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D Zivkovic

Publications and source records attributed to D Zivkovic.

26 records · Page 2Linked to original sources
PubMed1988

Quantitative correlation of parasitological and serological techniques for the diagnosis of Trypanosoma congolense infection in cattle.

A comparison was made between serological and parasitological techniques for the diagnosis of bovine trypanosomiasis in Zambia. Overall sero-prevalence rates as determined by IFAT and ELISA were respectively 2.7-fold and 2.9-fold greater then the percentage of samples found positive with the dark ground/phase contrast buffy coat technique (DG). The results obtained by the two serological techniques were found to be closely correlated (94.2%) agreement) and titres obtained by ELISA tended to be slightly higher than those obtained by IFAT. Linear regression analysis of the results obtained by the IFAT and DG techniques revealed a highly significant correlation. This finding would permit the use of only one of the techniques in an epidemiological survey and to extrapolate the results from the regression line.

Animals↗
PubMed1988

Morphogenetic diapause in Amblyomma variegatum (Acari: Ixodidae).

In southern Africa, Amblyomma variegatum Fabricius is characterized by a strict seasonal activity. Experiments were carried out to determine whether a diapause mechanism regulates this seasonality. Engorged A.variegatum females were exposed to controlled laboratory conditions or natural field conditions at different times of the year. Females exposed in a natural environment in September-October (short day) had significantly longer pre-oviposition periods than females exposed from November to March. The season in which the previous instar fed had no apparent effect on the engorgement or pre-oviposition periods of the females. Furthermore, artificial changes in photoperiod during and after female engorgement had no significant effects on pre-oviposition periods. It is tentatively concluded that the unfed female is the responsive stage to photoperiodic changes which induce diapause. Diapause could be terminated and oviposition induced by exposing females to a short period of chilling (18 degrees C for 48 h). It is concluded that a morphogenetic diapause mechanism exists in A.variegatum, which is probably induced by short day responses and terminated following rainfall and a concomitant decrease in soil temperature. The diapause, which occurs in females which fed early in the season, causes a delay in oviposition and therefore effectively synchronizes the life-cycle to ensure that eggs and larvae occur at a climatically favourable period.

Animals↗
PubMed1987

Ticks (Acari:Ixodidae) of the Blue and White Nile ecosystems in the Sudan with particular reference to the Rhipicephalus sanguineus group.

Twenty-four adult ixodid tick species, infesting livestock and some wildlife hosts along the Blue and White Nile in the Sudan, were identified. Three species, Boophilus geigyi, Rhipicephalus camicasi and R. bergeoni, were recorded for the first time from the Sudan. Tick numbers on indigenous breeds of cattle (Bos indicus) were relatively low, ranging between 17.1 and 40.5 per animal. Young cattle grazing with the herd carried significantly fewer ticks than older animals. With the exception of B. annulatus and R. simus, which have extended their distribution further north into Blue Nile, Gezira and Khartoum Provinces, the distribution patterns of the most important cattle ticks have been relatively unchanged over the past 30 years. The Rhicicephalus sanguineus group was represented by six species. R. camicasi was the only species present on cattle, sheep and goats in the north in Kassala and Khartoum Provinces, whereas this species occurred sympatrically with R. guilhoni and R. turanicus further south in Gezira and Blue Nile Provinces. In the Southern Region of the Sudan only R. turanicus and R. guilhoni were present, the latter being by far the predominant species, with peak activity towards the end of the rains in the Jonglei Canal Area. R. bergeoni was collected once, from cattle near the Ethiopian border in Blue Nile Province, whereas R. sanguineus sensu stricto was collected throughout the study area, from domestic dogs only. Finally, R. sulcatus was found once on a hare. The distributions of the common tick species are correlated with the occurrence of tick-borne diseases of domestic animals and recommendations for the control of tick-borne diseases and their vectors in the Sudan are given.

Animals↗
PubMed1986

Biology of Rhipicephalus appendiculatus and R. zambeziensis and production of a fertile hybrid under laboratory conditions.

