roundworm
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Roundworm female ( Ascaris lumbricoides ) |
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| Linnaeus , 1758 |
The roundworm ( Ascaris lumbricoides ) is an earthworm-like parasite that is up to 40 centimeters long and infests humans, monkeys and bears and occurs without intermediate hosts . It also occurs very rarely in pigs, but usually does not reach sexual maturity in their intestines. The roundworm is one of the nematodes .
distribution
The first mention of this worm can be found in the Ebers papyrus , which dates from around 1540 BC. Was written. This makes it one of the longest known parasitic roundworms. It is particularly widespread worldwide in tropical and subtropical areas, but is bound to a certain level of soil moisture. Due to the very resistant eggs, which remain infectious for up to four years and are not killed by most chemicals, it can persist in certain areas for a long time. About 22% of the world's population are infected, of which up to 1% succumbs to the parasite. Humans can also become infected with the pig roundworm ( Ascaris suum ) , which cannot be distinguished morphologically from human roundworm ( Ascaris lumbricoides ) . However, genetic research in recent years suggests that both are in fact just one species.
features
Females are up to 40 cm long with a diameter of 5 mm, males reach up to 25 cm in length and 3 mm in diameter. The worms have a pink, earthworm- like appearance, hence the Latin name lumbricoides (from Lumbricus , the eponymous genus of the Lumbricidae family - earthworms ). The mouth has three lips, and the excretory ducts can be seen as white lines with the naked eye. Males differ from females by their mostly rolled-up tail end and by the protruding spicula .
Life cycle
The eggs, about 0.05 mm in size, deposited in the intestines by adult females enter the environment with the faeces. There, with sufficient humidity, temperatures of 9 ° C to 35 ° C and oxygen still in the egg, development takes place via the first larval stage with molting to the second stage of the larva, which takes about 12 days under laboratory conditions and 2 to 6 weeks outdoors can. The egg with the infectious L2 generation is usually ingested by the host with the food.
The mature larva, about 0.2 mm long, hatches in the small intestine and bores through the intestinal wall. It moves with the bloodstream to the liver, where it sheds its skin again and grows in the third larval stage. This L3 larva then reaches the heart via the inferior vena cava and further via the pulmonary arteries into the capillary network around the alveoli . From there it usually breaks through the wall of the blood vessel into the air space of the alveoli, where it sheds its skin again (fourth larval stage). The approximately 1.4 mm long L4 larva then reaches the larynx supported by the ciliated epithelium via bronchioles, bronchi and trachea. Often this triggers a cough reflex and it can be coughed up either spit out or swallowed. With the latter, the larva returns to the small intestine, where it grows into an adult animal. Eggs can then be detectable in the excretions about two months after infection. The adult females lay up to 200,000 eggs a day, and up to 27 million eggs are laid in their ovaries. The lifespan of the parasite can be up to one and a half years.
infection
The infection usually occurs through ingestion of contaminated water or contaminated food such as vegetables fertilized with animal feces.
Clinical symptoms
An infection with roundworms often remains unremarkable. Occasionally, allergic reactions occur. Signs of clinical disease usually only appear when the infection is severe. They are largely unspecific and primarily affect the lungs and airways (larval stages) and the digestive tract (adult worms). The migration of the Ascaris larvae through the lungs can not only trigger a cough , but also lead to pneumonia with fever, sputum, mucus and asthma-like attacks. Ascariasis is the most common cause of Löffler syndrome worldwide . In the intestine, the adult worms can block the pancreas or bile ducts and thus cause colic . A massive occurrence can lead to an intestinal obstruction, with subsequent intestinal paralysis ( ileus ). The chronic consequences of a severe infestation include underweight and stunted growth due to poor digestion ( maldigestion ) or insufficient intestinal absorption ( malabsorption ) of the food supplied.
diagnosis
The most effective way of diagnosing roundworm infestation is by examining the faeces using the flotation method . Here the thick-shelled, 70 to 80 µm eggs are detected. Furthermore, the serological detection of a larval roundworm infection is possible using ELISA . During the invasion phase, the stool examination is negative, as is the case with an infestation with exclusively male roundworms.
