Evercise 12. Say whether these sentences are true or false, and if they are false say why.
1. Helminths of the Echinococcus type have an indirect life cycle with numerous domestic and wild animals as final hosts.
2. Echinococcus worms belong to the phylum Nemathelminthes.
3. Echinococcus infections are fatal in almost all cases.
4. Hydatid cysts may develop in the liver, the lungs, the brain and other organs.
5. The clinical signs depend on severity of infestation and on the affected organs.
6. Cystic echinococcosis can be a serious disease for humans.
7. Diagnosis is made on egg identification in the feces.
8. The use of anthelmintics is strongly recommended in livestock.
Exercise 13. Match the term with its definition.
| cough | an examination of a dead body to determine cause of death or the changes produced by disease |
| anaphylactic reaction | an abnormal functioning of digestive system |
| hydatid cyst | the headlike part of a tapeworm, bearing hooks and suckers |
| digestive disturbance | a sudden noisy expulsion of air from the lungs that clears the air passages |
| scolex | a large bladder produced in men and animals during infestation by Echinococcus larval forms |
| necropsy | an acuteallergicresponse of an organism to a foreignprotein or toxin |
Exercise 14. a) Make up collocations using the words from both columns.
| adult | segment |
| hydatid | infection |
| gravid | test |
| contaminated | dose |
| heavy | worm |
| irreparable | food |
| reliable | harm |
| average | cyst |
b) Fill in the gaps with the words from the table above.
1. … usually live in the small intestine, whereas … may develop in the liver, the lungs, or the brain of the intermediate host.
2. … with eggs are shed with the dog’s feces.
3. Best prevention of this disease is to keep dogs away from … .
4. … are unusual for final hosts.
5. … may be caused if vital organs of intermediate hosts are affected.
6. There are no … for early detection of the disease.
7. Anthelmintics in … are ineffectivefor livestock.
Exercise 15. Translate from Russian into English.
1. Незрелыечервизавершаютциклсвоегоразвития, когдапопадаютвтелоокончательного хозяина. 2. Клинические признаки болезни зависят от того, какие органы поражены. 3. У промежуточных хозяев могут наблюдаться расстройства пищеварения, кашель, затрудненное дыхание. 4. Кровотоком личинки червей переносятся от печени к другим органам, включая легкие и головной мозг. 5. Диагностика заболевания у домашнего скота обычно осуществляется после забоя. 6. Глистогонные препараты не рекомендуются для домашнего скота, поскольку в средних дозах они неэффективны, а в более высоких – слишком дороги и плохо переносятся животными.
Exercise 16. Test yourself by answering the following questions to see how much you remember and understand.
1. What is the causative agent of echinococcosis?
2. Describe life cycle of the helmith.
3. Do final and intermediate hosts suffer equally from this infection?
4. What harm may Echinococcus worms cause to their intermediate hosts?
5. Why can hydatid cysts be a serious problem for humans?
6. What ways of diagnosis of this diseaseare known?
7. Can echinococcosis be prevented?
TEXT С
FASCOILOSIS
VOCABULARY LIST TO TEXT С
| cercaria (cercariae) n | [sǝˈkerɪǝ] [-ɪ:] | церкария |
| constipation n | [ˌkɒnstɪˈpeɪʃən] | запор |
| emaciation n | [ɪˌmeɪsɪˈeɪʃən] | истощение |
| eradicate v | [ɪˈrædɪkeɪt] | искоренять |
| fasciolosis n | [fǝˌsɪǝˈlousǝs] | фасциолёз |
| miracidium (miracidia) n | [ˌmɪrǝˈsɪdɪǝm][-dɪǝ] | мирацидий |
| obstruct v | [əbˈstrʌkt] | закупоривать |
| redia (rediae)n | [ˈrɪ:dɪǝ] [-ɪ:] | редия |
| snail n | [sneɪl] | улитка |
| spine n | [spaɪn] | шип |
| sporocyst n | [ˈspɔ:rəˌsɪst] | спороциста |
| walnut n | [ˈwɔːlnʌt] | грецкий орех |
Fasciolosis is a parasitic worm infection caused by two trematodes Fasciola hepatica and Fasciola gigantica. Adult flukes of both species are localized in the bile ducts of the liver or gallbladder of numerous domestic and wild mammals. They have an indirect life cycle with a snail as an intermediate host.
