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21 Cards in this Set
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Strongiloidea Ancyclostomatidae Family Ancylostomatidae - Morphology
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Most species are rather stout, and the anterior end is curved dorsally, giving the worm a hooklike appearance.
The buccal capsule is large and anheavily sclerotized, armed with cutting plates, teeth, lancets, or a dorsal cone The esophagus is stout, with a swollen posterior end, giving it a club shape. It is mainly muscular, corresponding to its action as a powerful pump. Esophageal glands Cervical papillae are present near the rear level of the nerve ring. Males have a conspicuous copulatory bursa, consisting of two broad lateral lobes and a smaller dorsal lobe, all supported by fleshy rays . Spicules are simple, needlelike. Females have a simple, conical tail. The vulva is postequatorial, and two ovaries are present. About 5% of the daily output of eggs is found in the uteri at any one time; Eggs is several thousand per day for as long as nine years. |
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Strongiloidea Ancyclostomatidae - copulatory bursa
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Ventral view of a typical strongyloid copulatory bursa. The basic pattern is found in all Strongyloidea.
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Necator americanus egg in early cleavage stage, as normally passed in feces.
Size is 65 µm to 75 µm by 36 µm to 40 µm. Eggs of Ancy-lostoma duodenale, 56 µm to 60 µm by 35 µm to 40 µm, are not distinguishable. |
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Hookworm egg containing fully developed J1.
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Strongiloidea Ancyclostomatidae - Life cycle (Biology)
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Hookworms mature and mate in the small in-testine of their host .
Embryos develop into 2,4 or several- cell stages by the time they are passed with feces Species infecting humans cannot be diagnosed reliably by their eggs alone. Eggs require warmth, shade, and moisture for continued de-velopment. Coprophagous insects may mix the feces with soil and air, thus hastening embryogenesis, which is completed within 24 to 48 hours in ideal conditions Newly hatched J1 larva has a oesophagus with characteristic constriction at the level of the nerve ring (like rhabditiform J1s of Strongyloides spp). Juveniles live and, feed on fecal matter, and molt their cuticle in two to three days. J2, continue to feed and grow and after 5 days molt to J3, which is infective to a host. J3 s have intestine filled with food particles that sustain them through the nonfeeding J3 Live in the upper few millimeters of soil or surface layer of water surrounding soil particles. Freezing or desiccation kills them quickly. They migrate vertically up or down, in the soil, depending on the weather or time of day following humidity. Under ideal conditions, they can live for several weeks . They are stimulated into sinusoidal motion by a variety of environmental cues, such as touch, vibration, water currents, heat, or light. Infection occurs when J3s contact a host’s skinWarmth and fatty acids in skin induces penetration behavior : They burrow into skin epidermis, shed second- stage cuticle as they they resume feeding . Necator americanus secretes a variety of enzymes that hydrolyze skin macro-molecules. Difference N. americanus v/s A.duodenale Necator americanus \must penetrate the skin to infect humans Ancylostoma duodenale can penetrate skin and oral mucosa, be passed in mother’s milk, and probably be acquired transplacentally. |
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Strongiloidea Ancyclostomatidae - J3Adult inside host
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Following Skin penetration J3 enter blood or lymph vessel then are carried to the heart and then to the lungs.
in Lungs They cross air spaces of alveoli and are carried by ciliary action up the respiratory mucociliary escalator to the glottis. They are swallowed and finally arrive in the small intestine. in intestine: There they attach to the mucosa, grow, and molt to the fourth stage J4, which has an enlarged buccal capsule. The worms feed heavily on blood for five weeks using a multi- protease cascade to digest host hemoglobin After further growth, worms become sexually mature Difference N. americanus v/s A.duodenale N americanus mature in 5 weeks A. duodenale can undergo developmental arrest for up to 38 weeks, its maturation coinciding with seasonal return of environmental conditions favorable to transmission. |
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Strongiloidea Ancyclostomatidae - Necator americanus - in New World
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Necator americanus
Anterior margin of the buccal capsule has a pair of dorsal and a pair of ventral cutting plates surrounding it. In addition, a pair of subdorsal and a pair of subventral teeth in the rear of the buccal capsule. The duct of the dorsal esophageal gland opens on a conspicuous cone that projects into the buccal cavity Males are 7 -9 mm long and have a bursa diagnos-tic for the genus The needlelike spicules have minute barbs at their tips and are fused distally. Females are 9 -11 mm long and have their vulva located in about the middle of their body. They produce about 5000 to 10,000 eggs per day, and the normal life span is three to five years. Primarily a tropical parasite, N. americanus is the most common species in humans in most of the world. About 95% of hookworms in the southern United States are this species. |
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En face view of the mouth of Necator americanus.
