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Vaccine efficacy and prophylactic treatment of infections are tested best when the vaccinated or treated individual is challenged through deliberate infection with the respective pathogen. However, this trial design calls for particular ethical caution. Awareness of the history of challenge trials is indispensable, including trials that were problematic or even connected to abuse. We briefly introduce historical aspects of experimental infections in humans and the ethical debate around them and give estimates of the numbers of volunteers participating in human experimental infection models. Challenge models can offer a great chance and benefit for the development of medical interventions to fight infectious diseases, but only when they are appropriately controlled and regulated. [ABSTRACT FROM AUTHOR]

The hematology of 25 pullets experimentally infected orally with 0.5 mL of 1 x 107 cfu/mL of Salmonella Paratyphi A was studied. By day 4 post-infection (p.i.), dullness, ruffled or unkempt feathers, somnolence, yellowish-green diarrhea, and decreased water and feed consumption were observed. Hematological parameters of the birds were monitored on days 7, 14 and 21 p.i. The values were analyzed with Duncan’s Multiple range test, at P < 0.05. The packed cell volume (PCV) was significantly higher at day 7 p.i. than during pre-infection and at day 21 p.i. However, it was similar at days 7 and 14 p.i. Likewise, hemoglobin concentrations in the birds were similar during pre-infection, and at days 14 and 21 p.i. In contrast, they were significantly higher at day 7 than during pre-infection and at day 21 p.i. The indicators of anemia showed no significant differences between pre- and post-infection values. The period coincided with that of decreased feed and water consumption in the course of the disease. There were no significant differences in total leukocyte counts for days 7, 14 and 21 p.i., whereas they were significantly (P < 0.05) lower during pre-infection than at days 7, 14 and 21 p.i. The course of Salmonella Paratyphi A infection depends on the infective dose of the organism. There was no anemia in pullets; leukocytosis was attributable to heterophilic leukocytosis, lymphocytosis, monocytosis and eosinophilia, which are indicators of acute infection and internal stress, to which the pullets adequately responded.

A study was carried out to investigate the chemotherapeutic effects of diminazene aceturate (Berenil®) and melarsamine hydrochloride (Cymelarsan®) on the alteration of biochemical parameters in red-fronted gazelles experimentally infected with Trypanosoma brucei. A significant (P < 0.05) increase in serum cortisol, alanine aminotransferase, aspartate aminotransferase, total bilirubin, creatinine, urea, uric acid, total lipids, and a significant (P < 0.05) decrease in total serum proteins, albumin level and serum glucose were observed in the gazelles following parasitemia. Alkaline phosphatase activity fluctuated around normal values (P > 0.05). These biochemical alterations were effectively modulated to preinfection levels before the end of the experiment in gazelles treated with either 0.3 or 0.6 mg/kg body weight (BW) of Cymelarsan, or 7.0 mg/kg BW of Berenil. The results therefore suggested that an initial stress associated with an increased serum cortisol level and its immunosuppressive effect might have been responsible for the establishment and clinical manifestation of the infection in the gazelles. Furthermore, the severity of the biochemical effects experimentally induced indicated that trypanotolerance in wild gazelles could be compromised, especially when they are subjected to the stress of captivity. Results also showed that Cymelarsan at 0.3 or 0.6 mg/ kg BW, and Berenil at 7.0 mg/kg BW were effective in managing the disease under experimental conditions.

Following experimental infectious bursal disease virus infections in four-weekold broiler chicks, turkey poults and ducklings, blood samples were chronologically collected and analyzed for postinfection (pi) changes. Although there was a net increase in packed cell volume values in chicks reaching a peak of 31% from 12 h to 144 h pi, there was, on the contrary, a general decline in the values in turkey poults and ducklings to minima of 26.5% at 12 h pi and 28.2% at 48 h pi, respectively. Leukocyte counts in chicks significantly increased (p < 0.05) to a peak of 66.83 x 103/μl at 120 h, while counts in poults decreased to a minimum of 26.75 x 103/μl at 96 h pi. Lymphocyte counts in chicks were reduced to a minimum of 5.9 x 103/μl at 48 h pi after an initial reduction between three and six hours postinfection. A similar decline occurred in poults with a minimum of 7.81 x 103/μl at 48 h pi. The trend of changes in heterophil counts for the three species was similar to those observed for leukocyte counts. While eosinophil counts in chicks initially increased to a peak of 1.93 x 103/μl at 6 h pi and subsequently declined, eosinophil values in poults declined to a minimum of 0.88 x 103/μl at 6 h pi, followed by an increase to a maximum of 5.7 x 103/μl at 72 h pi. However, all hematological values in ducklings remained relatively unchanged. These results showed that there was biphasic lymphopenia, eosinophilia and heterophilia in chicks, lymphopenia and delayed eosinophilia in poults, and relatively unchanged values in ducklings. This emphasizes the fact that different levels of susceptibility exist in the three poultry species studied.

