Trypanosome infection rate in Glossina tachinoides: infested rivers of Limmu Kosa District Jimma Zone, Western Ethiopia

OBJECTIVE

Trypanosomosis is a disease of domestic animals and humans resulting from infection with parasitaemic protozoa of the genus Trypanosoma transmitted primarily by tsetse flies. A cross-sectional study was conducted from January-March 2018, to estimate the infection rate of trypanosome in Glossina tachinoides, their distribution, magnitude and involved trypanosome species in Limmu Kosa District of Jimma zone.

RESULTS

Study methodology involved entomological survey using monoconical traps to study the magnitude of Fly density Flay/Trap/Day (FTD) and tsetse fly dissection to estimate infection rate of trypanosome in vector flies. The study result indicated that there was only one species of Tsetse fly Glossina tachinoides detected with FTD = 4.45. From the total of (n = 284) dissected Glossina tachinoides flies only (n = 5) positive for Trypanosome resulting in 1.76% Infection Rate. Peak trypanosome infections were observed in female tsetse 2.04%, n = 4 and 1.14%, n = 1 in males. Furthermore, 1.06% of Glossina tachinoides were infected by Trypanosome vivax and the remaining 0.70% was Trypanosome congolense. Finally, the study concluded with the recommendation of control and suppression of the vector and parasite was mandatory due to Pathogenic Animal Trypanosomosis.

Prevalence of bovine trypanosomosis and vector density in a dry season in Gamo-Gofa and Dawuro Zones, Southern Ethiopia

Trypanosomosis remains one of the biggest constraints of livestock productivity in sub-Saharan Africa. It is of particular concern in Ethiopia where crop production is largely dependent on animal traction power. This study was conducted between November 2015 and March 2016 to estimate the prevalence of bovine trypanosomosis and vector density in Gamo-Gofa and Dawuro Zones located in Southern Ethiopia. For the entomological survey, a total of 305 NGU traps were deployed for three consecutive days at different positions in the two study areas. For parasitological study, blood samples were collected from 2402 cattle and examined for the presence of trypanosomes by the buffy coat technique (BCT). Blood samples that were positive in the BCT were further tested with Giemsa-stained thin smears for identification of Trypanosoma species. In the entomological survey, a total of 4113 flies were captured of which 1605 (39%) were tsetse flies while 2508 (61%) were other biting flies of the genus Stomoxys and Tabanus. Glossina pallidipes was the only tsetse fly identified in the study areas. The overall mean apparent density of G. pallidipes was 1.8 flies per trap per day (FTD). The overall prevalence of trypanosomosis in the study areas was 5.1% (95% CI: 4.2-6.0); however, it was significantly (p < 0.001) higher in Dawuro Zone (10%) than Gamo-Gofa (1.9%). Prevalence was also noted to be significantly (p < 0.001) higher in cattle with black coat colour and those with poor body condition. Trypanosomosis was caused mainly by Trypanosoma congolense (61.8%) and to a lesser extent by T. vivax (28.5%). Mixed infection by the two spp. was seen in 9.8% of the total positive animals. Evaluation of the mean packed cell volume (PCV) of the study animals with infection status revealed a significantly (p < 0.001) lower mean PCV in parasitaemic animals (21.5 ± 0.46SE) than aparasitaemic ones (24.3 ± 0.11SE). Generally, the prevalence noted in the current study is moderate. However the observation of such level of infection in a dry season suggests that the disease is still an important constraint of cattle production in the study areas. Thus, we recommend that theexisting parasite and vector control interventions need to be strengthened with special emphasis to Dawuro Zone where the prevalence was significantly higher. As the current sampling was done only once and in a dry season only, further longitudinal studies including all the seasons of the year need to be considered in the future.

Bovine trypanosomosis and Glossina distribution in selected areas of southern part of Rift Valley, Ethiopia

Cross-sectional study was conducted in 9 selected districts of the southern part the Rift Valley, Ethiopia to estimate the dry period prevalence of bovine trypanosomosis as well as assessment of Glossina species. From a total of 1838 cattle examined for trypanosomosis by buffy coat technique 133 (7.2%) were found infected by trypanosome species. From the total positive animals 66.9 and 33.1% of them accounted to Trypanosoma congolense and Trypanosoma vivax, respectively. Significantly higher prevalence (19.4%., P<0.05) was recorded at Arba-Mnch district. Black colored cattle were the most highly affected (χ(2)=79.35, P<0.05) animals. The overall average PCV value for parasitaemic and aparasitaemic animals was 22.2 (95% CI=21.6-22.7) and 27% (95% CI=26.8-27.2), respectively. The fly caught per trap per day was 1.4 for Glossina species and 2.8 for other biting flies. Two species of Glossina identified namely Glossina pallidipes and Glossina fuscipes.

Prevalence of pathogenic trypanosomes in anaemic cattle from trypanosomosis challenged areas of Itezhi-tezhi district in central Zambia

BACKGROUND

The measure of anaemia status using packed cell volume (PCV) can be a reliable indicator of African trypanosomosis (AT) in the absence of other anaemia-causing conditions. However, studies that have estimated prevalence of anaemia in cattle from AT endemic areas have rarely reported the prevalence of the disease in the anaemic cattle. Therefore we investigated the prevalence of AT in anaemic cattle at sites that had recently reported the disease in Itezhi tezhi district of central Zambia.

METHODS

During a survey, blood samples were collected from 564 randomly selected cattle for anaemia determination from seven crush pens (Mutenda, Kapulwe, Banachoongo, Itumbi, Iyanda, New Ngoma and Shinampamba). At a PCV- value cut off of 26 %, all samples positive for anaemia were subjected to both parasitological examination on thick and thin blood smears and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) for detection of trypanosome DNA. Fisher's exact test and a mixed effect logistic regression analyses were used to determine and measures associations, respectively.

RESULTS

Of 564 cattle screened, 58 (10.3 %; 95 % CI: 7.8-12.8 %) had anaemia. PCR-RFLP results showed that 17 (29.3 %; 95 % CI; 17.2-41.4 %) anaemic cattle were positive for pathogenic trypanosomes compared to 1 (1.7 %; 95 % CI: 0.0-5.2 %) on parasitological examination using thick smears. The infections were caused by Trypanosoma congolense and Trypanosoma vivax. Fisher's exact test showed a strong association between PCV and pathogenic trypanosome infection (P = 0.004). A mixed effect multivariate logistic regression showed that a one unit increase in PCV reduced the likelihood of detecting AT with PCR-RFLP by 24.7 % (95 % CI: 4.6-40.6 %; P = 0.019) in anaemic cattle, taking into account their age and sex, with random effects for crush pen.

CONCLUSION

These results suggest that T. congolense and T. vivax could be important causes of anaemia in cattle reared in AT endemic areas of Itezhi tezhi in Central Zambia. This also suggests that even though pathogenic trypanosomal infection was strongly associated with PCV, it could only account for up to 41 % of the anaemia in cattle. Therefore further investigation to ascertain other factors responsible for anaemia in AT endemic areas of Itezhi tezhi in Central Zambia is needed.

