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G Uilenberg

Publications and source records attributed to G Uilenberg.

At least 37 records · Page 2Linked to original sources
PubMed1994

[Field trial of an attenuated vaccine against heartwater disease].

The results are given of a field trial using a Senegalese stock of Cowdria ruminantium which had been attenuated by passage in cell culture. Thirty vaccinated and thirty control sheep were exposed in the Niayes region of Senegal and were monitored daily. In the control group, 22 animals died of heartwater, associated in one case with anaplasmosis. In the vaccinated group, 13 animals died; Cowdria was found only in two sheep which had previously suffered from ehrlichiosis or anaplasmosis; three other cases of ehrlichiosis and two of anaplasmosis were also observed among these 13 animals. The resistance of the two vaccinated animals which showed Cowdria in their cerebral cortex was apparently lowered by the intercurrent infections. The other animals of the vaccinated group showed no evidence of Cowdria infection.

Animals↗
PubMed1993

Progress in research on tick-borne diseases: theileriosis and heartwater.

The rapid population growth in subsaharan Africa necessitates a great increase in animal production in the more humid zones. Vector-borne diseases occurring in these zones will assume more importance, but are difficult to control. They include theileriosis and heartwater. Recent developments in research on these diseases are presented. Indigenous animal populations in endemic areas, subjected to natural selection, are far less susceptible than exotic stock. Heartwater, caused by the rickettsia Cowdria ruminantium, transmitted by Amblyomma ticks, causes high mortality in exotic ruminants. It has received much attention in recent years, partly because the disease has been introduced from Africa into the Caribbean and threatens the American mainland. Since the recent success of in vitro culture, much progress in research has been made, but so far prevention still relies mainly on acaricidal tick control; an infection and treatment method is used on a limited scale. Antigenic diversity is a complication for immunization procedures. Theileria parva (East Coast fever, Corridor disease and January disease) and T.annulata (Mediterranean or tropical theileriosis) are the most pathogenic of the 6 species of this protozoan genus that infect cattle. Great progress has been made in recent years in knowledge on the immunology, the epidemiology, the taxonomy and the chemotherapy of theileriosis. Intensive acaricidal tick control can now be supplemented by an attenuated schizont vaccine against T.annulata, while immunization against East Coast fever is carried out on a limited scale using virulent sporozoite infection and treatment. Research on recombinant vaccines is promising. Antigenic diversity in T.parva is a serious complication.

Africa↗
PubMed1993

Vaccination against heartwater using in vitro attenuated Cowdria ruminantium organisms.

Sequential passage of Cowdria ruminantium (Senegal isolate) in cultures of bovine umbilical endothelial cells has resulted in loss of virulence without loss of immunogenicity, as previously demonstrated. We have carried out further immunization of 39 Dutch sheep using in vitro attenuated rickettsiae of passage 21 and challenged these animals either with the homologous or with heterologous Cowdria stocks. After vaccination several sheep developed elevated rectal temperatures for a maximum of 2 days, but no further clinical response to the vaccine was observed. All sheep developed high titres of antibodies to Cowdria. Challenge of 10 sheep with the homologous virulent stock did not provoke any clinical reaction, demonstrating that these animals were solidly immune. Reactions to heterologous challenge varied from virtually no reaction to fatal heartwater depending on the stock of Cowdria used. These results are discussed in relation to currently available vaccination methods against cowdriosis. In Senegal 30 susceptible sahelian sheep were immunized with attenuated rickettsiae of passage 21. Hyperthermia was seen in 13, the only other clinical symptom was a temporary diarrhoea. The immunized animals are at present exposed, together with 30 controls, to field challenge in the Niayes, the area where the Senegal isolate was originally isolated.

Animals↗
PubMed1991

Antigenic diversity of Cowdria ruminantium isolates determined by cross-immunity.

Antigenic diversity in five stocks of the tick-borne rickettsia Cowdria ruminantium, the causal agent of heartwater disease of ruminants, was studied by cross-immunity trials in goats and sheep. Complete absence of cross-protection was found only between the Kümm and Kwanyanga stocks, and in all other combinations there were various degrees of cross-immunity. Immunological strain differences were more pronounced in goats than in sheep.

Animals↗
PubMed1991

The tick-borne rickettsia Cowdria ruminantium has a Chlamydia-like developmental cycle.

