Lecture #2: THE INTESTINAL NEMATODES

Classification of Roundworms:

A.  The Nematodes

B.  The Cestodes

*********** THE NEMATODES  ************

Characteristics of nematodes in general:

1. They are dioecious, i.e., they have separate sexes; the female is usually larger than male.

2.  They are free–living or parasitic

3. They vary in sizes from microscopic to as large as lead pencil (Ascaris) or a meter in length (guinea worm).

4. They are cylindrical, non–segmented and tapered at both ends.

5. They have the shortest life cycle.

6. They have chemoreceptors (sensory organs

a.  Head – cephalic chemoreceptors – amphids

b.  Tail – caudal chemoreceptors – phasmids

Classification of Nematodes:

1. Based on the presence or absence of larva in shell

a. Oviparous – delivers egg without full develop larva in its shell.

b. Ovoviparous / oviviparous – delivers egg with fully develop larva in its shell.

c. Viviparous – do not deliver eggs but instead deliver fully develop larva.

2. Based on habitat

a. Intestinal

(1) Small Intestine

Capillaria, Ascaris, Strongyloides, Hookworm

(2) Large intestine

E. vermicularis, Trichiuris

b. Extraintestinal

(1)  Muscle: Trichinella

(2)  Meninges: Angiostrongylus

(3)  Lymphatics

Brugia malayi, Loa loa, Onchocerca volvulus, Wuchereria bancrofti, Manzonella ozzardi, Acanthocheilonema perstans, Dracunculus Medinensis

3. Based on presence or absence of caudal chemoreceptor

a. With phasmids

Hookworms, Ascaris, Strongyloides, Enterobius

b. Aphasmids

Trichiuris, Trichinella, Capillaria

Means of acquiring nematodes

1. Ingestion of embryonated egg thru contaminated food or drinks

e.g. Ascaris, T.trichiuria, E. vermicularis

2. Ingestion of encysted larva

e.g. T. spiralis

3. Skin penetration

e.g. S. stercoralis, Hookworm filariform

4. Thru bite of anthropods or insect vectors as in filariform worms

Modes of attachment

1. Oral attachment to mucosa by sucking (Hookworms)

2. By anchorage with their attenuated ends (Trichiuris)

3. By penetration in tissues (Strongyloides)

4. Retention in the mucosal folds pressure against it (Ascaris)

Means of nutrition

1.   Sucking and ingestion of blood (Hookworm)

2.   Ingestion of lysed tissues (Trichiuris)

3.   Feeding on intestinal contents (Ascaris)

4. Ingestion of nourishment from body fluids (Filarial worms)

************  ASCARIS LUMBRICOIDES  ************

·         Largest intestinal worm

·         Causes Acariasis in Intestine

·         Causes Ascaris pneumonia in lungs

Mode of transmission:       ingestion of embryonated egg

Infective stage:                   embryonated egg

Diagnosis:

1.  Bronchial washing for identification of larvae.

2. Serological test are not reliable since it may cross–react with other worms.

3. In intestinal ascariasis, stool exam to look for characteristic ova. It can also be seen in X–ray especially in barium enema where there is a cylindrical filling defect which is the worm itself.

Morphology

1. Adult:

a. Anterior end

Usually large, elongated and cylindrical tapering bluntly.  The lateral lines can usually be seen as a pair of whitish streaks along the entire length of the flesh colored body. The head is provided with three conspicuous lips (trilobite), a broad median dorsal one a pair of ventrolateral one, all of which are finely denticulated. Each lip has on its lateral margins, minute twinned papillae. Centrally located among the lips is a small buccal cavity

b. Posterior end

(1)  Females

·  20–35 cm x 3–6 mm

·  Larger than male

·  Attenuated end

(2)  Males

·  15–31 x 2–4 mm

·  Shorter than females

·  Curved end

2.     Ova

a. Fertilized

Broadly ovoidal with thick transparent shell with relatively impermeable innermost lipoidal vitelline membrane, thick middle glycogen layer and an outermost mamillated albuminous layer. This measures 45–75u x 35–50u. inside structure contains a mass of lecithin granules. This means it will undergo further development.

b. Unfertilized

88–94 x 44u. Internal structure consist of a mass of disorganized highly refractile granules of different sizes. May lack the outermost albuminous coat. This means it will undergo further development.

c. Embryonated

As fertilized, but inside structure contains the larva of the embryo.

