Parasitism arose early in the course of biological evolution (parasitology Photostat page.nio 3) Parasitic diseases have been with the mankind since the time immemorial. Even today, these diseases remain among the major cause of human misery and death in the world and are important obstacles to the development of economically less- favored countries.
Medical Parasitology deals with the parasites which infect man and the diseases caused by the clinical picture and the response generated by humans against them. It is also concerned with the various methods of their diagnosis, treatment and finally their prevention and control. Parasites are organisms that infect other living beings. They live in or on the body of another living being, host and obtain shelter and nourishment from it. The term parasite can be applied to any infectious agent but by convention it is generally restricted to infections caused by protozoa and helminths and excludes the viruses, bacteria, and fungi.
CLASSES OF PARASITE:
1. Ecto parasite – lives outside on the surface of the body of the host.
2. Endo parasite – lives inside the body of the host.
3. Temporary parasite – Visits its host for a short period.
4. Permanent parasite ”’ Leads a parasitic life throughout the whole period of its life .
5. Facultative parasite – Lives as a parasite when opportunity arises.
6. Obligatory parasite – Cannot exist without a parasitic life.
7. Accidental parasite – Attacks an unusual host.
8. Wendering parasite – Happens to reach a place where it cannot live.
Host: It is defined as an organism which harbors the parasite and provides nourishment and shelter to the latter. It is of following types
1. Definitive Host: The host in which the adult stage lives or the sexual mode of reproduction takes place.
2. Intermediate Host: The species in which the larval stage of the parasites lives or the asexual multiplication takes place.
3. Paratenic Host or Transport Host: A vertebrate host in which a parasite merely remains viable without development or multiplication. Such a host may serve to pass on the infection to another and so is sometimes called as transport host.
4. Reservoir Host: The host that harbors parasite and serves as important source of infection to other susceptible hosts. Reservoir hosts are important in the control of parasitic diseases.
Host – Parasite Relationship: Host-parasite relationships are of following types:
1. Symbiosis: An association in which both host and parasite are so dependent upon each other that one cannot live without the help of the other.
2. Commensalism: An association in which only the parasite derives benefit without causing any injury to the host.
3. Parasitism: Parasitism is a relationship in which a parasite benefits and the host provides the benefit. The host gets nothing in return and always suffers from some injury. This parasitism holds well in case of Ascariasis.
Sources And Modes Of Infection:
Parasitic infections originate from various sources and are transmitted by various routes. The major sources of infection are
”””Contaminated soil and water
”””Fresh water fishes
”””Raw or uncooked pork
”””Blood sucking insects
CLASSIFICATION OF PARASITES: (parasitology Photostat)
Parasites are broadly classified into two:
Protozoa are again classified into:
Helminths or parasitic worms are multicellular, bilaterally symmetrical, elongated, and flat or round animals. They are the metazoans belonging to phylum Scolecida. The term helminth (in greek helmins means worms) originally refers to intestinal worms, but now comprises many other worms including tissue parasites as well as many free living species
”””General Features of Helminths:
”””Helminths have an outer protective covering the cuticle or integument which may be tough and armed with spines or hooks.
”””Mouth is provided with teeth or cutting plates.
”””They possess suckers or hooks for attachment to host tissues.
”””They do not possess organs of locomotion. Locomotion is generally by muscular contraction and relaxation.
”””They do not possess a true coelomic or body cavity.
”””Digestive system is absent or rudimentary.
”””Primitive nervous system.
”””Reproductive system is well developed.
”””Helminths are monoecious or diecious.
”””The eggs or larvae are produced enormous in number as many 200,000 or
more per female per day.
”””Helminths are unable to multiply in the body of the host.
Classification of Helminths:(nelsons text book of paediatrics)
Helminths are classified broadly into two groups:
1. Phylum Nemathelminthes
2. Phylum Platyhelminthes
Chart 1: Classification of Nematohelminths and Platyhelminths
Classification Based On Life Cycle:
(Unicellular organisms) (Multi cellular organisms)
(a) Ascaris lumbricoids (1) Cestodes
(b) Ancylostoma Duodenal (a) Tenia Solium(Pork Tape worm)
(c) Necatar americanus (b)Tenia Saginata(Beef Tape worm)
(d) Enterobius vermicularis (2)Trematodes ”’flukes
Fasciola hepatica (Liver Fluke)
They are dorsoventrally flattened leaf like or tape like. Their alimentary canal is incomplete or entirely lacking and body cavity is absent. They are mostly hermaphrodites and are also called flat worms.
