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.

A Gambian infant with fever and an unexpected blood film

The authors describe the differential diagnosis, investigation, and management of a two-month-old infant with edema, malnutrition, and fever.

Glossina fuscipes fuscipes in the trypanosomiasis endemic areas of south eastern Uganda: apparent density, trypanosome infection rates and host feeding preferences

A study was undertaken in three districts in south eastern Uganda endemic for human and animal trypanosomiasis, to investigate the status of the vector tsetse fly population. Apparent density (AD) of tsetse was between 2 and 21 flies/trap/day across the three districts, with Glossinia fuscipes fuscipes identified as the predominant species. Trypanosomes were observed in G.f. fuscipes with an infection rate, as determined by microscopy, of 1.55% across the three studied areas. However, trypanosome infections were only identified in female flies giving an infection rate of 2.39% for the female tsetse when this sex was considered in isolation; no male flies were found to be infected. Bloodmeal analysis highlighted 3 principal vertebrate hosts, namely cattle, pigs and monitor lizards (Varanus niloticus). The implication of this, in relation to the cycle of transmission for human infective trypanosomes between domestic animals and man, is discussed.

Detection of trypanosome-specific antibodies in saliva, towards non-invasive serological diagnosis of sleeping sickness

OBJECTIVE

The detection of trypanosome-specific antibodies in saliva is technically feasible, and, if clinically validated, could become an attractive option for non-invasive diagnosis of sleeping sickness. We wanted to optimize the test format of an enzyme-linked immunosorbent assay (ELISA)-based antibody detection system.

METHODS

Different ELISA formats for antibody detection in serum and saliva were developed and standardized. Saliva and serum samples were collected from 78 patient and 128 endemic control samples, and sensitivity and specificity of saliva ELISAs, serum ELISAs and the card agglutination test for trypanosomiasis (CATT), were evaluated.

RESULTS

All ELISA formats showed sensitivity and specificity above 90%. Saliva ELISAs showed a similar test performance as serum ELISAs and the CATT on whole blood or serum.

CONCLUSIONS

This study confirms the potential of trypanosome-specific antibody detection in saliva.

Comparison of cytokine plasma levels in human African trypanosomiasis

BACKGROUND

Immunological studies suggest that human African trypanosomiasis (HAT) is associated with inflammatory responses. A better understanding of the complex cytokine interactions regulating HAT infections is essential to elucidate the mechanisms of generalized immunosuppression.

METHOD

We determined levels of interleukin (IL)-2, IL-4, IL-6, IL-10, tumour necrosis factor (TNF)-alpha and interferon (IFN)-gamma protein levels in plasma samples from three groups of individuals from the Democratic Republic of Congo: (i) HAT cases; (ii) seropositive individuals for whom parasite detection was negative and (ii) controls.

RESULTS

Plasma levels of six cytokines were significantly higher in HAT cases than in both controls (P<0.003) and seropositive individuals (P<0.016). IL-2 and IL-10 concentrations were significantly lower (P<0.02) in the seropositive group than in the control one.

CONCLUSION

Human African trypanosomiasis leads to the development of strong cytokine responses, indicating the potential involvement of IL-2 and IL-10 in the phenomenon of seropositivity without parasitological confirmation. This strongly suggests the involvement of immunity in this particular aspect of HAT epidemiology.

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 vervet monkey (Chlorocebus aethiops) as an experimental model for Trypanosoma brucei gambiense human African trypanosomiasis: a clinical, biological and pathological study

It has long been known that the vervet monkey, Chlorocebus (C.) aethiops, can be infected with Trypanosoma rhodesiense, but this model has not been described for T. gambiense. In this study, we report the development of such a model for human African trypanosomiasis. Twelve vervet monkeys infected with T. gambiense developed chronic disease. The duration of the disease ranged between 23 and 612 days (median 89 days) in five untreated animals. Trypanosomes were detected in the blood within the first 10 days post-infection and in the cerebrospinal fluid, with a median delay of 120 days (n = 4, range 28-348 days). Clinical changes included loss of weight, adenopathy, and in some cases eyelid oedema and lethargy. Haematological alterations included decreases in haemoglobin level and transitory decreases in platelet count. Biological modifications included increased gamma globulins and total proteins and decreased albumin. Pathological features of the infection were presence of Mott's cells, inflammatory infiltration of either mononuclear cells or lymphocytes and plasma cells in the brain parenchyma, and astrocytosis. These observations indicate that the development of the disease in vervet monkeys is similar to human T. gambiense infection. We conclude that C. aethiops is a promising experimental primate model for the study of T. gambiense trypanosomiasis.

