Saturday 2 April 2011

Hookworm & Trichostrongylus Ova

Hookworms & Trichostrongylus sp.
-Nematodes (Roundworms)

Ancycostoma duodenale (old world hookworm) -predominant in South-East Asia, China, India, Northern Africa and Southern Europe.
Necator americanus (new world hookworm) - America, Caribbean, Central America, Southern Africa, Polynesia -virtually World-wide.

Old & New World labels are historical and somewhat of a misnomer as geographic distribution overlap.
Hookworms are found in warm, moist areas of the world.

Adult Worms;
Adult males are about 7-11 mm long with A.duodenale usually slightly larger than N.americanus. Adult worms are rarely seen as they usually remain firmly attached to the intestinal mucosa by their mouth. A.duodenale has well developed teeth while N.americanus has cutting plates facilitating attachment. As such, diagnosis is usually made by finding hookworm eggs in stool specimens. Eggs (ova) are essentially identical for both hookworm species.

Infection is acquired through skin penetration of the filariform larvae from soil. Hookworms have hyaluronidase activity which facilitates the infective larvae penetration through skin. After penetration, the larvae are carried to the heart and then to the lungs where they enter the alveoli and migrate through the bronchi to the trachea and pharynx. Once they reach the pharynx they are swallowed and travel to the small intestine where they attach to the mucosal surface and further mature. Females usually begin to deposit eggs about 5 months after initial infection.

Eggs (~56µm to 75µm X 36µm to 40µm) that are passed in the stool are usually in the early cleavage stage and appear rather oval with broadly rounded ends and a clear space between the embryo and egg shell. Eggs will hatch within 1 to 2 days when in moist, shady warm soil. Infective filariform larvae develop within 5 to 8 days of hatching under optimal conditions and can remain viable in the soil for several weeks.

Hookworm Egg - Note broadly rounded ends, clear space around developing cells.
(click on image to enlarge for better viewing)
All photos from formalin-ethyl acetate concentrate at 400X
Clinical Disease;
Hookworm infections cause more morbidity rather than mortality. Symptoms usually are related to the larval load (how many). Infections may go unnoticed or may cause pruritus with further complication by secondary infection through scratching. Depending on the number of migrating larvae, pneumonitis may result.
Once attached to the intestinal mucosa, symptoms may include;
  • Necrosis of intestinal tissue
  • Blood loss through ingestion by the worm or direct bleeding facilitated by an anticoagulant secreted by the worm
  • Fatigue
  • Nausea & Vomiting
  • Abdominal pain
  • Diarrhea with stools that may be tinted red to black due to blood loss.
  • Chronic infections may result in anaemia from the blood loss.
Again, diagnosis is made by finding the hookworm eggs in stool samples, either in direct, concentrate or stained smears. Results should be reported as “Hookworm Ova” present as species (N.americanus, A.duodenale) cannot be determined by the egg.

Prevention & Treatment;
Sanitary treatment & disposal is the most effective way of reducing exposure to the filariform soil larvae. Wearing of shoes may also help prevent infection.
Anti-helminthic drugs such as albendazole prove effective in treatment.

Just for comparison- A Hookworm egg in the upper right compared to an Ascaris egg in the lower left of photomicrograph. Fecal concentrate at X250)
(click on photo to enlarge for better viewing)

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Trichostrongylus Species; (several species can infect humans with varying severity)
This nematode (roundworm) has worldwide distribution and is commonly found in herbivores.
Trichostrongylus species are similar to hookworms as they also take up residence on the mucosa of the small intestine however they differ in not having teeth or cutting plates.

Infections is usually acquired by ingestion of the infective larvae on contaminated plant material. Trichostrongylus larvae reach the small intestine without any migratory pathway through the lungs and mature there within 3 to 4 weeks.

The Trichostrongylus ova appear similar to Hookworm ova however they are slightly larger (~73µm to 95µm X 40µm to 50µm) and tend to have more pointed ends.
Eggs deposited in warm, moist soil may hatch as quickly as 24 hours and develop into infective larvae after about 60 hours.

Trichostrongylus Egg - Note similarity to Hookworm Egg above however end more pointed.
(click on image to enlarge for better viewing)

Trichostrongylus Egg - Note much more pointed end than Hookworm
(click on image to enlarge for better viewing)

As with the Hookworms, symptoms from Trichostrongylus infections are related to the worm burden and subsequent damage to the intestinal mucosa. Haemorrhage and desquamation may occur as with Hookworm infections.
Symptoms are not usually clinically significant unless there are large numbers of worms present.

Diagnosis is usually made through egg identification in the stool.

Prevention and Treatment;
Herbivores constantly reinfect grazing areas therefore the only effective prevention is the proper cleaning and cooking of vegetable foodstuffs. Treatment again is with anti-helmithic drugs such as albendazole.