They are unsegmented, diecious worms which are usually filiform.They have a body cavity with a high hydrostatic pressure, complete alimentary canal with an anteriorly terminal mouth and posteriorly sub terminal anus, no circulatory system, a simple excretory system and a body wall consisting of an outer layer of longitudinal muscles.
Table 1: Features of Cestodes, Trematodes and Nematodes
Features Features TREMATODES NEMATODES
Sexes Monoecious Monoecious except
schistosomes which Diecious
Head Suckers, often with
No hooks No suckers &
Hooks, Well developed
Alimentary canal Absent Present incomplete
No anus Present and
mouth and anus
Body cavity Absent Absent Present
Mode of infection By encysted larvae By larval stages By ingestion of
Nematodes are said to be the most worm like of all helminths, because they generally resemble in appearance a common earth worm. They are the most abundant and widespread animal group. Many species are free living in fresh or salt water, mud or soil and others are parasites of both animals and plants. The name nematode means thread like.
General Features of Nematodes:
”””Nematodes are elongated, cylindrical, unsegmented worms with tapering ends.
”””The adults vary greatly in size from about a mm to a metre in length.
”””Body is covered with a tough cuticle which may be smooth, striated, bossed or spiny.
”””They move by sinous flexion of the body.
”””The body cavity is a pseudocoele in which all the viscera are suspended.
”””The digestive system consists of the anteriorly placed mouth leading to the oesophagus which characteristically vary in shape and structure.
”””The intestine is lined with single layer of columnar cells and leads to the rectum, opening through anus.
”””In the male, the rectum and the ejaculatory duct open into the cloaca.
”””Simple excretory and nervous system.
”””The sexes are separate.
”””The male reproductive system consists of a single delicate tubule differentiated into testis, vas deferens, seminal vesicle and ejaculatory duct which opens into the cloaca.
”””The female reproductive system consists of the ovary, oviduct, seminal receptacle, uterus and vagina.
”””Namatodes may produce eggs (oviparous) or larvae (viviparous) some lay eggs containing larvae which immediately hatch out (ovoviviparous).
”””The life cycle consists of 4 larval stages and the adult form.
”””The cuticle is shed in passing from one stage to another.
Many species of nematodes are free living forms found in soil and water. Several species are parasites of plants, while others parasitisize invertebrate and vertebrate animals.
On the basis of the presence or absence of the migratory phase, the life cycle can be divided into direct and indirect types. The indirect type is seen in Ascariasis, hookworm and filariasis. Trichuris trichiura is an example of direct type in which ova are swallowed and become mature in intestine.
”””CLASSIFICATION OF NEMATODES:
Nematode parasites may be classified in various ways, such as:
1. Based on the Location of adult worms in the body:
Location of nematodes
Small intestine large intestine
Ascaris lumbricoides Trichris trichura
Ancylostoma duodenale Enterobius vemicularis
Lymphatic Lungs Subcutaneous Mesentery Conjunctiva
W.brancofti Strongyloides Loa loa D. perstans Loa loa
B.malayi stercoralis Onchocerca D. medinensis
3. Based on musculature of Nematodes
Three types of musculature are found in nematodes. Based on that these are divided into polymyarian, meromyarian,and homomyarian
Table ”’ Based on Musculature of Nematodes
Type Polymyarian Meromyarian Homomyarian
Size of cells Small,uniform Large, various Small, Uniform
Arrangements Projecting into body Irregular Regular
Lateral cords Cavity present Present Regular
Hook worms Trichuris
2. Based on Mode of infection
Table ”’ Mode of infection of worms
Mode of infection
By ingestion By cutaneous penetration By blood sucking By inhalation
A. lumbricoides Hook worm Filaria A. lumbricoides
T. trichura Strongyloides
3. Based on musculature of Nematodes
Three types of musculature are found in nematodes. Based on that these are divided into polymyarian, meromyarian,and homomyarian
3. Based on whether they lay eggs or larvaes
Table ”’ based on laying eggs or larvae of worms
Nematodes laying eggs / Larvae
Oviparous Viviparous Ovo – Viviparous
W. Bancrofti Stercoralis
Unsegmented eggs Segmented eggs Eggscontaining larvae
Ascaris Ancylostoma Enterobius
Trichuris Necator americanus
Among the intestinal nematodes Ascaris Lumbricoides and enterobius vermicularis are taken for the present study.
