Necator Americanus and Ancylostoma Duodenale (Hookworms)

Necator americanus and Ancylostoma duodenale (Hookworms) Necator americanus and Ancylostoma duodenale (Hookworms)  Hookworm Disease, Ancylostomiasis, Necatoriasis  “Tunnel disease” and “miner’s disease”  Buccal capsule well developed, usually with ventral teeth (Ancylostoma) or cutting plates (Necator)  Caudal bursa of male usually supported by rays  Soil-Transmitted Helminths (STH) or Geohelminths Hookworm species  Two common humans species: 1) Necator americanus (human) 2) Ancylostoma duodenale (human)  Further hookworms of animals are: 1) Ancylostoma ceylanicum (cats, dogs and human in Taiwan, SouthEast Asia and Suriname 2) A. braziliense (America, Asia in dogs, cats, wolves, bears) 3) A. caninum (worldwide in dogs, wolves, foxes, tigers, cats, pigs) 4) A. tubaeforme (Europe, in wild and domestic cats)  The larvae of these species, however, may also enter the skin of humans, but do not reach maturity, so that they stick somewhere in the organs of the final host. If these larvae (like those of A. braziliense) remain in the skin, they may induce skin elevation described as “larva migrans” or “creeping eruption” Geographic distribution/epidemiology:  Both species occur in warm and humid regions between 30℃ south and 45℃ north, but also worldwide in deep mines  About 20–25% of the human population on earth are (at least occasionally) infected by hook worms (Worldwide about 800 million people are infected)  Even in temperate regions, these worms occurred in mines, since down there the temperatures are increased  A. duodenale: is found in North Africa, North and South Asia,  N. americanus: occurs in America, Central Africa and regions in South and Eastern Asia  Iran (Both species in Caspian Sea area of Iran):  North of Iran: N  South of Iran: A Location in host:  Adult worms are present in the second and third portions of the jejunum and rarely in the duodenum with the buccal capsule attached to the mucosa  In heavy infections they may be found as far back as the caecum  The worms suck blood mainly in the region of the jejunum. This blood is not only used as food but also helps to supply the worm with oxygen Biology, morphology:  Adult worms:  The whitish adults of both species measure about 10–12 mm in length and the species can be clearly differentiated according to the below criteria: 128  The adults are cylindrical, greyish-yellow, nematodes tapering anteriorly and slightly curved, with the head bent back dorsally (forming a ‘hook’)  Males of both species are only slightly smaller than the females; however, they possess a hold-fast organ at their terminal end, which is described as bursa copulatrix (caudal bursa or capulatory bursa), looks hand-like and makes it possible that the males are able to copulate with the females  During copulation which apparently occurs permanently during blood sucking at the intestinal wall, the hand-like bursa copulatrix is firmly attached around the genital opening of the female Eggs (Ovum):  Eggs are practically indistinguishable in both species  The ovum is unsegmented when discharged by the worm  The females excrete per day 9000–10,000 eggs  The transparent egg is thin-shelled (thin-walled) and ovoid, with blunt, rounded ends  In fresh feces, the eggs contain only 2–8 cells  Egg size: 60 x 40 μm Eggs (Ovum):  Fresh excreted eggs of the hookworms can be distinguished from eggs of the worms belonging to the genera Trichostrongylus and Ternidens (e.g. T. deminutus) by the fact that they only contain 2–8 embryonic cells, while the eggs of the 2 other genera contain at least 32, 64 or even more cells Life cycle  The ovum is unsegmented when discharged by the worm but continues to develop and is usually at the 4- or 8-celled stage when passed in the faeces  It develops quickly and may already be at the morula stage in old faecal samples. On reaching soil the embryo develops into a first-stage larva (L1 or rhabditiform), which hatches out in 24–48 h  The conditions for maximum rate of development are warmth (+25°C), shade, moisture and a light sandy loam  After hatching of the larva 1 (L1) from the egg outside of the body, two more larvae are formed within 5–7 days. The third one (L3 or filariform stage) has a length of 500–650 μm and is still enclosed in the cuticle sheath of the secondstage larva and thus is called a “sheathed” larva  The infection of humans occurs by active penetration of the larva 3 (L3) into the skin, whereby the sheath is stripped off  After a heart–lung–trachea–esophagus passage (under occasional drifting in other organs), the larvae 3 (L3) reach the intestine within 3–7 days, where they become mature within 4–6 weeks Symptoms of the disease (Ancylostomiasis; hookworm disease) In general, the hookworm disease is always connected with considerable blood loss The worms suck blood mainly in the region of the jejunum. This blood is not only used as food but also helps to supply the worm with oxygen. Therefore, the worms suck much more blood than it is needed for feeding. This behaviour leads to the fact that infected persons discharge blood in their feces and suffer finally from anaemia if large numbers of worms are present  However, an infection with 30 adults of the species Necator americanus, which each suck about 0.03 ml blood per day, may remain unnoted, while 100–500 worms introduce medium sized damages and more than 1000 are lifethreatening  Ancylostoma worms suck about 10 times more blood than those of N. americanus. Thus, in the case of A. duodenale already 100 worms lead to severe anaemia  Furthermore, all worms change several times per day their sucking place, while the wounds are still bleeding. This behaviour leads to further considerable blood losses  In general, the following phases during an infection with hook worms may be noted: – Skin penetration phase: o Itching and formation of papulae at the penetration sites of the larva 3 (ground itch) – Lung passage: o Symptoms like bronchitis, lymph node swellings and lung and trachea inflammations – Acute disease: o In cases of mass infections haemoglobin becomes massively decreased, reddish and even black stools are excreted, fever, highgrade eosinophilia (hypochromic microcytic anaemia) – Chronic phase of disease:  This phase is very dangerous, since worms live up to 20 years. Thus, there is a constant blood loss which leads to a considerable weakness of the patient.  Further symptoms are abdominal pain, slight fever, obstipation, slightly occult bloody stool, increasing anaemia with consequences such as 143 cachexia, heart and circulation problems, which may lead finally to death Diagnosis:  Clinical:  Chronic anaemia and debility in patients living in an endemic area are suggestive  Parasitological:  Microscopical demonstration of eggs inside the feces parasitological methods  Fresh excreted eggs of the hookworms can be distinguished from eggs of the worms belonging to the genera Trichostrongylus and Ternidens (e.g. T. deminutus)  Ova must be cultured to the infective larva stage if it is required to differentiate between the two hookworm species Pathway of infection: Percutaneous by skin penetration of the larvae 3 (L3 or filariform stage), which stay alive for weeks in nature. Due to the lack of immune reactions of infected hosts, they can become repeatedly infected, thus enlarging their parasitic load for a long phase of their life. Prophylaxis (Prevention and control): Wearing of firm shoes in endemic avoidance of contact to human feces regions, Attention:  Working in laboratory with hookworm eggs must consider the fact that larvae hatch very quick; thus, tables and vessels must be intensively cleaned Treatment: Drugs of choice are mebendazole (2×100 mg for 3 days) and albendazole (1×400 mg; children below 2 years 15 mg/kg bodyweight) Also further anthelmintics are effective: ivermectin, levamisole, pyrantel or bephenium In cases of anaemia, iron substitution is obligatory; in extreme infections even blood transfusions may be needed Hookworms larva: