Parasitology - Aphasmids- Roundworm- Lecture PDF

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Topic: Aphasmids References: Old Trans + BelizarioINTRODUCTIONAphasmids  Roundworms  Characteristics: 1. Reduced/absent caudal papilla 2. Excretory system are without lateral canals 3. Most important characteristic  No caudal chemoreceptors Even with the prior 2 properties but with the 3rd, it wo...

Description

PARASITOLOGY Topic: Aphasmids References: Old Trans + Belizario INTRODUCTION

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Adult Female o Measures about 1.26 to 3.35 mm by 0.029 to 0.038 mm o Has a single ovary which is situated in the posterior part of the body o It has an oviduct, a seminal receptacle, a coiled uterus, a vagina, and a vulva o The vulva is situated in the anterior 5th on the ventral side of the body o The viviparous female lives for 30 days and is capable of producing more than 1,500 larvae in its lifetime

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Larva

Helminth

Roundworm

Flatworm

Aphasmids

Phasmids Aphasmids  Roundworms  Characteristics: 1. Reduced/absent caudal papilla 2. Excretory system are without lateral canals 3. Most important characteristic  No caudal chemoreceptors Even with the prior 2 properties but with the 3rd, it would still be considered an aphasmid     

Under subclass Adenophorea/Asphasmidia Dioecious Female is larger than Male Anterior portion is slightly widened and posterior portion is slightly pointed Species with medical importance: o Trichinella spiralis o Trichuris trichiura o Capillaria philippinensis

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Trichinella spiralis  Common name: Trichina worm  “Dead end alley”  infection cannot be transmitted from human to human  Pathology: Trichinosis, Trichiniasis, Trichinellosis  Discovered at autopsy in London  Parasite is carnivorous/omnivorous animals (cats, dogs, hogs, rats)  Not actually a parasite to humans  Accidental host: Human Based on Belizario:  First described in 1822 in Germany  It causes Trichinellosis  German investigators were able to prove that raw or insufficiently cooked meat was responsible for trichinellosis in humans Parasite Biology Morphology  Adult Male o Measures 0.62 to 1.58 mm by 0.025 to 0.033 mm o With a single testis located near the posterior end of the body, and is joined in the mid-body by the genital tube which, in turn, extends back to the cloaca o The posteriorly-located cloaca has a pair of caudal appendages and two pairs of papillae

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Measures 80 to 120 μm by 5.6 µm at birth, BUT reaches the size of 0.65 to 1.45 mm in length and 0.026 to 0.040 mm in width after it enters a muscle fiber It has a spear-like, burrowing anterior tip The digestive tract of a mature larva encysted in a muscle fiber resembles that of the adult worm The reproductive organs, at this stage, are not yet fully developed but even then, it is already possible to identify the sex of the parasite

Old Trans Info:  Adult Form: o Male measures 1.6 x 0.04 mm o Female measures 3.5 x 0.6 mm (Bigger) o With STICHOSOME (Stichocytes)  sensory organ; nerve cell  only in T. spiralis o With esophagus o Mouth bears protrusible stylet (only protrudes when eating) o With single testis and ovary o May be mistaken for Strongyloides due to its thread-like structure o Presence of stichosome is the differentiating characteristic o Stichosome – cell, a substitute receptor organ due to their lack of a phasmid Stichocytes – group of cells/stichosomes o

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PARASITOLOGY Topic: Aphasmids References: Old Trans + Belizario Old Trans Info continued…..  Larva: o At birth 120 x 5.6 microns o In the muscles: 1300 x 40 microns o May be lodged in various foci (brain, heart, body cavities) o Encyst/develop only in striated muscle  diaphragm, laryngeal, abdominal, psoas, pectoral, deltoid, gluteus, biceps o Liberated from female worm after 4-16 weeks o No egg stage, born larva o Migrates until it finds its permanent habitat: Skeletal Muscle o When it migrates, it can be trapped to other parts of the body, where they eventually die Reproduction:  After mating, MALES are dislodged from the mucosa, and die afterwards ( males mate only ONCE)  Female burrows deeply in the mucosa (duodenum to cecum)  Female dies after passing the larva  Affects small to upper part of large intestine

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Infective stage: Encysted larva Habitat: Skeletal Muscle Encystation: Muscle Excystation: Duodenum MOT: Ingestion of infected muscle with encysted larva Accidental host: Human

Based on Belizario:  In Trichinella infection, the host (i.e., humans, rats, dogs, cats, pigs, bears, foxes, walruses, or any other carnivore or omnivore) serves as both the final and intermediate host by harboring both the adult and the larval stages  Infective larvae are usually encysted in the muscle fibers of the host The infective encysted larvae enter the host through ingestion of raw or insufficiently cooked meat  