Hemorrhagic septicemia (HS) was experimentally induced in seven-month-old calves (n = 2) by intratracheal inoculation of 1010 colony-forming units of sixhour log-phase Pasteurella multocida serotype E:2 to study its clinicopathologic features and microbiology. The incubation period was within four hours postinfection. The general continuum of clinical signs in order of manifestation was pyrexia, anorexia, dyspnea, swelling of the throat-forelimb region, tympany, nasal discharge, profuse salivation, lethargy, recumbency and death. The prominent lesions observed at necropsy were congestion of the lungs with consolidation and pleural adhesions of the apical lobes, pleurisy, edematous swelling of the throat and dewlap which exuded yellowish serum-like fluid, petechial and ecchymotic hemorrhages. Histologically, the lung lesions were typical of fibrinous bronchopneumonia with thickened alveolar septa, hyperemia, edema and cellular responses of the lungs. P. multocida E:2 was re-isolated bacteriologically from the lungs, lymph nodes, liver, kidneys, spleen, edema fluid, and heart blood at necropsy. The organism was not detected in the venous blood until a few hours before death. The clinical and pathological features seen in the animals showed that there were striking similarities with P. multocida type B:2 HS. The data should help veterinarians recognize suspected cases of HS in the field.

The experimental transmission of contagious bovine pleuropneumonia (CBPP) was carried out by putting into close contact 14 naive zebu cattle with 12 naturally infected N’Dama cattle taken from a CBPP field outbreak. The healthy zebus originated from various CBPP-free herds and had not been vaccinated against CBPP in the past several years. Four control animals who had never been in contact with Mycoplasma mycoides subsp. mycoides Small Colony (MmmSC) were housed separately. The experiment lasted 12 months. All animals were monitored for clinical signs and regularly sampled for serological and bacteriological analyses. Postmortem analyses were performed on all animals to assess the presence of CBPP gross lesions and to take samples for MmmSC isolation. The results showed the efficacy of CBPP transmission by contact. Animals were assigned to three groups according to clinical, postmortem, and laboratory findings, as follows: acute form including two deaths (5/13), subacute to chronic form (6/13), and resistant form (2/13). Animals with obvious clinical signs of the disease showed various lung lesions at necropsy (hepatization, sequestra, pleural fluid, lung adhesions, fibrotic scars, etc.) as well as seroconversion. MmmSC was isolated from hepatized lungs and sequestral contents. In contrast, the two animals with a resistant form never presented any clinical nor any serological signs. The control animals remained clinically healthy throughout the experiment; at necropsy, no CBPP-characteristic lesion was noted and laboratory analyses remained negative. This study confirmed previous observations that showed that CBPP infection can be successfully transmitted to cattle by contact, and it could provide an experimental basis for future research such as the characterization of the host immune and pathological responses at various stages of the disease

The aim of this study was to assess trypanosome infection effects on the work performance of trypanotolerant cattle in the subhumid zone of Senegal. The study was conducted on Ndama cattle with a mean live weight of 288 kg and a mean age of six years. The animals were trained individually (single ox). The experimental design comprised two phases of four weeks each. In the first phase, the animals worked five hours a day, five days a week drafting the equivalent of 12% their body weight. A three-week rest period followed. Then, in the second phase, they were intradermally infected with a strain of Trypanosoma congolense (infective dose: 105 trypanosomes per milliliter) and subjected to the same work. The trypanosome infection had a significant effect on work power (P < 0.001), work speed (P < 0.001), distance traveled (P < 0.001), volume of pellets obtained by centrifugation (P < 0.05) and Andropogon gayanus intake (p < 0.01). However, the infection had no significant effect on the animals’ live weights. Results showed the work performance of infection-free animals was better than that of trypanosome-infected cattle. Healthcare and prophylactic measures against trypanosomes are proposed to improve the work performance of trypanotolerant Ndama cattle used for drafting: cattle should be treated against trypanosomosis with diminazene aceturate (Bérénil®) (7 mg/kg body weight) at the end of the dry season, and with isometamidium (0,5–1 mg/kg body weight) during the rainy season, to protect them during the land preparation period.

The objective of the trial was to determine the susceptibility of goats to the contagious bovine pleuropneumonia (CBPP) agent. Four inoculation routes – subcutaneous, endobronchial, intrapleural and intraperitoneal – were tested. One of the goats infected intraperitoneally died of peritonitis. The CBPP agent was isolated again from the ascitic fluid. The serological tests, competition ELISA in particular, revealed the occurrence of serological conversions in a number of animals. This should pave the way to further field studies to determine if goats in contact with CBPP-affected bovines may be naturally contaminated.

