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Diagnosis: stool examination for larvae (strongyloides) or eggs (the rest)

Treatment: albendizole or ivermectin (strongyloides) or mebendazole (the rest)

Worm	transmission	clinical picture & diagnosis
*Trichinella spiralis* or nativa	raw pork, bear, walrus	myositis, diarrhea Dx. eosinophilia, raised CPK, serology
Toxocara canis (visceral larva migrans)	oral	eosinophilia, hepatomegaly, fever Dx: serology
Wuchereria bancrofti or Brugia malayi (lymphatic filariasis)	mosquito vector	elephantiasis, chyluria or hydrocoele Dx: microfilaria in blood, serology, antigen capture
*Onchocera volvulus* (river blindness)	black fly vector	iitchiness, skin nodules, blindness Dx: adults in skin nodules, microfilaria in skin biopsies (snips)
Loa loa (eye worm)	horse fly vector	Calabar swellings (3-4 days), eye worm Dx: microfilaria in blood

Diagnosis: blood or tissue examination for microfilaria; serology for Trichinella and Toxocara

The helminths (from the Greek meaning worm) are higher, multicellular forms of parasite with specialized organs. There are two basic groups:
Nematodes - roundworms

Nematodes
  Characteristics
                     - round in cross section
                     - bilaterally symmetrical
                     - variable size - 1 mm to 1 meter
                     - organs - digestive, nervous, excretory, cuticle, muscle, sexual
                  - develops by molting (shedding cuticle
                     - separate sexes
                     - reproduction and development: egg
                                                                       egg fertilization
                                                                       embryo in egg
                                                                        larva
                                                                        4 molts
                                                                        adult

Categories

Bowel nematodes - with adults in bowel
                                   Trichuris trichiura
                                   Ancylostoma duodenale and Necator americanus
                                   Enterobius vermicularis
                                   Strongyloides stercoralis
                                   Enterobius vermicularis

       Tissue nematodes - adults or larval stage in tissue
                      Trichinella spiralis, native etc
                      Toxocara canis (visceral larva migrans)
                      Filaria - Wuchereria bancrofti
                                   Brugia malayi
                                   Onchocerca volvulus
                            Loa loa
                                   etc.

Epidemiology
- about 350 million infected, in some areas 90-100% of population
- restricted to warm climate by necessity for egg to embryonate on moist warm soil for10-14 days before becoming infective
- spread: fecal - oral (esp. via foods and hands)

Biology
- life cycle: people infected by swallowing embryonated egg egg hatches in small intestine attaches to colonic epithelium and matures to egg laying in 3 months.

Clinical
- clinical: 99% assymptomatic
- heavy load gives diarrhea, dysentery, anemia, rectal prolapse

Treatment
- mebendizole, albendizole

Problems
- lack of cost effective control methods in LDC (least developed countries)

Epidemiology
-very common in all geographic areas - 20%+ in Toronto's children
- spread: fecal - oral; eggs can survive days to weeks in environment

Biology
- infected by swallowing egg which hatches after contact with stomach acid and matures to adult which then resides in lumen of caecum (from egg to adult maturation in 15-43 days) . Female migrates onto perianal skin to lay eggs at night.
- organism: adult female approx. 10 mm long; egg approx. 55 �m long

Diagnosis
-less then 10% found in stools, i.e. not a useful examination;
-best is pinworm swab - cellophane tape swab, or sticky paddle

Problems
- insensitivity of pinworm swabs (intermittent deposition of eggs) : eradication of infection from rest of family.

Epidemiology
-About 650 million infected worldwide mainly tropics. Transmission is faecal-oral; egg very resistant, can survive years

Biology
-egg ingested, hatches in duodenum; larvae penetrate intestine wall, enter blood vessels and embolize through liver to lungs. They then migrate into airspaces, up trachea and are swallowed, taking up permanent adult residence in the small intestine; ~ 2 months from egg to mature adult

Adult worms1 live in the lumen of the small intestine. A female may produce up to 240,000 eggs
per day, which are passed with the feces 2. Fertile eggs embryonate and become infective after
18 days to several weeks 3, depending on the environmental conditions (optimum: moist, warm,
shaded soil). After infective eggs are swallowed 4, the larvae hatch 5, invade the intestinal
mucosa, and are carried via the portal, then systemic circulation to the lungs 6 . The larvae
mature further in the lungs (10 to 14 days), penetrate the alveolar walls, ascend the bronchial tree
to the throat, and are swallowed 7. Upon reaching the small intestine, they develop into adult
worms 1. Between 2 and 3 months are required from ingestion of the infective eggs to oviposition
by the adult female. Adult worms can live 1 to 2 years. (CDC 1999)

Clinical
- related to number of worms; small numbers asymptomatic
- large numbers of adults in intestine -- obstruction, pains
- at times adults migrate into bile duct, up esophagus or through surgical anastomoses of intestine
- cause malnutrition if in large numbers

Diagnosis: stool examination for eggs

Epidemiology
The only important helminth that can complete its life cycle in the human host and hence increase its numbers. Special problem in immunocompromized because of this. Mainly a tropical parasite because requires warm moist soil for transmission.

Biology
Larvae passed into soil in human feces where mature in several days to skin invasive (filariform) larvae. Can exist for months in soil "free living" by completing life cycle without contact with human host man. Larvae penetrate skin, move via blood vessels to lung, invade airspace, move up bronchi, are swallowed, and then penetrate small intestinal mucosa where they mature to adults in submucosa. They deposit eggs in submucosa and these hatch and migrate into intestinal lumen. Small numbers of larvae get into blood vessels and circulate again to produce more adults (internal autoinfective cycle) or invade perianal skin and enter blood vessels to eventually produce new adults (external autoinfective cycle).

Organism: female adult - 2.7 mm long, rhabditiform larvae approx. 0.38 mm, filariform larvae approx. 0.6 mm long

Clinical

most asymptomatic

GI - peptic ulcer like symptoms, diarrhea rarely, cutaneous larvae currens (trunkal itchy dermatitis)

hyperinfection (disseminated strongyloides) in immunocompromised; spread of larvae to peritoneum, lung, CNS with contamination of those organs with gram negative bacteria; transmural small intestine spread of larvae and bacteria with necrosis of intestine

Diagnosis

stool examination . NB: difficult to find strongyloides

duodenal aspirate or Enterotest duodenal string test

serology (the most sensitive)

culture of stool (Harada-Mori or Baerman) allows "free living" strongyloides to multiply

Problems: diagnostic techniques not sensitive
untreated it persists for life

Epidemiology: transmission by contact of skin with soil contaminated with larvae.

Biology: eggs in feces hatch and mature as larvae in warm moist soil; develops into to infective (filariform) larvae in 7 days. Filariform larvae penetrate skin of host (e.g. bare feet), circulate to lungs where they penetrate alveoli, move up bronchi and are swallowed. Then, as adults, they attach by mouth to small intestinal mucosa and suck blood. (Necator 0.03 ml/day, Ancylostoma 0.15 ml/day). Prepatent period (time from skin penetration to egg production) is 4-5 weeks. Adults can live 5-15 years.

Organism
Adult female 12 mm long (A.d); ova approx. 60 mu long
Adult female 10 mm long (N.a); ova approx. 65 mu long

Clinical
     usually assymptomatic 90%
   heavy infections (20 - 100 worms)
    iron deficiency anemia
    malnutrition from protein loss
    rarely itch at skin entry site

Diagnosis: Stool examination for ova

Treatment: mebendizole, albendazole

Cutaneous Larva Migrans

Ancylostoma caninum, Ancylostoma braziliensis etc.

Non-human (dog, cat etc) hookworms that penetrate human skin (as does human hookworm) but cannot go further. Migrate and produce serpiginous itchy traits in subcutaneous tissue.

Laboratory procedures for diagnosing intestinal helminths
Stool ova and parasite (O & P) examination

1. Direct microscopic (without a concentration technique) examination: not very sensitive

2. Kato technique: uses glycerin mixed with stool which "clears" (makes transparent) fecal debris making eggs visable. Can be used for counting eggs/gram feces.

3. Concentration techniques:
i. zinc sulfate solution flotation - eggs float to top of solution
ii. formal ethyl acetate sedimentation

4. Culture: Harada Mori or Baerman culture or charcoal culture - only Strongyloides will multiply in an incubated stool specimen - increases numbers of larvae and sensitivity of microscopy.

nema-cesta_fig4cdc.gif (55924 bytes)

Increased blood eosinophil counts are normal host response to helminth infection; not seen in protozoan infections

Trichinella spiralis, nativa (Trichinosis, Trichinellosis)

Epidemiology
Common in geographic areas where undercooked pork is eaten, in the Arctic where raw walrus is eaten and among bear hunters in North America; 5-15% of North American population infected at some time.This is a zoonosis infecting most carnivorous mammals; especially pigs, bear, walrus, and rats. Man infected by eating Trichinella infected uncooked meat.

Biology
Encysted larvae in meat, when eaten, excyst (hatch) and penetrate into small intestine submucosa where they mature to adults in 1-2 weeks producing larvae which penetrate blood vessels and diseminate to all muscles. There, they cause inflammation and encyst in muscle cells (not cardiac), remaining viable and quiet for many years. Adult female is 5 mm.long

Midterm (2-6 weeks) - myalgia, muscle weakness, facial and periferal edema, rash; sometimes encephalitis and myocarditis

Long term (months) - usually assymptomatic despite presence of trichinella "cysts"

Diagnosis

clinical picture with laboratory support (eosinophilia and raised creatine phosphokinase (CK)

microscopic examination of muscle biopsy

serology

Epidemiology: This is a zoonotic roundworm with the dog as reservoir. Uncommon human infection but consequences serious. Transmission is dog fecal (dog)-oral (human) .

Dog feces especially in sandboxes and parks where children play. Eggs in soil viable and infective for several months.

Biology: Adult has cycle in dog the same as Ascaris in man. Man an accidental "dead end" host. Eggs ingested by man/child, hatch after stomach passage and larvae migrate through small intestinal wall into vasculature and then to liver and lungs and beyond. Do not mature to adults but cause local inflammation especially in liver.