ROUND WORM : ASCARIS LUMBRICOIDES
Ascariasis is caused by the large nematode parasite, Ascaris Lumbricoides. It is the most common significant parasitic infection of man. It is estimated that perhaps one quarter of the earth”’s population is currently infected with Ascariasis and the infection occurs with greatest frequency in tropical and sub-tropical regions and in areas with inadequate sanitation and people with poor nutritional status. Children are more infected than adults.
Ascaris lumbricoides has world wide distribution, being especially prevalent in India, China, and South East Asia. It is estimated that more than 250 million people worldwide are infected by this parasite.
The adult worm lives in the lumen of small intestine (jejunum)and maintains its position by its muscle tone. and have a life span of 10-24 months. Usually Ascariasis is diagnosed by identification of the worm eggs in a sample of feces or of the worm itself,
This can be studied under two heading ”’ 1) Structure 2) Colour.
Features of Mature Adult Worms
The body of Ascaris Lumbricoides is cylindrical, tapering gradually at the anterior end and somewhat less so at the posterior end. White longitudinal streaks can usually be seen along the entire length of the pinkish cream body of the parasite. It resembles an ordinary earthworm and is the largest intestinal nematode parasitizing man. When fresh from intestine ,it is light brown or pink in colour, but it gradually changes to white The mouth opens at the anterior end.
It possesses three finely toothed lips, one dorsal and two ventral. The digestive and respiratory organs of the worm float inside the body cavity possessing a toxic fluid known as Ascarion .Allergic reactions seen in infected individuals are due to the toxin. The male measures 15-30 cm in length and 2-4 mm in thickness. Its posterior end is curved ventrally to form a hook and carries 2 copulatory spicules.
It is larger, 20-40 cm long and 3-6mm thick. Its posterior extremity is straight and conical. The vulva is situated mid ventrally near the junction of the anterior and middle thirds of the body. A distinct groove is often seen surrounding the worm at the level of the vulvar opening. This is called the vulvar waist or genital girdle. The vulva leads to a single vagina which branches into a pair of genital tubules that lie convoluted through much of the posterior 2/3rd of the body. The genital tubules of the gravid worm contain an enormous number of eggs as many as 27 million at a time. A single worm lays upto 2,00,000 eggs per day. The eggs are passed in faeces.
Three types of eggs are passed by the worm:
Fertilized eggs: Fertilized eggs lay by females inseminated by mating with a male, are embryonated and develop into infective eggs. It is spherical or ovoid, bile stained to a golden brown colour and measures 60-75”m in length and 40-50”m in breadth. It is enclosed in a stout translucent shell consisting of 3 layers. The outer coarsely mammilated albuminoid coat, a thick transparent middle layer and the inner lipoid vitelline membrane are the three layers. Some eggs are found in feces without the outer mammilated coat and such eggs are called Decorticated eggs. In the middle of the egg is a large unsegmented ovum containing a mass of coarse lecithin granules which nearly fills the egg, except for clear crescentic area at either pole.
Unfertilized eggs: Is longer up to 90”m in length and more elliptical. The shell is thinner with the outer mammillary coat scanty and irregular. The ovum is atrophic and contains numerous disorganized, highly refractile granules of various sizes. The unfertilized egg is relatively heavy and does not float in saturated salt solution used for concentration by salt floatation while the fertilized eggs float.
Semi Decorticated Fertilized Egg:
Some eggs are without outer mamillated coat and are called as decorticated eggs. In the middle of the egg is a large unsegmented ovum containing a mass of coarse lecithin granules. It nearly fills egg except for a clear cresentric area at either pole. It is single shelled, thick, round and a colourless granular central mass.