A flock of 160 six-week-old Harco cockerels was inoculated intramuscularly with a local Nigerian isolate of velogenic Newcastle disease virus (NDV) isolated from a dead guinea fowl. The birds came down with clinical signs on day 3 postinoculation (PI). The major signs were depression, greenish diarrhea, paralysis, opisthotonus and torticollis. Morbidity was 100% but mortality was 92%. By day 18 PI torticollis was the only sign persisting in some of the birds. The major gross lesions were hemorrhages in the proventricular mucosa, hemorrhagic ulcers in the intestines and transient atrophy of the lymphoid organs. Sections of the organs showed lymphocytic necrosis and depletion of the lymphoid organs, endotheliosis, gliosis and perivascular cuffing of the cerebrum and cerebellum. The above observations showed that the isolate was a viscerotropic velogenic strain. It is suggested that the hemorrhagic ulcers in the intestines could be regarded as diagnostic for viscerotropic velogenic NDV in the absence of epizootiological evidence of avian influenza.

Sahelian and Kirdimi goats of Chad were studied in an experimental farm for trypanotolerance. Fifty-five (55) animals, 28 Sahelians and 27 Kirdimis, whose hemoglobin types had been determined, were experimentally infected, each one with 10^6 trypanosomes (Trypanosoma congolense IL1180 stock, savanna type). The animals were regularly monitored for six months for clinical symptoms, bodyweight, hematological and biochemical parameters. The infection induced sudden significant weight loss in Sahelian goats. On the other hand, no significant weight variations were observed in Kirdimis. The average prepatent period was 7 and 12 days for Sahelian and Kirdimi goats, respectively. Parasitemia appeared to develop quickly in Sahelian goats (within a month). It was well under control in Kirdimis throughout the experimental period, and some self-cure cases were even observed. Sahelian goats, apparently more susceptible to the infection, displayed during the acute phase of the disease lack of appetite, pale ocular membranes, watering eyes, staggering movements and occasional diarrheas. The packed cell volume was stable in Kirdimis. It dropped rapidly in Sahelian goats and often reached the critical point of 15%. At that threshold the animals were unable to stand up and died unless a trypanocide treatment was applied. The T. congolense trypanosomosis evolution was mainly associated in Sahelian goats and at different levels with important changes in hematological and biochemical parameters. This study shows that Kirdimi goats control T. congolense infections better than Sahelian goats.

Numerous studies have shown the influence of some bacteria colonizing the breeding sites on the development of the parasite in Anopheles malaria vectors. The aim of this study was to evaluate the impact of the breeding sites of Plasmodium falciparum on the gametocytes infectivity of Anopheles gambiae sl using the membrane feeding method. We carried out an experimental infestation study from September 2010 to January 2011 in a village located in the southern savanna of Mali. Cross sectional surveys were conducted to collect larvae and to select gametocyte carriers. Female offspring of L3 and L4 stage larvae were used for the experimental infestation. The gametocyte carriers were children aged within 4 to 12 years. Bacteria identified in breeding water of larvae and adult mosquitoes were: Escherichia coli, Salmonella spp, Klebsiella oxytoca, Pseudomonas spp, Staphylococcus spp, Shigella sp. The oocyst load of infected mosquitoes did not significantly vary according to the cottages (F = 1.517, P = 0.230). Low infection rates (5.4% and 2.8%) were observed in the larval bedding and in mosquitoes containing K. oxytoca and Shigella. The blood feeding rates (62.4%; 60.9%; 67.7%) and mortality (66.4%; 64.9%; 61.9%) of An. gambiae did not significantly vary depending on the breeding sites [(P = 0.15); (P = 0.22)]. [ABSTRACT FROM AUTHOR]

Un ELISA de détection des antigènes circulants de Trypanosoma vivax mis au point par Nantulya et Lindqvist en 1989, a été comparé à celle du test de Woo lors d'infections expérimentales de deux moutons avec une souche guyanaise de T. vivax. Quelle que soit la période d'infection, que la parasitémie soit détectable ou non, la sensibilité du test ELISA a été très basse. L'association des deux techniques n'apporte aucune sensibilité supplémentaire. Déjà observé au Burkina Faso et en Gambie, ce défaut de sensibilité risque d'affecter fortement les résultats des enquêtes épidémiologiques entreprises avec ces réactifs en Afrique. Il est nécessaire de développer de nouveaux anticorps monoclonaux afin de mettre au point un test de détection des antigènes de T. vivax dont la sensibilité soit plus satisfaisante.

Trois chiens ont été infectés par une souche ILRAD 1797 de Trypanosoma brucei par voie sous-cutanée. Une anémie hémolytique a été provoquée artificiellement chez deux autres chiens par phlébotomie, traitement thermique et réinjection de sang, alors que deux autres chiens ont servi de témoin. Les animaux infectés ont manifesté une panleucopénie et une thrombocytopénie, alors que les chiens atteints d'une anémie hémolytique provoqué artificiellement ont présenté une leucocytose et une thrombocytose. Ces résultats laissent supposer l'existence d'un facteur d'aplasie médullaire dans le plasma des chiens infectés à T. brucei, d'autant plus que la production leucocytaire a été affectée.

