Helminthes.docx

HELMINTHS  Platyhelminthes (flatworms)  Nematoda (roundworms) Characteristics of Helminths  multicellular eukaryotic animals  possess digestive, circulatory, nervous, excretory, and reproductive systems  lack a digestive system – absorb nutrients from the host’s food, body fluids, and tissues.  nervous system is reduced – do not need an extensive nervous system because they do not have to search for food or respond much to their environment. The environment within a host is fairly constant.  reduced or completely lacking means of locomotion – transferred from host to host, don’t need to search actively for a suitable habitat.  Complex reproductive system – Individuals produce large numbers of eggs, by which a suitable host is infected. *Parasitic helminths must be highly specialized to live inside their hosts. Life Cycle  involve a succession of intermediate hosts for completion of each larval (developmental) stage of the parasite & definitive host for the adult parasite  Adult helminths may be dioecious; male reproductive organs are in one individual, and female reproductive organs are in another. - reproduction occurs only when two adults of the opposite sex are in the same host.  Adult helminths may also be monoecious, or hermaphroditic—one animal has both male and female reproductive organs. Two hermaphrodites may copulate and simultaneously fertilize each other. A few types of hermaphrodites fertilize themselves.

PHYLUM PLATYHELMINTHES Characteristics: • Kingdom Animalia • Habitat: Mostly parasitic • Symmetry: Dorsoventrally flattened • Reproduction - Sexual by gametic fusion - Asexual by regeneration 2 Classes of Plathyhelminths a. Trematodes b. Cestodes

CLASS TREMATODA Characteristics: • All parasitic • Flat, leaf-shaped bodies with a ventral sucker and an oral sucker. • Obtain food by absorbing through their non-living outer covering

CLASS CESTODA Characteristics: • Intestinal parasites • Head or Scolex, has suckers • Lack digestive system • Absorb food through their cuticle • Proglottids are continually produced by the neck region of the scolex • Mature proglottids contains both male and female reproductive organs and are essentially bags of eggs.

Humans as Definitive Hosts  Taena saginata - parasite of both cattle and humans but it can only reproduce in human - the beef tapeworm live in humans and can reach length of 6m. - scolex is 2mm long and followed by thousand or more proglottids - as the proglottids wriggle away from the fecal material they increase their chances of being ingested by an animal that is grazing. • When the cysticerci are ingested by humans, all but the scolex is digested. • The scolex anchors itself in the small intestine and begins producing proglottids. • Diagnosis of tapeworm infection in humans is based on the presence of mature proglottids and eggs in feces. Cysticerci - can be seen macroscopically in meat, - presence is referred to as “measly beef” - inspecting beef that is intended - for human consumption - for “measly” appearance is one way to prevent infections by beef tapeworm - another method of prevention is to avoid the use of untreated human sewage as fertilizer in grazing pastures.  Taenia solium - humans are the only known definitive host of pork tapeworm. - when egg are eaten by pigs, the larval helminth encysts in the pig’s muscles, - humans become infected when they eat undercooked pork. - common in Latin America, Asia and Africa. - Eggs shed by one person and ingested by another person hatch, and the larvae encyst in the brain and other parts of the body causing Cysticercosis

Humans as Intermediate Hosts o Humans are the intermediate hosts for Echinococcus granulosus o Dogs and coyotes are the definitive hosts for this minute (2-8mm) tapeworm. NEMATODA GENERAL CHARACTERISTIC  Cylindrical and tapered at each end  Have complete digestive system consisting of mouth, intestine and an anus  Dioecious  Males are smaller than females and have one or two hardened spicules on their posterior ends.  Spicules – used to guide sperm to the female’s genital pore.  Some are free-living in soil and water and others are parasite of plants and animals.  Some nematodes pass their entire life cycle, from egg to mature adult in a single host.  Intestinal roundworms are the most common causes of chronic infectious diseases. The most common are Ascaris, hookworms and whipworms infecting more than 2 billion people Nematodes infections of humans can be divided into two categories: a. the egg is infective b. the larva is infective

EGGS INFECTIVE FOR HUMANS:

LARVAE INFECTIVE FOR HUMANS

Ascaris lumbricoides  Is a large nematode (30 cm in length) that infects over 1 billion people worldwide and is dioecious with sexual dimorphism

Strongyloides  endemic in other countries  Most infections are limited to a rash where the nematode entered, but the larvae can migrate to the intestine, causing abdominal pain, or to the lungs, causing a cough

Baylisascaris procyonis (Racoon Roundworm)  An emerging roundworm and are the definitive host, although the adult roundworm can also live in domestic dogs Toxocara canis (from dog) and T.cati (from cats)  can also cause larva migrans, a condition in which larvae migrate through a variety of tissues  These companion animals are the intermediate and definitive hosts, but humans can become infected by ingesting Toxocara eggs shed in the animals’ feces Trichuris trichiura (Whipworm)  The worms are spread from person to person by fecal–oral transmission or through fecescontaminated food  The disease occurs most often in areas with tropical weather and poor sanitation practices and among children Enterobius vermicularis (Pinworm)  Spends its entire life in a human host

Necator americanus & Ancylostoma duodenale (Adulthookworms)  live in the small intestine of humans where in the eggs are excreted in feces *Trichinellosis is caused by a nematode that the host acquires by eating encysted larvae in undercooked meat of infected animals Dirofilaria immitis  A nematode which is spread from host to host through the bites of Aedes mosquitoes.  It primarily affects dogs and cats, but it can infest human skin, conjunctiva, or lungs *Heartworm-the parasitic worm where larvae injected by the mosquito migrate into various organs such as the heart. Anisakines (Wriggly worms)  Four genera of roundworms that can be transmitted to humans from infected fish and squid.