Presentation on theme: "Ancylostoma spp. and Necator spp ."— Presentation transcript:
1Ancylostoma spp. and Necator spp . Hookworms鈎蟲Ancylostoma spp. and Necator spp .Human hookwormNecator americanus and Ancylostoma duodenale.美洲鈎蟲 十二指腸鈎蟲Cat hookwormAncylostoma ceylanicum, also reported from man錫蘭鈎蟲
2Geographical Distribution N. americansMainly in moist tropical regions :S.E. Asia, sub-Sahara Africa and tropical America.A. duodenaleMainly in dryer and colder areas :North India, Pakistan, North China, Middle East and North Africa.Ancylostoma duodenale and Necator americanus,which infect an estimated 800,000,000 persons,the dog and cat hookworms, A. caninum andA. braziliense, respectively.
3MorphologyThe adults: cylindrical with the head bent sharply backwardsgiving them a hooked appearanceabout 10 mm in lengthThe males: bursa at posterior end; smaller than the femalesThe hookworm species aremainly differentiated bytheir buccal capsule andthe arrangement of rays 肋in the bursa美洲鉤蟲
5The eggs: ovoid with a thin transparent shell; easy exit for larva measure 74 to 76 x 36 to 40μmvarious species are indistinguishableFemale can produce 10,000-25,000 eggs per dayDepending on the speciesWhen passed in the host intestine they are single celledThey are discharged in the faeces: often at the 4- or 8-cell stagethis is the diagnostic stage of the parasiteWithin several hours of being passed, a multicell stage developsand then a rhabditiform larva (first stage) forms桿狀線蟲.
7The rhabditiform larva: Differentiated from species Various morphological differenceIt is possible to differentiate the third stage larva of N. americanus from A. duodenale by certain morphological features
8Life CycleFirst stage larva: hatches out from the egg in 24 to 48 hoursActively feeds on organic debris and bacteria in the soil2nd stage larva: on the third day3rd stage larva: on the fifth dayfilariform絲狀蟲; nclosed in a sheathdoes not feed; actively motile.The third stage larva initiates the infection by penetrating the skin and passing into blood circulation.Through the blood it is carried to the right heart and then to pulmonary blood vessels.It soon breaks out of the pulmonary blood vessels into the alveoli.
11It then crawls up the trachea and is swallowed with saliva to re-enter the intestinal tract. Finally, it attaches itself to the mucous membrane of the small intestine to mature into adults. During copulation the male firmly encircles the female vulva with its bursa and the gravid female starts egg laying 5-7 weeks after infection. The adult worm survives for 1-14 years. In the case of Ancylostoma duodenale, infection can also be established by swallowing filariform larvae on leafy vegetables and other food contaminated with soil. Another important recent finding is that A. duodenale larvae can persist in somatic tissues of man. This kind of arrested development apparently helps the survival of the worm in case of a seasonably unfavourable external environment.
12Clinical Aspects Ground itch: The stage of skin penetration Intense itching and dermatitis at the site of entry;between the toesPneumonitis and bronchitisThe larval migration through the lungsThis is less severe than the Loeffler's syndrome seen duringthe migration of Ascaris larvae.The final stage of development and attachment to the intestineis often asymptomatic.Heavy infections: induce microcytic hypochromic anaemiaThe blood loss is from sucking by the worm and also fromcontinuing haemorrhage at the site of attachment.
13Clinical AspectsOne Necator worm results in the loss of 0.03 to 0.05 ml ofblood/dayAn Ancylostoma worm results in the loss of 0.15 ml ofIt is important that there is a difference betweenhookworm disease and hookworm infection.Hookworm infection does not necessarily mean that thedisease is present, as blood loss produced by lightinfections can be compensated by adequate foodintake. Disease occurs when the intake of food isunable to compensate for the blood lossInfected children are often oedematous indicating thatthese is a protein-losing enteropathy as well.
14Diagnosis Stool examination This is based on finding the eggs in the faeces.An estimation of worm load is often necessary for anycorrelation of the anaemia with the hookworminfection.