In addition to infection with the human roundworm Ascaris lumbricoides , infection with other roundworms is possible, such as the pig roundworm ( Ascaris suum ) or those of pets such as dogs and cats ( Toxascaris leonina , Toxocara canis , Toxocara mystax ). For these, humans are a false host, so that sexually mature worms do not develop. Therefore, no eggs can be detected in these cases and the stool test remains negative.
prevention
An effective preventive measure is consistent hand washing before every meal. The consumption of manure-fertilized vegetables should be avoided, faeces should be removed from a hygienic point of view. Small animals kept in the family require regular deworming .
Combat
For the treatment of people infected with roundworms, the antiparasitic drugs mebendazole or albendazole are administered and the administration is repeated after two to four weeks.
The use of drugs to combat roundworms ( anthelmintics ) is particularly important in the field of veterinary medicine . The most important class of substances at the moment are the benzimidazoles , the most widely used representatives of which, besides flubendazole , are primarily fenbendazole and mebendazole. Also frequently used groups of active substances are tetrahydropyrimidines (here especially the pyrantel ) and imidazothiazoles (especially levamisole ). Ivermectins ( e.g. moxidectin , doramectin , milbemycin ) are considered a relatively new group of active ingredients . Older anthelmintics such as piperazine or organic phosphoric acid esters such as dichlorvos only play a subordinate role.
A study on school children found that the daily consumption of papaya kernels can reduce roundworm infestation, similar to the intake of albendazole.
In rare cases, invasive interventions in the form of a colonoscopy removal are necessary in humans . The worms are grasped with a gripper arm on the head of the endoscope and removed through the anus. Another, seldom necessary surgical procedure is only used in cases of intestinal blocking. The affected area in the patient's intestine is opened with an incision and the accumulation of worms is carefully pushed out by the doctor in the direction of the incision opening, or the corresponding intestinal section is resected .
See also
swell
- H. Mehlhorn, G. Piekarski: Outline of parasite science. 6th edition. Heidelberg 2002.
- Hans Adolf Kühn: Ascaris lumbricoides (roundworm). In: Ludwig Heilmeyer (ed.): Textbook of internal medicine. Springer-Verlag, Berlin / Göttingen / Heidelberg 1955; 2nd edition, ibid. 1961, p. 837 f.
Web links
Individual evidence
- ^ Josef Boch: Veterinary Parasitology . Georg-Thieme-Verlag, Stuttgart, 6th edition 2006, ISBN 9783830441359 , p. 386.
- ↑ CDC Centers for Disease Control and Prevention: CDC - Ascariasis - Biology. July 19, 2019, Retrieved December 1, 2019 (American English).
- ↑ Peter Nejsum, Mohamed Hawash BF, Martha Betson, J. Russell. Stothard, Robin B. Gasser: Ascaris phylogeny based on multiple whole mtDNA genomes . In: Infection, Genetics and Evolution . tape 48 , March 2017, p. 4–9 , doi : 10.1016 / j.meegid.2016.12.003 ( sciencedirect.com [accessed July 9, 2017]).
- ↑ http://ticker-grosstiere.animal-health-online.de/20060628-00000
- ↑ Gaspary, Kist, Stein, Infektiologie des Gastrointestinal Tract , Springer-Verlag, Berlin 2006, p. 45.
- ↑ a b Gholamreza Darai et al .: Lexicon of infectious diseases in humans: pathogens, symptoms, diagnosis, therapy and prophylaxis . Springer, 4th edition 2011, ISBN 9783642171574 , p. 209.
- ↑ H, Hof, R. Dörries: Medical Microbiology. Thieme, 5th edition 2014, ISBN 9783131529657 , p. 547 .
- ↑ goFeminin de GmbH, 50678 Koeln Germany: roundworm (Ascaris lumbricoides). July 25, 2019, accessed December 1, 2019 .
- ^ Marianne Abele-Horn: Antimicrobial Therapy. Decision support for the treatment and prophylaxis of infectious diseases. With the collaboration of Werner Heinz, Hartwig Klinker, Johann Schurz and August Stich, 2nd, revised and expanded edition. Peter Wiehl, Marburg 2009, ISBN 978-3-927219-14-4 , p. 290.
- ↑ Fortification of Carica papaya fruit seeds to school meal snacks may aid Africa mass deworming programs: a preliminary survey.
- ↑ Mwenda AS, Ilkul JH: Images in clinical medicine. Obstructive ileal ascariasis . N Engl J Med. 2013; 368: 943. doi : 10.1056 / NEJMicm1205279 , PMID 23465104 .