Hookworm Picture Download PORTABLE
Dashawn Steed
An estimated 576-740 million people in the world are infected with hookworm. Hookworm was once widespread in the United States, particularly in the southeastern region, but improvements in living conditions have greatly reduced hookworm infections. Hookworm, Ascaris, and whipworm are known as soil-transmitted helminths (parasitic worms). Together, they account for a major burden of disease worldwide.
Hookworms live in the small intestine. Hookworm eggs are passed in the feces of an infected person. If the infected person defecates outside (near bushes, in a garden, or field) or if the feces of an infected person are used as fertilizer, eggs are deposited on soil. They can then mature and hatch, releasing larvae (immature worms). The larvae mature into a form that can penetrate the skin of humans. Hookworm infection is mainly acquired by walking barefoot on contaminated soil. One kind of hookworm can also be transmitted through the ingestion of larvae.
Most people infected with hookworms have no symptoms. Some have gastrointestinal symptoms, especially persons who are infected for the first time. The most serious effects of hookworm infection are blood loss leading to anemia, in addition to protein loss. Hookworm infections are treatable with medication prescribed by your health care provider.
Intestinal hookworm disease in humans is caused by Ancylostoma duodenale, A. ceylanicum, and Necator americanus. Classically, A. duodenale and N. americanus were considered the two primary intestinal hookworm species worldwide, but newer studies show that a parasite infecting animals, A. ceylanicum, is also an important emerging parasite infecting humans in some regions. Occasionally larvae of A. caninum, normally a parasite of canids, may partially develop in the human intestine and cause eosinophilic enteritis, but this species does not appear to reach reproductive maturity in humans.
Another group of hookworms infecting animals can penetrate the human skin causing cutaneous larva migrans (A. braziliense, A. caninum, Uncinaria stenocephala). Other than A. caninum noted above, these parasites do not develop further after their larvae penetrate human skin. See extraintestinal hookworms for more information.
Humans are the principal host for both A. duodenale and N. americanus. A. ceylanicum may be zoonotic, as two haplotypes have been identified, one found only in humans thus far and the other found in humans, dogs, and cats. A. caninum is the common dog hookworm.
Intestinal hookworm infections are commonly asymptomatic. Attachment of the hookworms to the intestinal wall may stimulate abdominal pain, nausea, and anorexia. Iron deficiency anemia caused by blood loss at the site of intestinal attachment of adult worms may occur especially in heavy infections. Occult blood in the stool may also be seen in heavy infections. In severe cases, protein malnutrition from chronic plasma protein loss has been reported.
The adult female hookworm releases eggs, which are passed in stool. Rhabditiform larvae are released in soil after hatching and undergo two molts before reaching an infective third-stage filariform larvae. These larvae can survive for 3 to 4 weeks in contaminated soil under favorable climate conditions. They penetrate human skin upon contact and reach the lungs through the heart via blood circulation. Once these larvae penetrate the pulmonary alveoli, they ascend the bronchus to the pharynx. From there they are swallowed and reach the small intestine, where they mature to adult worms.
"We didn't know we had the hookworm until a doctor diagnosed us on the third day at the hospital. We got home on the 18th and visited the hospital on the 20th but it wasn't until the 22nd that we were diagnosed with hookworm, that a doctor knew what it was," Stephens said.
"Cutaneous larva migrans basically means there is a larva, or the immature form of a hookworm, migrating around under the skin," Bobbi S. Pritt, parasitologist at the Mayo Clinic, tells BuzzFeed News. The microscopic larvae live in sand or soil that has been contaminated with dog or cat feces, says Pritt, and enter the foot by directly penetrating the skin. "The hookworm eggs come out of the stool and hatch in the sand or soil, where they live until an unsuspecting human walks on them barefoot," Pritt says.
The worms need a warm, moist environment to survive, so they love tropical areas. "You'll find hookworms in parts of the South in the US but they are endemic to many countries in the Caribbean, as well as Central and South America," Pritt says. The hookworms are common in beaches or rural areas where stray dogs are defecating, since the eggs come from infected feces. But even a glamorous beach resort can have hookworms, too. "Unless you know a beach doesn't allow dogs, you can't be sure," Pritt says.