Introduction. Bacterial canker, caused by P. syringae pv. syringae, is an important disease of stone fruit worldwide. The possibility of P. syringae pv. syringae infection through leaf scars and lenticels was evaluated in cherry, peach and prune. Materials and methods. Laboratory and field inoculations were performed using cherry, peach and prune stems to evaluate leaf scar age, chilling and freezing-thawing on bacterial infection through leaf scars and lenticels. Results and discussion. Increasing leaf scar age was associated with significant decreases in disease incidence and length of lesions resulting from leaf scar inoculation with Pseudomonas syringae pv. syringae in cherry, peach and prune. A significant reduction in incidence and lesion length was observed after 4 h of air exposure, and both measures of infection were reduced to essentially 0 by 2 days of exposure. Prolonged chilling temperature (2.2 °C) prior to leaf removal had no clear effect on disease incidence of leaf scar infection, but significantly decreased lesion length due to leaf scar infection. Cherry was more susceptible to P. syringae pv. syringae infection through leaf scars than peach and ‘French’ prune. The leaf scar inoculation results were consistent with the previous studies. The disease incidence of lenticel infection caused by bacterial inoculation in ‘French’ prune was very low, but significantly higher than the water control. Freezing-thawing significantly increased both the disease incidence and the lesion size via lenticel infection. The lenticel inoculation data suggest that P. syringae pv. syringae infection through lenticels is possible under field conditions. [ABSTRACT FROM AUTHOR]

Introduction. Bacterial canker, caused by Pseudomonas syringae pv. syringae, is a damaging disease of stone fruit worldwide. The effects of rootstock, temperature and incubation duration on bacterial canker in peach were assessed using both field and laboratory inoculation assays. Materials and methods. Both field and laboratory experiments were conducted to study the effects of rootstock, temperature and incubation duration on disease severity in peach. All inoculations were achieved with P. syringae pv. syringae strain B3A. Bacterial inoculations were applied to 1-year-old shoots of peach trees [Prunus persica (L.) Batsch]. After inoculation, the inoculated shoots were allowed to incubate either under field conditions or in a cold room at different temperatures [constantly at 0 °C, constantly at 14.4 °C, and in a fluctuating temperature regime of 12 h at 0 °C (night) and 12 h at 14.4 °C (day)] for excised shoots. The lesions were determined 1 to 6 weeks after inoculation to determine the effect of incubation duration. Results and discussion. The field experiment using peach grafted on three rootstocks (Nemaguard, K119-50 and P30-135) showed that shoots on Nemaguard developed the longest lesions and shoots on K119-50 the shortest among all three rootstocks. Shoots on Nemaguard had significantly lower bark calcium and higher nitrogen concentrations than those on K119-50 and P30-135. A negative correlation was found between lesion length and bark calcium concentration and the [calcium / nitrogen] ratio. Laboratory experiments with excised shoots on Nemaguard, K119-50, P30-135, Lovell and Guardian rootstocks growing in a second orchard showed inconsistent results. Shoots from Nemaguard developed significantly smaller lesions than those on K119-50 and P30-135. Shoots on Guardian and Lovell also developed significantly smaller lesions than those of shoots on K119-50 and P30-135. Temperature fluctuation during incubation (0 °C to 14.4 °C) had no effect on shoot lesion length compared with those incubated constantly at 14.4 °C, but produced significantly longer lesions than shoots incubated constantly at 0 °C. These inconsistent results suggest that, in the absence of major predisposing factors (i.e., ring nematodes or low soil pH), rootstocks may play a minor role in peach susceptibility to bacterial canker even under favorable disease development conditions. [ABSTRACT FROM AUTHOR]

The article discusses a study on the pathological changes associated to an experimental infection of ducks with low pathogen A influenza virus, the H6N2 strain. A total of 30 crossbred Peking x Turkish Mallard at 28 years old were used and kept in two separate isolated rooms and were not vaccinated. H6N2 inoculated ducklings had not respiratory, digestive and secretory clinical signs while some disturbances were observed in the body development and feathering in intravenously infected birds and those tracheally inoculated at a lesser extend. It concludes that the virus inoculation either by intravenous and tracheal route has induced a systemic disease involving the heart, liver and pancreas.

The article discusses a study which determined the association between blood concentration of C reactive protein (CRP) and fibrinogen with obesity among dogs with induced staphylococcal infection. Obese dogs infected with staphylococcus bacteria exhibited longer periods of fibrinogen concentration compared to dogs of normal weight. Researchers concluded that occurrence of acute phase protein (APP) synthesis is higher in obese dogs due to the activation of defense mechanisms that prevent microorganism growth, and cell damage by free radicals.

