats respectively. The majority of the infections (91.2%) were due to Trypanosoma congolense. The presence of a trypanosome infection in cattle and pigs resulted in a significant decline in the packed cell volume. The outcome of the study clearly shows that despite the availability of goats and pigs, cattle seem to be the major livestock species affected by the disease in trypanosomiasis endemic areas. The high proportion of infections in cattle could be partly attributed to their higher availability and attractiveness to tsetse.

Age prevalence of trypanosomal infections in female Glossina morsitans morsitans (Diptera: Glossinidae) on the plateau area of eastern Zambia.

Trypanosomal infections in female Glossina morsitans morsitans were investigated in an area in the Eastern Province of Zambia between 1992 and 1994. A total of 4416 flies were captured, aged using the ovarian ageing method and screened for trypanosomal infections in both the mouthparts, salivary glands and the midgut. Congolense-type infections were identified in 4.8% of the flies. Vivax-type and immature infections were identified in 1.8% and 6.8% of the flies, respectively. The prevalence of congolense-type, vivax-type and immature infections increased with age. For vivax-type infections the age-prevalence relationship could be described by a model assuming a constant per capita rate of infection. For congolense-type and midgut infections, a polynomial term was added to the model significantly improving the fit. The per capita at which flies become infected was significantly higher for immature compared to mature infections. Observations strongly suggest that tsetse acquire new midgut infections at any age and that maturation of these infections is not limited to those obtained during the first blood meal.

Comparison of the survival on ice of thawed Theileria parva 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.

Building capacity for improved veterinary epidemiosurveillance in southern Africa.

A workshop to produce recommendations on training requirements for improved epidemiosurveillance of livestock diseases in southern Africa was organised at the Department of Veterinary Tropical Diseases in the Veterinary Faculty of the University of Pretoria. It was attended by 23 persons representing 10 different southern African countries. The majority of the participants were actively involved in veterinary epidemiosurveillance and many of them were members of the SADC Epidemiology and Informatics Subcommittee. Discussions focused on (i) epidemiosurveillance networks and their 2 main components, i.e. (ii) diagnosis and (iii) information flow. The debates were guided by 3 questions; (i) what are the requirements for an effective network, (ii) what cannot be achieved with existing capacity and (iii) how can the current capacity be improved. Workshop participants developed lists of realistic capacity building needs, which were divided into structural needs and training requirements. Structural needs mainly concerned communication means and quality assurance. With regard to training, the need for appropriate continuing education of all actors at the various disease management levels (non-professional, para-professional, professional) was expressed. Special emphasis was put on capacity building at the lowest level, i.e. the livestock owner and the para-professionals at the community level. At the international level, it was felt that special emphasis should be put on building capacity to improve the understanding of international agreements on trade in animals and animal products and to improve the capacity of negotiating such agreements.

A modified AFLP for Trypanosoma congolense isolate characterisation.

The amplified fragment length polymorphism (AFLP) technique is a reliable and powerful DNA fingerprint tool for genetic characterisation and analysis. In this paper, we described a modified AFLP with high resolution for Trypanosoma congolense using one enzyme and agarose or Elchrom gel electrophoresis. Eleven allopatric and fourteen sympatric isolates of T. congolense savannah were used to assess the resolution of the method and its ability to characterise T. congolense isolates. Two enzymes (Eco RI or Bgl II) and corresponding non-selective and selective primers were used to identify the most appropriate combination. Patterns generated by Bgl II enzyme and a single selective primer A, C, G or T produced clear profiles. Each of the four selective primers produced different profiles for all the 25 T. congolense isolates. Due to the reduction in the number of bands, profiles could be analysed using agarose or Elchrom gels. Although comparison of a great number of samples could benefit from software help, this technique did not require flurochrome detection methods. The results of the present study demonstrated that this modified AFLP makes the characterisation of T. congolense easier while maintaining high resolution.

SSCP analysis of the P2 purine transporter TcoAT1 gene of Trypanosoma congolense leads to a simple PCR-RFLP test allowing the rapid identification of diminazene resistant stocks.

