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Volume 45 Tables of Contents

Acta Parasitologica, Vol.45, No. 2, 2000, 123-124
Machnicka Barbara - Fasciolosis (Ed. J. P. Dalton), CABI Publishing - CAB International 1999, Wallingford, Oxon OX10 8DE, U.K.

W. Stefanski Institute of Parasitology Polish Academy of Sciences, Twarda 51/55, 00-818 Warszawa, Poland
The book "Fasciolosis" contains 15 chapters covering the large spectrum of problems connected with the life-cycles, development, intermediate and final hosts as well as pathology and control of Fasciola hepatica, a common parasite of livestock and humans in temperate climatic zones. Fasciolosis is still the disease of the great economical importance. According to some estimates every year about 600 mln of domestic animals became infected worldwide; only in the USA alone the economical losses are determined at over $ 2 bln. Moreover, during the last decade the human fasciolosis was stated as an emerging food-born zoonosis in some parts of the world. Reports estimate that as many as 2.4 to 17 mln people are infected. It is worth mentioning that the number of reported clinical cases and of infected people identified during epidemiological surveys have been increasing since 1980.
Economic effects of fasciolosis in livestock can range from sudden death as a result of massive infection to subclinical infections which produce marked economic effects. Ovine fasciolosis can result in significant blood losses with all associated consequences. In sheep and cattle, the reduction of weight gain and other adverse effects depend on the parasite burden. Infection has also deleterious effect on milk quantity and quality; it causes lower fertility rates in cattle and sheep.
The first two chapters deal with the life cycle of the parasite and development in the intermediate host as well as the control of snail transmission by drainage programme or fencing of wet areas, chemical and biological control.
The description of the parasite anatomy, its tegument, parenchyma, musculature, nervous and reproductive systems are given at a light and electron microscopy levels. The development and function of each organ system is described in detail. This chapter is very important for understanding the cellular and tissue organisation, physiology and self-defence of the parasite. This chapter shows the progress accomplished recently in our understanding of the fine structure of all the major organ systems of the liver fluke.
The chapter on the epidemiology and control describes the main conditions, which determine the occurrence of fasciolosis such as climatic and environmental conditions. All these factors have their influence on the development of F. hepatica eggs and intermediate host, parasite development in the snail, and metacercarial survival.
Particular attention is paid to the problems connected with resistance to F. hepatica and F. gigantica. Infection with F. hepatica may result in a different degree of acquired resistance which varies depending on the host species. Horses and adult pigs show a marked degree of innate resistance. Level of acquired resistance in sheep shows individual variations; some "primitive" races demonstrate well expressed innate resistance.
The protective immunity is mainly expressed at the gut mucosa level, but it must be taken into account that acquired resistance in cattle may be a consequence of fibrosis of liver parenchyma and fibrosis and calcification of the bile ducts.
A wealth of fascinating new knowledge is gathered on the ways of parasite evading the persistent attacks from the host immune system. It is achieved in many cases by the secretion of antibody-cleaving enzymes and anti-inflammatory agents. Several mechanisms allow to repulse offensives of immune effector cells and their toxic products. Liver flukes release immunosuppressive factors which probably facilitate the parasite passage through the liver parenchyma.
The chapter on the control of fasciolosis is important from practical viewpoint. The control options depend on the local husbandry and climatic conditions together with socio-economic factors. The treatment as the principal method employed to control fasciolosis, should reduce the intensity of infection in a flock or herd and is beneficial for lowering the parasite burden on the pasture. Because of the presence of wild reservoir hosts, usually it is not possible, however, to achieve a total eradication of fasciolosis in a certain area.
The expected prevalence of fasciolosis may be forecasted for bigger territories and developed further to computerised system in order to design the better ways of fasciolosis control and optimise strategic preventive measures for the control of disease over the following year, among them the frequency of drug application.
The chapter on the fluke metabolism represents the background knowledge for the new chemotherapeutics development. Metabolic pathways are increasingly becoming targets for anthelmintic drugs and, therefore, attention has to be especially focused on differences in metabolism between the host and the parasite.
Research developments on the neuromusculature of trematodes offer the further prospect of identifying pharmacologically important receptors and ion channels and of determining the potential targets for chemotherapeutic exploitation. Recent information demonstrates that neuromuscular receptors in helminth parasites have a unique physiology which often considerably differs from those in vertebrates.
The vaccine development will provide producers with an alternative, environmentally friendly, cost effective and sustainable strategy for the control of fasciolosis. F. hepatica infection can induce host immune responses which are effective in killing of the parasite and conferring the protection against fasciolosis. In contrast to cattle, sheep do not acquire resistance to a secondary F. hepatica infection following primary exposure. The ability of the merino sheep to acquire resistance to F. gigantica indirectly suggests that F. hepatica and F. gigantica differ in some fundamental biochemical trail.
The chapter covering current development of research on vaccines summarises contemporary knowledge beginning from the use of irradiation-attenuated metacercariae, some substances being excretions/secretions of the fluke such as: fatty acid binding proteins, glutatione S-transferases, cathepsin L, hemoglobin, paramyosin, Kunitz-type serine proteinase, and finally naked DNA encoding protective antigens. Each of the above substances was tested experimentally as a vaccine and showed diversified activity from the damage of tegument of developing flukes to the reduction of adult worms' fecundity. These experiments demonstrated significant differences among animal species in the induction of protection against liver flukes.
The genetic organisation and variability of F. hepatica are the main problems of molecular studies presented in the book. Another direction of research deals with the ability of appropriate gene expression systems of the liver fluke to produce substances which could serve as vaccines. The main problem to be solved is the mechanism by which flukes can co-ordinate the complex changes in gene expression that need to occur during their development.
The separate chapter is devoted to the epidemiology, immunology and molecular biology of Fasciola gigantica, a causative agent of similar illnesses in zones with a tropical climate. Although not fully comprehensive, it is very useful for comparative purposes.
"Fasciolosis" edited by J. P. Dalton, is written by a group of 34 authors, deserving full credits for producing this work of excellent quality. The book is well presented and readable with a good balance between review chapters and general background reference-type material. Inspite being rather research-oriented, it remains, at the same time, an excellent reference book which can be recommended for undergraduate and postgraduate students in medical, veterinary and life sciences as well as for those conducting investigations in the field of fasciolosis.

KEY WORDS: Fasciolosis
Page compiled by Aleksander H.Kedra. Last modification: 04-07-2000