Ординатура / Офтальмология / Английские материалы / Basic Sciences in Ophthalmology_Velayutham_2009
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Clinical Manifestations
Symptomatic primary pulmonary infection is manifested by fever, cough, chest pain, malaise, and sometimes the hypersensitivity reactions listed above. Chest radiographs may show an infiltrate, hilar adenopathy, or pleural effusion. Mild peripheral-blood eosinophilia may be found. Spontaneous improvement begins after several days to 2 weeks of illness and usually culminates in complete recovery.
The symptoms of a chronic thin-walled cavity include cough or hemoptysis in half of cases; the other half are asymptomatic. Chronic progressive pulmonary coccidioidomycosis causes cough, sputum production, variable degrees of fever, and weight loss.
Diagnosis
When coccidioidomycosis is suspected, sputum, urine, and pus should be examined for C. immitis by wet smear and culture. The laboratory request should indicate clearly that coccidioidomycosis is suspected, because the mold form must be handled with extreme care to prevent infection of laboratory personnel. On biopsy, smaller spherules must be distinguished from nonbudding forms of Blastomyces and Cryptococcus, but the appearance of the mature spherule is diagnostic.
Serologic tests are very helpful in the diagnosis of coccidioidomycosis. Latex agglutination and agar gel diffusion tests are useful in screening sera for antibody to Coccidioides. The complement fixation test is used for CSF determinations and for the confirmation and quantitation of serum antibody detected by screening tests.
Treatment
Amphotericin B or itraconazole can be used to treat the infection.
CRYPTOCOCCOSIS
Etiologic Agent
Cryptococcosis is an infection caused by the yeastlike fungus Cryptococcus neoformans. This fungus reproduces by budding and forms round, yeastlike cells. Within the host and on certain culture media, a large polysaccharide capsule surrounds each yeast cell. The fungus grows well in smooth, creamywhite colonies on Sabouraud's or other simple media at 20 to 37°C. Identification of the organism is based on gross and microscopic appearance, biochemical test results, and growth at 37°C. The results of nucleic acid hybridization or the formation of brown pigment on Niger seed agar can also be used for identification.
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The fungus has four capsular serotypes, designated A, B, C, and D. There are also two mating types. Coculture of opposite mating types creates a transient diploid state called Filobasidiella neoformans var. neoformans for serotypes A and D and F. neoformans var. bacillispora for serotypes B and C. Organisms not cultured under mating conditions are designated C. neoformans var. neoformans for serotypes A and D and C. neoformans var. gattii for serotypes B and C; a simple color medium distinguishes the two varieties.
Pathogenesis and Pathology
Infection is thought to be acquired by inhalation of fungus into the lungs. Pulmonary infection has a tendency toward spontaneous resolution and is frequently asymptomatic. Silent hematogenous spread to the brain leads to clusters of cryptococci in the perivascular areas of cortical gray matter, in the basal ganglia, and, to a lesser extent, in other areas of the central nervous system. The inflammatory response around these foci is usually scant. In the more chronic cases, a dense basilar arachnoiditis is typical. Lung lesions are characterized by intense granulomatous inflammation. Cryptococci are best seen in tissue by staining with methenamine silver or periodic acid-Schiff. Although a strongly positive result on mucicarmine staining of tissue is diagnostic, staining varies from intense to absent.
Clinical Manifestations
Most patients have meningoencephalitis at the time of diagnosis. This form of the infection is invariably fatal without appropriate therapy; death occurs any time from 2 weeks to several years after the onset of symptoms. Early manifestations include headache, nausea, staggering gait, dementia, irritability, confusion, and blurred vision. Both fever and nuchal rigidity are often mild or lacking. Papilledema is evident in one-third of cases at the time of diagnosis. Cranial nerve palsies, typically asymmetric, occur in about one-fourth of cases.
Pulmonary cryptococcosis causes chest pain in about 40% of patients and cough in 20%. The chest X-ray shows one or more dense infiltrates, which are often well circumscribed. Cavitation, pleural effusions, and hilar adenopathy are infrequent. Calcification is not evident, and fibrotic stranding is rarely noticeable.