The article discusses a study which assessed how Staphylococcus intermedius infection among dogs can affect blood serum protein and lysozome levels. It describes the physiological function of plasma proteins present in humans and animals, and its classification based on electrophoretic mobility. Researchers proposde that total protein (TP) concentration in dogs can change during an infection with bacteria that causes pyodermitis. The article also notes the function of lysozyme as a natural defense of chickens from coccidiosis infection.

Abstract: As a model of persistent infection, various aspects of Bartonella birtlesii infection in laboratory mice, including some immunodeficient mice, are presented, particularly focusing on conditions mimicking natural infection. Bacteraemia was explored using different mice strains routes and inoculum doses (3.4–5×107 CFU/mouse). Mice became bacteraemic for 5 (C57Bl6/6) to 10 weeks (Balb/c, Swiss) with peaks ranging from 2×103 to 105 CFU/mL of blood. The ID route induced the most precocious bacteraemia (day 3) while the higher and longer bacteraemia in immunocompetent mice was obtained with SC when infecting Balb/c with approximately 103 CFU/mouse. As opposed to ID, SC and IV routes, bacteraemia was obtained with the oral and ocular routes only for high doses (107) and in 33–66% mice. It was significantly higher and longer in CD4−/− mice compared to CD8−/− and double KO mice at most time points. CD8−/− mice and the control group had near to superimposed kinetics. These results confirm the relevance of the present model. [Copyright &y& Elsevier]

Abstract: To reveal whether bats serve as an amplifying host for Yokose virus (YOKV), we conducted a serological survey and experimentally infected fruit bats with YOKV isolated from microbats in Japan. YOKV belongs to the Entebbe bat virus group of vector unknown group within the genus Flavivirus and family Flaviviridae. To detect antibodies against YOKV, we developed an enzyme-linked immunosorbent assay (ELISA) using biotinylated anti-bat IgG rabbit sera. Serological surveillance was conducted with samples collected in the Philippines and the sera supplied from Malaysia. One of the 36 samples from the Philippines (2.7%) and 5 of the 26 samples from Malaysia (19%) had detectable ELISA antibodies. In the experimental infections, no clinical signs of disease were observed. Moreover, no significant viral genome amplification was detected. These findings revealed that YOKV replicates poorly in the fruit bat, suggesting that fruit bats do not seem to serve as an amplifying host for YOKV. [Copyright &y& Elsevier]

Abstract: Objective. – Most of coxsackieviruses A (CV-A) are difficult to isolate in cell culture and are responsible for flask paralysis in suckling mice. The aim of the present work was to analyze the ability of immune and RT-PCR techniques to detect viral components of three different serotypes, CV-A6, CV-A13, and CV-A14, in skeletal muscles of experimentally infected suckling mice. Material and methods. – The antigen detection was done by immunofluorescence technique on trypsinized muscular cells and by immunoperoxidase assay on frozen sections of skeletal muscle, using a monoclonal antibody directed towards a conserved epitope of the VP1 capsid protein among enteroviruses. The nested RT-PCR technique used primers located in the 5′ non coding region of viral RNA. Results. – The group antigen was present in muscle cells of suckling mice infected by the three serotypes of CV-A which were assayed. Similarly, the muscle specimens were positive by nested RT-PCR. A kinetic study performed with CV-A13 and CV-A14 showed that the RT-PCR assay was positive as soon as 24 h after infection whereas the detection of VP1 antigen and symptoms of flask paralysis were observed only 48 and 72 h after infection, respectively. Conclusion. – These results show that the tested serotypes of CV-A can be easily detected in muscle specimens of suckling mice by using antigenic and molecular techniques currently available for the diagnosis of enterovirus infections. [Copyright &y& Elsevier]

Abstract: In this work, a role for the genes encoding glycoproteins I (gI) and E (gE) and the US9 protein of bovine herpesvirus type 5 (BHV-5) in neuropathogenicity and reactivation of latent infections was examined. Calves infected intranasally with a gI/gE/US9 deleted recombinant shed up to 102.85 TCID50/ml infectious virus in nasal secretions. Calves infected with the wild type BHV-5 parental virus shed up to 105 TCID50/ml virus. No signs of disease were observed in calves infected with the recombinant virus, whereas those infected with wild type virus displayed respiratory and neurological signs. The recombinant was only able to reach the basal portions of the central nervous system. In contrast, wild type virus was found widespread within the brain. Reactivation with dexamethasone 60 days post-infection resulted in reactivation of wild type virus, whereas the recombinant virus could not be reactivated. These studies demonstrate that genes gI, gE and US9 of BHV-5 are important for its neuropathogenicity and its ability to reactive from latency. [Copyright &y& Elsevier]

L'activité de deux anticoagulants, l'éthylène diamine tétra-acétate (EDTA) et l'héparine, a été comparée sur du sang de chèvres cliniquement infectées par Cowdria ruminantium. Les neutrophiles ont été extraits du sang et mis en culture pour la production de l'antigène correspondant. L'EDTA s'est révélé supérieur à l'héparine du point de vue du taux de récupération et d'une meilleure séparation des neutrophiles par rapport aux autres leucocytes. L'antigène produit a été testé avec le test d'immunofluorescence indirecte (IFAT). Il est apparu de bonne qualité. La production de l'antigène par cette méthode est recommandée pour les laboratoires relativement bien équipés dans les zones où la cowdriose est endémique.