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.

Intrathecal cytokine responses in Trypanosoma brucei rhodesiense sleeping sickness patients

Intrathecal cytokine levels and blood-cerebrospinal fluid (CSF) barrier function were studied in 91 Trypanosoma brucei rhodesiense-infected patients. The CSF concentration of the cellular immune activation marker neopterin and the cytokines IL-6 and IL-10 were increased over control and post-treatment levels in all patients, with maximal levels observed in late-stage (meningoencephalitic) individuals. Analysis of CSF/serum concentration quotients indicated that IL-10 and neopterin were derived from central nervous system synthesis in at least 25% of the patients. Blood-CSF barrier dysfunction occurred in 64% of late-stage patients but not in early-stage patients. While the high level of neopterin observed in the late-stage patient CSF is indicative of widespread cellular activation, the increased levels of IL-6 and IL-10 suggest that counter-inflammatory cellular responses may be important in the regulation of neuropathogenesis in late-stage human African trypanosomiasis.

Susceptibility of Grammomys surdaster thicket rats to Trypanosoma brucei gambiense infection

Human African Trypanosomiasis is caused by Trypanosoma brucei gambiense and T. b. rhodesiense. Historically, a treatment relapse rate of about 5% is observed in patients treated with melarsoprol, an arsenical derivative used for treatment of both gambiense and rhodesiense second stage sleeping sickness. More recently, relapse rates up to 30% are noted in gambiense sleeping sickness foci in Angola, Sudan and Uganda. Therefore, WHO established a Network on Treatment Failure and Drug Resistance in Sleeping Sickness. One of its objectives is to improve isolation of T. b. gambiense from relapsing cases for research on drug resistance mechanisms. Trypanosoma b. gambiense isolation techniques suffer from low success rates and long periods needed to adapt the parasite to its new host. Usually, rodents are inoculated with patient's blood or cerebrospinal fluid and sub-passaged until the strain becomes sufficiently adapted to yield high parasitaemia within few days after inoculation. Until now, the best recipient for T. b. gambiense is Mastomys natalensis, with a success rate of about 50%. In this study, Grammomys surdaster (former Thamnomys surdaster) was investigated as a potential recipient for isolation of T. b. gambiense. Comparative experimental infections of Swiss mice, Wistar rats and G. surdaster thicket rats with T. b. gambiense clearly show that this trypanosome grows faster in G. surdaster. Inoculation of the same rodent species with patient's blood and cerebrospinal fluid in Kinshasa (R.D. Congo) confirms the observation that the thicket rats are more susceptible to T. b. gambiense infection than typical laboratory rodents.

Influence of an experimental Trypanosoma congolense infection and plane of nutrition on milk production and some biochemical parameters in West African Dwarf goats

The interactions of trypanosomosis and plane of nutrition on health and productivity of multiparous and primiparous West African Dwarf (WAD) does were studied in a multi-factorial experiment including diet (supplementation or basal diet) and infection (infected or control). Experimental does were infected with Trypanosoma congolense at the beginning of the second week post-kidding and monitored for 16 weeks after infection. Trypanosome infection significantly reduced packed cell volume (PCV) (control: 30.1+/-0.3% versus infected: 22.2+/-0.3%; P<0.0001). Regardless of infection, the drop in PCV from the pre-infection period to the end of the experiment was more severe in animals under restricted diet (interaction dietxperiod, P<0.001). Trypanosome parasitaemia tended to be higher in the supplemented group than in the basal diet group (P>0.05) and multiparous animals had a higher parasitaemia (score: 2.6+/-0.1) than primiparous animals (score: 2.2+/-0.1) (P<0.05). Trypanosome infection as well as dietary supplement had a significant effect on lactation length. Milk off-take from trypanosome-infected does was significantly lower than that from the uninfected control group (17.5+/-3.2l versus 35.5+/-3.2l, P<0.001) and there was a positive effect of plane of nutrition (supplemented: 32.8+/-3.2l and basal diet: 20.2+/-3.5l, P=0.01). The drop in milk off-take due to trypanosome infection was more severe in the supplemented group (control: 46.7+/-4.7l versus infected: 18.9+/-4.2l) than in the group receiving a basal diet (control: 24.2+/-5.0l versus infected: 16.1+/-4.7l) (interaction infectionxdiet, P=0.04) due to the number of does from the supplemented group that were withdrawn from the experiment. The effect of trypanosome infection on doe's live-weight was only noticeable during the first 8 weeks of lactation and there was no significant effect on offspring growth rate unless the mother died. Plasma total protein (TP), albumin and cholesterol concentrations were significantly reduced by the infection but were significantly increased by supplementation. Supplemented does had a higher level of cholesterol and a tendency for a higher parasitaemia. Does of high parity also had a higher cholesterol level than primiparous does and, based on the number of animals that were withdrawn from the experiment, they showed a lower resistance to the infection.