15Treatment Anthelmintic treatment: Bephenium hydroxynaphthoate: for Ancylostoma duodenaleThe dose for adults is 5 g (2.5 g base) as a single dose andChildren: under 2 years 2.5 g (1.25 g base) / a single dose.The drug is available in granule form and is given beforebreakfast with a drink.Bephenium is poor in cases of N. americanus infectionSide effect : Bephenium salts often produce nausea, vomitingand gastrointestinal disturbances.
16Treatment Pyrantel pamoate: N. americanus: is more efficacious A single dose of pyrantel pamoate (10 mg/kg body weight) is generally sufficient in cases of A. duodenale infection, and light infections of N. americanus.In heavy infections of N. americanus, treatment may have to be repeated after 3 days.Mebendazole : also a good antihookworm drugIt is given as 100 mg twice daily for 3 days, irrespective of age. However, it should not be given to pregnant women.Iron and folic acid: Anaemia patient should be given
17Prevention and Control 3 interaction factors determine the hookworm epidemiology(a) Faecal - soil contact.(b) Infected soil - human contact.(c) Suitability of soil and climate for the development of eggsand larvae.Faecal-soil contact-Deposition of faeces containing eggs contaminates the soilThe key to proper control is provision of latrines andsanitary disposal of faeces.If fresh human faeces is used as a fertilizer, it should betreated by composting堆肥 or chemicals to kill the larvae
18Infected soil - human contact- Wearing of protective footwearCooking or washing of vegetables which may be contaminatedwith larvae.Suitability of soil and climate for the development of eggs and larvae –A. duodenale eggs are able to withstand desiccation better thanN. americanus, and in suitable soil the larvae can survive forseveral months.No simple method available for destroying the larvae in soil.Health education and mass chemotherapyAn important part of controlHave been tried with considerable success in some parts of theworld.
19 Hookworms average about and live in the small intestine of the host.
20About two days after passage the hookworm egg hatches, and the juvenile worm (or larva) develops into an infective stage in about five days. The next host is infected when an infective larva penetrates the host's skin. The juvenile worm migrates through the host's body and finally ends up in the host's small intestine where it grows to sexual maturity. The presence of hookworms can be demonstrated by finding the characteristic eggs in the feces; the eggs can not, however, be differentiated to species
21The mouthparts of hookworms are modified into cutting plates 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.
22Juveniles (larvae) of the dog and cat hookworms 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). This 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.
23A histological section of a hookworm in the host's small intestine. The following image provides an excellent example of how hookworms are attached to and embedded in the epithelium of the host's gastrointestinal tractA histological section of a hookworm in the host's small intestine.
24Ancylostoma braziliense, a common hookworm of cats Ancylostoma braziliense, a common hookworm of cats. The oral opening contains one large (and one smaller) cutting "tooth" one each side. One of the large "teeth" is marked (*). Juveniles (larvae) of this species are an important source of cutaneous larval migrans.
25The anterior end of Ancylostoma caninum, a common parasite of dogs The anterior end of Ancylostoma caninum, a common parasite of dogs. This species is characterized by the presence of three cutting "teeth" on each side of the oral opening (not all of them can be seen in this image).
26Another image of the anterior end of Ancylostoma caninum Another image of the anterior end of Ancylostoma caninum. The cutting "teeth" (6 total, 3 on each side) can be seen clearly.
27The anterior end of Necator americanus, one of two species of hookworms infecting humans. The oral opening of this species contains cutting "plates" as opposed to "teeth." The muscular esophagus is labeled in this image (*).
28The anterior end of Uncinaria stenocephala, a caninum hookworm The anterior end of Uncinaria stenocephala, a caninum hookworm. This species, like Necator americanus, has cutting "plates."
29Scanning electron micrograph of the oral opening of Ancylostoma duodenale, another species of human hookworm. Note the presence of four cutting "teeth," two on each side.
30In this image, the bursa of the male canine hookworm (A In this image, the bursa of the male canine hookworm (A. caninum) can be seen wrapped around the female hookworm during the act of copulation.