Spread of parasites transported with their hosts: case study of two species of cattle tick.

Like all parasites, ticks can be spread easily along with their hosts. Ticks are obligate parasites of vertebrates, to which they attach themselves for varying periods of time, and are well-adapted to this mode of transport. Once the transport stage is complete and they have detached at destination, they are also able to wait several months for the arrival of a new host on which they will continue their life cycle. This leads to the establishment of a secondary tick population. Two tropical cattle tick species, Rhipicephalus microplus and Amblyomma variegatum, have perfected this strategy of colonisation and occupation of favourable zones. Rhipicephalus microplus, which originated from South and Southeast Asia, is highly specific for ungulates, and thanks to cattle movements it has spread throughout the tropical belt, apart from the remotest areas. Amblyomma variegatum, which originated in Africa, was transported to Madagascar and the Mascarene Islands, as well as to the West Indies, during the time of the Atlantic triangular trade. These two ticks are vectors of particularly serious cattle diseases: babesiosis and anaplasmosis in the case of R. microplus, and heartwater (cowdriosis) in the case of A. variegatum. Anticipated climate changes are likely to modify the potential geographical range of these two parasite species and numerous others. Even now there are still many areas of the Americas, Asia and Oceania into which A. variegatum has not yet spread, but which it would find favourable. It could be spread not only by the transport of cattle, but also by the migration of some of its other hosts, such as birds. Surveillance--and know-how--is needed to identify these parasites when they first appear and to rapidly contain new outbreaks. Efforts should be made to raise the awareness of livestock professionals about the risks of transporting cattle. Regulations should be implemented and precautions taken to avoid such artificial expansion of the range of ticks and the diseases they transmit.

[Tick-borne rickettsioses of domestic ruminants: taxonomic elements and laboratory diagnosis]. / Les rickettsioses des ruminants domestiques transmises par les tiques: elements taxonomiques et diagnostic de laboratoire.

Tick-borne rickettsioses are diseases which remain comparatively unknown to field veterinarians. The authors present a literature review, focusing on taxonomic aspects and on laboratory diagnosis.

[Microscopic diagnosis of tick-borne diseases in Maghreb]. / Diagnostic microscopique des maladies transmises par les tiques au Maghreb.

Direct microscopic examination of smears, carried out in the farm, in combination with the clinical symptoms, is in general the quickest and cheapest way to diagnose tick-borne diseases. It is however not always sufficiently specific, as different species of a parasite genus may ressemble each other morphologically. Also, it is not suitable for epidemiological studies. On the other hand, serological and molecular methods may be more sensitive and/or specific, but are not suitable for diagnosing the cause of disease in an individual animal and in any case are not sufficiently rapid. The focus of the paper is on practical details and pitfalls to be avoided in sample taking, smear preparation, fixing and staining, microscopic examination and interpretation of the results

The global importance of ticks.

Ticks and tick-borne diseases affect animal and human health worldwide and are the cause of significant economic losses. Approximately 10% of the currently known 867 tick species act as vectors of a broad range of pathogens of domestic animals and humans and are also responsible for damage directly due to their feeding behaviour. The most important tick species and the effects they cause are listed. The impact on the global economy is considered to be high and although some estimates are given, there is a lack of reliable data. The impact of ticks and tick-borne diseases on animal production and public health and their control are discussed.

Tick reference collection of the late Dr. P.C. Morel: a tool for tick taxonomists and veterinarians.

Host preference of ticks is an important, but still controversial, subject. Recent developments in molecular biology provide new opportunities to test some hypotheses about host preference in a given environment if appropriate specimens are available. Since the unique collection gathered by Dr. P.C. Morel could help achieve this goal, we present an overview of the samples available in his collection.

Immunization against diseases caused by Theileria parva: a review.