Experimental trypanosomiasis in Yankasa ewes: the body weight response

Sleeping sickness (African Trypanosomasis) is an anthropozoonosis transmitted primarily by the tsetse fly. It is associated with a host of clinical indices ranging from fever, aneamia and anorexia to reproductive failures in man and his domestic animals. The main objective of this study is to appraise the responsiveness of the body weight as a clinical indicator of sleeping sickness in experimentally infected Yankasa ewes. Twelve mature Yankasa sheep (6 infected and 6 control ewes) were used in this study. Weekly body weights and daily rectal temperature were taken while blood samples for haematology were collected twice a week from all animals before and after the experimental infection. Undulating parasitaemia was observed, two days post infection and was sustained through out the study period of about fifty days in all the infected ewes. Decreased body weight was found to be very prominent in the infected animals. All the infected ewes progressively lost weight during the experiment with a decrease of about 17.9% of the original weights while the control ewes had increased by 4.2% at the end of the study period. The body weight is therefore a very sensitive parameter in the surveillance and management of Trypanosome infections especially in Yankasa ewes as experimental animal models.

Effects of an experimental Trypanosoma congolense infection on the reproductive performance of West African Dwarf goats

Thirty-six West African Dwarf (WAD) goats were used to assess the effects of an experimental Trypanosoma congolense infection on their reproductive system. Estrous cycles were synchronised and when confirmed pregnant (n = 31), the does were randomly allocated into control and trypanosome-infected groups. After infection, the animals were carefully observed till parturition. Trypanosome infection caused an increase of rectal temperature, a significant drop in PCV (infected: 23.3 +/- 0.3%; control: 28.5 +/- 0.4%; P < 0.0001) and abortions in 27.8% of the infected does. Kids born from infected does had a lower birth weight than kids born from control goats (0.9 +/- 0.1 kg versus 1.6 +/- 0.1 kg; P < 0.0001). Eight out of 13 kids (61.5%) that were born alive from infected does died during their first week of life. Plasma pregnancy-associated glycoprotein (PAG) and progesterone concentrations were lower in the infected animals than in the controls. In general, PAG concentration in does which aborted dropped before abortion. Our results revealed that artificial T. congolense infection affected reproductive performance of WAD goats with abortions, premature births and perinatal losses being observed. Neither transplacental transmission of T. congolense nor histopathological lesions of the placenta could be demonstrated.

Plasma kinetics and efficacy of oral megazol treatment in Trypanosoma brucei brucei-infected sheep

Experimentally infected sheep have been previously developed as an animal model of trypanosomosis. We used this model to test the efficacy of megazol on eleven Trypanosoma brucei brucei-infected sheep. When parasites were found in blood on day 11 post-infection, megazol was orally administered at a single dose of 40 or 80mg/kg. After a transient aparasitaemic period, all animals except two relapsed starting at day 2 post-treatment, which were considerated as cured on day 150 post-treatment and showed no relapse after a follow-up period of 270 days. In order to understand the high failure of megazol treatment to cure animals, a kinetic study was carried out. Plasma concentrations of megazol determined, by reverse-phase high-performance liquid chromatography at 8h post-treatment in these animals, were lowered, suggesting slow megazol absorption, except in cured animals. However, megazol plasma profiles in uninfected sheep after a single oral dose of megazol showed a fast megazol lowered absorption associated with a short plasma half-life of drug. Inter-individual variation of megazol pharmacokinetic properties was also observed. These findings suggested that the high failure rates of megazol treatment were related to poor drug availability after oral administration in sheep. In conclusion, megazol could cure sheep with T. b. brucei infection but oral administration was not an effective route.

