Nematoda Zoology 2015

Phylum Nematoda Adaptive Benefits of a Pseudocoelom - a space between the guts and the body wall It is not lined with a peritoneum therefore is termed a false cavity It is an improvement over the acoelom of the platyhelminthes but not as advanced as the eucoelom / it lacks mesenteries

Phylum Nematoda It does offer adaptation potential – Greater freedom of movement Space for development and differentiation of digestive, excretory and reproductive organs Storage for waste products Simple means for distribution and circulation of materials Hydrostatic support for the body

Phylum Nematoda General features of this phylum – Very diverse phylum, about 25,000 species have been catalogued but estimate that there are 500,000 In good topsoil there are billions per acre of ground. They live in all habitats, from mountains to the deep oceans, from the polar ice to the tropics

Phylum Nematoda Free-living nematodes feed on yeast, bacteria and algae Predatory nematodes feed on other invertebrates and protozoans Nematode worms are important food for mites, insects and fungi Almost all animals and most plant species have nematode parasites

Phylum Nematoda Form & Function of body systems – Bilateral symmetry Complete digestive system with both a mouth and an anus

Phylum Nematoda Form & Function of body systems – Nematodes all have a cylindrical shape Muscles in body wall only run longitudinally Nematodes express Eutely which means they all show a set number of cells Examples – C. elegans Researchers use this worm Females have 1057 cells Males have 959 cells

Phylum Nematoda Form & Function of body systems – Dorsal and ventral cords bear nerves while lateral cords bear excretory ducts Longitudinal muscles run in four bands – between the nerve and excretory cords The digestive system consists of mouth, pharnyx, intestine, rectum and anus. This is considered a complete digestive system.

Phylum Nematoda Form & Function of body systems – Senses include papillae (sensory hairs) at the head and tail and amphids on the head. Parasitic nematodes also have phasmids (chemo-receptors) at the tail end Nematodes are dioecious and the males are smaller than the females and fertilization is internal. Males bear a pair of copulatory spicules.

Phylum Nematoda Form & Function of body systems – Nematodes have a non-cellular cuticle that is shed between each of four juvenile stages (no larval stage) this is called molting Skeletal system is hydrostatic

Nematode Parasites Ascaris lumbricoides – large intestinal roundworms of humans More than 1.2 billion people affected worldwide Southeastern US more than 64% of people affected

Nematode Parasites They feed on intestinal contents and a large infestation may block or perforate the intestines. They may cause a serious anemia in children Females may be 50 cm – 20 inches) long and males 30 cm - (12 inches)

Nematode Parasites Ascaris Life Cycle A female roundworm lays 200,000 eggs a day which pass out in the host’s feces Eggs remain viable for long periods in the soil – (10-20 years) When a host swallows the eggs, juveniles hatch and burrow through intestinal wall into the blood supply

Nematode Parasites Ascaris Life Cycle (con’t) 4. Carried through the heart to the lungs, they break into the alveoli and crawl upward into the trachea where they are coughed up and then swallowed with saliva

Nematode Parasites Ascaris Life Cycle (con’t) 5. They mature in the intestine where they feed on the intestinal contents. They sometimes cause allergic reactions or perforation of the intestine which results in peritonitis. Wandering worms may occasionally emerge from the throat or anus and have even been known to appear wriggling out of the ears, mouth or nose if there is a heavy infestation

Nematode Parasites Ascaris Life Cycle Also see Page 311 Fig. 15-7

Nematode Parasites Hookworm Necator americanus – the hookworm – name means “American Killer” These are small worms, only 11 mm and their anterior end has a dorsal curving hook (male) Large sharp cutting plates in their mouth cut into the intestinal mucosa and they attach and suck the host’s blood (see page 310, figure 15-6)

Nematode Parasites Hookworm Hookworms become blood pumps because they pump much more blood than they can digest, pumping the blood through their intestines, partially digesting it and absorbing the nutrients. They suck much more blood than they need for food and heavy infestations can cause anemia. Children with hookworms may experience retarded mental and physical growth.

