Hookworm

Hookworms are a type of parasitic roundworms. Their eggs are fertilized inside a host’s body and the eggs are hatched outside in the soil.(Miller, p.692) Some hookworm’s infections can be very serious, but others are not as extreme. Newborn babies, children, pregnant woman, and people who are malnourished are at the most at risk. Dogs and cats are also at a high risk. Most infections are found in subtropical and tropical regions. It is estimated that one billion people are infected by hookworms; this is one-fifth of the world’s population.

Anatomy
Hookworms are long, skinny worms that are unsegmented. There are many different sizes, from as little as microscopic to as long as one meter. They have three germ layers that consist of the endoderm (innermost layer), exoderm (outermost layer), and mesoderm (middle layer). Something that it is unique about the hookworm is the cavity between the mesoderm and endoderm tissues, which is called a pseudocoelom, meaning "false coelom." Hookworms also have a very different digestive track. Unlike flatworms their digestive system contains two openings. One way the structure of a roundworm is described is a tube-within-a-tube. The inside tube is the digested tube and the outside tube is the body wall, which keeps everything together. This whole system makes roundworms very unique because the food being digestive moves in one direction. Anything that the worms does not use exits the body through the anus. The anus is the opening, located at the posterior (end) part of the worm.(Miller, p.692)

Reproduction
Hookworms, like other roundworms, reproduce by sexual reproduction. Some worms are hermaphroditic (male and female organs) but not hookworms. They have both sexes, male and female. When the eggs of a hookworm are fertilized they are still inside the female’s body, which is internal fertilization. The male hookworm shoots sperm into the reproductive tract of the female.(Miller, p.692) When the eggs are all fertilized, they exit the body through the host feces. The first three larval stages take place in the feces or dirt. The fourth and final stage takes place within the hookworm’s new host. The adult hookworm then lives inside its host and starts this whole process of reproduction creating more hookworms. 

Ecology
Hookworms are most known for infecting dogs. The reason they are found here is because of the way they live. Dogs can get hookworms when they lick and get dirt in their mouth were the hookworms live. They also can get them through their feet of or stomachs. When a hookworm finds a bare foot or an animal, they hook onto the by passer with its sharp teeth-like plates and then burrow into the skin. After they burrow into the skin they get in their new host's bloodstream. They then travel through the bloodstream to get to the lung, then to the intestines. In the intestines the hookworm starts to cause its host problems by sucking its blood. The hookworms then causes its host weakness and bad growth.(Miller, p.692) The hookworm doesn't really have any predators because if it gets eaten it's a good thing for them. They find their food and habitat by being eaten. It would also be a lot easier for the hookworm because then they don't have to go through the whole process of going through the bloodstream to get to the intestines. When they are eaten and then swallowed they go straight to the intestines.

Being Infected
Dogs are not the only ones that can get infected. Hookworms can also affect puppies that have not been born yet. Humans can also be infected by hookworms in the same way dogs are. They can be eaten from unclean vegetables and can get into the bloodstream through a unconvered body part. Running bare foot through places where dog’s feces are, create a risk of getting a hookworm.  Some signs of being infected by a hookworm are vomiting, constipation, and diarrhea. 

Related References

 * hookworm infection by Fact Sheet
 * Hookworm From Wikipedia
 * Hookwroms by marvistavet
 * Prentice Hall Biology. by Kenneth Miller, Joseph Levine. Pearson Prentice Hall. 2008.