Analyses were made on a Trypanosoma congolense contig coding a putative P2-like nucleoside transporter (the contig was named in this study TcoAT1). The sequence includes a start and stop codon and presents a high similarity with the gene TbAT1 of T. brucei (Smallest Sum Probability 2.8e-136). To investigate a possible link between point mutations and diminazene aceturate (DA) resistance in mice, the TcoAT1 putative genes of 26 T. congolense strains, characterised for DA sensitivity in the single dose mouse test, were screened by means of the Single Strand Conformation Polymorphism technique (SSCP). Results showed that the SSCP profiles of 23 out of 26 (88.5%) T. congolense strains were confirmed by the sensitivity test in mice with the commonly accepted criterion for sensitivity to diminazene being a CD80 of 20mg/kg in the mouse test. The remaining T. congolense strains showed a resistant SSCP profile and relapsed in mice after treatment at doses lower than 20mg/kg indicating that the SSCP is more sensitive than the single dose mouse test for the detection of resistance to diminazene. However, none of the strains used in this study showed a sensitive SSCP profile while they were resistant in the single dose mouse test. The sequencing of the TcoAT1 gene of two sensitive, two intermediate and two resistant strains allowed the set up of a PCR-RFLP test for the discrimination between sensitive and resistant strains confirming the SSCP results for the 26 strains of this study.

Effect of isometamidium chloride treatment on susceptibility of tsetse flies (Diptera: Glossinidae) to trypanosome infections.

Experiments were conducted to determine the effect of a single isometamidium chloride treatment of teneral tsetse flies, Glossina morsitans morsitans Westwood (Diptera: Glossinidae), on the subsequent susceptibility to an infection with Trypanosoma congolense or Trypanosoma brucei brucei. Flies were offered a first bloodmeal on sterile gamma-irradiated defibrinated bovine blood that contained either 10 or 100 microg ofisometamidium chloride/ml. Treated flies were subsequently infected with T. congolense IL 1180 or T. b. brucei AnTAR1 on day 3, 5, 10, or 20 posttreatment. To determine the effect of a single treatment with isometamidium chloride at 10 microg/ml on the fly's susceptibility to infection with isometamidium chloride-resistant trypanosome strains, treated flies were infected with one of two resistant isogenic T. congolense IL 1180 strains 3 d after the first feed. Results showed that a single isometamidium chloride treatment at 10 microg/ml blood sufficed to reduce significantly the fly's subsequent susceptibility to infection. Only 6.8% of the flies that were treated with isometamidium chloride developed a mature infection with T. congolense in the mouthparts compared with 34.3% of the control group. None of the flies that were administered isometamidium chloride and subsequently infected on day 3 or 6 with T. b. brucei developed a metacyclic infection in the salivary glands compared with 22.7% of the control flies. Likewise for the resistant T. congolense strains, a single treatment with isometamidium chloride significantly reduced the subsequent susceptibility to infection (6.5 and 33.5% of flies with metacyclic infections for treated and untreated flies, respectively). In practice and with respect to the release of sterile male flies to eradicate an isolated tsetse fly population, our results show that administering isometamidium chloride during the first bloodmeal (and before release) would significantly reduce the ability of these released males to transmit trypanosomes.

The transmissibility of Trypanosoma congolense seems to be associated with its level of resistance to isometamidium chloride.

In large parts of Africa the control of livestock trypanosomiasis relies on the use of trypanocidal drugs. Resistance against the available compounds is developing rapidly in the trypanosome population. The effect of the development of drug resistance on the fitness of the trypanosome is not well known. To determine the effect of the development of resistance to isometamidium chloride on the trypanosome's transmissibility, transmission experiments were conducted. Use was made of three isogenic clones of Trypanosoma congolense with different susceptibility to the drug. The infection rate in Glossina morsitans morsitans differed significantly between clones and was significantly higher in tsetse flies infected with the T. congolense clone with the highest level of drug resistance.