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There are many species of hookworms that infect mammals. The most important, at least from the human standpoint, are the human hookworms, Ancylostoma duodenale and Necator americanus, which infect an estimated 15-20% of the world's population.
Hookworms average about 10mm in length and live in the small intestine of the host. The hookworm life cycle begins when the adult males and females mate, and the female produces eggs that are passed in the feces. Depending on the species, female hookworms can produce 10,000-25,000 eggs per day. These eggs can then contaminate the soil and, in warm moist conditions, they will hatch and develop to the stage where they can become infective. About two days after passage the hookworm egg hatches, and the juvenile worm (or larva) develops into an infective stage in about five days. The larvae live in the surface of the soil. These larvae infect humans by burrowing through the skin (for example, through bare feet), and migrating through the blood system to the lungs. From here they pass to the throat, where they are swallowed, and move down to the intestine. The adult worms feed in the intestine by attaching themselves to the lining with sharp "teeth". Here they produce eggs, which are then passed out with the feces.
Juveniles (larvae) of the dog and cat hookworms (A. caninum and A. braziliense, respectively) can infect humans, but the juvenile worms will not mature into adult worms. Rather, the juveniles remain in the skin where they continue to migrate for weeks (or even months in some instances) until killed by the host's inflammatory response. This causes local intense itching and results in a condition known as "cutaneous" or "dermal larval migrans" or "creeping eruption." Hence the importance of not allowing dogs and cats to defecate indiscriminately.
Causes & Development
Individuals become infected, usually by walking bare footed across contaminated soil. Soil contamination can be extremely heavy, particularly in those cultures which utilise human excreta as fertilizer. The eggs are susceptible to urine, however, and it has been found that if fecal material is mixed with urine the eggs can be killed.
There are three pathological phases to hookworm infections:- Cutaneous or invasive phase: When larvae initially penetrate the skin they can cause irritation and itching and if they fail to locate a blood capillary they can wander through the skin causing a condition known as cutaneous larval migrans, leaving a track visualized under the skin by the presence of the host inflammatory reaction.
- Pulmonary phase: This occurs during the period when the larvae are bursting out of the capillaries in the lungs into the alveolar spaces. This causes local haemorrhaging at the site. This is rarely symptomatic, except when there is a heavy infection, when it can result in pneumonitis, and can also cause a cough and a sore throat.
- Intestinal phase: Adult worms are usually restricted to the anterior third of the small intestine, but where infections are very heavy they can occupy the whole length of the small intestine. The worms clamp onto the mucosa abrading the surface and sucking the blood. Proteolytic enzymes from the dorsal pharyngeal gland are released into the buccal cavity which aid in digestion.
Signs & Symptoms
The most common effect from hookworm infections is the varying degrees of anemia, depending on the level of the infection and the nutritional state of the patient. Patients also can suffer from protein deficiency which manifests as dry hair, skin and edema, but protein loss can have far-reaching effects including reduced immunocompetence and reduced ability to produce gama globulin (Antibody).
The infection is particularly severe in children, and the development of a pot belly, as a result of the edema, is a common symptom of the infection. The protein deficiency also can result in significantly delayed physical development in children. In its most progressive state can result in death.
Diagnosis & Tests
The presence of hookworms can be demonstrated by finding the characteristic eggs in the feces; the eggs can not, however, be differentiated to species.
Treatment & Prevention
The drug of choice for the treatment of hookworm disease is mebendazole which is effective against both species, and in addition, will remove the intestinal worm Ascaris also, if present. The drug is very efficient, requiring only a single dose and is inexpensive -- the "perfect drug". However, treatment requires more than giving the anthelmintic, the patient should also receive dietary supplements to improve their general level of health, in particular iron supplementation is very important.
Topical treatment with thiabendazole ointment is very effective in controlling dermal larval migrans.
Complications
The mouthparts of hookworms are modified into cutting plates. Attachment of hookworms to the host's small intestine causes hemorrhages, and the hookworms feed on the host's blood. Hookworm disease can have devastating effects on humans, particularly children, due to the loss of excessive amounts of blood. Heavy hookworm infections can account for as much as 200ml of blood loss per day.
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Conditions that suggest Hookworm Infection:
Risk factors for Hookworm Infection:
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GLOSSARY
Alveolar
Pertaining to a small hollow space, as in the lung, e.g. pulmonary alveolus.
Anemia (Anaemia, Anemias)
A condition resulting from an unusually low number of red blood cells or too little hemoglobin in the red blood cells. The most common type is iron-deficiency anemia in which the red blood cells are reduced in size and number, and hemoglobin levels are low. Clinical symptoms include shortness of breath, lethargy and heart palpitations.