Resistance of eggs
Roundworm eggs are adversely affected by excessive heat and drying as caused by direct exposure to sun, however, they are remarkably resistant to most other environmental conditions. Laboratory studies have revealed that the eggs can survive and continue maturation even when immersed in 2 per cent formalin, potassium dichromate, 50 per cent solutions of acetic, nitric, hydrochloric and sulphuric acid. This factor adds to the longevity of the eggs in the environment. Life span of an adult Ascaris is 10-12 months and that of an egg is 3-7 years
Structure of Eggs of Ascaris Lumbricoides
Mode of Infection:
Infection is effected by swallowing ripe Ascaris eggs (embryonated eggs). Infection may also occur by the inhalation of descicated eggs in the dust reaching the pharynx and swallowed. Instead of being swallowed the eggs may hatch on moist mucous surface of the upper air passages and the larvae may directly penetrate into the blood stream. The other possible ways for the Ascariasis are
”’ Raw vegetables cultivated on a soil fertilized by infected human excreta .
”’ Drinking contaminated water .
”’ Polluted soil .
”’ Ascaris eggs may directly be coveyed to the mouth by dity fingers.
”’ Ascaris Lumbricoides is one among the nematodes taken for the present study.
The infective stage eggs are invariably obtained from human sources.
”’ Infective agent ”’ Embryonated egg.
”’ Portal of entry ”’ Alimentary canal.
”’ Migration of larvae ”’ Through lungs.
”’ Site of location ”’ Small intestine.
Structure of Ascaris lumbricoides
ASCARIS LIFE CYCLE( ackar 110)
The ascaris worm passes its life cycle in one host , no intermediate host is required . Man is the only known definite host. The various stages in the life cycle are described below.
I. Stage 1 : Eggs in faeces ”’ Adult worms live in the lumen of the small intestine. A female may produce approximately 200,000 eggs per day . Fertilised eggs containing the unsegmented ovum are passed with the faeces. If it is freshly passed, not infective to man.
II. Stage 2: Development in soil ”’ A rabditiform larva is developed from the unsegmented ovum within the egg shell in 10 -40 days time. Fertile eggs embryonate and become infective after 18 days to several weeks .The ripe egg containing the coiled up embryo is infective to man. Unfertilized eggs may be ingested but are not infective.
III. Stage 3: Infection by ingestion and liberation of larvae- When ingested with food, drink or raw vegetables, the embryonated eggs pass down to the duodenum where the digestive juices weaken the egg shell and rabditiform larve liberated in the upper part of the small intestine.
IV. Stage 4 : Migration through lungs ”’ The larvae liberated in the small intestine burrow their way through the mucus membrane of the small intestine and are carried by the portal circulation to the liver ,where they live for a period of 3-4 days. Finally they pass out of the liver and are carried via the portal, then systemic circulation and/or lymphatics to the lungs. The larvae , mature further in the lungs (10 to 14 days), grow much bigger and increase in length and break through the capillary wall and reach the lung alveoli.
V. Stage 5: Re entry into the stomach and the small intestine ”’ From the lung alveoli, the larvae crawl up bronchi and trachea and aided by the current caused by the ciliated epithelium of respiratory tract , they are propelled in to the larynx and pharynx and are once more swallowed. The larvae pass down the esophagus to the stomach and localize in the upper part of the small intestine.
VI. Stage 6 :Sexual maturity and egg liberation- mature in about 6-10 weeks time. The gravid females begin to discharge eggs in the stool within about two months from the time of infection. The cycle is again repeated. Adult worms can live 1 to 2 years.
Effect: This can be considered under two ways
1) Pathogenic effect caused by larvae: the larvae produces pathogenic effect while entering the skin and during migration through lungs.
a) Ankylostome dermatitis and creeping eruptions.
b) Lesion in the lungs: When the larvae breaking through the pulmonary capillaries and enter alveolar spaces, Bronchitis or Broncho ”’pneumonia may occur. The Ascaris pneumonia is characterized by low grade fever, dry cough, asthmatic wheezing, urticaria, eosinophilia and mottled lung infiltration in the chest Radiograph.
c) Gastrointestinal manifestations: Occasionallly patient may have an subnormal appetite, or may shows a perverted taste for such things as earth, mud or lime. Bowels are generally constipated.