Life Cycle  

The cysts are digested in the stomach, and the larvae EXCYST either in the stomach or in the small intestine The larvae then burrow into the subepithelium of the villi where they undergo 4 molts Maturation takes about 2 days, and adult worms begin to mate 5 to 7 days post infection The female produces eggs that grow into larvae in its uterus The larvae penetrate the mucosa, pass through the lymphatic system into the circulation, and finally into striated muscles In the muscles, the larvae grow and develop. After about 3 weeks, they start to coil into individual cysts Encapsulation is completed 4 to 5 weeks after infection

Trichinellosis is acquired by ingesting meat containing cysts (encysted larvae) (1) of Trichinella. After exposure to gastric acid and pepsin, the larvae are released (2) from the cysts and invade the small bowel mucosa where they develop into adult worms (3) (female 2.2 mm in length, males 1.2 mm; life span in the small bowel: 4 weeks). After 1 week, the females release larvae (4) that migrate to the striated muscles where they encyst (5). Trichinella pseudospiralis, however, does not encyst. Encystment is completed in 4 to 5 weeks and the encysted larvae may remain viable for several years. Ingestion of the encysted larvae perpetuates the cycle. Rats and rodents are primarily responsible for maintaining the endemicity of this infection. Carnivorous/omnivorous animals, such as pigs or bears, feed on infected rodents or meat from other animals. Different animal hosts are implicated in the life cycle of the different species of Trichinella. Humans are accidentally infected when eating improperly processed meat of these carnivorous animals (or eating food contaminated with such meat).

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The larva in the cyst remains viable for many years The average lifespan of the encysted larva is about 5 to 10 years, and can survive for up to 40 years in humans

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In humans, calcification of the collagen capsule in the infected muscle cell and the larva may occur This process may be observed 6 to 12 months after infection and may lead to the destruction or death of the larva

Pathogenesis & Clinical Manifestations  Light infection - harboring up to 10 larvae, are usually asymptomatic  Moderate infection (50-500 larvae) show symptoms o Infection with a few hundred larvae can result in gastroenteritis, diarrhea, & abdominal pain approximately two days post infection o Infection with 100 to 300 larvae may lead to symptomatic trichinellosis  >1,000 to 3,000 larvae can result in severe disease  Clinical phases and condition: o Enteric phase – incubation and intestinal invasion  Acute food poisoning  Diarrhea  Vomiting  Abdominal cramps  Malaise  Nausea o Invasion phase – larval migration and muscle invasion  It results to immunological, pathological and metabolic reactions  Inflammatory reaction to the infection results in eosinophilia, which results in the release of histamines

PARASITOLOGY Topic: Aphasmids References: Old Trans + Belizario Invasion phase continued….. 

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Treatment  Mebendazole (DOC) o Dose: 5 mg/kg body weight daily  Albendazole o Adult dose: 1 mg/kg per day in two divided doses for 1015 days o Pedia dose: 10 mg/kg

Histamines, serotonins, bradykinins, and prostaglandins contribute to an ↑ in vascular permeability, resulting in tissue edema The cardinal signs and symptoms of trichinellosis include:  Severe myalgia  Periorbital edema  Eosinophilia Other typical signs and symptoms include:  High remittent fever and chills  Headache  Dyspnea  Dysphagia  Difficulty in chewing Occasionally, there is paralysis of the extremities and splenomegaly In severe cases, there may be gastric and intestinal hemorrhages Larval migration into the heart muscle can result in:  Pericardial pain  Tachycardia  ECG abnormalities Pericardial effusion, congestive heart failure, and other chronic heart abnormalities have also been observed

Thiabendazole is NO LONGER USED due to its associated adverse drug reactions Epidemiology  Trichinella infection has never been documented in a small number of island countries, including the Philippines  Trichinellosis is primarily a zoonosis  Humans get infected after ingestion of raw or insufficiently cooked meat from infected animals  The infection is usually maintained in a pig-to-pig or pig-to-rat-to-pig cycle Prevention & Control  Health education  Regular animal monitoring  Disposal of carcasses  Cooked and store the meats properly Trichuris trichiura  Common name: Whipworm  Soil-transmitted helminth, and is classified as holomyarian