In vivo experimental drug resistance study in Trypanosoma vivax isolates from tsetse infested and non-tsetse infested areas of Northwest Ethiopia

Ethiopia, particularly in the Northwest region, is affected by both tsetse fly and non-tsetse fly transmitted trypanosomosis with a significant impact on livestock productivity. The control of trypanosomosis in Ethiopia relies on either curative or prophylactic treatment of animals with diminazene aceturate (DA) or isometamidium chloride (ISM), respectively. However, since these two trypanocides have been on the market for more than 40 years, this may have resulted in drug-resistance. Therefore, in vivo drug resistance tests on two Ethiopian isolates of Trypanosoma vivax were completed, one from an area where tsetse flies are present and one from an area where tsetse flies are not present. Twenty four cattle (Bos indicus) aged between 6 and 12 months, purchased from a trypanosome-free area (Debre Brehan: Northcentral Ethiopia) and confirmed to be trypanosome-negative, were randomly assigned into four groups of six animals, which were infected with T. vivax isolated from a tsetse-infested or non-tsetse infested area, and in each case treated with curative doses of DA or ISM. Each animal were inoculated intravenously 3×10(6) trypanosomes from donor animals. Parasitaemia became patent earlier in infections with non-tsetse T. vivax (∼7 days post-infection) than tsetse (∼14 days post-infection). Both groups were treated at the highest peak parasitaemia with DA or ISM and nine cattle, four with non-tsetse T. vivax (two ISM- and two DA-treated) and five with tsetse T. vivax (three ISM- and two DA-treated) showed relapses of parasitaemia. Moreover, treatment did not improve diagnostic host markers of trypanosome infections in these animals. In conclusion, in vivo drug tests indicated the presence of resistant parasites (>20% of treated animals in each group relapsed) against recommended doses of both available trypanocidal drugs.

A comparison of phenotypic traits related to trypanotolerance in five west african cattle breeds highlights the value of shorthorn taurine breeds

BACKGROUND

Animal African Trypanosomosis particularly affects cattle and dramatically impairs livestock development in sub-Saharan Africa. African Zebu (AFZ) or European taurine breeds usually die of the disease in the absence of treatment, whereas West African taurine breeds (AFT), considered trypanotolerant, are able to control the pathogenic effects of trypanosomosis. Up to now, only one AFT breed, the longhorn N'Dama (NDA), has been largely studied and is considered as the reference trypanotolerant breed. Shorthorn taurine trypanotolerance has never been properly assessed and compared to NDA and AFZ breeds.

METHODOLOGY/PRINCIPAL FINDINGS

This study compared the trypanotolerant/susceptible phenotype of five West African local breeds that differ in their demographic history. Thirty-six individuals belonging to the longhorn taurine NDA breed, two shorthorn taurine Lagune (LAG) and Baoulé (BAO) breeds, the Zebu Fulani (ZFU) and the Borgou (BOR), an admixed breed between AFT and AFZ, were infected by Trypanosoma congolense IL1180. All the cattle were genetically characterized using dense SNP markers, and parameters linked to parasitaemia, anaemia and leukocytes were analysed using synthetic variables and mixed models. We showed that LAG, followed by NDA and BAO, displayed the best control of anaemia. ZFU showed the greatest anaemia and the BOR breed had an intermediate value, as expected from its admixed origin. Large differences in leukocyte counts were also observed, with higher leukocytosis for AFT. Nevertheless, no differences in parasitaemia were found, except a tendency to take longer to display detectable parasites in ZFU.

CONCLUSIONS

We demonstrated that LAG and BAO are as trypanotolerant as NDA. This study highlights the value of shorthorn taurine breeds, which display strong local adaptation to trypanosomosis. Thanks to further analyses based on comparisons of the genome or transcriptome of the breeds, these results open up the way for better knowledge of host-pathogen interactions and, furthermore, for identifying key biological pathways.

Development of real time PCR to study experimental mixed infections of T. congolense Savannah and T. b. brucei in Glossina morsitans morsitans

Tsetse flies are able to acquire mixed infections naturally or experimentally either simultaneously or sequentially. Traditionally, natural infection rates in tsetse flies are estimated by microscopic examination of different parts of the fly after dissection, together with the isolation of the parasite in vivo. However, until the advent of molecular techniques it was difficult to speciate trypanosomes infections and to quantify trypanosome numbers within tsetse flies. Although more expensive, qPCR allows the quantification of DNA and is less time consuming due to real time visualization and validation of the results. The current study evaluated the application of qPCR to quantify the infection load of tsetse flies with T. b. brucei and T. congolense savannah and to study the possibility of competition between the two species. The results revealed that the two qPCR reactions are of acceptable efficiency (99.1% and 95.6%, respectively), sensitivity and specificity and can be used for quantification of infection load with trypanosomes in experimentally infected Glossina morsitans morsitans. The mixed infection of laboratory Glossina species and quantification of the infection suggests the possibility that a form of competition exists between the isolates of T. b. brucei and T. congolense savannah that we used when they co-exist in the fly midgut.

Proteomic selection of immunodiagnostic antigens for Trypanosoma congolense

Animal African Trypanosomosis (AAT) presents a severe problem for agricultural development in sub-Saharan Africa. It is caused by several trypanosome species and current means of diagnosis are expensive and impractical for field use. Our aim was to discover antigens for the detection of antibodies to Trypanosoma congolense, one of the main causative agents of AAT. We took a proteomic approach to identify potential immunodiagnostic parasite protein antigens. One hundred and thirteen proteins were identified which were selectively recognized by infected cattle sera. These were assessed for likelihood of recombinant protein expression in E. coli and fifteen were successfully expressed and assessed for their immunodiagnostic potential by ELISA using pooled pre- and post-infection cattle sera. Three proteins, members of the invariant surface glycoprotein (ISG) family, performed favorably and were then assessed using individual cattle sera. One antigen, Tc38630, evaluated blind with 77 randomized cattle sera in an ELISA assay gave sensitivity and specificity performances of 87.2% and 97.4%, respectively. Cattle immunoreactivity to this antigen diminished significantly following drug-cure, a feature helpful for monitoring the efficacy of drug treatment.

Animal African Trypanosomosis (AAT) is a set of diseases whereby animals are infected with single-cell parasites that replicate in their bloodstream. The disease in cattle results in weight-loss and death, and AAT is a significant veterinary problem for sub-Saharan Africa. One of the principal trypanosome species responsible for AAT in cattle is Trypanosoma congolense and, although there are drug-treatments for these infections, current diagnostic methods are impractical for field use. Our aim was to discover protein molecules from the parasite to which infected animals make antibodies, to then make these proteins in bacteria and to subsequently demonstrate that they can be used to detect antibodies in cattle serum, thus diagnosing AAT. To discover the diagnostic proteins, we dissolved parasites in a detergent solution and applied them to beads coated with antibodies from infected cattle and to beads coated with antibodies from un-infected cattle. We then compared the proteins bound to each and selected those proteins that were at least 100-fold enriched by the infected cattle antibodies. We refined this list, according to practical and performance considerations, and settled on one protein, called Tc38630. Testing Tc38630 with cattle sera showed that it can detect about nine out of ten AAT infections.

High prevalence of drug resistance in animal trypanosomes without a history of drug exposure

Background

Trypanosomosis caused by Trypanosoma congolense is a major constraint to animal health in sub-Saharan Africa. Unfortunately, the treatment of the disease is impaired by the spread of drug resistance. Resistance to diminazene aceturate (DA) in T. congolense is linked to a mutation modifying the functioning of a P2-type purine-transporter responsible for the uptake of the drug. Our objective was to verify if the mutation was linked or not to drug pressure.

Methodology/Principal Findings

Thirty-four T. congolense isolates sampled from tsetse or wildlife were screened for the DA-resistance linked mutation using DpnII-PCR-RFLP. The results showed 1 sensitive, 12 resistant and 21 mixed DpnII-PCR-RFLP profiles. This suggests that the mutation is present on at least one allele of each of the 33 isolates. For twelve of the isolates, a standard screening method in mice was used by (i) microscopic examination, (ii) trypanosome-specific 18S-PCR after 2 months of observation and (iii) weekly trypanosome-specific 18S-PCR for 8 weeks. The results showed that all mice remained microscopically trypanosome-positive after treatment with 5 mg/kg DA. With 10 and 20 mg/kg, 8.3% (n = 72) and 0% (n = 72) of the mice became parasitologically positive after treatment. However, in these latter groups the trypanosome-specific 18S-PCR indicated a higher degree of trypanosome-positivity, i.e., with a unique test, 51.4% (n = 72) and 38.9% (n = 72) and with the weekly tests 79.2% (n = 24) and 66.7% (n = 24) for 10 and 20 mg/kg respectively.

