HookwormsAssociated prof. Tian

1. Hookworms are the voracious blood feeders of the nematode world

Hookworms parasitize more than 900 million people worldwide.

2. Ancylostomiasis is second only to ascariasis in infections by parasitic worms.

Background

3. There are two species of hookworms of medical importance

Ancylostoma duodenale: - Africa, India, China and South East Asia (Asia hookworms)

Necator americanus: - First reported in Brazil, then Texas, but since found in Africa, India and South East Asia.

(American hookworms)

The adult parasites are small cylindrical worms, 0.5 - 1.5cm long (Ancylostoma duodenale being slightly larger than Necator americanus ).

Adult:

A. duodenale N. americanus

Morphology

buccal capsule(mouth capsule)

The anterior end of the parasites are formed into a buccal capsule

Curved teethAncylostoma duodenale

Necator

americanus

cutting plates(semilunar)

The posterior end of the male worm is equip with a characteristic copulatory bursa

Copulatory bursa of male of A.duodenale

(umbrella-shaped bursa)

Copulatory bursa of male of N.americanus

Comparison of Hookworms

N. americanes A. duodenale

Size (lenth) about 10 mm slight larger

Shape “ S ” “ C ”

buccal capsule a pair of two pair of

cutting plates curved teeth

Eggs:

Morula(4-8cell)

shell

Size 57-76 µm by 35-47 µm 

Oval or ellipsoidal shape Thin shell, colorless. The eggs usually contain 4-8 cells in feces

 

A: Hookworm egg, advanced cleavage (iodine).B: Embryonated hookworm egg.

adultadult eggegg Rhabditiform larvae

Filariform larvaeFilariform larvae adultadult

Life cyclesLife cycleswarm moist shaded soilwarm moist shaded soil

5-8days

hatching 24-48h,

Contact host and penetrate the skin into the body

Contact host and penetrate the skin into the body

Intestinallumen

Are passed in the stool

Migrant by lungs

The route of larvae migrant

Skin lungs trachea

Oesophagus stomach intestine

Life Cycle

Soil polluted with human excreta is commonly responsible for exposure to infection with human hookworms

Individuals become infected, usually by walking bare footed across contaminated soil

Penetration of the intact skin by filariform larvae of hookworm, on coming in contact with fecal polluted soil.

A, B: Hookworm filariform larva (wet preparation).

 

A, B: Hookworm rhabditiform larva (wet preparation).

A, B, C: Hookworm filariform larva (A and B, wet preparations; C, iodine). Larva tail is depicted in Figures B and C.

Pathogenesis and clinical manifestation

(1)Cutaneous or invasive phase:

by hookworm larvae

Dermatitis(ground itch):

irritation and itching

The larva of a hookworm is visible in the center of this photograph

(2) Pulmonary phase: by hookworm larvae

Local haemorrhaging, pneumonitis

Symptoms in respiratory system

cause a cough and a sore throat.

(3) Intestinal phase: By adult worm

A)the intestinal mucosa are damaged

B)Anemia:

Protein and iron in-take is insufficient

Blood loss

Hypochromic microcytic anemia

Blood loss

a)Ingestion of the blood by the worm

b)Seepage of the blood around the site of attachment of the worm

c)Oozing of the blood from the burrowed site previously attached by the worm

d)Anticoagulants

This is a photograph of the hookworm's appearance against the lining of the intestine (intestinal mucosa).

Clinical features of hookworm disease

Site Symptoms Pathogenesis

DermalLocal erythema, macules, papules (ground itch)

Cutaneous invasion and subcutaneous migration of larva

PulmonaryBronchitis, pneumonitis and, sometimes, eosinophilia

Migration of larvae through lung, bronchi, and trachea

Gastro- intestinal

Anorexia, epigastric pain and gastro-intestinal hemorrhage

Attachment of adult worms and injury to upper intestinal mucosa

Hematologic

Iron deficiency, anemia, hypoproteinemia, edema, cardiac failure Intestinal blood loss

Diagnosis

Laboratory diagnosis

It includes parasitic diagnosis and immunodiagnosis

l) Microscopy Direct smear examination of feces is adequate to detect moderate or severe infections.

2) Concentration Concentration of stool by formalin-ether or simple salt floatation stool is essential to detect light hookworm infection.