Organism: In man larvae are 0. 5 mm long; egg in dog feces, looks like a round Ascaris egg.

toxocara_canis_eggs.jpg (15769 bytes)

  Toxocara eggs

Clinical
   Hepatomegaly, pneumonitis, encephalitis, fever and eosinophilia in heavy infections
   Retinal lesion (similar to retinoblastoma) or focal retinitis when single larva reaches retina.

Diagnosis
   Clinical syndrome with very high eosinophilia
   Serology
   Nothing in stools

Treatment: Steroids and albendizole

Problems: - Control of dog and cat feces in parks and sandboxes
- Diagnosis difficult because of nonspecificity of symptoms

1. Anisakis sp: Salt water fish (cod, herring etc) roundworm that when ingested produces a nematode inflammatory mass in stomach of raw fish consumer or eosinophilic gastritis (mainly Japan, Holland).

2. Angiostrongylus cantonensis: nematode of amphibians producing eosinophilic meningitis (mainly SE Asia).

3. Gnathostoma spinigerum: nematode of cat producing migratory local subcutaneous swelling, and at times encephalomyelitis (mainly SE Asia).

4. Capillaria philippinensis: small intestine nematode producing diarrhea and malabsorption (Philippines).

5. Bayliascaris procyonis: Raccoon nematode in North America producing a visceral larva migrans like Toxocaris (above) but with severe encephalitis

Filariases
Overview
This is a group of thread-like roundworms that are acquired via an insect (intermediate host) vector. The adults live in various tissues (lymphatics, subcutaneous etc.) and are usually difficult to remove for diagnosis. The microscopic larvae (called microfilaria) produced by the adult female are very motile, circulating in blood or subcutaneously and because they are produced in such large numbers, are much easy to find. Disease can be produced by either the adults or the microfilaria or both, depending on the species.

Wuchereria bancrofti and Brugia malayi (lymphatic filariasis)

Epidemiology: Cause lymphatic filariasis occasionally terminating in elephantiasis. 250 million humans affected; widely distributed throughout tropical and subtropical countries. Transmitted to humans by mosquitoes.

Microfilariae born to female adult worms circulate in the blood. W. bancrofti microfilariae circulate preferentially from 10:00 p.m. to 2 a.m. - this corresponds to peak activity of vector mosquitoes.

Microfilaria, ingested by mosquito when biting the human, develops to a 3rd stage juvenile larva in mosquito, and it is transmitted to new host at the time of feeding. Larva then matures to adult in the lymphatics; maturation to adult requires several months.

Clinical

Asymptomatic microfilaremia
   Lymphangitis and lymphadenitis
   Orchitis and epididymitis
   Elephantiasis
   Tropical pulmonary eosinophilia
   Chyluria

Diagnosis

Blood examinations (esp. Night blood) for microfilaria
Serology
Antigen capture

Treatment

Anti-inflammatory agents
Diethylcarbamazine (DEC), Ivermectin, albendizole
Prevention

Control of mosquitoes
Insect repellants

Epidemiology: 20 million affected. Predominantly Africa and South and Central America, most commonly along rivers, the breeding site of the black fly vector.

Biology

Infective larvae transmitted to man by black flies of the genus Simulium.
Larvae develop to adults in subcutaneous tissue
Adult female produces microfilaria which wander in subcutaneous tissue, cornea, and anterior chamber of eye. Black flies acquire microfilaria on biting infected humans .
Adult 33-50 cm x .3 mm Microfilaria 330 m x 6 m

Clinical : Skin nodules, onchocercal dermatitis, hanging groin, blindness

Biology

Adult worm lives in subcutaneous tissue and wanders freely
Microfilaria in subcutaneous tissues and blood
Transmitted by the bite of deer flies of the genus Chrysops
Adult: 55 mm x 0.5 mm Microfilaria: 280 m x 7m

Diagnosis

Excision of adult worm
Blood examination for microfilariae

Large Intestine	transmission	complications
Trichuris (threadworm)	oral	hemorrhagic colitis
Enterobius (pinworm)	oral	perianal itch

Small intestine
Ascaris (round worm)	oral	small intestine obstruction
Strongyloides	percutaneous and autoinfection	duodenitis, cutaneous larva currens, hyperinfection in immunocompromised
Ancylostoma & Necator (hookworm)	percutaneous	iron deficiency anemia

h mouth of Ancylostoma duodenale	filariform larva
h mouth of Ancylostoma duodenale	egg 60 x 40 m�

very high (30-80% of WBC)	moderate (10-30% of WBC)	low or absent (0-10% of WBC)
Trichinella	hookworm	Enterobius
Toxocara	Strongyloides	Ascaris
Fasciola		Trichuris


intestinal-- Strongyloides larva	systemic-- microfilaria (Wuchereria)


larva extracted from muscle	adult from intestine wall


onchocerca nodule (adult curled up within)	keratic precipitates and microfilaria on inside surface of cornea

Clinical Calabar swelling (intermittant 2-3 day focal migratory angioaedema) migrating worm in conjunctiva
	Calabar swelling


adult	filariform (invasive) larva


	elephantiasis


microfilaria 260 �m long