Recirculation of Trypanosoma brucei brucei in cattle after T. congolense challenge by tsetse flies

The effect of challenging cattle, chronically infected with Trypanosoma brucei brucei, with T. congolense on the development of the T. b. brucei infection was investigated. For this purpose, nine experimental animals were first infected with T. b. brucei through the bites of infected tsetse flies. Once the T. b. brucei had developed into a chronic infection, that was difficult to detect using routine parasitological diagnostic tools, seven of the experimental animals were challenged by tsetse flies infected with T. congolense. Two of the animals infected with T. b. brucei were kept as control. The infection with T. congolense resulted in a sudden increase in the parasitaemia of T. b. brucei. In the T. b. brucei control animals, on the other hand, the parasitaemia remained below the level of detection. The epidemiological repercussions of this increase in the parasitaemia of T. b. brucei after infection with T. congolense are discussed.

Prevalence of Trypanosoma evansi infection and associated risk factors in camels in eastern Chad

A cross-sectional study was conducted to estimate the prevalence of Trypanosoma evansi infection (Surra) in herds of camels from the eastern area of Chad. The risk factors associated with disease were also identified. From August 1997 to April 1998, a random sample of 2831 camels from 136 herds was selected. Blood samples were collected and examined for the presence of T. evansi using an antibody (card agglutination test-CATT/T. evansi) and a parasite detection test (buffy-coat technique-BCT). Standardized questionnaires with information about the host and management practices were collected and evaluated for their association with seroprevalence (model 1) and parasitological prevalence (model 2) as indications of host sensitivity. In both models, risk factors were selected using ordinary logistic regression (OLR) and herd effect was evaluated using a generalized estimating equations (GEE) model. The apparent prevalence was 5.3% using BCT and 30.5% with CATT. Real prevalence was estimated at 16.9% +/- 1.4 (alpha = 5%). Overall, 27.9% (BCT) and 94.9% (CATT) of the herds had a least one-positive animal. Real herd prevalence was estimated at 42.6 +/- 8.3% (alpha = 5%). Camels of the large transhumants had the highest prevalence (estimated to 30.3% +/- 2.5; 62.9 +/- 12.0 in herds). Risk factors associated with seroprevalence were age, ethnic group, length of seasonal migration and longitude of pasture area in the dry season. Risk factors associated with BCT prevalence were age, length of seasonal migration, longitude of pasture area in the dry season, latitude of pasture area in the rainy season and season of sampling.

Trypanosoma brucei gambiense trypanosomiasis in Terego county, northern Uganda, 1996: a lot quality assurance sampling survey

We estimated the pre-intervention prevalence of Trypanosoma brucei gambiense (Tbg) trypanosomiasis using the lot quality assurance sampling (LQAS) methods in 14 parishes of Terego County in northern Uganda. A total of 826 participants were included in the survey sample in 1996. The prevalence of laboratory confirmed Tbg trypanosomiasis adjusted for parish population sizes was 2.2% (95% confidence interval =1.1-3.2). This estimate was consistent with the 1.1% period prevalence calculated on the basis of cases identified through passive and active screening in 1996-1999. Ranking of parishes in four categories according to LQAS analysis of the 1996 survey predicted the prevalences observed during the first round of active screening in the population in 1997-1998 (P < 0.0001, by chi-square test). Overall prevalence and ranking of parishes obtained with LQAS were validated by the results of the population screening, suggesting that these survey methods may be useful in the pre-intervention phase of sleeping sickness control programs.

The challenge of Trypanosoma brucei gambiense sleeping sickness diagnosis outside Africa

Sleeping sickness is a lethal African disease caused by parasites of the Trypanosoma brucei subspecies, which is transmitted by tsetse flies. Occasionally, patients are reported outside Africa. Diagnosis of such imported cases can be problematic when the infection is due to Trypanosoma brucei gambiense, the chronic form of sleeping sickness found in west and central Africa. The low number of trypanosomes in the blood and the non-specific, variable symptoms make the diagnosis difficult, particularly when the index of suspicion is low. When the trypanosomes have penetrated into the central nervous system, neuropathological signs become apparent but even at this stage, misdiagnosis is frequent. Rapid and correct diagnosis of sleeping sickness can avoid inappropriate or delayed treatment and even death of the patient. In this article, an overview on diagnosis of imported cases of T b gambiense sleeping sickness is given, and possible pitfalls in the diagnostic process are highlighted. Bioclinical parameters that should raise the suspicion of sleeping sickness in a patient who has been in west or central Africa are discussed. Techniques for diagnosis are reviewed. A clinician suspecting sleeping sickness should contact a national reference centre for tropical medicine in his or her country, or the WHO, Geneva, Switzerland, or the Centers for Disease Control and Prevention (CDC), Atlanta, GA, USA, for clinical consultation and provision of specific diagnostic tests. Appropriate drugs for sleeping sickness treatment are also provided by WHO and the CDC.