Anterior
In the front or forward part of the organ or toward the head of the body.
Anthelmintic
Agent that expels or destroys intestinal worms.
Antibody (Antibodies)
A type of serum protein (globulin) synthesized by white blood cells of the lymphoid type in response to an antigenic (foreign substance) stimulus. Antibodies are complex substances formed to neutralize or destroy these antigens in the blood. Antibody activity normally fights infection but can be damaging in allergies and a group of diseases that are called autoimmune diseases.
Buccal
Pertaining to, located near, the cheek.
Capillary
Any of the smallest blood vessels connecting arterioles with venules and forming networks throughout the body.
Edema
Abnormal accumulation of fluids within tissues resulting in swelling.
Enzymes (Enzyme)
Specific protein catalysts produced by the cells that are crucial in chemical reactions and in building up or synthesizing most compounds in the body. Each enzyme performs a specific function without itself being consumed. For example, the digestive enzyme amylase acts on carbohydrates in foods to break them down.
Gland (Glands)
The glandular system is one of the most important and complicated systems of the body. Gland tissue can be either an organ or general tissue that secretes chemicals and there are two types of gland: exocrine and endocrine. Those glands which secrete chemicals through tubules or ducts are called exocrine and include sweat, tear and salivary glands. Ductless glands - part of the endocrine system - secrete special chemicals (hormones) directly into the blood.
Hookworm (Ancylostoma duodenale, Ancylostomiasis, Hookworms, Necator americanus)
Hookworms average about 2/5 of an inch (10mm) in length and live in the small intestine of the host. The most common effect from hookworm infections is a varying degree of anemia.
Iron
An essential mineral. Prevents anemia: as a constituent of hemoglobin, transports oxygen throughout the body. Virtually all of the oxygen used by cells in the life process are brought to the cells by the hemoglobin of red blood cells. Iron is a small but most vital, component of the hemoglobin in 20,000 billion red blood cells, of which 115 million are formed every minute. Heme iron (from meat) is absorbed 10 times more readily than the ferrous or ferric form.
Lung (Lungs, Pulmonary)
Organ of the body, located in the chest cavity which is designed to bring oxygen from the air into the blood stream, while also expelling carbon dioxide and other waste gases out of the body. Pulmonary: Related to the lungs.
Milliliter (mL)
0.001 or one thousandth of a liter.
Millimeter (Millimeters, mm)
A metric unit of length equaling one thousandth of a meter, or one tenth of a centimeter. There are 25.4 millimeters in one inch.
Mucous Membranes (Mucosa, Mucous Membrane, Mucus Membranes)
The membranes, such as the mouth, nose, anus, and vagina, that line the cavities and canals of the body which communicate with the air.
Pharynx (Pharyngeal)
A hollow tube about five inches long that starts behind the nose and goes down to the neck to become part of the esophagus (the tube that goes to the stomach).
Pneumonia (Pneumonitis)
Inflammation, usually infectious, of the lungs. Unless the result of only moderate chemical or smoke irritation, it is a potentially life-threatening condition. There are so many defenses against an infection this deep in the body that the very presence of pneumonia signals a pathogen of great virulence or impaired or exhausted immunity, or all three. Pneumonitis: Inflammation of the lungs, from whatever cause. It may be concurrent with pneumonia or pleurisy.
Protein (Proteins)
Compounds composed of hydrogen, oxygen, and nitrogen present in the body and in foods that form complex combinations of amino acids. Protein is essential for life and is used for growth and repair. Foods that supply the body with protein include animal products, grains, legumes, and vegetables. Proteins from animal sources contain the essential amino acids. Proteins are changed to amino acids in the body.
Proteolytic
Commonly: Proteolytic (protein-digesting) Enzymes. Enzymes that are able to break down certain proteins, yet do not attack the beneficial proteins that make up the normal cells of the body. These proteolytic enzymes are said to have great value in fighting cancer as well as many other diseases. If the body were always capable of producing adequate proteolytic enzymes, it is possible that cancer would not develop. In theory, cancer cells have a type of protein coating that is destroyed by these proteolytic enzymes. When this protein is destroyed, the body's white cells are able to attack the cancer cells and destroy them.
Small Intestine (Small Bowel)
The small intestine lies between the stomach and the large intestine. It is about 6 meters (20 feet) long and its primary function is to digest (break down) food and absorb nutrients (vitamins, minerals, proteins, carbohydrates, and fats). The small intestine makes up more than 70% of the length and 90% of the surface area of the gastrointestinal (GI) tract.
Topical
Most commonly 'topical application': Administration to the skin.
Last updated: May 30, 2009
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