Note the two broad cutting plates in the ventrol-ateral margins |
The anterior margin of the buccal capsule has two ventral plates, each with two large teeth that are fused at their bases A pair of small teeth is found in the depths of the capsule. The duct of the dorsal esophageal gland runs in a ridge in the dorsal wall of the buccal capsule and opens at the vertex of a deep notch on the dorsal margin of the capsule.
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Strongiloidea Ancyclostomatidae - Ancylostoma duodenale - Epidemiology and Morphology
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Ancylostoma duodenale Old World southern,Europe, northern Africa, India, China, and Southeast Asia, in-cluding small areas of the United States, Caribbean Islands, and South America
It was known since the first century, to cause a serious anemia in miners. Mines offer an ideal habitat for egg and juvenile development because of their constancy in temperature and humidity. The problem is apt to occur whenever miners are promiscuous in defecation habits. Adult males are 8 mm to 11 mm long and have a bursa characteristic for the species .The needlelike spicules have simple tips and are never fused distally. Fe-males are 10 mm to 13 mm long, with the vulva located about a third of the body length from the posterior end. A single female can lay from 10,000 to 30,000 eggs per day, and the normal life span is one year. |
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Ancylostoma duodenale, dorsal view. Notice the powerful ventral teeth.
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Life cycle of hookworms.
( a) Shelled embryo passed in feces. ( b) First- stage juvenile ( rhabditiform) hatches. ( c) Two molts ensue and then third- stage juvenile ( infective, filariform) enters developmental arrest until it reaches a new host. ( d) Ancylostoma duodenale may infect humans by oral route. ( e) Filariform juveniles penetrate skin of humans. ( f) Juveniles migrate through circulatory system to lungs. ( g) Juveniles break out of circulatory system into alveoli and then migrate to small intestine via the trachea. ( h) Adult worms develop in small intestine, mate, and produce eggs. |
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Life Cycle (intestinal hookworm infection):
Causal Agents: The human hookworms include the nematode species, Ancylostoma duodenale and Necator americanus. A larger group of hookworms infecting animals can invade and parasitize humans (A. ceylanicum) or can penetrate the human skin (causing cutaneous larva migrans), but do not develop any further (A. braziliense, A. caninum, Uncinaria stenocephala). Occasionally A. caninum larvae may migrate to the human intestine, causing eosinophilic enteritis. Ancylostoma caninum larvae have also been implicated as a cause of diffuse unilateral subacute neuroretinitis. Eggs are passed in the stool , and under favorable conditions (moisture, warmth, shade), larvae hatch in 1 to 2 days. The released rhabditiform larvae grow in the feces and/or the soil , and after 5 to 10 days (and two molts) they become filariform (third-stage) larvae that are infective . These infective larvae can survive 3 to 4 weeks in favorable environmental conditions. On contact with the human host, the larvae penetrate the skin and are carried through the blood vessels to the heart and then to the lungs. They penetrate into the pulmonary alveoli, ascend the bronchial tree to the pharynx, and are swallowed . The larvae reach the small intestine, where they reside and mature into adults. Adult worms live in the lumen of the small intestine, where they attach to the intestinal wall with resultant blood loss by the host . Most adult worms are eliminated in 1 to 2 years, but the longevity may reach several years. Some A. duodenale larvae, following penetration of the host skin, can become dormant (in the intestine or muscle). In addition, infection by A. duodenale may probably also occur by the oral and transmammary route. N. americanus, however, requires a transpulmonary migration phase. |
Eggs are passed in the stool , and under favorable conditions (moisture, warmth, shade), larvae hatch in 1 to 2 days. The released rhabditiform larvae grow in the feces and/or the soil , and after 5 to 10 days (and two molts) they become filariform (third-stage) larvae that are infective . These infective larvae can survive 3 to 4 weeks in favorable environmental conditions. On contact with the human host, the larvae penetrate the skin and are carried through the blood vessels to the heart and then to the lungs. They penetrate into the pulmonary alveoli, ascend the bronchial tree to the pharynx, and are swallowed . The larvae reach the small intestine, where they reside and mature into adults. Adult worms live in the lumen of the small intestine, where they attach to the intestinal wall with resultant blood loss by the host . Most adult worms are eliminated in 1 to 2 years, but the longevity may reach several years. Some A. duodenale larvae, following penetration of the host skin, can become dormant (in the intestine or muscle). In addition, infection by A. duodenale may probably also occur by the oral and transmammary route. N. americanus, however, requires a transpulmonary migration phase.