Cette étude a été menée pour étudier les interactions entre la glossine et le trypanosome dans la détermination de la métacyclogenèse. A cet égard, 5 257 mouches ténérales des deux sexes des lignées Glossina palpalis gambiensis (Maisons-Alfort), G. p. palpalis (Mongo-Bemba) et G. morsitans morsitans (Mall) ont été utilisées. Elles ont été nourries une fois sur rats infectés par Trypanosoma brucei gambiense (souches Mba et Phanzu), T. b. brucei (souche EATRO 1125) et T. congolense (clone IL 1180 et stock Agriumbe). La compétence vectorielle (CV) des mouches des deux lignées palpalis a été nulle ou négligeable vis-à-vis de tous les trypanosomes testés, excepté pour les clones et stock de T congolense. Celle de G. m. morsitans a été nulle pour les deux souches gambiense, mais relativement élevée (32 %) pour T. b. brucei EATRO 1125. La CV de G. m. morsitans pour T. congolense, s'est révélée plus importante pour le clone IL 1180 (95,45 %) que le stock Agriumbe (48,40 %). Ces résultats montrent une très bonne interaction entre les mouches de la lignée G. m. morsitans (Mall) et la souche clonale T. congolense IL 1180.

L'étude a concerné la compétence vectorielle (CV) de 1 257 mouches ténérales des deux lignées parentales Bobo-Dioulasso (BD) et Maisons-Alfort (MA) appartenant à Glossina palpalis gambiensis. Les individus de ces lignées ont été nourris une fois et simultanément sur un cobaye infecté par Trypanosoma brucei brucei EATRO 1125. Ils ont été dissèques après un entretien de 33 jours sur des cobayes sains. L'analyse statistique des résultats n'a pas montré de différence significative d'indice procyclique entre les mâles et les femelles de la lignée BD. Par contre, cet indice a été plus marqué chez les mâles que chez les femelles de la lignée MA. L'indice procyclique des mâles de la lignée MA a été plus élevé que celui des mâles de la lignée BD. Aucune différence significative d'indice métacyclique n'a été observée entre les mâles ni entre les femelles des deux lignées. Cependant, la CV des mouches de la lignée MA a été plus importante que celle des mouches de la lignée BD. Aucune différence significative de CV n'a été notée entre les mâles et les femelles de la lignée BD, tandis que chez la lignée MA, la CV des mâles a été plus importante que celle des femelles.

Six bovins de race Boran ont été infectés par la souche chimiorésistante IL 3338 de Trypanosoma congolense. Au premier pic de parasitémie, 200 Glossina morsitans centralis ténérales organisées en plusieurs groupes ont été nourries sur chaque animal, juste avant leur traitement à l'acéturate de diminazène à la dose de 3,5 mg/kg de poids corporel (p.c.). Les animaux ont ensuite étaient suivis par prélèvement sanguin trois fois par semaine et ont été traitées comme précédemment chaque fois que l'hématocrite baissait dans trois prélèvements consécutifs, pour au moins un des animaux. Après huit traitements à approximativement deux semaines d'intervalle, la longueur moyenne de la période prépatente après chaque traitement n'a pas augmenté, restant à 7,8 +- 1,1 jours. La valeur moyenne de l'hématocrite est descendue de 33,2 +- 0,6 % lors du premier traitement, à 23,7 +- 2,6 % entre les huitième et neuvième traitements. En conséquence, à la suite du huitième traitement, l'acéturate de diminazène a été administré comme précédemment, mais à la dose de 7,0 mg/kg p.c. Résultant de l'augmentation de la dose, la valeur moyenne de l'hématocrite entre deux traitements est montée de 25,4 +- 2,4 % sitôt après le premier traitement à 32,9 +- 1,7 pour les deux mois qui ont suivi le cinquième traitement.