Conclusion/Significance

The widespread presence of the DA-resistance linked mutation in T. congolense isolated from wildlife suggests that this mutation is favourable to parasite survival and/or its dissemination in the host population independent from the presence of drug. After treatment with DA, those T. congolense isolates cause persisting low parasitaemias even after complete elimination of the drug and with little impact on the host's health.

Trypanosomosis is responsible for the death of 3 million heads of cattle yearly, with 50 million animals at risk in sub-Saharan Africa. DA, a commonly used drug against the disease, was marketed decades ago. Drug resistance is reported in 21 African countries. A common argument about the origin of drug resistance is the selection by the drug of rare individuals that are naturally resistant and the propagation of those individuals in the population because of the competitive advantage they have when exposed to drug. When the drug pressure decreases, the wild-type individuals regain their supremacy. The principal objective of this study was thus to estimate the prevalence of trypanosomes resistant to DA in a population that was never exposed to the drug. Our results showing a high prevalence of drug resistance in environments free of any drug pressure is thought provoking and suggests that ceasing the use of DA will not allow for a return to a DA-sensitive population of trypanosomes. Drug resistance in animal trypanosomes thus present a pattern different from what is observed with Plasmodium sp. (causative agent of malaria) where a complete stoppage in the use of the chloroquine allows for a return to drug sensitivity.

Trypanosoma vivax, T. congolense "forest type" and T. simiae: prevalence in domestic animals of sleeping sickness foci of Cameroon

In order to better understand the epidemiology of Human and Animal trypanosomiasis that occur together in sleeping sickness foci, a study of prevalences of animal parasites (Trypanosoma vivax, T. congolense "forest type", and T. simiae) infections was conducted on domestic animals to complete the previous work carried on T. brucei gambiense prevalence using the same animal sample. 875 domestic animals, including 307 pigs, 264 goats, 267 sheep and 37 dogs were sampled in the sleeping sickness foci of Bipindi, Campo, Doumé and Fontem in Cameroon. The polymerase chain reaction (PCR) based method was used to identify these trypanosome species. A total of 237 (27.08%) domestic animals were infected by at least one trypanosome species. The prevalence of T. vivax, T. congolense "forest type" and T. simiae were 20.91%, 11.42% and 0.34% respectively. The prevalences of 7 vivax and T. congolense "forest type" differed significantly between the animal species and between the foci (p < 0.0001); however, these two trypanosomes were found in all animal species as well as in all the foci subjected to the study. The high prevalences of 7 vivax and T congolense "forest type" in Bipindi and Fontem-Center indicate their intense transmission in these foci.

A cross-sectional study of trypanosomosis and its vectors in donkeys and mules in Northwest Ethiopia

A preliminary study was conducted in January 2009 in four peasant associations (PAs) selected from two districts in Benishangul Gumuz Regional State, Northwest Ethiopia to investigate the prevalence and species of trypanosomes infecting donkeys and mules and identify the fly vectors playing a role in the transmission of trypanosomosis. Blood samples were collected from a total of 334 donkeys and 52 mules and examined by dark ground/phase contrast buffy coat technique and Giemsa-stained blood smears. Accordingly, trypanosome species were encountered in 6.3% of the examined donkeys (n = 21) while none of the mules examined was positive for trypanosome infection. Trypanosomes and tsetse flies were detected in two of the four PAs surveyed (Tsetsa adurno and Bamadone) with significant (P = 0.004) difference in prevalence. The inability to find trypanosomes in the other two PAs (Ura and Ashura) was most likely due to the absence of appropriate fly vectors. Three species of trypanosomes were detected in donkeys, which in order of predominance were Trypanosoma congolense (52.4%), Trypanosoma brucei (28.6%), and Trypanosoma vivax (19.05%). There was a significant (P = 0.008) difference in mean PCV between trypanosome infected and non-infected donkeys. The body condition score of the donkeys was significantly associated with both prevalence of infection (P = 0.009) and mean packed cell volume (PCV; P < 0.0001). No significant difference was observed between male and female donkeys regarding both prevalence of infection and mean PCV (P > 0.05 for each factor). The entomological surveys revealed the presence of Glossina morsitans submorsitans and other biting flies of the family Stomoxys, Tabanus, and Haematopota. In conclusion, the prevalence of trypanosomosis obtained in the current study is generally low compared to previous studies. As the present study design was a cross-sectional, one that only depicts a momentary picture of the infection status in the herd, a further longitudinal study that makes use of more sensitive techniques and entomological survey is recommended.

The effect of aqueous extracts of Hibiscus sabdariffa (Sorrel) calyces on heamatological profile and organ pathological changes in Trypanasoma congolense - infected rats

The effects of aqueous extract of Hibiscus sabdariffa calyces on haematology and pathological changes in some selected organs during experimental Trypanosoma congolense infection of rats were investigated. Three groups of rats were intraperitoneally infected with T. congolense (Karu stock). One group was administered with the aqueous extract and another given a solution of vitamin C in drinking water; the remaining infected group was left untreated. Data from these groups were compared with those of two groups of healthy rats, one of which was similarly treated with the aqueous extract. The experiment was terminated three weeks, post-infection (pi). The uninfected and infected rats administered the extract consumed the equivalent of 9.94 mg - and 9.61 mg ascorbic acid / 100g / day during the experiment. Consumption of the extract significantly (p<0.01) retarded the rate of weight gain in both healthy and infected rats; even though the feed-intake was not significantly affected. After two weeks of infection the extract and vitamin C kept the parasitaemia significantly (p<0.01) lower than the untreated infected group. The anaemia in the untreated infected group was significantly (p<0.01) more severe than that of the corresponding extract- or vitamin-treated groups. Trypanosoma congolense infection caused significant (p<0.01) decreases in serum total proteins and albumin; serum and organ ascorbic acid as well as significant (p<0.01) elevation of serum alanine amino transferase levels in untreated rats. Consumption of the extract or vitamin C, however, prevented these disease-induced anomalies in the treated infected rats. Serum creatinine and urea levels were not affected by infection but the extract elevated these parameters significantly (p<0.01) above infection levels. It was concluded that consumption of the extract ameliorated the pathological changes in blood and organs of T. congolense-infected rats.

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.

Does isometamidium chloride treatment protect tsetse flies from trypanosome infections during SIT campaigns?

African animal trypanosomosis is a major pathological constraint to cattle breeding across 10 million km2 of sub-Saharan West African countries infested by tsetse flies, their cyclic vectors. The release of sterile males (sterile insect technique [SIT]) is a potentially important control technique aimed at eliminating the vectors. Prior to release, tsetse are generally treated with isometamidium chloride, a trypanocide, to prevent them from transmitting parasites. The present study investigated the preventive action of isometamidium chloride (0.5 mg/L) on the subsequent susceptibility of tsetse released into the wild. A total of 1755 Glossina palpalis gambiensis Vanderplank and 744 Glossina tachinoides Westwood were released, of which 50 and 48, respectively, were recaptured 22-43 days after release. Their probosces were analysed by polymerase chain reaction to identify mature infections with three trypanosome species (Trypanosoma vivax, Trypanosoma brucei sensu lato and Trypanosoma congolense savannah type). Two mature infections with T. vivax and four with T. congolense were detected, indicating that the use of this treatment regimen in an SIT campaign would not totally prevent sterile males from transmitting trypanosomes.