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Neurological complications, which are caused by small subacute cortical infarcts, may occur in chronic infections  Meningitis and meningoencephalitis may also develop  In heavy infections:  Ocular disturbances  Diplegia  Deafness  Epileptiform attacks  Coma Convalescent phase – encystment and encapsulation  Fever, weakness, pain, and other symptoms start to abate  Full recovery is expected since trichinellosis is a self-limiting disease However, protean neurologic signs arising from brain damage may persist

Parasite Biology Morphology:  The worms have an attenuated anterior three-fifths traversed by a narrow esophagus resembling a string of beads. The robust posterior two-fifths contain the intestine and a single set of reproductive organs  Adult Male: o 30 to 45 mm o Shorter than the female o Has a coiled posterior with a single spicule and retractile sheath

Prognosis is good, especially in mild infections Death is uncommon except in cases of heart failure, encephalitis, or other complications such as pneumonia or septicemia Low-grade or absent peripheral blood eosinophilia is indicative of poor prognosis

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Adult Female: o 15 to 50 mm o Has a blunt posterior end o A female lays approximately 3,000 to 10,000 eggs per day

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Egg: o o o o

Diagnosis  Muscle Biopsy – the most definitive diagnostic examination Muscle biopsy is done through histological examination of 0.2 to 0.5 g of muscle tissue 

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Non-specific laboratory tests to detect eosinophilia, muscle enzymes (creatine phosphokinase, lactate dehydrogenase, and myokinase), and total IgE in serum may be useful in diagnosis ELISA is recommended for the diagnosis of Trichinellosis

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50 to 54 µm by 23 µm It is lemon or football-shaped with plug-like translucent polar prominences It has a yellowish outer and a transparent inner shell Fertilized eggs are unsegmented at oviposition and embryonic development takes place outside the host when eggs are deposited in clayish soil Trichuris eggs in soil are more susceptible to desiccation

Larvae are not usually described probably because soon after the embryonated eggs are ingested, the larvae escape and penetrate intestinal villi where they remain for 3 to 10 days

PARASITOLOGY Topic: Aphasmids References: Old Trans + Belizario Life Cycle

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In patients with heavy intensity infection, the worms may be found throughout the colon and rectum, and may result in Trichuris dysentery syndrome manifested by chronic dysentery & rectal prolapse Such cases of heavy chronic trichuriasis are often marked by frequent bloodstreaked diarrheal stools, abdominal pain and tenderness, nausea and vomiting, and weight loss

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Anemia is strongly correlated to heavy intensity trichuriasis, and blood loss from such infections can range from 0.8 to 8.6 ml per day Infection with over 800 worms can result in anemia in children Light infections are moderately associated with anemia, although these infections are usually asymptomatic and the presence of the parasite may be discovered only in routine stool examinations

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Diagnosis  Direct Fecal Smear (DFS)  Kato thick smear  this method is highly recommended in the diagnosis of trichuriasis  Kato-Katz technique  a quantitative method that employs egg counting to determine the intensity of helminth infection This technique can be used to assess the efficacy of anthelminthic drugs in terms of cure rate (CR) and egg reduction rate (ERR)

The unembryonated eggs are passed with the stool (1). In the soil, the eggs develop into a 2-cell stage (2), an advanced cleavage stage (3) , and then they embryonate (4); eggs become infective in 15 to 30 days. After ingestion (soil-contaminated hands or food), the eggs hatch in the small intestine, and release larvae (5) that mature and establish themselves as adults in the colon (6). The adult worms (approximately 4 cm in length) liv e in the cecum and ascending colon. The adult worms are fixed in that location, with the anterior portions threaded into the mucosa. The females begin to oviposit 60 to 70 days after infection. Female worms in the cecum shed between 3,000 and 20,000 eggs per day. The life span of the adults is about 1 year

Based on Belizario:  Trichuris worms inhabit the cecum and the colon  The worms secrete a pore-forming protein, called the TT47 that allows them to imbed their entire whip-like portion into the intestinal wall  After copulation, the female worm lays eggs, which are passed out with the feces and deposited in the soil  Under favorable conditions, the eggs develop and become embryonated within 2 to 3 weeks  If swallowed, the infective embryonated eggs go to the small intestine and undergo 4 larval stages to become adult worms This process takes about 12 weeks  

Trichuriasis has also been shown to result in poor appetite, wasting, stunting, as well as reduced intellectual and cognitive development in children The prognosis of trichuriasis is very good Because there is no larval migration through the lungs as in Ascaris and hookworm infections, no lung pathology occurs

This technique can also be used for epidemiological surveys for the monitoring of a helminth control program 

