R S SILAYO

50 cattle immunized by an infection and treatment method with 3 strains of Theileria parva (Mugaga, Kiambu 5 and Serengeti transformed), together with 19 controls, were exposed to natural tick infestation in Tanzania, in a site where a continuous influx of infected ticks from different regions of the country may be expected to occur. Exposure lasted for 2 months, monitoring continued for 3 more weeks after exposure ended. All 19 controls contracted East Coast Fever and died. 40 of the 50 immunized animals survived the whole period of monitoring; the other 10 died of accidents (2), heartwater (3) and unidentified causes (5); none died of ECF. It is recommended that this method of immunization be routinely applied to protect valuable animals at risk. An attempt to immunize against pathogenic Theileria mutans, by injecting blood containing piroplasms of a strain of low pathogenicity, showed that this method may protect against high parasitaemias caused by natural tick-borne infections ...

The relative resistance to tick infestation of zebu (Bos indicus) in comparison to crossbred (B. indicus x B. taurus) cattle was investigated. B. indicus breeds, all belonging to Tanganyika shorthorn zebu were Meru, Mbullu and Iringa red. Crossbreds were Meru x Friesian and Iringa red x Friesian. Parameters to distinguish between 'tick resistant' and 'tick susceptible' cattle were tick counts on naturally exposed animals, serum complement levels and delayed skin hypersensitivity response to phytohaemagglutinin. Results have shown that pure zebu cattle are less infested with ticks when compared to zebu-taurine crosses under identical field conditions. Zebu cattle also had significantly higher serum complement level than crossbred cattle. While serum complement and tick burden were negatively associated (r = -0.27, P < 0.001), the cutaneous response to phytohaemagglutinin did not vary with tick infestation. The influence of cattle breed on tick infestation and serum complement level is demonstrated.

MicroELISA tests for the detection of trypanosomal antibodies in cattle infected withTrypanosoma brucei, T. vivax andT. congolense were carried out using antigens prepared from culture forms and bloodstream forms ofT. brucei. Antigens prepared from culture forms gave similar microELISA values to those obtained with bloodstream form antigens and statistical analysis of the results obtained with both antigen preparations and sera from the infected animals showed significant high positive correlation. It would thus be possible to use culture form antigens as an alternative to bloodstream form antigens in diagnostic tests for trypanosomiasis, with the advantage that culture form antigens are more easily prepared free from extraneous protein. Les tests MicroELISA pour la détection des anticorps trypanosomiens chez le bétail infecté parTrypanosoma brucei, T. vivax etT. congolense ont été effectués en utilisant des antigènes préparés à partir de formes de culture et de formes sanguines deT. brucei. Les antigèns de culture ont donné des titres semblables à ceux obtenus avec les antigènes des formes sanguines et l'analyse statistique a montré une corrélation positive élevée entre les résultats fournis par les deux types d'antigène vis-à-vis des mêmes sérums d'animaux infectés. Il serait donc possible d'utiliser les antigènes de culture comme alternative des antigènes de formes sanguines pour le sérodiagnostic des trypanosomoses, avec l'avantage qu'ils sont plus faciles à préparer à l'état pruifié. Se llevaron a cabo estudios de laboratorio con la prueba microELISA para detectar anticuerpos contra tripanosomiasis en ganado infectado conTrypanosoma brucei, T. vivax y T. congolensis. Los antígenos se prepararon con formas cíclicas deT. brucei obtenidas de cultivos y de formas sanguíneas. Los antígenos preparados con formas cíclicas obtenidas de cultivos, dieron valores microELISA similares a los obtenidos con antígenos preparados con formas sanguíneas del tripanosoma. Los análisis estadísticos de los resultados obtenidos con preparaciones de ambos antígenos y sueros de animales infectados tuvieron una alta correlacíon positiva. Se concluye que, sería posible preparar antígenos con formas del triposoma obtenidas de cultivos para el diagnóstico de la tripanosomiasis, como alternativa de antígenos preparados con formas sanguíneas. También se sugiere que los antígenos preparados de cultivos tienen la ventaja de estar libres de proteinas extrañas.