Life cycle

Pathogenesis

1. Larva

a. As it breaks the capillaries, minute hemorrhage are produced which may lead to the production of cellular infiltration (PMN and eosinophils). These serous exudation and consolidation is called ascaris pneumonia or pneumonitis which is characterized by fever (39.5–40^oC), chest pain, rapid, shallow breathing, spasms of cough, non–crepitant bronchial rales, pronounced eosinophilia, characteristics of respiration is of asthmatic type.

b. Also causes allergic reaction (Loeffler’s syndrome) composed of high eosinophilia, fever and phitisis in the lungs as seen by X–ray.

c. If the larva fails to penetrate the alveoli, they go to the general circulation and lodged in different organs. The most complicated is seen in the brain, spinal cord, eyeball and kidney.

2. Adult

a. Asymptomatic in light infection but even a single worm can produce a deadly disease. They can produce ileus because of mechanical obstruction and they can aggregate themselves into a mass or bolus of Ascaris and produce volvulus and intrussuception. A single worm can block the following:

(1)  Ampulla of Vater

(2)  Common bile duct to produce obstructive jaundice

(3)  Liver causing liver abscess

(4)  Appending to produce acute appendicitis to erratic movements of worm

b. Its presence in the small intestine may contribute to the protein–calorie malnutrition and its byproducts or metabolites can cause allergic manifestation. When the larva penetrates the intestinal wall, they can carry microorganisms with them leading to bacteremia and septicemia.

************  ENTEROBIUS VERMICULARIS  ************

·         Also known as Pinworm, Seatworm, Oxyuris

·         Disease produced: Enterobiasis, Oxyuris

Infective stage:       embryonated egg

Mode of transmission:

1. By anus to mouth thru contaminated fingers or fomites, common in children.

2. Through contaminated food and drinks, especially if the food handler is a carrier.

3. Airborne or by inhalation, viable ova can float in the air.

4. Retroinfection – gravid female after laying their eggs in the perianal area, goes back thru the anus to the large intestine. The larvae, upon hatching migrate back the large intestine.

Diagnosis:

1. Anal swab or Graham scotch tape method

2. NIH (National Institute of Health) method

3. Schuffner and Swellengrebel method

Morphology:

1. Adult

Small worms with a cuticular expansion at its interior portion called cephalic alae or cuticular alae. These are diagnostic of the parasite differentiating them from other nematodes of medical importance. The esophagus has a predominant posterior bulbus with a prebulbar swelling.

a. Males

Measures 2–5 mm, smaller than the female with a ventrally curved tail with a single spicule and caudal alae.

b. Females

Measures 8–12 mm with long pointed tail and a rigid body; uteri of gravid female are distended with egg.

2. Ova

Measures 50–60u, when laid at the perianal area, they are already embryonated. They show a double lined refractile chorionic shell and are transparent and colorless. They are elongated or ovoidal with one side flattened giving an appearance similar to the letter “D.”

Two layers of the ova

a. Inner embryonic

b. Outer transparent albuminous shell

Life cycle

Pathogenesis

Causes minute ulceration, hemorrhages from the ulceration, which may become infected causing intolerable itchiness

Nocturnal pruritus ani – very mild tingling sensation to an acute pain resulting to scratching till the area is scarified (exzamatous lesion or dermatitis) sometimes leading to secondary bacterial infections.

**********  TRICHURIS TRICHIURA  ***********

·  Common name: Whipworm

·  Disease produced is Trichiuriasis, Trichocephaliasis

Mode of transmission:       ingestion of embryonated egg

Infective stage:                   embryonated egg

Diagnosis:

1.  Direct fecal smear

2.  Concentration method

3.  Sedimentation

4.  Egg counts to determine worm burden

Morphology

1. Adult

These are attenuated in the anterior 3/5 and fleshy in the posterior 2/5. The esophagus is a delicate capillary tubules surrounded by rows of cells (sticocytes).