The efficacy of ascofuranone in a consecutive treatment on Trypanosoma brucei brucei in mice

Consecutive administration of ascofuranone without glycerol was found to have therapeutic efficacy against Trypanosoma brucei brucei infection in mice. A suspension of ascofuranone (25-100 mg/kg) was administrated intraperitoneally every 24 h for 1-4 consecutive days to trypanosome-infected mice and efficacy was compared with oral treatment. With intraperitoneal administration, all mice treated with 100 mg/kg ascofuranone for 4 consecutive days were cured. On contrary, with oral treatment a higher dose of ascofuranone (400 mg/kg) was needed for 8 consecutive days to cure the mice. With intraperitoneal treatment, parasitemia was strongly suppressed, with almost all long slender bloodstream forms of the parasite changed to short stumpy forms by day 3 and the parasites have been eliminated 4 days after the start of treatment. These ascofuranone-induced short stumpy forms were morphologically analogous to the stumpy forms 2 days after peak parasitemia of pleomorphic clone of T. b. brucei GUTat 3.1. However, the properties of ubiquinol oxidase activity, which is the target of ascofuranone, in mitochondria isolated from before and after treatment, were almost same. The enzymatic activities of ubiquinol oxidase were only decreased to approximately 30% within a day after treatment, and then kept at nearly the same level. In the present study, we have improved regimen for administration of ascofuranone without glycerol, and demonstrated that consecutively administrated ascofuranone showed trypanocidal effects in T. b. brucei infected mice. Our present results strongly suggest that consecutive administration of ascofuranone may be an effective chemotherapy for African trypanosomiasis.

A bloodstream Trypanosoma congolense sialidase could be involved in anemia during experimental trypanosomiasis

The release of Sialic acid (SA) into the serum by Trypanosoma congolense infected BalbC mice was investigated. A progressive increase in the level of serum SA corresponding to anemia and parasitemia was observed. At maximum parasitemia, the level of total SA from the red blood cells (RBC) dropped by about 45%. Solved polynomials revealed an association between free serum SA and RBC-SA. Positive roots of quadratics were used to predict complete cleavage of RBC-SA on day 7.01 and maximum accumulation of free serum SA on day 6.6. A steady rise in the level of serum sialidase (SD) activity and a low packed cell volume (PCV) with an increase in parasitemia were observed. Mice infused with galactose, methyl-beta-gal, lactose, mannose, or L-arabinose and challenged by intraperitoneal inoculation with Trypanosoma congolense neither developed anemia nor secreted free SA above the control level even though there was detectable SD activity. Bloodstream Trypanosoma congolense parasites were isolated using DEAE cellulose from heparinized blood of experimentally infected BalbC mice. The parasites were lysed with 0.2% Triton-CF 54 to release membrane bound SD. The activity of the SD was proportional to the number of parasites. The enzyme was partially purified on Q-Sepharose and Fetuin agarose columns successively. The final active fraction from the latter column was used as the partially purified SD. The enzyme had an optimum pH of 6 and was maximally active at 37 degrees C with a requirement for the divalent ions Ca(2+) and Mg(2+). The enzyme was highly specific for NeuAc5alpha2,3 lac and Methylumbelliferyl-Neu5Ac (4-MU-Neu5Ac) with K(M) values of 0.34 and 0.025 mM, respectively. It was inhibited competitively by 2,3-didehydroneuraminic acid (Neu5Ac2en) and para-nitro-phenyloxamic acid (pNPO) with inhibition binding constants K(i) of 65 and 215 micro M, respectively. In deviation from the procyclic trypanosomal SD, it lacked trans-sialidase (TS) activity. The possible role of a secreted bloodstream Trypanosoma congolense SD and the development of anemia in the pathogensesis of trypanosomiasis are discussed.