Bovine trypanosomosis in three districts of East Gojjam Zone bordering the Blue Nile River in Ethiopia

BACKGROUND

Bovine trypanosomosis is a serious constraint to agricultural production in extensive areas of Ethiopia.

METHODOLOGY

A cross-sectional study was conducted to determine the prevalence of bovine infection with trypanosomes and to identify the prevailed trypanosome species in three districts of the East Gojjam zone bordering the Blue Nile River from March 2005 to February 2006. Cattle from 9 different localities were checked using microscopical examination of wet blood smears, thin and stained bloodsmears, and by blood centrifugation followed by the examination of the resultant buffy coats.

RESULT

Of the total 3,360 cattle investigated, 8.2% (3.5%, 11.6% and 9.4% from Dejen, Machakel and Baso-Liben districts respectively) were found to be infected with trypanosomes. Of the total 275 positive animals, 249 (90.5%) appeared to be infected with Trypanosoma vivax; 11 (4%) were infected with T. congolense; and 15 (5.5%) were infected with mixed infection of T. vivax and T. congolense. The prevalence of infection with T. vivax was significantly higher than that of T. congolense (P<0.001). Taking 24-46% as normal PCV value, the mean PCV for the trypanosome-infected cattle (22.09%) was lower than those for the trypanosome-negative animals (26.03).

CONCLUSION

Trypanosomosis is a disease of considerable importance to the major economic districts bordering the Blue Nile River of the East Gojjam zone, Ethiopia, given the disease's potential to threaten the health and productivity of cattle in this region.

First report of canine African trypanosomosis in the UK

A six-year-old neutered male Jack Russell terrier was presented two years after importation into the UK from southern Africa with severe anaemia and abdominal distension. Abdominal ultrasonography revealed the presence of hepato-splenomegaly and ascites. A diagnosis of trypanosomosis was made by blood smear examination. Shortly after admission the dog collapsed and died. PCR analysis revealed a single infection with Trypanosoma congolense savannah type. This is the first reported case of canine African trypanosomosis in Europe and suggests that chronic trypanosomosis may allow importation of the disease in apparently asymptomatic animals, even with extended quarantine periods.

A comparative longitudinal study of bovine trypanosomiasis in tsetse-free and tsetse-infested zones of the Amhara Region, northwest Ethiopia

A study was conducted to determine the incidence of trypanosome infections in cattle in tsetse-free and tsetse-infested zones of the Amhara Region of northwest Ethiopia. A total of six sentinel herds were established and the cattle observed during a period of 8 consecutive months. The prevalence of seropositive cattle was high in both the tsetse-free and tsetse-infested zones. The average monthly incidence of trypanosome infection, determined using molecular diagnostic tools, was 20.9% and 25.7% in the tsetse-free and the tsetse-infested zones, respectively. In the tsetse-free, Trypanosoma vivax was responsible for 90.9% of the cattle trypanosome infections. In the tsetse-infested zone, Trypanosoma congolense and T. vivax contributed almost equally to the trypanosome infections in cattle. Trypanosome infection, regardless of species, resulted in anaemia as evidenced by a significant decrease in the packed cell volume of the infected animal. The outcome of this longitudinal study suggests that control of trypanosomiasis in the Amhara Region cannot be achieved by tsetse control alone. Supplemental measures to include drug therapy and biting fly control are discussed.

An update of the bovine trypanosomosis situation at the edge of Hluhiuwe-Imfolozi Park, Kwazulu-Natal Province, South Africa

To obtain updated data on and assess the contribution of trypanosomosis to the disease burden of cattle kept at the edge of the Hluhluwe-iMfolozi Park, a survey was conducted at Mvutshini Dip. Use was made of a purposeful sampling strategy by restricting sampling to animals that the livestock owner considered to be in poor condition. Of a total of 76 blood samples collected, 26 were parasitologically positive and 46 were positive on PCR/RFLP. Almost all infections were due to Trypanosoma congolense savannah subgroup. A total of 63 animals had a PCV < or = 24% and were considered to be anaemic. Results from the survey show that trypanosome infections contribute significantly to the overall burden of disease in the area. Further research is required to develop appropriate control methods.

The application of PCR-ELISA to the detection of Trypanosoma congolense type savannah (TCS) in bovine blood samples

PCR-ELISA was set up to detect strains of Trypanosoma congolense type savannah (TCS) in field samples of buffy coats. Results of PCR-ELISA and PCR were compared and the effectiveness of both techniques was also compared with the Murray's method for the detection of TCS in 257 bovine buffy coats. The PCR products were labelled with digoxigenin (DIG-dUTP) during amplification cycles of the repetitive satellite DNA. A biotinylated DNA capture probe was used to detect the PCR products by ELISA in streptavidin coated microplates. Both the PCR-ELISA and PCR were more sensitive and more specific than the Murray's method. Of the 257 buffy coats analysed by the three techniques, PCR-ELISA and PCR detected TCS in 98 and 97 buffy coats respectively, whereas the Murray's method detected only 39 samples. PCR-ELISA and PCR had almost the same sensitivity and specificity. PCR-ELISA and PCR respectively detected TCS in 39.2% and 38.6% in all the 334 samples analysed by both techniques in this study.

Trypanosomosis prevalence in cattle on Mafia Island (Tanzania)

During two consecutive surveys (February and August/Sept 2002), a total of 970 cattle from the cattle population of Mafia Island (United Republic of Tanzania) were blood-sampled. All blood samples were microscopically screened for the presence of trypanosomes and a portion of these were checked for antibodies with an Ab-ELISA and for the presence of trypanosomal DNA with PCR. Microscopic evidence of trypanosomes of the congolense group (sub-genus Nannomonas) was found in 0.8% of the animals (8/970) and in two cases the species identified was confirmed by PCR as Trypanosoma congolense savannah type. Non-pathogenic Trypanosoma theileri were detected in 3.2% (31/970) of the samples using the Dark Ground-Buffy Coat (DG-BC) technique. For survey 1 (S1), detection of antibodies (Ab-ELISA) against pathogenic trypanosomes indicated a seroprevalence of 14.2% (68/480). Of the samples, either DG positive or with a PCV lower then 25, examined by PCR, a total of 8.4% (5/59) (selected from 970 samples), were found positive for T. congolense. The low prevalence of pathogenic trypanosomes on Mafia Island is intriguing, especially in view of the omnipresence of the tsetse fly Glossina brevipalpis. Although the presence of detected trypanosomal antibodies does not necessarily indicate a current infection, the combination of serological/parasitological examinations and the results of the PCR do support this low prevalence of trypanosomosis in cattle. Despite the low prevalence, pathogenic trypanosomes are present on Mafia Island and possible reasons for this low infection rate, taking account of the relation between Glossina species present, transmission risk and trypanosomes found in cattle, are discussed also in view of a future appropriate intervention strategy.

Beneficial effect of erythropoietin administration on murine infection with Trypanosoma congolense

The effect of erythropoietin treatment on Trypanosoma congolense infection in mice was studied. Survival rates of mice were dramatically improved by treatment with recombinant human erythropoietin (r-hu-EPO; 5,000 U/kg) when infected with 1,000 cells of T. congolense IL3000 (P < 0.05). All the untreated mice infected with T. congolense IL3000 died by day 9 of infection; however, 100%, 50%, and 25% of the mice treated with r-hu-EPO for 8 days survived to day 20, day 40, and day 60 of the parasitical infection, respectively. Anti-8-hydroxy-2'-deoxyguanosine antibody, a biomarker for oxidative damage of DNA, yielded positive reactions in the cytoplasm of the parasites recovered from the mice treated with r-hu-EPO. These results, taken together, indicate that erythropoietin administration is effective for the treatment of T. congolense infection.