Life span:      4 – 6 years

a. Males

Measures 30–45 mm with a posterior portion coiled at 360 or more. The male genitalia have long, sacculate testes, vas deferens, ejaculatory tubule which empties into the cloaca. It has a lanceolate spicule which protrudes thru a refractile pineal sheath.

b. Females

Measures 35 – 50 mm. The reproductive system consists of a single sacculate ovary, oviduct and uterus which constricts as it nears the vulva at the anterior extremity of the fleshy portion of the ovum.

2. Ova

Measures 50–54u x 22–23u, passed with stools in unsegmented condition requiring at least 2 weeks of embryonation in the soil. They are barrel–shaped with 3 layers, the outermost of which is bile–stained, possess bipolar unstained intralami.

Life cycle

**********  TRICHINELLA SPIRALIS  *********

Common Name:       Trichina worm (viviparous)

Disease:                     Trichinosis, Trichiuriasis, Trichinellasis

Mode of transmission:       ingestion of encysted larva

Infective stage:       encysted larva

Diagnosis:

1.  Muscle biopsy – use the gastrocnemius or biceps; do a double slide compression method.

2.  Bachman intradermal test

3.  Serological test – demonstrates appearance of antibodies by precipitin test

4. Xenodiagnoses (Beck’s method) – feed scrap meal to laboratory animal and detect for viable larva afterward.

Habitat:

1.  Intestinal: Adult (small intestine)

2.  Extraintestinal: Larva (muscles)

Muscles involved: Heart, lungs, diaphragm, gastrocnemius, eyes

Morphology

1. Adults

a. Males

Measure about 1–2 mm x 40–60u in its transverse diameter. They are delicate anteriorly and rounder posteriorly. The cloaca which is situated at the caudal portion is guarded by 2 conspicuous papillae which is revertible during coitus

b. Females

Measures about 3–4 mm with the vulvas opening situated at the anterior 5^th of the body with a single ovary found near the caudal end.

2. Larva (encysted)

Life cycle:

Two hosts are required for completion of its life cycle. Man acquires the infection by consuming inadequately cooked pork. Country sausages as well as some European style sausages are some sources of infection.

******  CAPILLARIA PHILIPPINENSIS  ******

Common name: Pudoc worm

Disease: Intestinal capillariasis, Mystery disease

Mode of transmission: eating of raw partially cooked fishes, bagsil, bagsan, ipon

Diagnosis:

1.  Direct Fecal Smear

2.  Concentration & Sedimentation methods

·         All stages of the parasite (ova, larva & adult) can be seen in the stool specimen

Morphology

1. Adult worm live borrowed into the mucosa of the small bowels with both ends hanging or free.

a. Males measure 2–3 mm with the characteristic caudal alae and a long non– spiny sheath.

b. Females measure from 2.5–4 mm with the body divided almost into 2 equal parts; the anterior half is occupied by the esophagus and esophageal glands and the posterior part containing the intestines, reproductive organs with slightly prominent vulva. Females usually have eggs in the uterus which may either be 8–10 eggs arranged in rows or 45–50 eggs arranged in rows of 2 or 3. Eggs belonging to the former are segmented with thick striated shell and bipolar mucus plugs; in the latter, the eggs are multisegmented or embryonated with thin shell and devoid of bipolar plugs.

2. Ova are similar to the Trichiuris except for its smaller size and more striated shell. Plugs are protruded and the shells are more straight than convex.

a.  Atypical – no polar plugs, ovoid, striated

b.  Typical – peanut shaped, with polar plugs, striated

************  STRONGYLOIDES STERCORALIS ************

·         Smallest intestinal nematode

·         Ovoviparous

Common name:       Threadworm

Disease:                     Cochin–China diarrhea, Vietnam diarrhea, Strongyloidiasis 

Mode of transmission:       skin penetration

Infective stage:                   Filariform Larva

Diagnosis:

1. Stool (fresh) and diarrheic – motile rhabditiform larva (Strongyloides stercoralis)

2. Not fresh and constipated – rhabditiform larva (Hookworm)

Morphology:

Strongyloides have 2 phases of development: the free–living or indirect phase and the parasitic or direct phase. They are known as facultative parasites due to its ability to survive both in a free–living and parasitic condition. Under favorable condition, the rhabditiform larva moults several times into the free–living rhabditoid adult males and females which reproduce and multiply in the soil. Such existence is indefinite depending upon the environmental conditions. When the conditions become unfavorable to the parasites, the worm follows the parasitic form of development.

