Worms - basic information, development cycle
Worms They make up a large and diverse group of multicellular animals, united by one common feature - a parasitic way of life.
Medical importance flat (class tape, or cestodes - Cestoda, Class flukes, or trematodes - Trematode) and roundworms (Class of nematodes - Nematodes).
Most human helminth parasite in different parts of the intestine, as well as in the bile ducts of the liver, lung, spleen, muscles and subcutaneous fat. The human body can parasitize multiple helminth species.
The life cycle of worms in different species has significant differences, However, the general scheme of it from some individuals similar. Adult, inhabit the body of the final (definitive) owner, After fertilization, eggs or larvae form. The final host for the majority of worms, with medical value, a man. For a number of worms definitive hosts, along with the person are allowed, and for some - only animals (echinococcus).
Eggs or larvae of worms stand out from the host, and their further development is dependent on whether, group to which they belong: to geohelminths or biohelminths.
Geohelminths develop without changing owners. Their eggs or larvae mature to the infective stage (capable of causing infection) in the external environment, mainly in soil. By geohelminths are Ascaris, vlasoglav, Ancylostoma, etc.. This also can be roughly classified and pinworms, although the development of her eggs are not in the soil, and on the patient's body or the surrounding objects, but without an intermediate host.
Ripe in the environment geohelminthes eggs or larvae enter the body through the mouth of the final host, some of them (Hookworm larvae, strongiloida) actively penetrate the skin.
Development biohelminthes It comes to the change of owners: along with the definitive host they have intermediate, in the body which develop into larvae, and some of them - and the additional master to complete larval development. The larvae enter the body in different ways the final host, but more often it occurs by eating tissues of the intermediate host (eg, meat of cattle with bovine tapeworm larvae). The transmission of vector-borne larvae by (filaria).
Development of worms
The process of maturation of the larvae into adult parasites in the body of the final host continues various times: two weeks (pinworms) up to several months (askaridы) and even up to one year (filaria). If swallowed, the larvae develop them is either in the gut (bovine and pork tapeworm, broad tapeworm), or by migration into the bloodstream, tissue of various organs (askarida, Ancylostoma, strongiloid et al.).
Each type has a specific localization of helminths, but some of them can parasitize in any organ (echinococcus in the larval stage), sometimes there is a distorted localization. Some species of helminths have a different location depending on the phase of development (mature Trichinella live in the intestines, and larvae in the striated, or striated, muscle).
Worms sensitize the host, causing allergic reaction, toxic effect on the central nervous system, liver and other organs; mechanically damage the tissues and blood vessels. The larvae of the parasite may facilitate entry of bacteria into the host tissue and the development of inflammatory processes.
The similarity of the clinical picture of many helminthisms hampers their differential diagnosis. The final diagnosis can be made only on the basis of positive results:
- laboratory testing of stool (most helminths infest the digestive tract or in the liver and gall bladder);
- perianal scrape, as well as research data contents of the duodenum;
- muscle - Trichinella larvae;
- blood - on the microfilariae;
- sections of skin - to detect onhotserkov.
In some cases, used for the diagnosis of helminthiasis funduscopy.
