Necator Americanus

Infectious Agent/Disease

Scientific name : Necator

americanus

Common name: New World

hookworm of humans, the American killer

Kingdom:Animalia

Phylum:Aschelminthes

Class:Nematoda

Order:Strongiloidae

Family:Ancylostomatidae

subfamily Necatorinae;

Genus:Necator

The hookworm is a parasitic nematode worm that lives in the small intestine of its host, which may be a mammal such as a dog, cat, or human.

Two species of hookworms commonly infect humans, Ancylostoma duodenale and Necator americanus.

Hookworms are thought to infect 800 million people worldwide

Hookworm is a leading cause of maternal and child morbidity in the developing countries of the tropics and subtropics. In susceptible children hookworms cause intellectual, cognitive and growth retardation, intrauterine growth retardation, prematurity, and low birth weight among newborns born to infected mothers.

Characteristics:

has a pair of dorsal and a pair of ventral cutting plates surrounding the anterior margin of the buccal capsule

In addition, a pair of subdorsal and a pair of subventral teeth are near the rear of the buccal capsule.

Males are 7 to 9 mm long and have a bursa diagnostic for the genus. The needlelike spicules have minute barbs at their tips and are fused distally.

Adult males are 8 to 11 mm long and have a bursa characteristic for the species. The needlelike spicules have simple tips and are never fused distally.

Females are 9 to 11 mm long and have the vulva located in about the middle of the body.

AdultsFemales are 10 to 13 mm long, with the vulva located about a third of the body length from the posterior end.

eggs are 64-76 X 35-40 µm head curves opposite to curvature of body, giving a hooked appearance to the anterior end

intestinal nematode parasite

Hookworm egg

Hookworm eggs in the stool examination from the patient

Hookworm, various eggs in the stool examination from the patient.

Hookworm ova and larva in the stool examination from case.

Hookworm egg from feces of cat.

Female and Male

Female and Male

Mode of TransmissionInfective larvae, develop from eggs excreted in feces and penetrate the skin, usually by the dorsum of the bare feet or between the toes; vertical transmission from mother to child is possible.

Epidemiology Widely in tropical and

subtropical countries, where improper disposal of human feces is practiced; occurs in South East Asia, South Pacific and East Africa and South America - moisture and temperature conditions favour development of larvae; sporadic cases occurs in southeastern US; prevalence higher in rural areas; universal susceptibility

INCUBATION PERIOD:-Variable; GI symptoms can appear 35-40 days after exposure to filariform larvae

COMMUNICABILITY: -Not directly transmitted from person-to-person

PathogenicityInfective larvae penetrate

skin and travel via the lymphatics to enter the bloodstream, the lungs and the small intestine; adult parasites attached to the villi of small intestines suck blood causing abdominal discomfort, diarrhea, cramps, anorexia, weight loss; clinical features correspond mainly to the intensity of infection;

heavy infection leads to development of iron deficiency and hypochromic microcytic anemia;leading causes of iron-deficiency anemia in children resulting in physical and mental retardation in development; infection causes cutaneous larva migrans - a self-limiting condition characterized by skin eruption; fatality is rare; no evidence of immunity in the infected.

Life Cycle

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 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 veins 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 longevity records can reach several years.

ViabilityDRUG SUSCEPTIBILITY: Sensitive to, mebendazola, pyrantel

pamoate, levamisole and albendazole-is effective both in the intestinal stage and during the stage the parasite is still migrating under the skin.

DRUG RESISTANCE: Mebendazola resistant strains have been

reported.

SUSCEPTIBILITY TO DISINFECTANTS:

-Susceptible to 1% sodium hypochlorite, 2% glutaraldehyde.

PHYSICAL INACTIVATION:-Larvae sensitive to desiccation and

freezing.SURVIVAL OUTSIDE HOST:

-Larvae can survive up to 3-4 weeks in moist, optimal survival in moist, sandy or loamy soil with ambient temperatures of 24-32° C.

Similarities between the Ancylostoma duodonale and Necator americanus.

Infective stage:

Filariform larvaDefinitive host man:

Man

HabitatSmall Intestine

Mode of AttachmentOral attachment to

mucosa by suckingMode of Nutrition

Sucking and Ingesting of blood

Laboratory diagnosisConcentration methods

and Direct Fecal SmearTreatment

Albendazole, Mebendazole, or Pyrantel Pamoate

Diagnostic Feature - EggIn Morula

Difrerences between Necator Americanus and Ancylostoma duodonale.

Common NameN.C.-New world hookworm, American murderer

A.C.-Old world hookworm

Etiologic Agent ofN.C-.Necatoriasis,

UncinariasisA.C.-Ancylostomiasis, Wakana disease

Portal of EntryN.C.-Usually via skin penetration rather than ingestion

A.C.Usually via ingestion rather than skin penetration

Thank you for Listening!!!!!!

By: Frances Arcel T. Quiblat

4th-year Biology