Une souche de Trypanosoma (Duttonella) vivax isolée dans la région des Niayes du Sénégal a pu être transmise à des souris de laboratoire (Balb/c). La parasitémie a été suivie après son apparition pendant plus de 100 jours chez l'une des souris. Cette observation confirme que T. vivax peut être spontanément transmissible aux rongeurs.(Résumé d'auteur)

De la difluorométhylornithine (DFMO, eflornithine) a été donnée par voie intraveineuse (lV) à des chiens infectés expérimentalement par Trypanosoma brucei. Une posologie de 400 g/kg/jour répartie en trois doses quotidiennes pendant 7 jours pour les primo-infections ou 21 jours lors de rechutes ne s'est pas révélée curative. Le traitement des primo-infections aussi bien que de leurs récidives s'est caractérisé par un déclenchement lent de l'action (le coefficient d'épuration parasitaire a été atteint après 4 à 5 jours de traitement) et de courtes périodes sans parasitémie (6 jours). L'administration simultanée de DFMO et d'une seule dose de Berenil (7 mg/kg) pour les primo-infections a permis d'obtenir des résultats chimiothérapeutiques plus importants que ceux de la monothérapie car elle n'a pas été suivie de rechute. L'administration orale de DFMO a provoqué, dans les quatre jours qui ont suivi, une perte d'appétit, des vomissements, une diarrhée abondante et une déshydratation avancée. Ces inconvénients importants font de la voie IV une véritable alternative à celle de la thérapeutique orale.

Des taurins Holstein et zébus Bororo blancs ont été infectés avec AnTat 1.1, un variant antigénique de T. b. brucei. Les paramètres cliniques, ainsi que l'hématocrite, la parasitémie, la réponse immunehumorale et l'activité hémolytique du complément ont été examinés en vue de préciser l'allure clinique de la trypanosomose à T. b. brucei chez ces deux races bovines, ainsi que leur degré de sensibilité. Les animaux des deux races se sont montrés très sensibles à l'infection. Les Holstein ont contracté une maladie aiguë, mortelle en quelques semaines, les zébus Bororo blancs une maladie chronique avec inanition progressive et mortaprès quelques mois. Tous sont restés parasitémiques jusqu'à la phase terminale de la maladie. Des anticorps trypanolytiques AnTat 1.1-spécifiques ont été produits en grande quantité. L'infection a induit une hypocomplémentémie persistante chez les deux races. Le comportement des zébus Bororo blancs et Holstein est très différent de celui observé antérieurement chez les bovins Lagunaire et Borgou soumis à un protocole expérimental similaire. Les variations individuelles sont importantes chez toutes les races étudiées.

Des bovins Borgou (n = 10), Lagunaire (n = 10) et zébus Bororo blancs (n = 10) du Bénin ont été infectés expérimentalement avec un clone de Trypanosoma brucei brucei en vue d'évaluer le test ELISA de détection d'antigènes circulants. Aucun des trois témoins non inoculés de chacune des races n'a développé d'infection. Les bovins Lagunaire et Borgou ont développé une maladie bénigne suivie de guérison spontanée, les zébus Bororo blancs une maladie typique à allure chronique et fatale après plusieurs mois. Pour tous les animaux confondus, la sensibilité du test de détection des antigènes circulants de T. brucei a été de 20,46 %, nettement inférieure à celle de la détection des parasites par la méthode du buffy coat (40,24 %). La sensibilité du test varie fortement en fonction du type d'animaux infectés et de l'allure de l'infection; elle est la plus élevée chez les bovins Borgou aux parasitémies élevées mais de durée plus courte (44,44 %) et la plus faible chez les zébus Bororo blancs aux parasitémies faibles et intermittentes (4,09 %). Augmenter la sensibilité du test de détection des antigènes circulants en abaissant la densité optique de 0,050 (seuil de positivité) à 0,025 paraît impossible sans altérer sa spécificité. Comparés au buffy coat, les faux négatifs du début d'infection et les faux positifs d'après la guérison spontanée compromettent également la valeur du test pour le diagnostic des infections actives à T. brucei.

Un stock pathogène de Theileria a été isolé à partir de bovins témoins, lors d'un test d'immunisation sur le terrain contre la theilériose bovine à Kasoba, près de la ville de Karonga au Nord du Malawi. Un stabilat issu de ce stock a causé des fièvres graves et une parasitose prolongée chez du bétail n'ayant jamais été infecté par Theileria parva, provoquant la mort de 5 animaux sur 12 en dépit du traitement. D'un autre côté, ce stock de parasites a seulement causé des réactions légères à modérées chez 17 bovins préalablement immunisés avec un stabilat trivalent de T. parva, excepté chez trois animaux qui ont développé des réactions sévères et l'un d'eux en est mort. Une autre fois, le bétail immunisé avec Theileria parva (Serengeti transformé) provenant de buffle a résisté à une inoculation potentiellement fatale en ne montrant que des réactions légères et modérées. Ce stock de parasites s'est avéré morphologiquement et sérologiquement semblable à Theileria parva (Muguga); il était virulent et pouvait provoquer la mort, en particulier chez du bétail n'ayant jamais été infecté par T. parva. Ce stock de parasites a été ainsi appelé Theileria parva (Kasoba).