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.

Comparison of the virulence of Trypanosoma congolense strains isolated from cattle in a trypanosomiasis endemic area of eastern Zambia

The virulence of 31 genetically different Trypanosoma congolense strains belonging to the Savannah subgroup and isolated from cattle at 11 sites in a trypanosomiasis endemic area of eastern Zambia was compared. Virulence testing, done in OF1 mice, revealed three virulence categories. Strains were considered extremely virulent when the median survival time ranged between 5 and 9 days. Moderately virulent strains had a median survival time between 10 and 30 days and low virulence, more than 30 days. For each strain, the prepatent period was determined and the PCV of the infected animals was measured at regular intervals. A total of six (19.4%) strains belonged to the extremely virulent category with a short prepatent period (mean 2.3+/-0.3 days), high parasitaemia, decline in PCV of 15.6+/-1.1% during the first 7 days p.i. and a short median survival time (mean 6 days). The remainder of the strains belonged to the moderate (13 strains) or low (12 strains) virulence categories with median survival times of 13 and 60 days, respectively. They had longer prepatent periods (means 3.2+/-1.6 days and 3.5+/-1.6 days for moderately virulent and strains with low virulence, respectively) and the decline in PCV was less steep (decline of 14.2+/-0.6 and 9.7+/-0.6% during the first 7 days of infection with moderately virulent strains and strains with low virulence, respectively). Extremely virulent strains were isolated from cattle at four sampling sites with 60% of the cattle from one sampling site harbouring such extremely virulent strains. Results from this study demonstrated substantial differences in the virulence of T. congolense strains of the Savannah subgroup, isolated in one geographic area from a single host species. On the assumption that information on virulence obtained from tests in mice can be extrapolated to cattle, the high proportion of strains with low to moderate virulence is thought to be attributed to the important role of susceptible cattle as reservoirs of trypanosomes in the study area and the ensuing selection against extremely virulent strains.

Isometamidium sensitivity of Trypanosoma congolense stocks from cattle in West Africa tested in mice and the drug incubation infectivity test

Four Trypanosoma (T.) congolense reference clones with known isometamidium sensitivity and 16 T. congolense stocks from cattle in Kénédougou in south-western Burkina Faso, an area with known history of drug resistance, were characterised with the standard mouse test (SMT) and the drug incubation infectivity test (DIIT). All field stocks from Kénédougou were resistant to 1.0 mg/kg bw isometamidium in the SMT. Fourteen stocks (87.5%) also proved to be refractory to 10 mg/kg bw. Testing with the DIIT confirmed the results of the SMT. By comparison to reference clones, all the Kénédougou populations expressed high levels of resistance to isometamidium.

Ability of trypanosome-infected tsetse flies (Diptera: Glossinidae) to acquire an infection with a second trypanosome species

The epidemiology of human and animal trypanosomiasis is determined to a large extent by the number of infected tsetse flies in a specific area. In the field, a substantial proportion of infected flies carry mixed trypanosome infections. The way in which these tsetse flies acquire a mixed infection is not fully understood. In particular, the susceptibility of tsetse flies to sequential infection with trypanosomes is not well understood. Accordingly, laboratory studies were made of the effects of age and prior infection on the probability of Glossina morsitans morsitans (Westwood) developing an infection of Trypanosoma congolense and Trypanosoma brucei brucei after feeding on infected mice. Results of these experiments clearly showed that 20-30-d-old G. m. morsitans can still pick up and develop a mature infection in the mouthparts/hypopharynx for T. congolense or in the salivary glands for T. b. brucei. However, their ability to acquire infection was significantly lower compared with teneral flies. Furthermore, 20-30-d-old flies that already carry a mature T. congolense or T. b. brucei infection remained at least as susceptible to a secondary trypanosome infection compared with noninfected flies of the same age. The immunological and epidemiological repercussions of those findings are discussed.

Seasonal prevalence of bovine trypanosomosis in a tsetse-infested zone and a tsetse-free zone of the Amhara Region, north-west Ethiopia

During a period of four consecutive years, trypanosomosis surveys were conducted in a tsetse-infested and tsetse-free area of the Amhara Region of north-west Ethiopia. In each study area randomly selected communal cattle were sampled and their blood was investigated using parasitological diagnostic methods. At the same time the population of biting flies was sampled. The monthly average prevalence of trypanosome infections in cattle did not differ significantly between study areas. In both study areas, the prevalence of trypanosome infections was highest during the long rainy season. Trypanosome infections were mainly due to Trypanosoma vivax and they significantly reduced the average packed cell volume and the body condition of the animals. The monthly prevalence of infection was correlated with the density of biting flies, such as Tabanidae and Stomoxys spp., in the preceding month suggesting an important role of mechanical transmission in the epidemiology of trypanosomosis in both areas.

Inhibition of the DNA amplification of trypanosomes present in tsetse flies midguts: implications for the identification of trypanosome species in wild tsetse flies

The present study was carried out in order to investigate if there was really a failure of PCR in identifying parasitologically positive tsetse flies in the field. Tsetse flies (Glossina palpalis gambiensis and Glossina morsitans morsitans) were therefore experimentally infected with two different species of Trypanosoma (Trypanosoma brucei gambiense or Trypanosoma congolense). A total of 152 tsetse flies were dissected, and organs of each fly (midgut, proboscis or salivary glands) were examined. The positive organs were then analysed using PCR. Results showed that, regardless of the trypanosome species, PCR failed to amplify 40% of the parasitologically positive midguts. This failure, which does not occur with diluted samples, is likely to be caused by an inhibition of the amplification reaction. This finding has important implications for the detection and the identification of trypanosome species in wild tsetse flies.

Bovine trypanosomiasis in south-western Uganda: packed-cell volumes and prevalences of infection in the cattle

Following confirmed cases of trypanosomiasis ('nagana') and reports of trypanosome-attributable deaths among local cattle, a cross-sectional study was undertaken to determine the prevalence of bovine infection with trypanosomes in south-western Uganda. Cattle from 10 different localities were checked by the microscopical examination of wet bloodsmears and thin, stained bloodsmears, and by blood centrifugation followed by the examination of the resultant buffy coats. Of the 1309 cattle investigated, 6.42% (5.56% and 7.26% of those from the Mbarara and Mubende districts, respectively) were found to be infected. Of the positive animals, 71 (84.5%), 11 (13.1%) and two (2.4%) appeared to be infected with Trypanosoma vivax only, T. congolense only and both T. vivax and T. congolense, respectively. The prevalence of infection with T. vivax was significantly higher than that with T. congolense (P<0.001). The mean packed-cell volumes (PCV) for the trypanosome-positive animals were lower than those for the trypanosome-negative, whether the cattle considered were all those investigated (22.3% v. 29.0%; P<0.001) or just those from the Mbarara (22.8% v. 28.2%) or Mubende (21.5% v. 29.7%) districts. South-western Uganda has been relatively free of both human and bovine trypanosomiasis for the past three decades. The factors leading to the current resurgence of bovine trypanosomiasis need further investigation.