1. Adult worm

a. Parasitic males measure about 0.7 mm rhabditoid in type and almost identical with the free–living males except for the highly larger buccal cavity of the latter. Posterior end of the parasitic male (which is believed to be the same in the free–living males) is curved ventral to the tail. It has two short equal copulatory spicules and a gubernaculum but no caudal alae.

b. Parasitic females measure about 2.2 mm in length by 0.4 mm with a slender tapering anterior end and a conical short pointed posterior end. The esophagus is cylindrical occupying 2/5 on the anterior 3^rd of the body. It has a paired uteri, oviduct and ovarian tubules which arise from a short vagina giving rise to the anterior and posterior reproductive system. Vulvar opening is situated in the posterior 3^rd of the worm.

c. Free–living females measure about 1mm x 0.6mm; rhabditiform in shape possessing two horned uteri and a short vulva which opens near the middle of the ventral side. The reproductive organs are paired. The uteri contain a single column of thin – shelled, transparent segmented ova occupying most of the space along the intestine. Ova measure about 70 x 40u. The uterus of the parasitic females contains a single row of 8–12 thin shelled transparent segmented ova (50–58 x 30–34u) and occupies the posterior half of the body.

·  Females are parthogenic, they are able to produce eggs without the help of males.

2. Larval stages

a. Rhabditiform larva measures 175 x 225u, has a short and wide buccal cavity. It has a muscular esophagus with a characteristic club–shaped anterior portion, post–median constriction and a posterior bulb. It has a very conspicuous genital primordium located ventrally. The posterior end is sharply attenuated.

b. Filariform larva are long, delicate organism with a long esophagus occupying about 40% of the body length. A forked posterior end notched caudal end.

3. Ova: 50–58u, partially emrbyonated when laid, thin–shelled transparent ovoidal ova which usually hatch in the tissue.

Life cycle:

Direct – primarily responsible for human infection since it requires parasitic phase for its continuation

************  TOXOCARA CANIS & TOXOCARA CATI  ************

Diseases:       Visceral larva migrans, chronic endopthalmitis, toxocariasis

                        Visceral larva migrans can also be caused by:

a.       A. braziliensis

b.      S. stercoralis

c.       Spiroids & Filarial worms

Morphology

                                                T. canis                      T. cati

Size:    male                            4 – 6 cm                      4 – 6 cm

            Female                        6.5 – 10 cm                4 – 13 cm

Cervical alae (winglike          longer than broad     broader than long

            structure)

Egg (unembryonated)          75 – 85u                     65 – 70u

                                                subglobular with       subglobular with thin,

                                                thick & coarsely         freely fitted shell

                                                fitted shell

Life cycle

Pathogenesis

1. Larva don’t develop into adult in incompatible host like men. They just migrate to different organs. During migration, host cells attack the larva producing a granulomatous reaction

2. Sign and symptoms depends on the organ involved, number of larva, number of granulomatous lesions produced is directly related to the number of infective stage (ova) ingested and the number of hatched larva which gained entry to the extraintestinal viscera.

3. In older children, most common is eye involvement without generalized infection. Three types of ocular involvement:

a.  Chronic endopthalmitis

b.  Solitary granulomatous retinitis

c.  Peripheral retinitis

4. Signs and symptoms vary from asymptomatic with persistent eosinophilia to those characterized by hypereosinophilia, hepatomegaly, cardiac disturbances, pulmonary disease, nephrosis and allergic manifestation.

************  ANISAKIS SP.  ************

Common name:         Ascaris of sea mammals (whales, seals, dolphins, etc)

Disease:                      Anisakis or Hearing worm disease

Life cycle:

Pathogenesis:

Man acquired the disease upon ingestion of larva in raw, “cold smoked” or “lightly salted” fish. The larva invades the wall of the digestive tract and produces eosinophilic phlegmonous enteritis causing fever, intestinal colic, eosinophilic intestinal abscess and intestinal obstruction.