In some areas of Eastern and Southern provinces of Zambia Rhipicephalus appendiculatus and R. zambeziensis are sympatric, and numerous intermediate forms as well as typical R. appendiculatus and R. zambeziensis are found. Experiments were carried out in order to clarify the taxonomic status of the intermediate forms. Biology and hybridization capacities of two strains of R. appendiculatus (A and D) and one strain of R. zambeziensis (H) were studied. Infestations on rabbits and calves were performed at the beginning and at the end of the Zambian rainy season. The adults of both species showed preference for the bovine host and performed better at the end of the rainy season. A recently isolated strain of R. appendiculatus had notably higher larval production per unit engorgement weight than the strain that had been maintained for prolonged periods under laboratory conditions. R. zambeziensis produces fewer larvae and had longer development periods than R. appendiculatus. The two species cross-breed under laboratory conditions. A fertile hybrid is produced by R. zambeziensis females and R. appendiculatus males, whereas a sterile hybrid is a result of a reciprocal cross. Morphology of adults of the fertile hybrid (H/A) is indistinguishable from the maternal species, whereas adults of the sterile hybrid (A/H) are of maternal, paternal and intermediate forms. Larval production indices (LPI) vary from 0.4 to 3.7 for the H (females) X A (males) cross, approximately three-fold less than in the maternal species. For the reciprocal cross, LPI ranges from 0.1 to 2.7, five- to thirty-fold less than in the maternal species. The fertile hybrid has a higher LPI than both first crosses, and under the most favourable climatic conditions LPI is even higher than for the maternal species. Adults of the sterile hybrid rarely formed pairs. Only partially engorged female ticks detached, which produced no viable eggs. Both hybrids may occur in areas where the two species are sympatric. However, detailed field studies will have to be performed in order to gain knowledge on population dynamics, interbreeding and the vector role of the two species and their hybrids under field conditions.

Animals↗
PubMed1985

Immunity to Babesia in mice. III. The effects of corticosteroids and anti-thymocyte serum on mice immune to Babesia rodhaini.

BALB/c mice, immunized against Babesia rodhaini by an amicarbalide controlled infection, were exposed to selective immunosuppressive treatment with corticosteroids and anti-thymocyte serum (ATS) respectively. Hydrocortisone acetate, 100 mg/kg, given i.p. six times during the three weeks after challenge inoculation caused a rising parasitaemia and high mortality (6/7). Dexamethasone in the drinking water at 20 mg/l or 10 mg/l for 22 days had a similar suppressive effect on the protection against B. rodhaini. Mortality, 100% at the dose rate of 20 mg/l and 50% at 10 mg/l, occurred both in challenged and in carrier animals after the reappearance of parasites in the bloodstream. All the ATS-treated immune mice demonstrated parasitaemia after challenge, although at a lower level than did the corticosteroid treated mice. Seven out of 9 animals died. Corticosteroid-sensitive macrophages together with T-lymphocytes are considered to play an important role in protection against B. rodhaini in specifically induced immunity in mice.

Animals↗
PubMed1984

Immunity to Babesia in mice. I. Adoptive transfer of immunity to Babesia rodhaini with immune spleen cells and the effect of irradiation on the protection of immune mice.

Immunisation of Balb/c mice against Babesia rodhaini by an amicarbalide-controlled infection resulted in a solid immunity which lasted for 216 days. With spleen cells of immune mice protection could be transferred both to naive mice pretreated with cyclophosphamide. Treatment of naive mice with cyclophosphamide (300 mg/kg) five days before a lethal B. rodhaini inoculation resulted in over 50% survival. This protective effect of cyclophosphamide is explained by its inhibiting effect on suppressor T-cells. The protection against B. rodhaini challenge infection afforded to immune Balb/c mice was completely resistant to a sublethal irradiation of 400 rad. Since B-lymphocyte function in antibody production is suppressed by this dose, the role of antibodies in the effector phase of the immunity appears to be of minor if any importance. A considerable degree of protection was still preserved after irradiation of immune animals with 875 rad. Sensitivity to this irradiation dose of all immunocompetent cells except macrophages and a small fraction of T-lymphocytes indicates the involvement of these cell types in the effector phase of the specific immunity. Highly radioresistant macrophages are therefore considered to play the major role but T-lymphocytes are also required for complete protection.

Animals↗
PubMed1984

Immunity to Babesia in mice. II. Cross protection between various Babesia and Plasmodium species and its relevance to the nature of Babesia immunity.

Mice immunized against B. rodhaini by means of a drug-controlled infection were subsequently resistant to infection with B. microti and B. ratti. In the reciprocal experiments the protection against B. rodhaini was less effective. B. rodhaini immunized mice were also considerably protected against P. vinckei infection, whereas protection against P. berghei did not occur. Antibody determinations indicated that the heterologous protection cannot be explained by the occurrence of cross-reacting antibodies. Because of similarity with the non-specific suppression of babesiosis in BCG-infected mice, the same effector mechanism is postulated to explain the infection-induced homologous and heterologous protection. Unlike non-specifically induced protection, the induction of acquired resistance by means of a drug-controlled B. rodhaini infection is thymus-dependent.

Animals↗