Trypanocidal drug resistance in eastern province of Zambia

A survey to investigate resistance to drugs used in the treatment of bovine trypanosomosis was conducted in the eastern province of Zambia between 1996 and 1998. A cross-sectional study was conducted in three districts (Petauke, Katete, Lundazi) at 34 village sampling sites selected at random from villages that had shown greater than 6% prevalence of bovine trypanosomosis during an earlier survey. A longitudinal study was conducted in same three districts over a 1-year period. The study sites were chosen from the cross-sectional study and included eight sites showing high trypanosomosis prevalence and where no control activities were recorded. Use was made of parasitological methods, tests of resistance in cattle and mice and isometamidium-ELISA. Overall mean prevalence of trypanosomosis was 14.4, with 96% of infections caused by Trypanosoma congolense. The remainder was caused by Trypanosoma vivax (2%) and Trypanosoma brucei (2%). Tests in mice showed that of the stabilates collected, 24 (34%) were resistant to only isometamidium chloride, 8 (11.3%) were resistant to only diminazene aceturate, 1 (1.4%) was resistant to both drugs, and 38 (53.5%) were sensitive to both drugs. At least 2 out of 27 stabilates tested in cattle appeared to be resistant to trypanocidal drugs, 1 to isometamidium and 1 to diminazene. Isometamidium could be detected in only 63 (4.1%) of 1526 serum samples from cattle in the study. Only 6 (2.8%) of 212 serum samples from trypanosome-infected cattle had serum levels of the drug above 0.4 ng isometamidium per ml serum which is indicative for drug resistance in the infecting parasite population. Although some drug resistance is apparent, diminazene aceturate and isometamidium chloride can still be expected to be effective as a sanative pair in this area in most cases, since not more than 1 stabilate of 71 investigated showed evidence of resistance to both drugs.

PCR-RFLP using Ssu-rDNA amplification: applicability for the diagnosis of mixed infections with different trypanosome species in cattle

The use of a single restriction fragment length polymorphism (RFLP)-PCR assay which is able to characterise all important bovine trypanosome species was evaluated for the detection of mixed infections with Trypanosoma brucei brucei, Trypanosoma theileri, Trypanosoma congolense and Trypanosoma vivax. Results showed that mixed infections are detectable at a minimum ratio of 2%/98% of standardised DNA solutions with a concentration of 10 ng ml(-1). All mixed infections gave clear profiles that could be easily differentiated except with T. theileri and T. congolense where the T. theileri band was concealed by the T. congolense profile.

A comparative study on the clinical, parasitological and molecular diagnosis of bovine trypanosomosis in Uganda

The clinical, parasitological and molecular diagnosis of bovine trypanosomosis were compared using samples from 250 zebu cattle exposed to natural trypanosome challenge in Uganda. Clinical examination, molecular and parasitological diagnoses detected 184 (73.6%), 96 (38.4%) and 36 (14.4%) as diseased, respectively. The sensitivity and specificity of clinical examination were 87.5% and 35%, and 78 % and 27 % based on molecular and parasitological diagnoses, as gold standards, respectively. Of the 33, 3, 13 and 12 parasitological-positive cattle that had Trypanosoma brucei, Trypanosoma congolense, Trypanosoma vivax or mixed infections, 78 %, 33 %, 84 % and 100 % respectively manifested clinical signs. Of the 24, 89, 12, 3, 6 and 27 cattle detected by molecular diagnosis to have mixed infections, T. brucei, T. vivax, T. congolense forest-, Savannah- and Tsavo-type, 100%, 83%, 91%, 100%, 67% and 81 % had clinical signs, respectively. In conclusion, treatment of cattle based on clinical examination may clear up to 87.5 % or 78 % of the cases that would be positive by either molecular or parasitological diagnosis, respectively. Under field conditions, in the absence of simple and portable diagnostic tools or access to laboratory facilities, veterinarians could rely on clinical diagnosis to screen and treat cases of bovine trypanosomosis presented by farmers before confirmatory diagnosis in diagnostic centres for few unclear cases is sought.

Susceptibility of heat shock protein 70.1-deficient C57BL/6 J, wild-type C57BL/6 J and A/J mice to Trypanosoma congolense infection

The heat shock protein (HSP) 70.1 gene lies on mouse chromosome 17 among the candidates for Tir1, the major quantitative trait locus associated with response to Trypanosoma congolense infection. To evaluate whether the HSP70.1 gene is involved in the response, we compared the susceptibility of HSP70.1-deficient C57BL/6 J, resistant wild-type C57BL/6 J and susceptible A/J mice. No differences were observed between HSP70.1-deficient and wild-type C57BL/6 J mice in survival time, levels of parasitemia and anemia, suggesting that there is no involvement of the HSP70.1 gene in control of T. congolense infection. The course of infection was markedly different between A/J and C57BL/6 J mice. A/J mice showed a bi-phasic survival pattern, which seemed to be associated with two waves of high parasitemia, but developed only moderate anemia. C57BL/6 J mice controlled parasitemia well but developed severe anemia in the late stage of infection.

Identification of trypanosomes in wild animals from southern Cameroon using the polymerase chain reaction (PCR)

One possible explanation of the maintenance of many historical foci of sleeping sickness in Central Africa could be the existence of a wild animal reservoir. In this study, PCR was used to detect the different trypanosome species present in wild animal captured by hunters in the southern forest belt of Cameroon (Bipindi). Trypanosomes were also detected by a parasitological method (Quantitative buffy coat: QBC). Parasite could not be isolated in culture medium (Kit for in vitro isolation: KIVI). Specific primers of T. brucei s.l., T. congolense forest type, T. congolense savannah type, T. vivax, T. simiae and T. b. gambiense group 1 were used to identify parasites in the blood of 164 animals belonging to 24 different species including ungulates, rodents, pangolins, carnivores, reptiles and primates. Of the 24 studied species, eight were carrying T. b. gambiense group 1. Those parasites pathogenic to man were found in monkeys (Cercocebus torquatus and Cercopithecus nictitans), in ungulates (Cephalophus dorsalis and C. monticola), in carnivores (Nandinia binotata and Genetta servalina) and in rodents (Cricetomys gambianus and Atherurus africanus). 13 species (54%) were carrying T. brucei s.l. identified as non-gambiense group 1.

Parasitological prevalence of bovine trypanosomosis in Kindo Koisha district, Wollaita zone, south Ethiopia

A cross sectional survey to determine the distribution and prevalence of trypanosomosis was conducted in Kindo Koisha district, in the Wollaita zone in southern Ethiopia. A total of 1 008 adult cattle was examined at eight different localities. Dark field examination of the buffy coat, as well as stained thin blood film examination and packed cell volume (PCV) evaluation were the diagnostic techniques used. The overall prevalence of bovine trypanosomosis was 15 %. Among the positive animals, 108 (71.1%), 43 (28.4%) and 1 (0.6%) were due to Trypanosoma vivax, Trypanosoma congolense and mixed infection (T. vivax and T. congolense), respectively. The infection rate of T. vivax and T. congolense varied significantly (P < 0.01). The mean PCV of the positive and negative animals ranged between 18.3-32.1% and 26.8-33.4%, respectively. The mean PCV of negative animals (28 %) was significantly higher than the mean PCV of positive animals (22.3%) (P < 0.001). There was an inverse association of PCV with the prevalence of trypanosomosis (P > 0.05). The herd average PCV values of each site decreased with increasing proportion of the positive herds of that particular site. Of the diagnostic tests employed, the microhaematocrit buffy coat technique is relatively sensitive and it has an added advantage of indicating the general condition of the animal by haematocrit measurement. In view of the risk of trypanosomosis, a control intervention through the strategic application of appropriate trypanocidal drugs is recommended. A tsetse fly control scheme to reduce host-tsetse fly contact is equally as important as chemotherapy and chemoprophylaxis against trypanosomosis.