The development of the tick-borne rickettsial pathogen Cowdria ruminantium (S stock) was studied in bovine umbilical endothelial (BUE) cell cultures and in goat choroid plexus, by light- and electron microscopy. Cowdria divided by binary fission within intracytoplasmic vacuoles resulting in large colonies of reticulate bodies. After three to four days in culture, reticulate bodies developed into smaller intermediate bodies characterized by an electron-dense core. Shortly before disruption of the host cells, intermediate bodies condensed further into electron-dense elementary bodies, which were released into the culture medium. Elementary bodies invade other endothelial cells thus initiating a new infectious cycle which lasts between 5 and 6 days. In the infected goat choroid plexus similar reticulate and intermediate bodies were identified within vacuoles of capillary endothelial cells. However, extracellular elementary bodies were not detected. Another stock of Cowdria (W) showed an identical developmental cycle as that of the S stock. The W isolate was also pathogenic for mice, making it possible to test the infectivity of reticulate and elementary bodies in these animals. Reticulate bodies appeared to be less infective than elementary bodies. The developmental cycle of Cowdria resembles the cycle known to occur in Chlamydia. Moreover, Cowdria has other similarities with Chlamydia. It has a Gram-negative envelope, it does not store iodine-stainable carbohydrates and may lack peptidoglycan as does Chlamydia. It is concluded, that Cowdria and Chlamydia are to a certain extent related, confirming a recent report that both organisms have certain antigenic determinants in common. Since Cowdria is also related to Ehrlichia it may well be that Cowdria takes an intermediate position between Chlamydia and Ehrlichia. The phylogenetic relationship between Cowdria and Chlamydia and also with Ehrlichia should be further elucidated by molecular analysis using 16S ribosomal DNA sequences.

Animals↗
PubMed1990

Immunization of cattle against Theileria parva bovis and their exposure to natural challenge.

Theileria parva bovis isolates were tested for their immunizing capacity under natural field challenge on Willsbridge Farm in the highveld of Zimbabwe. Fifteen susceptible Sussex yearlings were immunized with the Boleni stock and 15 with a mixture of three isolates from the farm, using tick-derived sporozoite stabilates. No chemoprophylaxis was used. A dose of 0.1 ml of stabilate appeared to be safe in preliminary laboratory experiments, but the reactions were severe in the Sussex cattle and one died despite treatment. Twenty-nine immunized animals and 10 controls first experienced a mild infection, starting about 15 days after their arrival at the farm. Ten of the immunized animals and four controls had schizonts in peripheral lymph nodes for variable periods; one third of those had pyrexia. Nymphal Rhipicephalus appendiculatus ticks applied to three of the reacting immunized calves transmitted Theileria taurotragi to two animals and T. parva to a third. A second Theileria infection, due to T. parva bovis, was detected shortly after the first one. Schizonts were detected in seven out of 10 controls. Pyrexia was more severe and prolonged. Two of the controls died of theileriosis. At the same time schizonts were seen in three immune animals and eight of them had short periods of pyrexia. Intercurrent infections with Babesia bigemina, Borrelia theileri and Eperythrozoon were detected and may have contributed to the fever. Tick infestations were low during the exposure. In the second year of exposure, four out of eight new control animals had severe reactions, and one died. None of the immunized animals became ill, but one animal from the first year control group, which had not reacted previously, had clinical theileriosis. It is concluded that immunization provided an effective protection against field challenge.

Animals↗
PubMed1990

Present and future possibilities for the control of cowdriosis and anaplasmosis.

Cowdriosis and anaplasmosis are most important tick-borne rickettsial diseases of ruminants. After a short introduction, in particular of their aetiology, epidemiology and diagnosis, present methods and future prospects for their control are briefly reviewed. The value and disadvantages of the four possible approaches, chemotherapy, tick control, the utilisation of inverse age-resistance in order to attain endemic stability, and artificial immunisation, are reviewed. Promising future developments in the field of immunisation are indicated.

Anaplasmosis↗
PubMed1990

The indirect fluorescent antibody test for bovine anaplasmosis.