2 ) Symptoms due to adult worm : The pathogenic effects are
a) Spoliative action: The spoliative or nutritional effects usually seen when the infection is very heavy. Patients may develop loss of appetite and often restless. This interferes with the proper digestion and absorption of food.
b) Toxic reaction: This is developed due to the worm antigens and may be manifested as fever, urticaria, angioneurotic edema, wheezing and conjunctivitis.
c) Mechanical effects: This is the most important manifestation of Ascariasis. This may be due to masses of worms causing luminal occlusion or even a single worm infiltrating into a vital area. That may cause reflex peristalsis, causing recurrent and often severe colicky pain in the abdomen. The worms may be clumped together into a mass filling the lumen, leading to intussusceptions or intestinal obstruction. Appendicitis, obstructive jaundice,
When Ascaris worms obstruct the sphincter of oddi or migrate up the biliary tree producing acute abdominal pain suggestive of a passage of a gall stone, pancreatitis or cholangitis may result and surgical removal of the worms has often been necessary.
ENTEROBIUS VERMICULARIS (ackar 115)
Enetrobius vermicularis, the human pin worm, thread worm or seat worm formerly called Oxyuris vermicularis has been known from ancient times. The name Enterobius vermicularis means a tiny worm living in the intestine. The term Oxyuris means ”’sharp tail”’, a feature of female worm. From which the name ”’pin worm”’ is also derived. (parsitology page no 180). Pin worm has a worldwide distribution. 200 million people worldwide are thought to be infested by pinworms. Pinworms are particularly common in children. The incidence rate is 11.4% among children with prevalence rates in this age group having been reported as high as 61% in India.(http://web.stanford.edu/class /humbio103/ParaSites2006/ Enterobius/general%20 information.htm). Pin worm infestations are more common in temperate countries. Children and individuals living in crowded conditions are more commonly infected with this.
The adult worm lives in the caecum, appendix and adjacent part of ascending colon.
The adults are short, white, fusiform worms with pointed ends, looking like bits of white thread. The mouth is surrounded by three wings ”’like cuticular expansions, which are transversely striated.
The female pin worms are larger ranging between 8-13 mm x 0.3-0.5 mm.. The posterior third is drawn into a thin pointed pin like tail. The vulva is located just in front of the middle third of the body and opens into the single vagina which leads to the paired uteri, oviduct and ovaries. In the gravid female worm the whole body is filled by the distended uteri carrying thousands of eggs.
The male pin worms are smaller ranging between 2-5 mm x 0.1-0.2 mm. Its posterior end is tightly curved and contains a prominent copulatory spicule(parasitology Photostat page no181).
Pin Worm Eggs:
The egg, when laid it is colourless and not bile stained. It is elongated ovoid, flattened on one side and convex on the other side, measuring 50”m -60 ”m. The egg shell is relatively thick transparent double layer. The outer albuminous layer makes the eggs stick to each other and to clothing and other objects. The egg contains a tadpole- shaped coiled embryo which is fully formed, but becomes infectious only 6 hours after being deposited on the skin. Under cool moist conditions, the egg remains viable for about 2 weeks.
Biology And Life Cycle.
Enterobius vermicularis is monoxenous, the entire life cycle of Enterobius vermicularis, from egg to adult worm occurs in the human gastrointestinal tract. It has no intermediate host. It will take around 2-4 weeks or about 4-8 weeks. The whole life span of pin worm is approximately 2months. (http://web. stanford. edu/class/ humbio103 / Para Sites2006/Enterobius/general%20 information.htm)
The adult worms live in the caecum, appendix and adjacent parts of the ascending colon. After mating, the males usually dies is passed in the feces. The gravid female migrates down to the colon to the rectum. At night time, the worms come out through the anus and crawls about on the perianal and perineal skin to lay its sticky eggs. The worms may retreat into the anal canal and comes out again to lay more eggs. The worms may wander into the vulva, vagina, and even into the uterus and fallopian tubes sometimes reaching the peritoneum. A single worm lays about 5000-17000 eggs. When the eggs are laid, the worms dies or gets crushed by the host during scratching. The worms may often be seen on the feces, having been passively carried from the rectum. The eggs, however, are only infrequently found in feces. The eggs containing larvae newly laid on the perianal skin completes its development in 24-36 hours time in the presence of oxygen. Infection occurs through the ingestion of these eggs. When eggs containing infective lavae are swallowed, the egg shells are dissolved by the digestive juices and the larvae escape in the small intestine. They moult in the ileum and enter the caecum, where they develop into adult worms. It will take 2 weeks to 2 months from the time the eggs are ingested, to the development of the gravid female, ready to lay eggs.(parasitology Photostat 182 pageno)