3) Third-stage larvae in the fecal culture

Distribution Hookworm diseases is widely epidemic parasitic disease in the world. Hookworm distribute these areas between northern latitude 45○ to southern latitude 30○. A.duodenale is chiefly found in tropic areas and subtropic areas, N.americanus is commonly found in warm zone.

Epidemiology

Distribution of Hookworm in china

                                                                                                          

                                                                     

Hookworm: World Distribution

Reservoir, source and transimission of infection

Human is the only reservoir of infection

Human feces is the only source of infection

l ) Sanitary disposal of human feces;

2) Treatment of infected persons;

3) Health education with improved use of sanitary latrines and use of foot wears

Prevention and control

Treatment of hookworm infection consists of

a) treatment of worm infection by anthelmintics such as mebendazole;

b)treatment of anemia.

TRICHINELLA SPIRALIS

Trichinosis is related to the quality of pork and consumption of poorly cooked meat. Autopsy surveys indicate about 2 percent of the population is infected.

Morphology

femalefemalemale

Adult worm The adult worms are very small and slender with slightly tapered anterior ends, white and just to the naked eye. female 2.2 mm in length, males 1.2 mm;

male

papilla

pharynx

Its pharynx is one third or half of worm body long, and posterior part of pharynx consists of a column of cells called of stichocytes.

female

juveniles

Cyst (larvae)Cyst (larvae)

The cyst are found in skeletal muscle commonly, its size is about 0.25~0.5

Larvae in Muscle Section Larvae in Muscle Press

 

Larvae of Trichinella, freed from their cysts, typically coiled; length: 0.8 to 1.0 mm.

Trichinella spiralis: Electron microscopy

adult larvae

larvaeadult

cycstIntestine of the humans 、 pigs 、rats 、 cats 、 dogs

Life cyclesLife cycles

dischargeing

( 1 month) Swallowed by

another host

Into skeletal via bloodstream

 

lavae

adult

cyst

cyst

Trichinellosis is acquired by ingesting meat containing cysts (encysted larvae) of Trichinella.

  After exposure to gastric acid and pepsin, the larvae are released

from the cysts and invade the small bowel mucosa where they develop into adult worms

(life span in the small bowel: 4 weeks).

After 1 week, the females release larvae

that migrate to the striated muscles where they encyst

< Adults attach to the intestinal mucosa and being to release larvae in one week.  The adults live for about 4 weeks and may release more than 1000 larvae.

< Larvae penetrate the intestinal wall and move to muscle tissue where they encyst in individual cells (nurse cells).  Active muscles, such as the diaphragm and tongue, often have the greatest numbers of larvae.

Life Cycle< Infection occurs by ingesting encysted larvae in undercooked meat.

Pathogenesis and clinical manifestation

The process of pathological change can be divided three phases.

1)Invade phase : intestinal inflammation

intestinal inflammation For invading of larvae and adult worms, the wall of intestine is damaged Gastrointestinal signs

2) Migratory phase : toxic and allergic

severe systemic disease

allergic phenomena such as edema, pneumonitis, and pleural transudate

3) Encystation of the larvae and tissue

repair formation of cyst

clinical manifestation (Symptoms)

Infection with Trichinella spiralis may be asymptomatic, especially in light infections.  Adults in the intestine may cause diarrhea, abdominal pain, and vomiting.  Larvae moving into the tissues may cause facial swelling, fever, muscle pain, splinter hemorrages (under fingernails) or rashes.

Heavy infections may lead to heart problems or central nervous system involvement.  Large numbers of larvae in other muscles may lead to soreness and weakness which often lessens over time.

Diagnosis a) clinical manifestations with a history

of ingesting meat that may contain larvae;

b) immunodiagnosis; c) muscle biopsy. The definitive diagnosis is made by d

emonstration of free or encapsulated Trichinella larvae in the skeletal muscles obtained either in biopsy or at autopsy.

Epidemiology

Trichinella spiralis (T-1) (green) is the most common member of the genus. The world distribution as depic

ted is almost certainly an under-representation

Prevention and control

avoidance of eating raw or undercooked pork and meat of other wild animals; and avoidance of feeding raw garbage to pigs will prevent transmission of infection to man.