The common liver fluke occurs worldwide but is particularly abundant in humid regions with temperate climate where it can be endemic. It is one of the most damaging helminth parasites of grazing ruminants. It is particularly harmful, even fatal for sheep. Prevalence and incidence in a particular region depends strongly on ecologic and climatic conditions and on livestock management practices.
Adult liver flukes have a flat body, an oval shape, and a pink-grayish to dark red color. Liver flukes have two suckers, both in the ventral side. The body surface is covered with numerous spines. Adult flukes produce eggs in the bile ducts of their hosts. These eggs reach the gall bladder, pass to the host's gut, and then are expelled with feces.
Once outside the host, the larvae called miracidia hatch out of the eggs in 7 to 15 days. These larvae can survive for weeks off a host if there is enough humidity. They can swim and penetrate actively into the snails where they remain for 4 to 8 weeks and develop successively to sporocysts, rediae and cercariae, the usual larval stages of most fluke species. A single miracidium can asexually produce up to 600 cercariae.
Mature cercariae leave the snail, attach to the vegetation, lose their tail and produce cysts of about 0.2 mm, the so-called metacercariae, which are infective for the final host. Such cysts can survive for months in the vegetation, even under dry conditions. Livestock becomes infected by grazing on contaminated pastures or eating infected hay.
Liver flukes are very harmful for their hosts, particularly for sheep. Young immature flukes migrating through the liver tissues and crossing the wall of the bile ducts cause the major harm. This process destroys the tissues and causes bleeding. The spines on the surface of the flukes irritate the tissues that become inflamed. All this leads to cell death and fibrosis. Affected livers increase in size and become fragile. Some flukes can become encapsulated in the liver tissues and build cysts as large as walnuts. The bile ducts are also damaged: they become thickened and can be calcified and even obstructed. Infections with secondary bacteria can also happen, mainly due to the general weakness of the host. In addition, flukes produce own toxins that impair the normal function of the liver.
Besides fatalities, the major economic damage is the reduced weight gains of young animals (up to 30% less, even after slight infections) and the condemnation of livers at slaughter. Light infection can reduce milk production in dairy cattle.
There are no really typical and easily recognizable symptoms of a liver fluke infection in livestock or other animals. The major symptoms are related to the inflammation of the liver and of the bile ducts. Infections with a few dozen adult flukes may not cause clinical signs other than general weakness and reduced productivity.
Chronic fasciolosis in sheep, goats and cattle develops along the gradual establishment of adult flukes in the bile ducts. It is characterized by the progressive development of such symptoms as anemia, edema, digestive disturbances such as diarrhea or constipation, and emaciation.
Acute fasciolosis is seldom in cattle but can occur in sheep. It is caused by the sudden migration of many immature flukes through the liver, which leads to complete organ failure. Animals may be killed in a few days.
Diagnosis is based on feces examination and immunological methods. Clinical signs, biochemical and haematological profile, season, climate conditions, epidemiology situation, and examinations of snails must be considered as well.
AsFasciola infection is almost impossible to eradicate in endemic regions, preventive measures have to deal with reduction of the snail population and keeping the pastures dry. To diminish fluke infestation rotational grazing is highly recommended.
EXERCISES TO THE TEXT
Exercise 17. Look through the text and find the information about:
-fasciolosis causative agent;
- animals that are susceptible to fasciolosis;
- life cycle of the helminth and its final and intermediate hosts;
- harmful effects of the parasitic worm on sheep;
- major symptoms of the infection;
- difference between chronic and acute fasciolosis;
- factors that should be taken into consideration while diagnosing the infection;
- preventive measures.