Glycosylphosphatidylinositol-dependent protein trafficking in bloodstream stage Trypanosoma brucei

We have previously demonstrated that glycosylphosphatidylinositol (GPI) anchors strongly influence protein trafficking in the procyclic insect stage of Trypanosoma brucei (M. A. McDowell, D. A. Ransom, and J. D. Bangs, Biochem. J. 335:681-689, 1998), where GPI-minus variant surface glycoprotein (VSG) reporters have greatly reduced rates of endoplasmic reticulum (ER) exit but are ultimately secreted. We now demonstrate that GPI-dependent trafficking also occurs in pathogenic bloodstream trypanosomes. However, unlike in procyclic trypanosomes, truncated VSGs lacking C-terminal GPI-addition signals are not secreted but are mistargeted to the lysosome and degraded. Failure to export these reporters is not due to a deficiency in secretion of these cells since the N-terminal ATPase domain of the endogenous ER protein BiP is efficiently secreted from transgenic cell lines. Velocity sedimentation experiments indicate that GPI-minus VSG dimerizes similarly to wild-type VSG, suggesting that degradation is not due to ER quality control mechanisms. However, GPI-minus VSGs are fully protected from degradation by the cysteine protease inhibitor FMK024, a potent inhibitor of the major lysosomal protease trypanopain. Immunofluorescence of cells incubated with FMK024 demonstrates that GPI-minus VSG colocalizes with p67, a lysosomal marker. These data suggest that in the absence of a GPI anchor, VSG is mistargeted to the lysosome and subsequently degraded. Our findings indicate that GPI-dependent transport is a general feature of secretory trafficking in both stages of the life cycle. A working model is proposed in which GPI valence regulates progression in the secretory pathway of bloodstream stage trypanosomes.

Multiple infection in bovines from the tropics: observation of blood parasites by scanning and transmission electron microscope

Blood samples from a splenectomized bovine, experimentally inoculated with blood from a field cow living in southwestern Venezuela, were processed for transmission and scanning electron microscopy. The blood sample showed multiple infection with hemoparasites of the genera Anaplasma marginale, Eperythrozoon wenyonii and Trypanosoma vivax. Scanning electron microscope showed that the blood from bovines with multiple infection had profound deformation in knob-like protruding structures with reduced cellular volume similar to echinocyte red blood cells. E. wenyonii parasites appear associated with the membrane, grouped in shallow to severe invaginations at the surface of the erythrocytes. The morphology of the parasites is predominantly rod-like; they also appear as coccoid-shaped and bifurcate or triskelion-shaped organisms. The organisms are present in pairs or clusters. T. vivax appeared with double flagella, which indicates active cellular division and infection processes. Transmission electron microscope study showed erythrocytes infected with intracytoplasmic bodies of A. marginale and with E. wenyonii embedded in the external membrane cell, with mature, juvenile and dividing forms present.

Susceptibility of trypanotolerant West African Dwarf goats and F1 crosses with the susceptible Sahelian breed to experimental Trypanosoma congolense infection and interactions with helminth infections and different levels of diet

Forty pure West African Dwarf (WAD) goats and 35 of its F1 crosses with the Sahelian breed were used in a multifactorial experimental design to evaluate the effects of an experimental Trypanosoma congolense infection and interactions with natural helminth infections and different levels of diet on health and productivity of these two breeds. Trypanosome infection caused a severe drop in packed cell volume (PCV), but this was not significantly affected by breed. Neither deworming nor diet had any effect on the course of anaemia after trypanosome infection. The mean score of parasitaemia tended to be higher in crossbreeds than in WAD goats although this was not significant (P>0.05). Similarly, the antibody response to trypanosome infection was not significantly different between breeds. Parasitaemia level was significantly influenced by the level of diet with the group under high supplementation having a higher mean parasitaemia score than the group under low supplementation. Weight loss due to trypanosome infection tended to be greater in crossbreeds than in WAD goats (P>0.05). During this study, there was no difference in mean helminth egg output between crossbred and WAD goats. However, between weeks 4 and 10 after trypanosome infection (corresponding to a period of heavy rainfall and highly infective pastures), the mean egg output was higher in the crossbreeds. The immunosuppressive effect of trypanosome infections was revealed by a lower antibody response to Haemonchus contortus in infected animals compared to the uninfected controls. Trypanosome infection tended to increase strongyle egg output. This study did no reveal any superior trypanotolerance of WAD goats compared to crossbreeds.