Progress and priorities in research on heartwater.
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Animals↗
Biomedical subjects
G Uilenberg
Publications and source records attributed to G Uilenberg.
Integrated control of tropical animal parasitoses.
In the past, the control of parasites of domestic animals has relied mainly on the use of drugs and pesticides. Although these compounds are still of great importance in the prevention and treatment of parasitic diseases, the accent has shifted in recent years to a more flexible approach, integrating various other control measures. The main reasons for this change are: development of resistance of the parasites against the compounds used; reduced development of new compounds to overcome resistance (increasingly stringent regulations on toxicity and residues, resulting in very high research and development costs, insufficient return for industry because of short life-span of new products due to resistance, and limited and poor markets for compounds against parasites in developing countries); increasing cost of new products for the user; problems associated with toxicity, environmental pollution and residues in animal products. Integrated parasite management makes use, where possible, of biological and mechanical control methods, of acquired and innate host resistance, and of genetical, ecological, sanitary and regulatory procedures, although chemical control can seldom be entirely abolished. Cost-effectiveness and sustainability in all respects are of primary importance.
Animals↗
Review of Australian species of Theileria, with special reference to Theileria buffeli of cattle.
This review describes 4 species of parasites in Australia generally regarded as Theileria. The physiological and epidemiological characteristics of the species that occurs in cattle are discussed. Confusion still surrounds the relationship of this species with benign species of Theileria in other countries. Arguments are presented to support the proposal that the bovine species in Australia is correctly designated Theileria buffeli and that this name should apply to all the benign species of Theileria of cattle in Eurasia. The other 3 species considered in the review are proposed species from marsupials. Of these, only Theileria tachyglossi can confidently be included in the genus Theileria, because schizonts have yet to be detected in the other 2 species.
Animals↗
Piroplasms of domestic animals in the Macedonia region of Greece. 1. Serological cross-reactions.
During a serological survey on haemoparasites in Macedonia, serum samples were collected from cattle, sheep and goats. All sera were tested by the indirect immunofluorescence test (IFAT); the cattle sera against Theileria orientalis, T. annulata, Babesia bigemina, B. bovis, B. divergens and B. major antigens; the sheep and goat sera against T. ovis, B. ovis, B. motasi and B. crassa antigens. Parallel tests of negative and positive control sera against all the antigens showed the existence of cross-reactions of different degrees between species of the same genus. In cattle, the most important cross-reactions were obtained against B. bigemina antigen, especially with the anti-B. bovis serum, in small ruminants against B. motasi with the anti-B. crassa serum. In the field sera, there was a high correlation between the antibody titres of B. bigemina and B. bovis, and also between the titres of these two Babesia spp. and B. divergens. A high correlation was also found between B. motasi and B. crassa, and lower ones between these two and B. ovis. The correlations of the sera titres were due to mixed infections or to cross-reactions. Therefore, the use of the IFAT is not always satisfactory for diagnosing infections in regions where animals are infected with different piroplasms.
Animals↗
[Integrated control of tropical parasitic diseases in animals].
In the past, parasite control in domestic animals has relied mainly on the use of drugs and pesticides. Although these compounds are still of great importance in the prevention and treatment of parasitic diseases, in recent years the emphasis has shifted to a more flexible approach, integrating various other control measures. The main reasons for this change are:--development of parasite resistance to the compounds used; --reduced development of new compounds to overcome resistance (increasingly more stringent regulations on toxicity and residues, resulting in very high research and development costs, insufficient return for industry because of the short life-span of new products due to resistance and because the market for compounds in developing countries is limited and poor);--increasing cost of new products for consumers;--problems associated with toxicity, environmental pollution and residues in animal products. Integrated parasite management makes use, where possible, of biological and mechanical control, of acquired and innate host resistance, and genetical, ecological, sanitary and regulatory procedures, although chemical control can seldom be entirely eliminated. Cost-effectiveness and sustainability in all respects are of primary importance.
Animals↗
International collaborative research: significance of tick-borne hemoparasitic diseases to world animal health.
A general review is given of the tick-borne hemoparasitic diseases of greatest economic importance in ruminants, babesiosis, anaplasmosis, theileriosis and cowdriosis, each caused by one or more species of hemoparasites. Most affected are cattle and small ruminants, buffalo are more resistant and little is known regarding camels. The situation varies from one continent or region to another. Innate and breed susceptibility to these diseases are of tremendous importance. Disease in the field cannot be considered separated from the whole complex of tick-borne diseases and from the ticks themselves, particularly if the aim is to attain endemic stability. International coordination is needed now that research funds are scarce. An appendix contains tables with hemoparasites of various domestic animals and notes with background details.
Animal Welfare↗
Ticks and control methods.
Ticks are the most important ectoparasites of livestock in tropical and sub-tropical areas, and are responsible for severe economic losses both through the direct effects of blood sucking and indirectly as vectors of pathogens and toxins. Feeding by large numbers of ticks causes reduction in live weight gain and anaemia among domestic animals, while tick bites also reduce the quality of hides. However, the major losses caused by ticks are due to the ability to transmit protozoan, rickettsial and viral diseases of livestock, which are of great economic importance world-wide. The authors review general aspects of tick biology, the taxonomy, pathogenic effects and vector role of these species, and methods for the control of ticks. The distribution of ticks is continuously changing, as illustrated by the spread of the African tick Amblyomma variegatum in the Caribbean, where a large-scale eradication campaign is now under way.
Animals↗
[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↗
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↗
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↗
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↗
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↗
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↗
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↗
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↗
[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↗
[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↗
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↗