Nematode Parasites Hookworm Necator life cycle –similar to that of the Ascaris Eggs pass in feces, but if soil conditions are warm and moist the eggs hatch and the juveniles live in the soil, eating bacteria. When juvenile worms come into contact with bare skin, they burrow into the blood vessels and then they follow the same path as Ascaris to get to the intestine. Penetration usually occurs through soles of the feet. Southern US population had a 55% infection rate at the turn of the century but because of the practice of wearing shoes the infection rate is now 5-10%.

Nematode Parasites Necator americanus life cycle –

Colour SEM of Trichinella spiralis roundworms Nematode Parasites Trichinella spiralis – trichina worm Causes the potentially lethal disease trichinosis About 2.4% of the US population is infected Adult worms are tiny, about 1.5 – 3 mm long Colour SEM of Trichinella spiralis roundworms

Nematode Parasites Trichinella spiralis – trichina worm (con’t) Infection occurs when meat containing live encysted juveniles is eaten, adults burrow into intestinal mucosa and females give birth to live young Muscle tissue with encysted larval trichina

Nematode Parasites Trichinella spiralis – trichina worm (con’t) E. Trichina worms infect hogs, rats, cats, and dogs . . . People usually become infected by eating undercooked pork. Hogs become infected by eating infected meat scraps or infected rats.

Nematode Parasites Trichinella spiralis life cycle In an infected host, living juvenile worms are born in the intestine Juveniles penetrate blood vessels and circulate through the body invading all organs, tissues and intestinal spaces

Nematode Parasites Trichinella spiralis life cycle When they invade skeletal muscles, they redirect genes and muscle looses its striations and becomes a nurse cell of the parasite. This this encysted meat is eaten, it cause the infection. While the juveniles are wandering in the body, they can cause death if large numbers invade the heart or the brain.

Nematode Parasites Trichinella spiralis life cycle

Nematode Parasites Enterobius vermicularis – the pinworm This is the most common worm parasite in the US but it causes little disease (just irritation) Adults live in the large intestine They attain a body length of 12 mm

Nematode Parasites Enterobius vermicularis – the pinworm 30% of US children are infected Up to 75% of college students who live in dorms are infected There are several oral drugs that are effective against this infection but all people living in the household must be treated because they are very infectious

Nematode Parasites Enterobius vermicularis – pinworm Exhibit haplodiploidy Males are haploid – come from unfertilized eggs Females are diploid – come from fertilized eggs

Nematode Parasites Enterobius vermicularis – the pinworm Diagnosed by scotch tape test or flashlight test

Nematode Parasites Enterobius life cycle – Adults live off of intestinal contents in the large intestine Females detach from the intestinal lining and migrate to the anus at night to lay eggs on the external surface. This causes intense itching. Scratching the itch contaminates hands and bed clothes Eggs develop rapidly and can become infective in just 6 hours at body temperature Contaminated hands put eggs into mouth and airborne –eggs hatch in the duodenum and mature in the large intestines.

Nematode Parasites Enterobius life cycle –

Nematode Parasites Filarial Worms – “Elephantiasis” Wucheria bancrofti and Brugia malayi 250 million people in the tropics are infected Worms live in the lymph system and obstruct the ducts Worms may grow to 100 mm Females release live young called microfilariae which circulate in the blood stream Brugia malayi Wucheria bancrofti

Nematode Parasites Filarial Worms – “Elephantiasis” Elephantiasis is a disease caused by repeated exposure. Blockage and swelling of lymph ducts causes gross enlargement of certain body parts

Nematode Parasites Filarial Worms – “Elephantiasis”

Microfilarial worm infestation of eye tissue Nematode Parasites Filarial Worms – River blindness - another filarial worm disease Microfilarial worm infestation of eye tissue

Nematode Parasites Filarial Worms – Dog heartworm is the most common filarial worm disease in the US. It reaches a 60% infection rate in the south and eastern seaboard states and can infect dogs, cats, otters and occasionally humans.

Dog Heartworm Life Cycle Nematode Parasites Dog Heartworm Life Cycle

Nematode Parasites Filarial Worms Life Cycle – Adult worms live in the lymph ducts Females bear live tiny juveniles called microfilariae At night, microfilariae congregate in vessels near the surface of skin Mosquitoes transmit disease when they ingest the microfilariae as they feed The microfilariae develop into the infective stage in the mosquito, considered the intermediate host and then they infect a new definitive host by moving into a bite wound through the proboscis of the mosquito.