An indirect fluorescent antibody test was used successfully for the serodiagnosis of experimental Anaplasma infections in cattle. Specific antibodies were detected three to ten days after anaplasma bodies were found in the blood, and persisted at least 15 weeks post-infection. An American and an African stock of A. marginale were used to prepare antigens, and gave comparable results when tested on sera positive to either of these stocks, as well as to an A. central-like stock from Korea. There were no cross-reactions with several Theileria, Babesia, Trypanosoma and Eperythrozoon species.

Anaplasma↗
PubMed1990

[Spreading of the tick Amblyomma variegatum in the West Indies: how can this serious menace be explained and what should be done?].

The author presents a brief history of the introduction and extension of the African tick Amblyomma variegatum in the Caribbean. The tick is particularly dangerous for the livestock industry because of its role as a vector of heartwater and its association with severe dermatophilosis. It is already distributed in the Lesser Antilles from Puerto Rico to Barbados and St. Vincent. The chronology of its sudden unexplained expansion since the 1960s corresponds well with the multiplication of the cattle egret (Bubulcus ibis) in the region, while the tick had hardly extended its distribution during more than 130 years, before this African bird arrived in the western hemisphere. These birds are often infested with larvae of the tick and carry out important movements between islands. The imminent invasion of the American continent appears unavoidable, with incalculable disastrous consequences for the livestock industry, unless the tick is rapidly eradicated from all infested islands. While presenting practical, human and social problems, eradication from the islands is technically feasible and its cost/benefit ratio is very positive.

Animals↗
PubMed1990

[Presence of Theileria annulata in Mauritania].

A fatal case of bovine theileriosis by Theileria annulata is reported from Mauritania in a Friesian cow born in a dairy farm in Nouakchott. The farm was originally established with cattle imported from France. Specific diagnosis was based on piroplasm morphology and on high specific antibody titres in some of the animals. The only tick found in the herd was Hyalomma dromedarii. Four of 49 local zebus sampled at random in the south of the country had high specific antibody titres to T. annulata, while 14 had lower or doubtful titres. The infection therefore appears to be autochthonous.

Animals↗
PubMed1990

Methods currently used for the control of heartwater: their validity and proposals for future control strategies.

Major advances made in the last few years in the knowledge of heartwater have not yet resulted in significant improvement of its prevention and control. Acaricide resistance and the high cost of chemical vector control stimulate research on alternative methods of vector control, such as immunization against the tick and the use of pheromones. Recently developed in vitro methods for the culture of Cowdria ruminantium may make it possible to arrive at safe recombinant or molecular vaccines. Specific chemotherapy may be improved by new laboratory screening methods, and studies on the pathogenesis of heartwater could lead to better non-specific treatment as well. Studies on the heritability of natural resistance to heartwater should determine whether or not practical selection and transfer of resistance is feasible. More research is also needed on the immunology and diagnosis of the disease and the factors involved in the resistance of young animals.

Animals↗
PubMed1990

Observations on mouse-infective stocks of Cowdria ruminantium: microscopical demonstration of the Kwanyanga stock in mouse tissue and the carrier-status of the Senegal stock in mice.

The behaviour of two different stocks of Cowdria ruminantium was investigated in mice. The mouse-pathogenic Kwanyanga stock of C ruminantium was microscopically demonstrated in mice in capillary endothelial cells of the lung, spleen, kidney, liver and brain. Mice of the ninth passage of the Senegal stock, which is infective but not pathogenic to mice, were kept alive for a year. Their blood and homogenised spleens, inoculated intravenously, caused fatal heartwater in a goat. However, the Senegal stock could not be demonstrated microscopically in mice. These results indicate the possible role of rodents in the epidemiology of heartwater.

Animals↗
PubMed1989

Monitoring of naturally acquired and artificially induced immunity to Amblyomma variegatum and Rhipicephalus appendiculatus ticks under field and laboratory conditions.