Familial infection is common, the infection occurs mostly in children. It is commoner in females than in males. The infection may occurs either contagious from close association or due to contaminated food and drink. Persons handling the night clothes and bed linens of infected patients are more prone to infection. There is also a possibility of the infection being air born especially in an infected place. Pinworm is a very contagious organism. AUTO INFECTION:
The movement of worms during egg laying time causes intense itching, inducing the patient to scratch the affected part and thereby carrying the eggs containing the infected larvae on their fingers. Most of the cases these eggs are subsequently transferred to food and swallowed by the patient himself. In children the infection may occur direct from anus to mouth, because of thumb sucking nature and improper hand washing. RETROINFECTION:
In this process the eggs laid on the perianal skin immediately hatches into the infective stage larvae and it migrate through the anus to the intestine and develop into adolescent forms in the colon. The frequency with which this happen is unknown. (http://web.stanford. edu/class /humbio103 /ParaSites2006/Enterobius /general%20 information.htm)
Life cycle of Enterobius vermicularis
Eggs of Enterobius Vermicularis
”’ Intense irritation and pruritis of the perianl and perineal area.
”’ Interrupted sleep due to itching that mainly occurs at night time.
”’ Constant scratching causes the excoriation of the skin around the anus.(pubmed)
”’ If the worm crawling into the vulva and vagina causes irritation and and mucoid discharge.(parasitology Photostat 182 pageno).
”’ Nocturnal enuresis sometimes seen.
”’ If the pinworms are migrate upto the uterus, fallopian tubes, and into the peritoneum The symptoms of salpingitis may developed.
”’ Loss of appetite and weight are seen in sever infestation.
”’ The pinworms sometimes found in surgically removed appendix and has been claimed to be responsible for appendicitis.(parasitology Photostat page no 182)
The risk factors for worm infestation includes
”’ Poor sanitation
”’ Poor personal hygiene.
”’ Living or visiting warm tropical climate
”’ Crowded conditions, such as day care or institutional settings.
”’ Compromised immune system.
”’ Eating uncooked meat of carnivorous animals.
”’ Eating dirt or clay.
”’ Contact with animal feces
”’ Multiple insect bites.
1) Parasitic diagnosis: Diagnosis of Ascaris lumbricoides infection can be made by
a) Demonstration of adult worms: Worms may be passed through anus, mouth, and nose and rarely through ear. Barium meal may occasionally reveal the presence of adult worms in the small intestine.
b) Demonstration of larvae: Ascaris larvae may be detected in the sputum during the stage of migration
c) Demonstration of both fertilized and unfertilized eggs: These may be detected by direct microscopy or concentration of feces by salt floatation or formalin ether concentration method.
2) Sero Diagnosis: Ascaris antibody can be detected by indirect haemoagglutination immune fluorescence antibody test. The tests are useful for the diagnosis of extra intestinal Ascariasis like Loffler”’s syndrome.
3) Eosinophilia: It is seen in larval invasion stage Depending on the nature of the parasitic infection, the following materials should be collected for specific diagnosis.
In those parasitic infection parasite itself or in any stage of its development circulate in the blood stream. E.g. In malaria the parasites are found inside the erythrocytes.
Stool (www. Ncbi.nlm.nih.gov)
It is an important part in the diagnosis of intestinal parasitic infection and also for those, helminthic parasite which localize in the biliary tract and discharge their egg in to intestine. In protozoal infection either cyst or trophozoietes may be detected. In helminthic infection, either the adult worms or their eggs are found in the stool.
(i) Eggs are found in intestinal helminthiasis like Ascariasis, Trichuriasis and Hook
(ii) In Enterobiasis eggs are rarely found in the stool because they are deposited on the perianal skin and hence anal swabs are to be taken for the diagnosis.
(iii) In Strogyloidiasis larvae not eggs are commonly present in freshly passed
(iv) Adult worms are found in Ascariasis, Enterobiasis and Hook worm infestation segments of adult worms are found in Taeniasis and Tape worm infection.
