worms disease

           the arthropods that can lead to disease in humans, the other group of multicellular animals that causes human disease are the helminths. In humans, the helminths that cause disease generally belong to one of three classes:

1) the nematodes, or roundworms

2) the cestodes, or the tapeworms

3) trematodes, or the flukes

Nematodes or Roundworms

• The nematodes or roundworms have a cylindrical tapered body with a tubular digestive tract that extends from the mouth to the anus.
•  There are both male and female nematodes.
•  Nematodes include a large number of species.
•  Many nematodes are free-living in soil and water.
•  Others are parasites of human and other animals and plants and produce serious disease.

The nematodes that cause disease can be divided into two groups:

        the ones that inhabit the gastrointestinal tract of the host, and the ones that are found in the blood and other tissues of the host.

           Generally, diagnosis of worm infestation depends on microscopic identification of the worms or their ova (eggs), or on blood tests for antibody to the worms.  summarizes the major diseases caused by these parasites.

Cestodes or Tapeworms

• Cestodes or tapeworms have flat, ribbon-shaped bodies that are segmented.
• The head (scolex) of the tapeworm has suckers for attachment and sometimes has hooks. 
• Directly behind the head is a region that produces the reproductive segments .

 Each segment has both male and female sex organs.

•  The tapeworm does not have a digestive system but rather absorbs nutrients directly. Tapeworms are often associated with beef, lamb, pork, and fish. Transmission of these organisms to humans often occurs when the flesh of these animals is eaten either uncooked or undercooked. 
• Some tapeworms are transmitted to humans from ingesting fleas infected with dog or cat tapeworms.

Trematodes or Flukes

• Trematodes or flukes are bilaterally symmetrical, flat, and leaf- shaped. 
• They have suckers that hold the organism in place as well as suck fluids from the host.
•  Most species are hermaphroditic.
•  Most trematodes have a complicated life cycle, which may include one or more intermediary hosts.
•  Usually, the worms begin with a larval form developing within the egg.
•  These larvae escape into the environment, where they are taken up by one or more intermediate hosts such as a snail. Eventually, the last stage is a tail-bearing larva known as a cercaria, which is released from the snail and is ready to attach to the susceptible host.
•  For example, if a human is wading in water and the cercaria of Schistosoma mansoni have been discharged into that water, the cercaria can penetrate the skin and work its way through the circulation to the liver and intestine, where it matures and lays eggs.

How do mosquitoes cause disease?

 The female mosquito needs the blood of a warm-blooded animal for the proper development of her eggs. To get this, she needs to bite such an animal.

 The mosquito can take in as much as twice its body weight in blood, thus giving it a relatively good chance of picking up infectious agents such as malarial parasites circulating within the host’s capillaries.

 The anatomy of a mosquito is particularly adapted to transmit disease . The mouthparts of the female mosquito consist of sharp stylets that are forced through the host’s skin to the subcutaneous capillaries. One of these needlelike stylets is hollow, and the mosquito’s saliva is pumped through it. 

The saliva increases blood flow and prevents clotting as the victim’s blood is sucked into a tube formed by the other mouthparts of the insect. The saliva can also cause allergic reactions (the itch of a mosquito bite). After the mosquito has taken more than one blood meal, she can transmit disease from one animal to the next. Viruses found in the blood of the first animal are then transmitted to the next, and so on.

Mosquitoes in an area of arthropod-borne disease can be trapped and identified microscopically, and the blood they have ingested can be tested to see on which kinds of animals the different species are feeding. Precise identification of species and subspecies of these genera is important because different species of mosquitoes differ greatly in their breeding areas, time of feeding, and choice of host.

 Identification depends largely on microscopic examination of antennae, wings, claws, mating apparatus, and other features. Correct identification is often essential in designing specific control measures.