Theileria parva is the causative agent of three epidemiologically different diseases, East Coast fever (ECF), Corridor disease and January disease, caused by 3 types of T. parva, T. p. parva, T. p. lawrencei and T. p. bovis, respectively. The history of immunization against these diseases has been marked by salient discoveries such as the immune status in recovered animals, the activity of tetracyclines during the incubation period, the possibility for cryopreserving supernatant of prefed ticks and the development of useful serological tests. The possibility of simultaneous administration of stabilate and long-acting tetracycline have greatly contributed to making the infection and treatment method operational. The importance of antigenic diversity in T. parva has been reflected in the difficulties related to the selection of the immunizing stock or combinations of stocks: a 'cocktail' of East African isolates may give broad protection against field challenge by ECF (T. parva parva), but Corridor disease is more problematic. On the other hand, certain single isolates may give equally good protection against ECF field challenge. Studies on the immunology of T. parva infection and the application of molecular tools have led to the discovery that sera of recovered animals neutralize sporozoites of various isolates, and to the p67 molecular vaccine; yet so far the only available method of immunizing against T. parva infections is the infection and treatment method or, in the case of T. parva bovis, the use of sublethal stabilate doses. Infection and treatment is applied on a fairly large scale in Zambia, and on a more limited scale in a few other countries. Immunity by this rather crude method is long-lasting and solid, but cross-immunity problems against some field strains remain. Furthermore, as immunized animals remain carriers, immunization may contribute to attaining and improving endemic stability in endemic areas in indigenous breeds with an adequate level of genetic tolerance to ECF. On the other hand, carrier animals may constitute a risk for spreading the disease into ECF-free areas where the vector is present. Other disadvantages of the method are that immunization of cattle during the incubation of naturally contracted East Coast fever will not prevent the disease and jeopardize its reputation. Furthermore, stabilates have to be cryopreserved, often a technical drawback, and contamination with undesirable pathogens may occur in tick-derived material. Therefore the need remains for the development of effective molecular vaccines and it must be remembered that immunization must be cost-effective and sustainable and it is only one aspect of integrated control of theileriosis and other tick-borne diseases. There is no universally valid strategy. Several factors have to be considered: value and susceptibility of cattle to theileriosis and to other tick-borne and tick-associated diseases, infestation by various ticks present in the area, the type of theileriosis (ECF, Corridor disease or January disease) and the epidemiological situation where immunization is taking place. The optimal age for immunization of the calves in endemic areas needs to be determined: when calf mortality by naturally occurring theileriosis is a problem, the sooner calves are immunized the better, but a proportion will have contracted natural infection before they can be reached, and immunization of very young calves might not be fully effective.

Importance of ticks and tick-borne diseases of domestic ruminants in Southern Europe.

In Southern Europe, as elsewhere, the importance of ticks and tick-borne diseases (TBD) depends on the species of tick vectors present and also varies to a great extent according to the genetic susceptibility of the livestock involved, as well as other factors such as management and vegetation. There are large gaps in our knowledge of the tick species in the various countries, and of the prevalence and economic importance of the diseases they transmit. There is a great need for tick surveys as well as surveys of tick-borne infections. It is essential to distinguish between infection and disease. A list is given of TBD and their vectors known or to be expected to occur in domestic ruminants in Southern Europe. It is hoped that the exchange of knowledge during this workshop will indicate the importance of these parasites in the various countries involved.

General review of tick-borne diseases of sheep and goats world-wide.

A general review of the tick-borne diseases of sheep and goats is given, with the emphasis on those thought to be of greatest economic importance. These include babesiosis, theileriosis, cowdriosis, anaplasmosis, ehrlichiosis, Nairobi sheep diseases and tick paralysis. A commented list of tick-borne diseases and their vectors is presented. It is stressed that large gaps remain in our knowledge of the real importance in the field of many of these diseases, especially in local stock.

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.

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.

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.

[Integrated control of tropical parasitic diseases in animals]. / Lutte intégrée contre les parasitoses animales tropicales.

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.

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.

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.