L'infection expérimentale de trois races de mouton du Nigéria, les moutons Djallonké, Yankasa et Oudah, provoqua la maladie mortelle causée par la souche Zinga du virus de la fièvre de la Vallée du Rift. Cette infection caractérisée par une hyperactivité, des écoulements nasaux séro-muqueux, une diarrhée sanglante et très liquide, une hémorragie externe et des manifestations cliniques de troubles nerveux. La virémie fut suivie d'un faible taux de développement des anticorps chez tous les moutons infectés. Les transformations hématologiques comportèrent une forte baisse de l'hématocrite, de la concentration d'hémoglobine et du taux des globules rouges pendant l'évolution de la maladie. Les transformations dans les composants biochimiques du sérum comportèrent une forte augmentation progressive du niveau de l'alanine aminotransférase et de l'aspartate aminotransférase. Les taux de sodium baissèrent graduellement, mais ceux de potassium, bien que stables au début, augmentèrent par la suite jusqu'à la mort des animaux infectés. Il y eut une augmentation importante de l'azote uréique à partir du 3ème jour p.i. qui se poursuivit jusqu'à la mort des animaux infectés. L'examen macroscopique et microscopique des carcasses a montré des lésions importantes dans beaucoup d'organes, y compris des coagulations intravasculaires disséminées.

Des foyers de la peste des petits ruminants (PPR) ont été étudiés en 1993 et 1994 dans des troupeaux de chèvres de race sahélienne au Tchad. Si le virus n'a pu être isolé des premiers foyers de 1993, le sondage sérologique par le test ELISA de compétition ponant sur 475 sérums récoltés dans la zone d'épidémie a montré une prévalence de 34 %. Pour la première fois au Tchad, le virus fut isolé et des cas cliniques caractéristiques de la PPR furent observés sur les chèvres sahéliennes réputées peu sensibles à ce virus. La maladie a été reproduite expérimentalement par inoculation des chèvres avec des broyats de ganglions et de poumons, ces derniers ayant provoqué les symptômes les plus sévères. La réaction d'immunodiffusion en gélose s'est révélée positive vis-à-vis de l'antisérum anti-PPR avec les broyats de poumons et de ganglions mésentériques, métis pas avec ceux de ganglions préscapulaires. La caractérisation du virus isolé, en particulier sur le plan génomique, s'avère nécessaire.

Deux souches de Theileria parva ont été isolées sur du bétail-témoin pendant des essais d'immunisation sur le terrain contre la theilériose à SAO Hill et West Kilimanjaro, dans les parties Sud et Nord de la Tanzanie respectivement. Ces deux souches de parasites ont engendré une affection grave au point de vue clinique qui a nécessité un traitement antitheilérien pour 3 des 5 bovins infectés expérimentalement. Les animaux guéris de cette infection avec les deux souches de T. parva en cause n'ont pas présenté de signes fébriles, et un seul animal sur quatre a présenté une parasitose avec de rares schizontes pendant un jour, au cours d'un test d'infection avec Theileria parva (Kasoba) originaire du sud du Malawi. A l'inverse, les deux témoins ont montré des signes de fièvre avec la présence de schizontes, et l'un d'entre eux a dû subir un traitement antitheilérien pour être sauvé.

Les valeurs biochimiques du sérum et du plasma ont été déterminées chez des brebis de la race naine de l'Afrique de l'Ouest expérimentalement infectées par Trypanosoma brucei. Les résultats montrent une élévation du fer sérique, des chlorures, du bicarbonate, des phosphates inorganiques, de la créatinine, de l'urée, des protéines totales, des globulines et du fibrinogène plasmatique. L'albumine sérique, le rapport albumine/globuline ainsi que les valeurs du potassium, du cuivre et du magnésium ont baissé. Les résultats semblent montrer un mauvais réemploi du fer au niveau de I'érythropoïèse et un dysfonctionnement probable au niveau de la parathyroïde, du foie et/ou du rein.

Pour comparer leurs degrés respectifs de sensibilité à l'égard de la trypanosomose, 24 moutons et chèvres de race naine Djallonké, et 16 moutons et chèvres Peul du Sahel, ont été inoculés avec des souches de Trypanosoma vivax et de Trypanosoma congolense. Un animal de chaque race a servi de témoin. Une anémie est observée chez tous les animaux inoculés. Pour l'infection à T. vivax, 1 chèvre Djallonké sur 6, 3 chèvres sur 4 et 2 moutons sur 4 de race Peul du Sahel sont morts en 16 semaines d'expérimentation. Une seule mortalité sur 4 est enregistrée dans le lot des moutons Peul du Sahel, pour l'infection à T. congolense. Les chutes de poids et de concentration leucocytaire observées ne diffèrent pas significativement entre Djallonké et Peul du Sahel durant 8 semaines. Cette étude montre une bonne résistance des moutons et chèvres Djallonké à l'infection à T. vivax. Par contre, il n'y a pas de différence significative entre les deux races de moutons et de chèvres infectés à T.congolense.