Ascaris Lumbricoides

Phylum Ashelminthes: SubPhylum Nematoda Class: Rhabditea Subclass: Rhabditia (Phasmidea, Secernentea) Order: Ascaridida Super Family: Ascaridorea Family: Ascarididae

Ascaris lumbricoides Common Name: Large intestinal roundworm  

Disease: Ascariasis Morphology:    

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Adult male: smaller, curved posteriorly with 2 spicules 

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Creamy white or pinkish yellow when freshly expelled Elongated, cylindroidal, tapering bluntly anteriorly Provided with pair of lateral line Genital ring

> 30 cm X 3 mm

Adult female: large, tapered posteriorly 

> 20 – 25 cm X 5 mm (*45 cm)

Female and male Ascaris lumbricoides

Morphology:

(cont.)  In both sexes the mouth is  surrounded by one dorsal and  2 ventrolateral lips The female is prodigious in  egg production, depositing  about 200,000 – 240,000  eggs daily! Uterus may contain up to  27 million eggs at one time!!! 1 Ascaris female produces  approx. 65 – 75 M eggs  during its life span of about  12 months.

The “tri­lipped/ trilobed” anterior end  of Ascaris lumbricoides. 

Ascaris lumbricoides  Fertilized

ova

Ovoidal with thick transparent shell  Golden brown in color; 45 – 75 X 35 – 45 um  Egg shell consist of 3 layers: 

1. Vitelline membrane  2. Glycogen membrane  3. Albuminous layer The outer, albuminous coat of the egg is brown in color due to bile pigment absorbed from the feces 

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Ascaris lumbricoides Unfertilized  88

ova

– 94 um by 39 – 44 um  Larger, narrower & more elongated than the fertilized ova  Shell is thinner w/ an irregular coating of albumin  Inside the eggs are highly refractile granules  First 2 layers are absent  Sometimes eggs may be decorticated

Question: Is it possible that only unfertilized Ascaris ova are seen in the stool?  Explain. 

Ascaris lumbricoides (large intestinal roundworm) 

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Largest nematode adult males ( 200-300 mm) If no male present in small intestine, female will lay bizarre shaped unfertilized eggs No intermediate host

A large mass of Ascaris lumbricoides that was passed from the intestinal tract.

Typical fertilized ova

Ascaris lumbricoides

lips and face

developing embryo

Ascaris  Life Cycle

Life Cycle

• After being ingested, infective eggs hatch in the 

duodenum • Larvae actively burrow into the mucosal lining,  enter the circulatory system,  and are carried to the  liver, through the right side of the heart, and on to  the lungs by way of pulmonary arterial flow •Larvae remain in the lungs several days, but eventually rupture from the pulmonary capillaries and enter the alveoli From here they move up the lungs and trachea to the epiglottis, are coughed up, swallowed, and passed into the small intestine After molting the worms grow to sexual maturity

Life Cycle  • Adult worms live in the lumen of the small intestine and  get nourishment from semidigested food in the host • Copulation occurs here and eggs are passed with the feces •The zygote does not begin development until the egg has  reached the soil •Eggs are fairly resistant to desiccation and low  temperatures •With proper temperatures and oxygen levels the embryo  molts at least once in the shell and develops to an infective  larva •Eggs can remain viable in the soil for 2 years

Epidemiology • Distribution of A. lumbricoides is worldwide, but 

it is prevalent in warmer climates • It depends upon poor sanitation for its  proliferation • It is most prevalent in children: • they are exposed to contaminated soil,  • do not wash before eating,  •put hands in mouth, etc.

Pathogenesis & Symptomatology 2 Types: 3. Produced by migrating larva 4. Produced by the adult worms • • • • •

Most cases of ascariasis are asymptomatic The most frequent symptom is upper abdominal discomfort Little damage results from larval penetration of the host’s mucosa However, aberrant larvae migrating in such organs as the spleen,  liver, lymph nodes, and brain usually result in an inflammatory  response Also, larvae escaping from capillaries in the lungs and entering the  respiratory system cause small, hemorrhagic foci accompanied by  coughing, fever, and difficulty in breathing

Pathogenesis & Symptomatology, cont. 2. Due to adult worms:   

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Worms sometimes cause mechanical blockage of the intestinal tract Also, worms may penetrate the intestinal wall or appendix causing local hemorrhaging Overcrowding may also lead to wandering; worms can enter the appendix and cause blockage; worms have been known to migrate all the way to the anus Some worms migrate anteriorly and have been known to block pancreatic and bile ducts; others have gotten into the stomach and some even as far as the esophagus and tracheae

Diagnosis 

Finding the characteristic ova in the stool of a patient:  DFS  Kato

Thick Smear Technique  Kato Katz Technique – quantitative method

Treatment 

2 ways:  1.

Mass treatment  2. Selective treatment 

DOC: Mebendazole  Pyrantel pamoate 

Toxocara canis • Found in the small intestine of dogs and other canines • Causes visceral larval migrans among humans (an accidental  host); most common among children • It usually results from the ingestion of eggs and the subsequent   migration of second stage larvae within the internal organs  • The second stage larvae hatching from the eggs penetrate the  intestinal wall and quickly invade the liver • Although a majority of these larvae remain in the liver, some pass  on to the lungs and, sometimes, the CNS and eyes • Although most of the larvae eventually gravitate to a single  location and become encapsulated by host tissues, for a period of  time they actively migrate through the tissues, leaving long trails of  inflammatory  reaction cells

Visceral Larval Migrans Case Study • A previously healthy 37-year-old black man had fever, abdominal cramping, vomiting, and diarrhea. After 1 week of symptoms, a chest radiograph showed multiple noncavitating pulmonary nodules • On further questioning, the patient stated that he had acquired a puppy 1 month before onset of the abdominal pain. The puppy was being housetrained, and the patient had had no previous household exposure to dogs. Subsequently, tests for serum antibodies against • T canis IgG and IgM were obtained and were positive at 11.5 and 9.3 standard deviations above the mean of a reference group of normal subjects. The Toxocara IgM titer indicated acute infection with T canis.

A chest radiograph showing multiple noncavitating pulmonary nodules