The most important method for the diagnosis of Ascariasis is the demonstration of eggs in the feces. Ascaris are prolific egg layers. A single female may account for about 3 eggs per mg of faeces. At this concentration, the eggs can be readily seen by microscopic examination of a saline emulsion of feces. Both fertilized and unfertilized eggs are usually present. Occasionally only one type is seen. The fertilized eggs may sometimes appear decorticated. Rarely, when the infestation is light, eggs are demonstrable only by concentration methods. The unfertilized eggs are not detectable by salt floatation. Eggs may not be seen if only male worms are present.
Sometimes the diagnosis becomes evident when the worm is passed either through the anus, or through the mouth or nose.
A skin test with Ascaris antigen gives a positive result, but is unreliable and not used for diagnosis.
Diagnosis may often be made by barium contrast radiography of the abdomen.
Demonstration of Eggs In Stool:
Each female worm produces massive numbers of eggs per day, one or two direct wet mounts are sufficient to diagnose the eggs in stool.
Quantification of Worm Burden:
Egg counts are not usually done in a clinical laboratory for routine diagnosis. It is usually done for Ascaris lumbricoides, Trichuris trichura and Hook worm for two purposes.
”’ Epidemiological surveys
”’ Therapeutic monitoring
The methods commonly used for doing egg counts are:
a. Direct smear egg count
b. Stoll dilution egg count technique
c. Scotch tape method
d. Entero test
Direct Smear Egg Count: (emedicine.medscape .com.article/2017)
”’ Approximately 2mg of faeces is mixed in a small drop of saline on a slide.
”’ Evenly mix the material, apply a cover slip avoiding the air bubbles formation.
”’ With the low power microscope systematically examine the entire preparation.
”’ Record counts of each species of eggs per smear. Count number of eggs per gram of feces using the following formula.
No. of eggs / gm of feces = N / 2 ” 1000. Where N = Number of eggs
Stoll Dilution Egg Count Technique:
This is commonly used method for determining the number of helminth eggs in feces.
This is done as follows.
”’ Weigh out 4gms of feces.
”’ Transfer the sample to a graduated flask (Stoll”’s flask). Add 0.1 NaOH solution up to 60ml mark.
”’ Add several glass beads. Close the flask with a rubber stopper and shake vigorously.
”’ Allow the specimen to stand for 12- 24 hours with occasional shaking.
”’ Withdraw 0.075 ml of the specimen and put on a glass slide for an egg count(=n)
”’ Total number of eggs per gram feces (N) is calculated by (n” 200).
”’ The estimated daily output of eggs can be calculated by multiplying ”’N”’ by the total weight of a24 hour fecal sample.
Scotch Tape Method:
(Adhesive Transparent Cellophane Perianal Swab Method)
This is used for detection of eggs or female Enterobius vermicularis worms and occasionally eggs of Taenia solium, Taenia saginata and Schistosoma mansoni. A piece of cellophane tape held, sticky side out, on a wooden tongue depressor. The mounted tape is firmly pressed against the anal margin, covering all slides. The tape is transferred to a glass slide, sticky side down, and with the low power microscope systematically examine the entire slide. A drop of toluene or xylol may be placed between the tape and the slide to clear the preparation. The specimen is best collected at night or early morning, before going the toilet or bathing because the female pin worms crawls out of the anus at night to lay eggs.
The Entero test is used to retrieve samples of material in the first part of small intestine without intubation. These samples are examined under a microscope for the potential presence of parasites. The device is composed of a weighted gelatin capsule that contains a spool of nylon string. One end of the nylon string is affixed to patients face and the capsule is then swallowed with the water. After 3-4 hour the natural digestive processes will gradually dissolve and move the capsule down through the stomach, unraveling the spool of string as it goes. The string gathers materials from the stomach and upper intestine, including any potential parasites. Which are squeezed on to a glass slide for examination by microscopy.
When parasite localizes in the urinary tract examination of the urine will be of help in establishing the parasitological diagnosis. e.g. in cases of chyluria caused by W. Bancrofti Microfilaria are found.
Examination of the sputum is useful. When the habitat of the parasite is in the respiratory tract as example P. Westermani. In case of amoebic abscess in lung and when amoebic lever abscess bursting in to lung the trophozoites of E. Histolytica are detected in sputum. In case of rupture of hydatid cyst of lung also sputum test is positive.
