Chapter 15: Phylum Nematoda: The Roundworms

Cryptosporidium Protozoan pathogen Drinking contaminated water Diarrhea/ Severe in immune-compromised

Elephantiasis Filarial worm (Nematode) Transmitted by mosquitoes Swelling of lymphatic system

Anisakis Nematode Ingesting fish/marine mammals

Tapeworm Parasitic flatworm Ingestion of contaminated/undercooked meat Malnutrition/ neurological damage

Giardia Protozoan parasite Ingestion of contaminated food, water, soil Intestinal infection, diarrhea, abdominal pain

Roundworms The common name for phylum Nematoda is roundworms. They are among the most numerous of all animals. Roundworms are pseudocoelomates

Nematode = Thread? In Greek, ”nematos” actually means thread, hence why they are called nematodes.

What is a Roundworm? Roundworms are slender, unsegmented worms with tapering ends. They can be microscopic or up to a meter in length. Most species of roundworms are free-living, inhabiting soil, salt flats, aquatic sediments, and water from polar to tropical regions. Still others are parasitic and live in hosts that include almost every kind of plant and animal.

What is a Roundworm? Nematodes parasitize virtually every type of animal and many plants. Almost all species of vertebrates and many invertebrates serve as hosts for one or more types of parasitic nematodes.

What is a Roundworm? Nematodes have a digestive tract with two openings. This body plan is often called a “tube-within-a-tube.” The outer tube is the body wall and the inner tube is the digestive tract.

Form and Function in Roundworms Roundworms have specialized tissues and organ systems that carry out essential body function. In general, the body systems of free-living roundworms tend to be more complex than those of parasitic forms.

Feeding Many free-living roundworms are carnivores that use grasping mouthparts and spines to catch and eat other small animals. Some soil-dwelling and aquatic forms eat algae, fungi, or pieces of decaying matter. Other nematodes digest the bacteria and fungi that break down dead animals and plants.

Response Nematodes have simple nervous systems, consisting of several ganglia. Several nerves extend from ganglia in the head and run the length of the body. These nerves transmit sensory information and control movement. Roundworms have several types of sense organs.

Reproduction Roundworms reproduce sexually, and most species of roundworms are dioecious (male/female) They reproduce using internal fertilization: the male usually deposits sperm inside the female’s reproductive tract. Parasitic nematodes often have complex life cycles that involve two or three different hosts or several organs within a host.

Nematode Parasites Many nematodes are very important pathogens of humans and domestic animals. Some of the nematodes we will discuss: Roundworms Hookworms Pinworms Filarial Worms

Roundworm Ascaris lumbricoides occurs in up to 64% of people in some areas of the southeastern U.S. More than 1.2 billion are affected worldwide.

Roundworm A female roundworm can lay 200,000 eggs per day, passing out through the host’s feces. Viable eggs remain after signs of fecal matter have disappeared. Eggs can survive long periods in the soil.

Roundworm When a host swallows the eggs, juveniles hatch and burrow through the intestinal wall. The juveniles then are carried through the heart to the lungs. When at the lungs, they break into the alveoli and are carried up to the trachea. Juveniles are coughed up and swallowed, then mature in the intestine two months after they were swallowed. They feed on intestinal contents and may block or perforate the intestines.

Hookworms Hookworms are so named because the anterior (head) end curves dorsally, resembling a hook. Necator americanus is most common species. They have large plates in their mouths that cut into the intestines so that they can suck on the host’s blood.

Hookworms Hookworms pump more blood than they can digest. A heavy infection can cause anemia. Eggs pass in feces and juveniles hatch in soil where they can live off of bacteria. If human skin comes in contact with the soil, infective juveniles burrow through the skin to blood. Their life cycle is similar to that of Ascaris.

Pinworms Pinworms are the most common worm parasite in the U.S., but causes little disease. It is estimated that 30% of children and 16% of adults in the U.S. have them. Adults live in the large intestine and cecum.

Pinworms Females, about 12 mm in length, migrate to the anal region at night and lay eggs, causing itching. Scratching the anal region contaminates hands and bedclothes.

Scotch Tape Method Doctors usually diagnose pinworms by fecal examinations and finding the eggs, but eggs are often not found in feces. Many times the female pinworm will deposit her eggs on the skin around the anus. Doctors have started using the “scotch tape method.”

Scotch Tape Method 1. The scotch tape method consists of placing the sticky side of cellulose tape onto the anus overnight. 2. The next morning the tape is umm...harvested and placed under a microscope to search for eggs.

Several drugs are effective against it, and all members of the family should be treated at the same time because the worms spread easily through a household.

Pinworms Eggs develop rapidly and become infective within six hours at body temperature. When swallowed, these eggs hatch in the anterior end of the small intestine (the duodenum) and mature in the large intestine. Members of this order have haploid (one set of chromosomes) males from unfertilized eggs and diploid females from fertilized eggs. This is known as haplodiploidy.

Filarial Worms There are eight species of filarial nematodes that infect humans. Some cause major and serious diseases. About 250 million people in tropical countries

Filarial Worms Females can be as long as 100 mm and can release live young into the blood and lymph.

Filarial Worms Mosquitoes ingest the microfilariae when they feed. The worms develop to the infective stage while inside the mosquito and move into the mosquito bite wound when it feeds.

Filarial Worm Diseases Filarial worms cause three main diseases in their hosts: Elephantiasis River blindness

Elephantiasis Elephantiasis symptoms are apparent after long and repeated exposure to filarial worms. It is marked by excessive growth of connective tissue and enormous swelling of affected parts, such as the legs and arms.

Onchocerciasis: River blindness River blindness is caused by a filarial worm that is carried by black flies. It infects more than 30 million people in parts of Africa, Arabia, Central America, South America, and virtually all other tropical areas.