New World Hookworm, Necator americanus

The New World hookworm (Necator americanus) is a hookworm that can be found in the New World. This species, along with other species in the Nematode phylum, is a parasitic worm that is commonly found in cats, dogs, and humans. Infections from this species are known as Necatoriasis. However, there are two common species of hookworm that infest humans, known as the Old World hookworm (Ancylostoma duodenale) and the New World hookworm, so infections are generally known as hookworm infections.

The New World hookworm was first discovered in Brazil, and later in Texas. Although this species occurs in the New World, its original range included Africa, India, Southeast Asia, and the southwest Pacific Islands. It prefers to reside in tropical habitats, and in southern areas of the United States, about ninety-five percent of all hookworm infections are caused by the New World hookworm.

The New World hookworm varies in size depending upon the sex, with males reaching an average size of up to .3 inches and females reaching up to .4 inches. This species can release between five thousand and ten thousand eggs per day. These eggs form into embryonated eggs after twenty-four to forty-eight hours of satisfactory conditions within soil and hatch shortly after. This first stage of life is known as rhabditiform. After reaching this stage, the larvae remain in the soil and molt until the reach stage two. Molting occurs once more, after which the larvae reach the third life stage, known as filariform.

It takes about ten days for the New World hookworm to grow from the first life stage to the third, which is the stage at which it can infect animals and humans. It can push through human skin at this stage, moving through the blood stream to the heart and lungs. From here, the larvae will travel again through the blood stream to the small intestine, where they will attach themselves and develop. Adult hookworms typically leave the human body at one to two years of age. This species will reproduce in the intestines, and infected animals or humans can experience blood loss. This species differs from the Old World hookworm in that it must travel through the lungs to reach the intestines and because it has no arrested development period.

Humans can become accidental hosts, when the main hosts are meant to be dogs or cats. Within these hosts, the life cycle is similar to that with hookworms found in humans. However, if a filariform stage worm enters a human, it cannot penetrate the deeper layers of human skin as it can in smaller animals. It will move through the epidermal layer of human skin, leaving a visible trail. This is known as cutaneous larva migrans, a type of zoonotic infection. Other symptoms of this type of infection include skin ruptures and violent itching.

The symptoms of adult hookworm infection include blood loss, because the worms feed on the blood of the host, and cramps, abdominal pain, diarrhea, and weight loss, which can lead to anorexia in the host. Severe infections cause blood issues like hypochromic microcytic anemia and iron deficiency. In children, hypochromic microcytic anemia can cause mental and physical retardation. The most common way to diagnose a human with a hookworm infection is for doctors to collect a stool sample. By using chemicals in a laboratory, experts can create moist sediment, which is studied under a strong microscope. Although the eggs cannot be seen in this sediment, larval specimens can be seen after leaving the sediment in an ambient setting for at least a day.

There are many ways of treating a hookworm infection in humans, but the most common ways include the administration of medications. These include albendazole, mebendazole, and benzimidazoles, and in severe cases, a blood transfusion may be conducted. Once a treatment is given, recovery can be made quicker by a diet that is high in protein and by using iron supplements. In areas where re-infection is common, those with slight infections are not typically treated. One study conducted on about sixty men with the New World hookworms and possibly round worms showed that albendazole might be the most effective treatment to fight hookworm infection, with a success rate of ninety-five percent. In cases of cutaneous larvae migrans, cryotherapy may be used. This process consists of having liquid nitrogen poured on the skin in order to kill the larvae within the skin. However, this process is not often used because it causes skin damage and is not as effective as less harmful, pharmaceuticals like topical crèmes. These topical treatments must be used periodically to effectively remove the hookworms. Prevention against hookworm infections includes education, controlled disposal of human waste, and enhanced sanitation. In areas where this species is abundant, it is recommended that humans where shoes, even if conditions do not appear to support the New World hookworm.

Image Caption: Necator Americanus (hookworm) L3 infectious larva at 100x magnification without any stains or special optics. Credit: Jasper Lawrence/Wikipedia (CC BY-SA 3.0)