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Life Cycle (cutaneous larval migrans):
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Strongiloidea Ancyclostomatidae - Hookworm disease
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Hookworm Disease
hookworm infection asymptomatic25 N. ameri-canus in a person will cause no symptoms hookworm disease depends on three factors: strongly on number of worms present, species of hookworm, and nutritional condition of victim 100 to 500 produce considerable dam-age and moderate symptoms, 500 to 1000 result in severe symptoms and grave damage, >1000 worms causes very grave damage that may be accompanied by drastic and often fatal consequences. Because Ancylostoma spp. suck more blood than N. americanus, fewer worms cause greater disease; little protective immunity, hook-worms have evolved strategies to evade the host’s defense sys-tem, and several :For example, Ancylostoma spp. secrete a neutrophil inhibition factor Necator americanus secretes acetyl cholinesterase, which inhibits gut peristalsis and possibly is an anti- inflammatory factor. It also secretes glutathione- S- transferase and superoxide dismutase, sub-stances that interfere with antibody- dependent, cell- mediated cytotoxicity ( ADCC, \). \ Hookworms secrete a protein that binds to human collagen, thus preventing blood clotting, |
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Strongiloidea Ancyclostomatidae - Epidemiology.
poor sanitation and appropriate environmental conditions is necessary for high endemicity. |
Environmental conditions : that favor the development and survival of juveniles pro-mote transmission. The disease is restricted to
warmer parts of the world because juveniles will not develop to maturity at less than 17° C, with 23° C to 30° C being optimal. Frost kills eggs and juveniles. Oxygen is necessary for hatching of eggs and juvenile development because their metabolism is aerobic. Thus, juveniles will not develop in undiluted feces or in waterlogged soil. Both heavy clay and coarse sandy soils are unfavorable for the parasite, the lat-ter because juveniles are also sensitive to desiccation. Alternate drying and moistening are particularly damaging to juveniles; hence, very sandy soils become noninfective after brief periods of frequent rainfall. However, juveniles live in the film of water surrounding soil particles, . Juveniles are quite sensitive to direct sunlight and sur-vive best in shady locations, such as coffee, banana, or sugarcane plantations. Humans working in such plantations often have preferred defecation sites, not out in the open where juveniles would be killed by sun, of course, but in shady, cool, secluded spots beneficial for juvenile development. Repeated return of people to the defecation site exposes them to continual reinfection. Furthermore, use of preferred defecation sites makes it possible for hookworms to be endemic in otherwise quite arid areas. Juveniles develop best near a neutral pH, and acid or alkaline soils inhibit development, Urine mixed with feces is fatal to eggs, disinfectants or fertilizers are lethal to free- living stages. Salt in the water or soil inhibits hatching and is fatal to juveniles. the juvenile larvae. |
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Strongiloidea Ancyclostomatidae - Hookworm disease pathogenosis
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Hookworm disease manifests three main phases of pathogenesis:
the cutaneous or invasion period, the migration or pulmonary phase the intestinal phase. When a juvenile enters an unsuitable host, it gener-ates another pathogenic condition, which will be dis-cussed separately. Cutaneous Phase. The cutaneous phase begins when juveniles penetrate skin. They do little damage to superficial layers, since they seem to slip through tiny cracks between skin scales or penetrate hair follicles. Once in the dermis, however, their attack on blood vessels initiates an innate immune reaction that may isolate and kill the worms. If, as usually happens, pyogenic bacteria are introduced into skin with the invading juvenile, a urticarial reaction will result, causing a condition known as ground itch. Pulmonary Phase. The pulmonary phase occurs when juveniles break out of the lung capillary bed into alveoli and progress up bronchi to the throat. Each site hemorrhages slightly, with serious consequences in massive infections; however, very large numbers of juveniles migrating through the lungs simultaneously are rare. The phase is usually asymptomatic, although there may be some dry coughing and sore throat. A pneumonitis may indicate severe infection. |
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Strongiloidea Ancyclostomatidae - Hookworm disease intestinal phase
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Intestinal Phase.