1. It varies with different parasitic infections as example. Spleen punctures in cases of Kala Azar
2. Rectal biopsy in the cases of schistosomiasis.
1) Cytological Changes In The Blood:
Eosinophillia often gives an Indication of tissue invasion by a helminth. Eosinophilia is not found when helminthes have settled at their location. When helminthes not adapted by Man, gain access to man’s tissue often provoke a marked eosinophilia. Neutrophilic leucocytosis is observed in amoebic liver abscess. Anaemia is a feature of hook worm infection and malaria.
2) Biochemical alteration of the blood ”’ hyper gamma globulinaemia in case of Kala Azar and visceral Larvae migrans.
3) Serological test – Specific complement fixation test is used in many protozoal and helminthic infections such as Amoebiasis and Non specific complement fixation test as in Kala Azar. Immobilisation test as in Amoebiasis.
4) Intradermal reaction (Skin test):
This is positive in many helminthic infections such as Hydatid disease, Filariasis, Ascariasis and Strongylodiasis. It is positive in certain protozoal test such as Amoebiasis and Toxoplasmosis.
Like all disease in human body it is necessary in parasitic infection to form an opinion how the disease can be tackle. But it is really a difficult task and it require years of clinical experience and special skill. In disease due to the parasitic infection, whether it will end in spontaneously recovery, recover with prolong convulsions, in danger life. In parasitic infection where a specific remedy is available, it is possible to alter the prognosis of individual case from unfavorable to favorable. But in second parasitic infection although prognosis as to the prospect of life may be good, they leads to chronic invalidism. In disease like hydatid cyst surgical intervention offer a favorable prognosis. Further it is to be noted that the complication and second infections often alter the prognosis of the case.
Many of the parasitic infection can be cured by specific chemotherapy. For the treatment of intestinal helminthiasis drugs are given orally for direct action on the helminths. To obtain maximum parasiticidal effect, it is desirable that the drugs administered should not be absorbed and the drugs should also have minimum toxic effect on the host.
”’ Albendazole – A broad spectrum antihelminthic agent which decreases ATP production in the worm, causing energy depletion, immobilization, and finally death. Single oral dose of 400 mg (200 for children aged below 2 yrs, contraindicated during pregnancy)
”’ Mebendazole – Causes slow immobilization and death of the worms by selectively and irreversibly blocking uptake of glucose and other nutrients in susceptible adult intestine where helminthes dwell. Dosage is 100 mg orally twice daily for 3 days.
”’ Piperazine: A flaccid paralyzing agent that causes a blocking response of helminthes muscle to acetylcholine. The narcotizing effect immobilizes the worm, which prevents migration and causes the worm to be passed out in the feces. Dosage is 75 mg/kg(max.3.5 gm) as a single oral dose.
”’ Pyrantel palmoate: Depolarizes ganglionic block of nicotinic neuromuscular transmission, resulting in the spastic paralysis of the worm. In case of heavy worm load the spastic (tetanic) paralyzing agents; in particular Pyrantel pamoate may induce complete intestinal obstruction. Dosage is – single oral dose of 11 mg/kg body wt.
The measures should consist of,
”’ Proper disposal of human feces.
”’ Treatment of parasitized individuals.
”’ Recommend good personal hygiene and food handling techniques.
”’ Wash hands with soap and water before handling food.
”’ Drink properly filtered and boiled water.
”’ Food must be properly cooked.
”’ Fruits must be properly washed and ideally pealed before consumption.
”’ Hands must be washed after each visit to toilet.
”’ Avoid soil consumption.
”’ Education of children in schools on sanitary laws and hygiene.
”’ Treatment of vegetables and other garden crops with water mixed with iodine 200 ppm for 15 minutes kills the eggs and larvae of Ascaris and other helminthes
”’ Agricultural workers should wear personal protection (i.e. boots and gloves etc.) when working in soil contaminated with animal and human feces.
”’ When traveling to countries where sanitation and hygiene are poor avoid water or food that may be contaminated, proper care has to be taken.
”’ Treatment of parasitized individuals.
”’ Periodic treatment with an effective anti-helminthic drug in communities that lack sanitary facilities
”’ Discontinuing the practice of using human feces as fertilizer,
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