The incidence of new and the prevalence and persistence of recurrent trypanosome infections in cattle in southwest Ethiopia exposed to a high challenge with drug-resistant parasites

A method is described for calculating new infection incidence from monthly field data collected between April 1994 and February 1998 from an average of 770 Ethiopian Highland Zebu cattle maintained under traditional management in the Ghibe valley, southwest Ethiopia and exposed to a high challenge with drug-resistant parasites. Each month cattle with a packed cell volume (PCV)<26% and detected as parasitaemic, or cattle showing clinical signs of trypanosomosis, were treated with diminazene aceturate at 3.5 mg/kg body weight. An infection was defined as a new infection if it was preceded by 2 previous months in which both samples had a PCV>/=26% and were not detected with trypanosomes. Using this definition the average monthly incidence of infections of Trypanosoma congolense in cattle over 36 months of age was 13.3%, and the prevalence of recurrent infections 13.0%. Assuming that an animal had recovered from infection when PCV again returned to 26% without parasites being detected, mean persistence of infection was 3.8 months (median between 2 and 3 months). In contrast, T. vivax infections were susceptible to diminazene. The incidence of T. vivax infections in adults was lower than for T. congolense (2.8%), and they were less pathogenic (mean reduction of 3.1% units of PCV due to T. vivax infection compared with 4.6% units for T. congolense). Also, fewer cases were treated. Calves were first detected parasitaemic at an average age of 8.8 months and their infections persisted longer than those in adults. The effect of age on incidence of infection was not significant beyond 15 months of age. Adult male cattle appeared to be more susceptible to T. congolense infection than adult female cattle.

The analysis of the cross-reactions occurring in antibody-ELISA for the detection of trypanosomes can improve identification of the parasite species involved

In Africa, the main pathogenic trypanosomes of livestock are Trypanosoma vivax, T. congolense and T. brucei. The geographical distributions and hosts of these three species are very similar. As they differ markedly in pathogenicity and epidemiology, however, a species-specific serological test for infection would be very useful for epidemiological studies. The antibody-ELISA (Ab-ELISA) that have been developed for detecting the Trypanosoma spp. most commonly infecting livestock give satisfactory sensitivity and genus specificity. Unfortunately, they are not species-specific because of strong cross-reactions between the pathogenic Trypanosoma spp. In the present study, carried out in Burkina Faso, the results of standardized Ab-ELISA for T. vivax, T. brucei or T. congolense were compared using 1288 plasma samples from sheep experimentally infected with T. vivax, T. evansi and/or T. congolense. If the results were interpreted, as usual, only using a positivity threshold (PT), the strong cross-reactions observed led to a mean species-specificity of < 30%. However, analysis of the reactions observed in the three types of Ab-ELISA revealed that the homologous reactions were stronger than the heterologous for almost all of the single and mixed infections (98.3% and 99.0%, respectively). In monospecific infections exceeding the PT study of the positivity score produced in each of the three types of Ab-ELISA increased species-specificity to > 96%. It therefore appears that comparison of the strengths of the reactions seen in Ab-ELISA could greatly improve sero-epidemiological surveys of trypanosome infections in domestic ruminants, although the technique remains to be evaluated in experimentally infected cattle.

The relationship between the parasitological prevalence of trypanosomal infections in cattle and herd average packed cell volume

The relationship between prevalence of trypanosomal infections (Trypanosoma congolense) and average packed cell volume (PCV) in herds of communally managed adult Angoni breed cattle was investigated in four districts of eastern Zambia. In all areas, regression analyses showed that the herd average PCV decreased with increasing prevalence of trypanosomal infections. The slope of the equation between average PCV and trypanosome prevalence decreased with increasing prevalence of trypanosomal infections. For the same increase in prevalence of trypanosomal infection, the decrease in herd PCV was higher in the areas with low to medium prevalence. Season of sampling also determined the slope of the regression equation. For the same increase in prevalence of trypanosomal infection, the decrease in herd PCV was higher during the dry compared to the rainy season suggesting that trypanosomosis is less well tolerated during the dry season. Results from the study suggest that the relationship between the prevalence of trypanosomal infections and herd average PCV could be a useful tool in the management of trypanosomosis and planning of its control. Reasons for the spatial and temporal variations in the relationship are discussed.

Application of PCR and DNA probes in the characterisation of trypanosomes in the blood of cattle in farms in Morogoro, Tanzania

Polymerase chain reaction (PCR) and deoxyribonucleic acid (DNA) probes were used to characterise trypanosomes from cattle in Morogoro region of Tanzania. Blood samples collected from 390 beef and dairy cattle in selected farms in Morogoro region were examined for presence of trypanosomes using the buffy coat technique (BCT) and blood smears (BSs). Fifty-two animals were found infected: 40 with Trypanosoma congolense, 10 with T. vivax and two with both T. congolense and T. vivax. DNA extracted from all the parasitologically positive and 62 randomly selected parasitologically negative samples were subjected to PCR amplification using primers specific for different trypanosome species. Using a set of seven specific-pairs of primers on the parasitologically positive samples, we detected only T. congolense, either the Savannah- or the Kilifi-type, as single or mixed infections. With the PCR, trypanosome DNA could be detected in 27 (43%) out of 62 samples that were parasitologically negative. DNA hybridisation using probes specific for Savannah- or Kilifi-types T. congolense, or T. vivax, confirmed the presence of these parasites in cattle kept on some farms in Morogoro region of Tanzania. From these studies, it is clear that there is a need to undertake molecular epidemiological studies to determine the distribution of trypanosome species and subspecies, and to assess the economic impact of these parasites in the productivity of livestock in Tanzania. In particular, it would be desirable to verify the assumed association between the different presentations of trypanosomosis on one hand and genotypes of T. congolense on the other.

Control of Glossina longipennis (Diptera: Glossinidae) by insecticide-treated targets at Galana ranch, Kenya, and confirmation of the role of G. longipennis as a vector of cattle trypanosomiasis

Glossina longipennis Corti was studied in Galana Ranch, Kenya over a four year period, in two areas (Tank E and Lali) where the species was abundant and other species were absent or scarce. There was active transmission of trypanosomiasis to cattle in both areas, the parasite species being Trypanosoma vivax Ziemann and T. congolense Broden. Mean infection rates of the G. longipennis were 1.1% and 0. 55% for T. vivax and T. congolense respectively at Tank E, and 0.88% and 0.15% at Lali. Experimental transmission studies showed that cattle in fly-proof enclosures challenged with wild G. longipennis collected from Galana became infected with both trypanosome species. A tsetse control operation in one area (Tank E) using targets impregnated with deltamethrin in an oil formulation reduced the population of G. longipennis by 98% over one year, despite evidence of re-invasion. Populations of G. longipennis in the other area (Lali) were relatively stable over the whole study period. The effect of tsetse control on the incidence of cattle trypanosomiasis at Tank E was less clear than that on tsetse numbers, probably due to the lack of a sustained reduction in tsetse numbers. However, a significant relationship was demonstrated between fortnightly incidence measurements and electric net catches of G. longipennis at Tank E. A further significant predictor of incidence was rainfall in the previous four to seven weeks. This study confirms the importance of G. longipennis as a vector of bovine trypanosomiasis in areas where it is the predominant tsetse present.

Polymerase chain reaction as a diagnosis tool for detecting trypanosomes in naturally infected cattle in Burkina Faso

African animal trypanosomoses constitute the most important vector-borne cattle diseases in sub-Saharan Africa. Generally it is considered that there is a great lack of accurate tools for the diagnosis of the disease. During a trypanosomosis survey in the agro-pastoral zone of Sideradougou, Burkina Faso, 1036 cattle were examined for trypanosomes using microscopy. The PCR was applied on a subset of 260 buffy-coat samples using primers specific for Trypanosoma congolense savannah and riverine-forest groups, T. vivax, and T. brucei. Parasitological examination and the molecular technique were compared, showing a better efficiency of the latter. In the near future, the PCR is likely to become an efficient tool to estimate the prevalence of African trypanosomoses in affected areas.