The good news? Humans are a dead-end host for these little guys. "The hookworms that cause cutaneous larva migrans can't complete their life cycle in humans, so they will eventually die in a few weeks," Pritt says. But the infection is also very easy to treat, and the right medication will kill the larvae and ease symptoms in a day or two. "Anthelmintics are drugs that rid the body of worms, like ivermectin, and are widely available in most countries," Green says.
"Another great thing people can do is to go to a travel clinic before your trip and they can tell you specifically what to look out for and whether you need certain medications or vaccines beforehand based on where you are going," Pritt says. Besides hookworm, there are other parasitic and bacterial infections and mosquito-borne diseases in tropical areas that can be a lot more serious.
Dr. Rojelio Mejia, infectious disease specialist at Baylor College of Medicine, says the parasites are no strangers to U.S. soil. In a paper published in 2017, Mejia and his team reported finding more than a third of the people in one Alabama county were infected with hookworm disease.
Mejia has worked to quell hookworm disease in Ecuador, Mozambique, the grassy plains of northern Argentina. Now, he and partners are leading efforts to control the outbreak in rural Alabama. We talked with him by telephone about the disease and the various struggles the U.S. has keeping it under control compared with resource-poor countries. His answers have been lightly edited for space.
We studied rural Alabama and found about 35% of people in one county are infested with hookworm. We chose Lowndes County because it previously had a high rate of hookworm, continues to have a high rate of poverty, and many residences have open sewage systems. (The study, "Human Intestinal Parasite Burden and Poor Sanitation in Rural Alabama," was published in October 2017, in American Journal of Tropical Medicine )
But one thing they do with great efficiency is give albendazole, a drug used to treat hookworm. I was in Argentina at a school, and they had all the kids line up for treatment. They took it in front of us.
Another disadvantage in the U.S. is diagnostics. In Ecuador, they know what a parasite looks like under a microscope. In the U.S., because hookworm is rare, physicians who won't know what to look for could miss it.
People do what's called straight piping for sewage, running a large pipe as far away from the home as possible. All the sewage goes through these pipes to a ditch or a landfill. But it's hilly and it rains, so the hookworm eggs end up getting spread throughout the environment.
This photograph shows the front section of the hookworm, and the mouth parts which it uses to feed. The cutting plates, used to attach to the lining of the intestine where they suck blood for nourishment, are visible. Three species of hookworm cause infection in the United States, including this species, Necator americanus. (Image courtesy of the Centers for Disease Control and Prevention.)
This is the mouth part of the hookworm Ancylostoma duodenale. The hookworm uses sharp, curved cutting plates to attach to the lining of the intestine where it sucks blood for nourishment. (Image courtesy of the Centers for Disease Control and Prevention.)
This is a hookworm egg. Hookworms hatch in damp vegetation. Their larvae can enter the human body through the skin, even without cuts or abrasions. Once through the skin, they begin the next step of their life cycle.
There is very little risk of getting the disease in the United States because of advances in sanitation and waste control. The important factor in getting the disease is walking barefoot on ground where there are feces of people who are infected with hookworm.
Soil-transmitted helminth (STH) infection has been associated with lower cognitive performance of schoolchildren. To identify pathways through which STH infection might affect school performance, baseline data from a large rice-fortification trial in Cambodian schoolchildren were used to investigate associations between STH infection, micronutrient status, anemia, and cognitive performance. Complete data on anthropometry, cognitive performance, and micronutrient status were available for 1,760 schoolchildren, 6-16 years of age. STH infection was identified using Kato-Katz, whereas cognitive performance was assessed using Raven's Colored Progressive Matrices (RCPM), block design, and picture completion. STH infection was found in 18% of the children; almost exclusively hookwork infection. After adjusting for age and gender, raw cognitive test scores were significantly lower in hookworm-infected children (-0.65; -0.78; -2.03 points for picture completion, RCPM, and block design, respectively; P < 0.05 for all). Hookworm infection was associated with iron status (total body iron), but not with vitamin A and zinc status, nor with inflammation or anthropometry. Body iron was negatively associated with increased intensity of hookworm infection (R = 0.22, P < 0.001). Hookworm infection in Cambodian schoolchildren was associated with lower cognitive performance, an effect most likely mediated through lower body iron. Interventions that are more effective against hookworm infection are needed to contribute to better health and improvement of cognitive performance.
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