MicroELISA tests for the detection of trypanosomal antibodies in cattle infected withTrypanosoma brucei, T. vivax andT. congolense were carried out using antigens prepared from culture forms and bloodstream forms ofT. brucei. Antigens prepared from culture forms gave similar microELISA values to those obtained with bloodstream form antigens and statistical analysis of the results obtained with both antigen preparations and sera from the infected animals showed significant high positive correlation. It would thus be possible to use culture form antigens as an alternative to bloodstream form antigens in diagnostic tests for trypanosomiasis, with the advantage that culture form antigens are more easily prepared free from extraneous protein. Les tests MicroELISA pour la détection des anticorps trypanosomiens chez le bétail infecté parTrypanosoma brucei, T. vivax etT. congolense ont été effectués en utilisant des antigènes préparés à partir de formes de culture et de formes sanguines deT. brucei. Les antigèns de culture ont donné des titres semblables à ceux obtenus avec les antigènes des formes sanguines et l'analyse statistique a montré une corrélation positive élevée entre les résultats fournis par les deux types d'antigène vis-à-vis des mêmes sérums d'animaux infectés. Il serait donc possible d'utiliser les antigènes de culture comme alternative des antigènes de formes sanguines pour le sérodiagnostic des trypanosomoses, avec l'avantage qu'ils sont plus faciles à préparer à l'état pruifié. Se llevaron a cabo estudios de laboratorio con la prueba microELISA para detectar anticuerpos contra tripanosomiasis en ganado infectado conTrypanosoma brucei, T. vivax y T. congolensis. Los antígenos se prepararon con formas cíclicas deT. brucei obtenidas de cultivos y de formas sanguíneas. Los antígenos preparados con formas cíclicas obtenidas de cultivos, dieron valores microELISA similares a los obtenidos con antígenos preparados con formas sanguíneas del tripanosoma. Los análisis estadísticos de los resultados obtenidos con preparaciones de ambos antígenos y sueros de animales infectados tuvieron una alta correlacíon positiva. Se concluye que, sería posible preparar antígenos con formas del triposoma obtenidas de cultivos para el diagnóstico de la tripanosomiasis, como alternativa de antígenos preparados con formas sanguíneas. También se sugiere que los antígenos preparados de cultivos tienen la ventaja de estar libres de proteinas extrañas.

An in vitro infectivity assay was used to examine five cryoprotectants for their suitability for preserving Theileria parva sporozoites. All five were capable of preserving T. parva sporozoites through freezing, the optimal concentrations being 7.5% for glycerol, 5% for dimethyl sulphoxide (DMSO), poly (vinylpyrrolidone) (PVP) and poly(ethylene glycol) (PEG), and 2.5% for hydroxyethyl starch (HES). When the five cryoprotectants were compared at their optimal concentrations, using a modification of the standard method of stabilate preparation, glycerol was significantly better than the others (p<0.05). Measurement of the effects of each cryoprotectant on the osmolality of the media revealed that glycerol and DMSO elevated the osmolality significantly (p<0.05). Resuscitation of glycerol-preserved sporozoites required the presence of glycerol in the diluent to maintain infectivity. Studies on the effects of equilibration time in glycerol on the infectivity of sporozoites showed that those frozen immediately after mixing (2 min) were as infective as those frozen after 60 min of equilibration.

Adult male and female Rhipicephalus appendiculatus ticks infected with Theileria parva (Muguga 3087) were fed on rabbits and the development of infection was monitored daily using light microscopy and an in vitro titration technique able to quantify the infectivity of sporozoite suspensions. The salivary glands stained with methyl green pyronine showed presence of infection in some unfed ticks. The intensity of staining was shown to increase with the number of days the ticks had fed. The in vitro technique, on the other hand, could detect infection only in ticks which had fed for 3-5 days. Feeding of ticks on rabbits for 4 days produced significantly more sporozoites than any other lengths of feeding (P = 0.001). The in vitro assay was also able to demonstrate differences between male and female R. appendiculatus in production of infective sporozoites. Female ticks produced significantly more sporozoites than male ticks (P = 0.002).

The effects of holding temperature, pH and medium on the infectivity of Theileria parva sporozoites were investigated using an in vitro infectivity assay. The sporozoite infectivity lasted for 72 h at a holding temperature of 4°C but for only 24 h at 24°C. Sporozoite infectivity was found to be sensitive to pH variations and sporozoites were most infective between pH 7 and pH 8. There was a significant loss in infectivity at pH 5 and infectivity was almost totally abolished at pH 9. Theileria parva sporozoites are usually held and manipulated in Eagle's minimum essential medium (MEM) with Earles' salts. In this study, Leibovitz-15 supplemented with 15% fetal bovine serum gave a significantly better infectivity than Eagle's MEM (3.8 log units versus 1.0 log units) or any other medium. The importance of proper management of the T. parva sporozoite environment in the laboratory or field is emphasized by the findings in these studies and might also explain some of the failures of vaccination when the pH of the holding medium was allowed to deteriorate.