The ability of rabbits, goats and cattle to acquire immunity to the ixodid ticks Amblyomma variegatum and Rhipicephalus appendiculatus was studied under laboratory and field conditions. Rabbits were successfully immunized with crude salivary gland extract (SGE) and midgut extract (ME) obtained from flat or partly fed female R. appendiculatus ticks. The lowest numbers of larvae were produced by females fed on rabbits immunized with unfed midgut extract. Similar reductions in larval production could be induced after three infestations of rabbits with adult R. appendiculatus. Also, successive feedings of nymphs of R. appendiculatus on rabbits resulted in significantly reduced engorgement weights. Skin testing with SGE induced delayed-type hypersensitivity reactions, which could be correlated with immunity to R. appendiculatus in rabbits. Moreover, circulating antibodies were detected in rabbits with an ELISA using SGE of R. appendiculatus. Immunity to A. variegatum nymphs could be induced in rabbits by repeated infestations, but this failed in goats. Immunization of goats with midgut extract from adult A. variegatum did not protect against subsequent nymphal challenge, but strong skin reactions were noticed when adults ticks fed on immunized goats. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of SGE and ME from A. variegatum revealed the presence of 48 protein bands in SGE and 29 bands in midgut extract. Western blotting employing serum from a rabbit immune to R. appendiculatus recognized a number of bands in SGE from R. appendiculatus, but also in SGE of A. variegatum. Immunity acquired by cattle to ixodid tick infestations under field conditions was monitored by skin testing with SGE and western blot analysis. In general, cattle with the lowest tick numbers manifested the strongest delayed-type hypersensitivity responses. Finally, western blot analysis employing sera from tick-infested and tick-naive cattle could not be related to actual immune status.

Animals↗
PubMed1989

Serotypes in Cowdria ruminantium and their relationship with Ehrlichia phagocytophila determined by immunofluorescence.

Two tick-borne rickettsial pathogens of ruminants, Cowdria ruminantium (causative agent of heartwater disease) and Ehrlichia phagocytophila (causative agent of tick-borne fever), were successfully cultivated in caprine or ovine neutrophilic granulocytes. Infected cultures were subsequently used as antigens in the indirect fluorescent antibody test. Low-level bilateral serological cross-reactions could be detected between Cowdria and Ehrlichia. In addition, comparison of five Cowdria stocks using immunofluorescence demonstrated the existence of distinct serotypes within the genus of Cowdria. It is concluded that the occurrence of these serotypes will considerably complicate the current serodiagnosis of heartwater.

Animals↗
PubMed1989

Three groups of Babesia canis distinguished and a proposal for nomenclature.

Two stocks of large Babesia from dogs originating in France, transmitted by Dermacentor reticulatus, two from North Africa, having Rhipicephalus sanguineus as vector, and one from South Africa, transmitted by Haemaphysalis leachi, were compared in cross-immunity tests in dogs and in the indirect fluorescent antibody test (IFAT). The French and North African stocks did not immunise against the South African one, while the North African stocks did not protect against a French one. The South African stock partially protected against a French one. The three groups could be clearly distinguished in the IFAT. These differences have practical implications for existing and future vaccines against canine babesiosis and for the serological diagnosis of atypical and chronic cases. It is proposed to use a trinomial system of nomenclature for these groups: Babesia canis canis (Piana and Galli-Valerio, 1895), Babesia canis vogeli Reichenow, 1937, and Babesia canis rossi (Nuttall, 1910), having Dermacentor, Rhipicephalus and Haemaphysalis ticks as their vectors respectively.

Animals↗
PubMed1988

Borrelia infections of ruminants in Europe.

The occurrence of Borrelia spirochaetes in cattle in the Netherlands is reported for the second time, and in red deer and roe-deer in Austria for the first time. It is postulated that these spirochaetes are Borrelia burgdorferi rather than B. theileri. The reservoir role of ruminants in the epidemiology of human disease caused by B. burgdorferi in Europe should be investigated.

Animals↗
PubMed1988

Antigenic differences between stocks of Cowdria ruminantium.

Stocks of Cowdria ruminantium from Senegal, Zambia and South Africa were compared in cross immunity tests in goats. The Senegal stock caused fatal heartwater in three of 10 goats immune to the South African reference stock Ball 3, and five others showed significant febrile reactions and recovered spontaneously. Four goats immune to the Senegal stock did not show any reaction on challenge with Ball 3. The stock from Zambia was fully cross-protective with Ball 3 in experiments with three goats, but these three goats, immune to the Zambia stock and to Ball 3, showed severe febrile responses upon further challenge with the Senegal stock. The Senegal stock was highly virulent for Dutch goats and there were exceptionally large numbers of rickettsiae in brain capillaries after death. This stock has been passaged eight times in mice, without causing disease; the presence of the organism in the mice was shown by subinoculating goats. The Senegalese stock of C ruminantium is the first stock outside South Africa against which the reference Ball 3 stock does not fully immunise.

Animals↗