. On reaching the small intestine, young worms attach to the mucosa with their strong buccal capsule and teeth, and they begin to feed on blood In heavy infections, worms are found from the pyloric stomach to the ascending colon, but usually they are restricted to the anterior third of the small intes-tine. Worms move from place to place, and blood loss is exacerbated by bleeding at sites of former attachment. Worms pass substantially more blood through their digestive tracts than would appear necessary Patients with heavy infections may lose up to 200 ml of blood per day, but around 40% or so of the iron may be reabsorbed before it leaves the intestine. Nevertheless, a moderate hookworm infection will gradually produce an iron- deficiency anemia as body reserves of iron are used up. Severity of anemia depends on worm load and dietary iron intake of a patient. Slight, intermittent abdominal pain, loss of normal appetite, and desire to eat soil ( geophagy) are common symptoms of moderate hook-worm disease. ( Certain areas in the southern United States became locally famous for the quality of their clay soil, and people traveled for miles to eat it. In the early 1920s an enterprising person began a mail- order business, ship-ping clay to hookworm sufferers throughout the country!) Heavy Infections. In very heavy infections, patients suf-fer severe protein deficiency, with dry skin and hair, edema, and potbelly in children and with delayed puberty, mental dullness, heart failure, and death. hookworm disease is usually manifested in the presence of malnutrition and is often complicated by infection with other worms and/ or malaria. The drain of protein and iron is catastrophic to a per-son subsisting on a minimal diet. Such chronic malnutri-ion, particularly in the young, often causes stunted growth and below- average intelligence, but treatment for the worms can significantly increase fitness, appetite, and growth. 42, 66 |
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Hookworm attached to intestinal mucosa. Notice how the ventral tooth in the depth of the buccal capsule lacerates the host tissue.
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Strongiloidea Ancyclostomatidae - Hookworm disease - Diagnosis and Treatment
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Diagnosis. Demonstration of hookworm eggs or worms themselves in feces is, as usual, the only definitive diagno-sis of the disease
PCR methods have been described for these identifications. Differentiation can be accomplished by recovery of adults after anthelmintic treat-ment or by culturing juveniles from feces. Differentiation with a simple PCR- RFLP method has promise. Treatment. It is not necessary or possible to distinguish N. americanus eggs from those of Ancylostoma ssp., Mebendazole is the drug of choice for treatment, as it removes both species of hookworm and also any concurrent infection with Ascaris lumbricoides. Single- dose therapy is inexpensive, convenient, and effective. Treatment for hookworm disease should always include dietary supplementation. |
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Strongiloidea Ancyclostomatidae - Hookworm disease - Creeping Eruption
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Creeping Eruption
Also known as cutaneous larva migrans, is caused by invasive juvenile hookworms of species or strains normally maturing in animals other than humans. Juveniles manage to penetrate the skin of humans but are incapable of successfully completing migration to the intestine. However, before they are overcome by immune effectors, they produce distressing and occasionally serious complica-tions of the skin Possibly any species of hookworm can cause this condition,. Ancylostoma braziliense appears to be the most common agent in its geographic range. It is a common parasite of dogs and cats of the Gulf Coast and New World tropics. Vacationers to tropical resorts may encounter difficulty obtaining a correct diagnosis and medication upon returning home where cooler weather prevails. After entering the top layers of epithelium, juveniles are usually incapable of penetrating the basal layer ( stratum ger-minativum), so they begin an aimless wandering. As they tunnel through skin, they leave a red, itchy wound that usu-ally becomes infected by pyogenic bacteria. Worms may live for weeks or months. It is known that some can enter muscle fibers and become dormant. Occur on feet and hands .Thiabendazole has revolutionized treatment of creeping eruption, and topical application of a thiabendazole ointment has supplanted all other forms of treatment. |
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Creeping eruption caused by infection with Ancylostoma sp. juvenile.
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