Hookworm infection is an infection by a type of intestinal soil-transmitted roundworm parasite classified as one of the neglected tropical disease. There are two species of hookworms that commonly infect humans: Ancylostoma duodenale and Necator americanus.
Other species of hookworms such as Ancylostoma tubaeforme, Ancylostoma braziliense, and Uncinaria stenocephala are transmitted by cats to human through bite or contact with the cat feces.
Dogs, birds, and cats may also be affected. Ancylostoma tubaeforme infects cats, Ancylostoma caninum infects dogs, and Ancylostoma braziliense infect both cats and dogs. Also hookworms are much smaller than the large roundworms nematoda Ascaris lumbricoides.
It is said to have infected about 428 million people in 2015. Heavy infections of hookworm can occur in both children and adults, but are less common in adults and It is rarely fatal.
It is estimated that between 576 and 740 million individuals are infected with Hookworms where by which about 80 million are severely affected. Necator americanus is mostly found in the Americas, sub-Saharan Africa, and Asia while Ancylostoma duodenale is found in more scattered focal environments such as Europe and the Mediterranean.
Other affected regions include: South Asia, Latin America and the Caribbean with about 50 million affected, South Asia (59 million), Middle East/North Africa (10 million) noting a majority of these infected individuals live in poverty-stricken areas with poor sanitation.
Morphology of Hookworm
- Ancylostoma duodenale worms are grayish white or pinkish in color with the head slightly bent in relation to the rest of the body. This bend forms a definitive hook shape at the anterior end for which the name hookworm.
- Ancylostoma duodenale also possesses a well-developed mouths with two pairs of teeth.
- Males worm measure approximately one centimeter by 0.5 millimeter,
- Females worms are often longer and stouter.
- Males can be distinguished from females based on the presence of a prominent posterior copulatory bursa.
Necator americanus is very similar in morphology to Ancylostoma duodenale.
- Necator americanus is generally smaller than Ancylostoma duodenale
- Males usually measures 5 to 9 mm long
- Females measures about 1 cm long.
- Necator americanus possesses a pair of cutting plates in the buccal capsule.
- The hook shape of Necator americanus is much more defined than in Ancylostoma duodenale
- The eggs of all hookworm species are indistinguishable
- Oval or elliptical, measuring a length of 60 by 40 µm width
- Colorless and not bile stained and with a thin transparent hyaline shell membrane.
- The Eggs ovum is Unsegmented when released by the worm in the intestine
- The ovum only develops when its passes down the intestine and thus the eggs passed in feces end up with a segmented ovum
- The segmented ovum of the egg is usually with 4 to 8 blastomeres.
Transmission of Hookworm
- Eggs of hookworm are mostly deposited in stools of infected people.
- If not properly handle and release in the environment by defecation,uses of untreated faeces as fertilizer and they end up contaminating the soil after hatching to immature worms which penetrate the skin of humans.
- Initially, itching and a rash may occur at the site of infection or penetration by the immature worm.
- It can also be transmitted walking barefoot in warm climates, where sanitation is poor with contaminated soil and through contaminated food.
life cycle of Hookworm
- These worms loves warm soil where temperatures are over 18°C.
- They exist primarily in sandy or loamy soil and are unable to live in clay or muck soil.
- Rainfall averages must be more than 1000 mm (40 inches) a year for them to survive.
- The above conditions favours hookworm eggs hatch.
- The Infective larvae of Necator americanuscan survive are thermophilic, that is can survive at higher temperatures
- Those of Ancylostoma duodenale are better adapted to cooler climates( psychrophiles). Generally, they can resist exposure to direct sunlight or desiccation and live for only a few weeks at most under natural conditions,
- The Infection of the host is by the larvae (Immature worm) and not the eggs.
- Ancylostoma duodenale can be ingested but the usual method of infection is through skin penetration by the larva or immature worm which is commonly caused by walking barefoot through areas contaminated with fecal matter.
- larvae worms are able to penetrate the skin of the foot, and once inside the body, they migrate through the vascular system to the lungs, and from there up the trachea, and are then swallowed.
- They passes down the esophagus and enter the digestive system, finishing their journey in the intestine of their, where the larvae mature into a complete adult worms
- Necator americanus worms tends to cause a prolonged infection, generally from 1 to 5 years (many worms die within a year or two of infecting), though some adult worms have been recorded to live for 15 years or more.
- Ancylostoma duodenale adults are short-lived, surviving on average for only about 6 months. However, the infection can be prolonged because dormant larvae can be “recruited” sequentially from tissue “stores” over many years, to replace expired adult worms.
- This can give rise to seasonal fluctuations in infection prevalence and intensity (apart from normal seasonal variations in transmission).
- These worms mate inside the host and the females lays up to 30,000 eggs per day and some 18 to 54 million eggs during their lifetimes, which are passed out in feces.
- Because 5 to 7 weeks are needed for adult worms to mature, mate, and produce eggs, in the early stages of very heavy infection, acute symptoms might occur without any eggs being detected in the patient’s feces. This can make diagnosis very difficult.
- Ancylostoma duodenale and Necator americanus eggs can be found in warm, moist soil where they eventually hatch into first-stage larvae
- The larvae or immature worm feeds on soil microbes and eventually molt into second-stage larvae, L2, which is also in the rhabditiform stage.
- These Larvae feed for about 7 days and then molt into the third-stage larvae, or L3.
- The third larva form is the nonfeeding infective form of the larvae.
- They are extremely motile and seek higher ground to increase their chances of penetrating the skin of a human host.
- This third larva form (L3) can survive up to 2 weeks without finding a host.
- Necator americanus larvae only infect through penetration of skin while Ancylostoma duodenale can infect both through penetration and orally (Food borne).
- After the third larvae form have successfully entered a human host, they then travel through the subcutaneous venules and lymphatic vessels of the human host.
- The L3 larvae then enters the lungs through the pulmonary capillaries and break out into the alveoli. They then travel up the trachea to be coughed and swallowed by the host.
- After being swallowed by the host, the L3 larvae move in the small intestine, where they molt into the fourth forme larvae (L4) which is the adult worm stage.
- This entire process starting from skin penetration to adult development takes about 5–9 weeks.
- Necator americanus adult female worms releases about 9,000–10,000 eggs/day
- Ancylostoma duodenale female releases about 25,000–30,000 eggs/day
- These eggs are passed in the feces of the human host where they hatch in the environment within several days and the cycle starts anew.
Incubation period of Hookworm
The incubation period of these worms can vary between a few weeks to many months which is largely dependent on the number of hookworm parasites an individual is hosting or infected with.Meaning the heavier the infection,the faster sign and symptoms manifestation.
Signs and Symptoms of Hookworm infection
No signs or symptom are specific for hookworm infection, but the following combination commonly found among people infected with hookworm
- intestinal inflammation
- Skin rash in one area that is typically red, raised, and itchy
- chest pain
- Weight loss
- Fever sometimes due to severe infection.
- Epigastric pains
- Diarrhea especially during early or in later stages
- Extreme tiredness and weakness
Symptoms of advanced severe infection are
- progressive iron-deficiency anemia or malnutriti
- protein deficiency
- cardiac failure
- distension with ascites.
Other gastrointestinal symptoms which tend to improve with time such as
Laboratory Diagnosis of Hookworm
Laboratory diagnosis depends on finding macroscopically and microscopically thats is
the characteristic hookworm eggs in stools sample although this is not possible in early infection.(For Hook eggs characteristics,Look above on Morphology of Hookworm)
- Complete blood count (CBC) with differential to evaluate anaemia
- Both Ancylostoma and Necator eggs are indistinguishable but can be differentiated by culturing in the lab to allow larvae to hatch out.
- The process is simple.The fecal sample is left for a day or more under tropical conditions mention above, this will permit the larvae to hatched out, so eggs might no longer be evident.
- In these case, it is essential to distinguish hookworms from Strongyloides larvae, as infection with the latter has more serious implications and requires different management.
- Adult Hookworm are rarely seen except through endoscopy, biopsy or surgery,
- Adult worm of each species of hookworm can be distinguished based on the length of the buccal cavity, the space between the oral opening and the esophagus mention on Morphology of Hookworm above.
- Not to confuse hookworm from rhabditiform larvae having a long buccal cavities from Strongyloides rhabditiform larvae having short buccal cavities.
Prevention of Hookworm infections
The infective larvae of hookworm develop and survive in the soil,an environment of damp dirt, particularly sandy and loamy soil. They are unable to survive in clay or muck. Therefore the main ways of precaution are those dictated by practising good hygiene behaviors such as :
- Avoid defecating in the open, but rather do in toilets.
- Avoid the use of untreated human excreta,raw sewage as fertilizer in agriculture.
- Avoid walking barefoot in known infected areas as the larva penetrate the skin
- Remember to deworm pet dogs and cats.
- Canine and feline hookworms rarely develop to adulthood in humans. Ancylostoma caninum, the common dog hookworm, occasionally develops into an adult to cause eosinophilic enteritis in human, but their invasive larvae can cause an itchy rash called cutaneous larva migrans.
- Using a barrier such as gloves,boots aprons etc to prevent the skin from touching the soil when sitting on the ground or working especially farmers,bricklayers,lumbermen,gardeners etc
- Avoiding consuming soil that may be contaminated with hookworm by properly washing fruits,cassava and other soil products
- Covering children’s sandboxes
- Covering moist soil requiring frequent contact with a waterproof liner
Treatment of Hookworm infections
Note that the goals of treatment of hookworm infections are
- To cure the infection
- Treat complications of anemia due to malnutrition
- Improve nutrition
Anthelmintic drugs such as
- pyrantel pamoate
In case where patient suffers from anemia, ferrous sulfate (200 mg) is recommended three times daily at the same time as anthelmintic treatment is giving; until hemoglobin values return to normal
How will you differentiate Hookworm eggs from Strongyloides stercolaris eggs