Necatoriasis is caused by N. Americanus. N. Americanus can be divided into two areas – larvae and adult stage. The third stage larvae are guided to human skin by following thermal gradients. Typically, the larvae enter through the hands and feet following contact with contaminated soil. A papular, pruritic, itchy rash will develop around the site of entry into the human host. This is also known as "ground itch". Generally, migration through the lungs is asymptomatic but a mild cough and pharyngeal irritation may occur during larval migration in the airways. Once larvae break through the alveoli and are swallowed, they enter the gastrointestinal tract and attach to the intestinal mucosa where they mature into adult worms. The hookworms attach to the mucosal lining using their cutting plates which allows them to penetrate blood vessels and feed on the host's blood supply. Each worm consumes 30μl of blood per day. The major issue results from this intestinal blood loss which can lead to iron-deficiency anemia in moderate to heavy infections. Other common symptoms include epigastric pain and tenderness, nausea, exertional dyspnea, pain in lower extremities and in joints, sternal pain, headache, fatigue, and impotence. Death is rare in humans.
The standard method for diagnosing necatoriasis is through identification of N. Americanus eggs in a fecal sample using a microscope. Eggs can be difficult to visualize in a lightly infected sample so a concentration method is generally used such as flotation or sedimentation. However, the eggs of A. Duodenale and N. Americanus cannot be distinguished; thus, the larvae must be examined to identify these hookworms. Larvae cannot be found in stool specimens unless the specimen was left at ambient temperature for a day or more.
The most common technique used to diagnose a hookworm infection is to take a stool sample, fix it in 10% formalin, concentrate it using the formalin-ethyl acetate sedimentation technique, and then create a wet mount of the sediment for viewing under a microscope.
When adult worms attach to the villi of the small intestine, they suck on the host's blood, which may cause abdominal pain, diarrhea, cramps, and weight loss that can lead to anorexia. Heavy infections can lead to the development of iron deficiency and hypochromic microcytic anemia. This form of anemia in children can give rise to physical and mental retardation. Infection caused by cutaneous larvae migrans, a skin disease in humans, is characterized by skin ruptures and severe itching.