Hookworms are small, thread-like worms that burrow into the intestinal wall and consume blood. They are most commonly found in warm climates. There are numerous species of hookworms capable of infecting mammals, including humans.
Of the many types of hookworm, the Ancylostoma duodenale and Necator americanus hookworms most commonly infect humans. In fact, they currently infect about 800,000,000 people worldwide. The A. caninum and A. braziliense hookworms, which most commonly affect dogs and cats, respectively, are next in line in terms of their frequency of infecting humans.
Hookworms are an average of .39 inches (10 mm) in length. When they mate, the female lays eggs in the host. Though the number of eggs produced depends on the species, females can lay as many as 10,000 to 25,000 eggs in one day. These eggs are then passed in the feces of the host.
Juvenile hookworm eggs hatch about two days after they are passed in fecal matter. Juvenile hookworms, called larvae, reach the infective stage in just five days. The larvae are able to infect a new host by penetrating the host's skin. Once inside, they travel through the host's body to take up residence in the small intestine. They remain there as they grow to sexual maturity.
After entering the body of a new host, hookworms travel through the blood of their host to the lungs. They then penetrate the pulmonary capillaries and enter the alveoli. The alveoli are thin sacs in the lungs in which carbon dioxide and oxygen are exchanged. After they penetrate the alveoli, hookworms are coughed up and swallowed, traveling on to the small intestine.
Hookworms have mouthparts equipped with cutting plates. They attach to the small intestine using their mouthparts, penetrate blood vessels, and consume the host's blood. When they infect humans, the result can be excessive loss of blood. Infection is particularly devastating to children.
Hookworm infection may cause not only the depletion of blood, but also the permanent loss of iron and blood proteins. This creates an iron deficiency anemia and protein malnutrition that can, in severe cases, be fatal. In children, it most often leads to severe growth and developmental retardation. It can also lead to a physical weakness and listlessness that is often incorrectly identified as laziness.
Though some species of hookworm grow to maturity in humans, the cat and dog species do not. Instead, they remain in the skin, continuing to migrate for weeks and even months at a time. Cat and dog hookworms eventually die in human hosts, but their migration and eventual death causes an inflammatory disease called cutaneous or dermal larval migrans. To treat this disease, the migrating larvae must be surgically removed.
To determine if a mammal is infected with hookworms, the presence of eggs must be detected. The feces of the suspected host must be examined to look for eggs. However, the particular species of hookworm eggs cannot be determined using this type of examination.