Kato-Katz technique – 91% sensitivity and 94% specificity

Other diagnostic techniques:  Acid-ether & Formalin-ether/Ethyl acetate concentration techniques  FLOTAC technique  shown to be more sensitive in the diagnosis of trichuriasis compared with Kato-Katz and ether/ethyl acetate concentration techniques

Unlike Ascaris, there is NO heart-lung migration Each female worm can produce about 60 million eggs over an average lifespan of 2 years

Pathogenesis & Clinical Manifestations  The anterior portions of the worms, which are embedded in the mucosa, cause petechial hemorrhages, which may predispose to amebic dysentery, presumably because the ulcers provide a suitable site for tissue invasion by E. histolytica  The mucosa is hyperemic and edematous; enterorrhagia or intestinal bleeding is common  The lumen of the appendix may be filled with worms, and consequent irritation and inflammation may lead to appendicitis or granuloma formation  Infections with over 5,000 T. trichiura eggs per gram of feces are usually symptomatic

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Treatment  Mebendazole (DOC) o Dose: 100 mg twice a day for 3 days o Has a higher cure rate than albendazole  Albendazole o Alternative drug Epidemiology  Occurs in both temperate and tropical countries  More widely distributed in warm, moist areas of the world  Approximately 604 to 795 million are infected globally  Prevalent in East Asia and Pacific Island regions  Least prevalent in the Middle East and North African regions Prevention & Control  Biannual mass drug administration with mebendazole 500 mg or albendazole 400 mg among school-age children in communities  Provision of safe water, environmental sanitation, and hygiene education

PARASITOLOGY Topic: Aphasmids References: Old Trans + Belizario Capillaria philippinensis  Common name: Pudoc worm  Disease: Intestinal capillariasis  Discovered in Ilocos Norte, Philippines  Native in the Philippines  Thinnest aphasmid Based on Belizario:  Was first reported by Chitwood et al. in 1963 in a 29 year old male from Northern Luzon  Intestinal capillariasis, a zoonotic disease, is characterized by abdominal pain, chronic diarrhea, & gurgling stomach The disease may also be associated with protein losing enteropathy, electrolyte imbalance, & intestinal malabsorption 

Fish-eating birds are the natural hosts of the nematode

Parasite Biology  Have a thin filamentous anterior end and a slightly thicker and shorter posterior end  The esophagus has rows of secretory cells called stichocytes, and the entire esophageal structure is called a stichosome  The anus is subterminal, and the vulva in females is located at the junction of anterior and middle thirds  Adult Male: o 1.5 to 3.9 mm in length o Male spicule is 230 to 300 µm long and has an unspined sheath  Adult Female: o 2.3 to 5.3 mm in length o Produce characteristic eggs  Eggs: o Peanut-shaped with striated shells and flattened bipolar plugs o 36 to 45 µm by 20 µm o Passed in the feces and embryonate in the soil or water They must reach the water in order to be ingested by small species of freshwater or brackish water fish

Typically, unembryonated, thick-shelled eggs are passed in the human stool (1) and become embryonated in the external environment in 5 —10 days (2) ; after ingestion by freshwater fish, larvae hatch, penetrate the intestine, and migrate to the tissues (3) . Ingestion of raw or undercooked fish results in infection of the human host. (4) The adults of Capillaria philippinensis are very small (males: 2.3 to 3.2mm; females: 2.5 to 4.3 mm) and reside in the human small intestine, where they burrow in the mucosa (5) . In addition to the unembryonated, shelled eggs which pass into the environment, the females can also produce eggs lacking shells (possessing only a vitelline membrane) (6) , which become embryonated within the female’s uterus or in the intestine. The released larvae can reinvade the intestinal mucosa and cause internal autoinfection (7) . This process may lead to hyperinfection (a massive number of adult worms).

Based on Belizario:  The eggs hatch in the intestines of the fish and grow into the infective larvae  When the fish is eaten uncooked, the larvae escape from the fish intestines and develop into adult worms in human intestines  The first generation of female worms produces larvae to build up the population  Subsequent generations predominantly produce eggs, although there are always a few female worms that produce both larvae and eggs, or larvae only  Some of these larvae are retained in the gut lumen and develop into adults This leads to hyperinfection and autoinfection, which result in the production of very large numbers of worms

Life Cycle

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Fish-eating birds are believed to be the natural hosts Humans are considered incidental hosts

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Intermediate host: Freshwater fish (If man defecates in the river or infected soil gets into the river) Infective stage: Larva MOT: Eating of infected fish with larva stage Diagnostic stage: Eggs in the feces (infective stage in fish)

Pathogenesis & Clinical Manifestations  Abdominal pain an...