Pitfalls in the application of enzyme-linked immunoassays for the detection of circulating trypanosomal antigens in serum samples

The experimental infection of two goats with Trypanosoma vivax trypanosomes provided samples for analysis using parasitology techniques and antigen-detection enzyme-linked immunosorbent assays (ELISAs) for T. vivax, T. congolense and T. brucei. Clinical, parasitological and serological findings were monitored during the course of infection to identify problems in the application of these ELISAs. The data clearly showed that the ELISAs examined were entirely unsuitable for the reliable detection of trypanosomal antigen. Consequently, research strategies pertinent to the development of a new generation of both antigen and antibody ELISAs are outlined considering the problems encountered. These were (1) the reactivity of the reagents; (2) the specificity of the reagents; (3) the nature of the test sample, e.g. the compartmentalisation of trypanosomes between plasma, serum and red blood cells; (4) possible interference with the ELISA through immune complexing; and (5) the biology of the host/trypanosome relationship to gain an understanding of fluctuations in trypanosomes in the systemic circulation.

The parasitological and serological prevalence of tsetse-transmitted bovine trypanosomosis in the Eastern Caprivi (Caprivi District, Namibia)

Between August 1995 and June 1997 a survey to determine the distribution of tsetse-transmitted trypanosomosis was conducted in the Eastern Caprivi (Caprivi District, Namibia). A total of 1,481 adult cattle was examined at 33 sampling sites. Direct parasitological diagnostic tests were used and eluted blood spots were screened for the presence of anti-trypanosomal antibodies. Tsetse-transmitted trypanosomal infections were detected in 66 animals (4.5%) from 14 different locations. The parasitological and serological prevalence of trypanosomosis was highest in the Mamili area. Trypanosomosis was virtually absent in the Linyanti/Chobe area and the target barrier along the Kwando River had significantly reduced the prevalence of trypanosomosis in cattle grazing to the east of it. This suggests that anti-trypanosomal antibody prevalence data can be used to evaluate and monitor the effectiveness of tsetse control measures. Survey results suggest that in the Katima Mulilo area, trypanosomal infections were being acquired when cattle grazed along the Zambezi River. Moreover, survey results indicate that tsetse have not been able to establish themselves in the Katima Mulilo area. The parasitological prevalence in a herd and the respective prevalence of anti-trypanosomal antibodies was significantly correlated to the percentage of anaemic animals in that herd. Furthermore, the parasitological prevalence in a herd was positively correlated with the prevalence of anti-trypanosomal antibodies of that herd. It is concluded that the prevalence of anti-trypanosomal antibodies in a herd can be used as an additional indicator of the extent of infection in that particular herd.

Aggregation and distribution of strains in microparasites

Recent research has shown that many parasite populations are made up of a number of epidemiologically distinct strains or genotypes. The implications of strain structure or genetic diversity for parasite population dynamics are still uncertain, partly because there is no coherent framework for the interpretation of field data. Here, we present an analysis of four published data sets for vector-borne microparasite infections where strains or genotypes have been distinguished: serotypes of African horse sickness (AHS) in zebra; types of Nannomonas trypanosomes in tsetse flies; parasite-induced erythrocyte surface antigen (PIESA) based isolates of Plasmodium falciparum malaria in humans, and the merozoite surface protein 2 gene (MSP-2) alleles of P. falciparum in humans and in anopheline mosquitoes. For each data set we consider the distribution of strains or types among hosts and any pairwise associations between strains or types. Where host age data are available we also compare age-prevalence relationships and estimates of the force of infection. Multiple infections of hosts are common and for most data sets infections have an aggregated distribution among hosts with a tendency towards positive associations between certain strains or types. These patterns could result from interactions (facilitation) between strains or types, or they could reflect patterns of contact between hosts and vectors. We use a mathematical model to illustrate the impact of host-vector contact patterns, finding that even if contact is random there may still be significant aggregation in parasite distributions. This effect is enhanced if there is non-random contact or other heterogeneities between hosts, vectors or parasites. In practice, different strains or types also have different forces of infection. We anticipate that aggregated distributions and positive associations between microparasite strains or types will be extremely common.

[Effect of the intensity of host parasitemia on the vectorial competence of Glossina morsitans Westwood, 1850 (Mall) infected by Trypanosoma (Nannonmonas) congolense IL 1180]

Two groups of teneral flies (aged less than 32 hours) of Glossina morsitans morsitans (Mall) were fed separately on two rats that had been infected with Trypanosoma (Nannomonas) congolense IL 1180, among which one had a low parasitaemia (antilog 5.4-5.7) and the other a high parasitaemia (antilog 7.8-8.1). Following to the two modes of parasitaemia, variations of the procyclic indexes were found between males and females. When both sexes were considered, it was found that the intestinal infection rate was relatively higher in the flies that were fed on the rat with a low parasitaemia than in those fed on the rat with a high parasitaemia. Although no significant differences in metacyclic indexes were observed between sexes, the mature infection rate was most pronounced in the flies that were fed on the rat with high parasitaemia. When both sexes were considered, the vectorial competence (VC) reached 0.5532 and 0.5521 in the flies that had been fed on the rats with low and high parasitaemia, respectively. The VC of the two modes of infectious feeding was not significantly different. However, when considering the parasitaemia of antilog 5.4-5.7, the VC was relatively more important in the females than in the males. No significant difference in VC was detected between sexes when considering the antilog 7.8-8.1 parasitaemia. It was found that there is discrepancy in the way the metacyclic infection and the VC evolve in relation to the procyclic infection, suggesting that the intensity of the parasitaemia only influences the intestinal stage.

Trypanosome infection rate in cattle at Nguruman, Kenya

Trypanosome infection rate in cattle at Nguruman was investigated in a study conducted in 1984-1986. Shifting pastoralism significantly reduced trypanosome infections in cattle. The cattle were more heavily infected with Trypanosoma congolense (16.5%) than Trypanosoma vivax (4.95%) and Trypanosoma brucei (0.19%). Trypanosoma theileri was observed only once among the cattle examined. Mixed trypanosome infections in cattle were observed to be 2.75% and 0.014% for T. congolense/T. vivax and T. congolense/T. brucei, respectively. The duration of infection in the cattle was 55 days for T. congolense and 79 days for T. vivax. High infections in cattle were observed 2 months after the rains, which were concomitant with high tsetse densities.

Detection and identification of trypanosomes by polymerase chain reaction in wild tsetse flies in Cameroon

The prevalence of various species and subgroups of trypanosomes in infected flies from three sleeping sickness foci in Cameroon was determined by the use of polymerase chain reaction (PCR). The predominant tsetse species found were Glossina palpalis palpalis. Microscopical examination of 943 non-teneral tsetse flies revealed an average infection rate of 10.4%. A total of 90 flies were analyzed for trypanosome identification with primer sets specific for Trypanosoma (Trypanozoon) brucei s.l., T. (Duttonella) vitax, T. (Nannomonas) simiae, and forest type T. (Nannomonas) congolense. PCR succeeded in identifying 52 of the 90 infected flies. Other primers were also tested on microscope positive/PCR-negative infections, and trypanosome subgroups were detected (Kilifi type and savannah type T. congolense). PCR amplification allowed identification of immature infections and revealed mixed-infections. The PCR technique failed to identify 42.2% (38/90) of the parasitologically positive flies and the reasons for this failure are discussed.

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.

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.