Diagnosis
An india ink smear of centrifuged cerebrospinal fluid (CSF) sediment reveals encapsulated yeast in more than half of cases, although artifacts can cause confusion.
Culture done on Saborauds dextrose medium.
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Treatment
Ampotericin B, Fluconazole are effective.
PARASITOLOGY
The major groups of parasites infecting human beings are Protozoa and Helminths. A relationship between two species; where one species (parasite) derives food and shelter from another species (Host).
Hosts and parasites share a dynamic relationship. Generally, parasites cannot exist independently. They generally inflict injury, affecting the wellbeing of the host.
Intestinal Parasites
Most helminths and protozoa exit the body in the faecal strain. The patient or the patient's attendant should be instructed to collect faeces in a clean cardboard container (now disposable plastic containers are available) and to record the time of collection on the container.
Intestinal Nematodes
Nematodes belong to the Phylum Nematoda. They are non-separated, cylindrical worm that taper both the ends. They possess a shiny, tough, acellular, hyaline cuticle (skin) which may be smooth, spiral or ridged. Digestive system is complete. It consists of mouth, esophagus, intestine and anus. Sexes are separate (diecious). Male is smaller than female and its posterior end is curved ventrally. Both possess reproductive system. Females are either vivi-parous (produce larvae), oviparous (lay eggs) or ovoviviparous (lay eggs which hatch immediately).
Ascaris Lumbricoides
It is the commonest intestinal nematode of human. It exists in 2 forms—Adult and larvae. Adult round worms are the largest intestinal nematodes. Freshly expelled worms are pink and cylindrical. They may measure upto 40 cm in length and have tapering ends. The anterior end when examined with a hand lens, shows a mouth surrounded by three finely toothed lips. The adult worm lives for 1 to 2 years (Fig. 33.18).
Adult male measures 15-30 cm in length and 2-4 mm in diameter.The posterior end is curved and has 2 copulatory spicules.
Adult female measures 20-40 cm in length and have a diameter of 3-6. Their posterior end is straight and conical. The vulva lies at the junction of
anterior and middle thirds of the body. This part of the worm is narrow and called vulvar waist. A lumbricoides females are oviparous. The mature female produce upto 2 lakh eggs a day which passes with the faeces. The size of the egg is 60 mm × 40 mm. They may be fertilized or unfertilized.
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They are bile stained. The ovum is at the center of the fertilized egg having 2 clear spaces both sides. The egg shell is curved with albuminous coat called cortications. Eggs are resistant to drying but can be killed by sunlight.
Fertilized eggs develop[p in soil over 30 - 40 days and infect the human. Unfertilised eggs measure about 90 µm × 45 µm and are bile stained having an atrophic ovum.
Fig. 33.17: Egg of A. lumbricoides
Life Cycle
Humans are the only host to complete its life cycle. The infection form is the fully developed egg containing a larva (Embryonated eggs). Eggs hatch in small intestine to release larvae. These mobile larvae penetrate mucosa to interportal circulation and reach liver. After 3-4 days these larvae enter systemic circulation to reach the lungs. After 10-14 days of development in lungs, these larvae penetrate through the capillaries and enter alveoli. From here the larvae ascend the bronchial tree, trachea, larynx and pharynx. Larvae then crawl over epiglottis are swallowed to the GI system . They finally reach small intestine and grow into adult worm in 6-10 weeks. After mating, the female lays fertilized eggs and thus the cycle is repeated.
Fig. 33.18: Adult worm of A. lumbricoides
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Pathogenicity and Clinical Features
The disease is called ascariasis. The clinical signs and symptoms are both due to the adult worm and the migratory larvae. Due to migration of larvae to the lungs, patients develop cough (non-productive ) and dyspnea. There may be hemoptysis. Fever, Abdominal pain and urticaria develop in most of the patients. The larvae induce an eosinophilia response which is referred as Loeffler's pneumonia.
The adult worm may be asymptomatic when present in large numbers especially in children. A lumbricoides interferes with absorption of food. This may contribute to protein energy malnutrition and vitamin A deficiency. Sometimes they even produce life-threatening emergencies causing industrial obstruction. They may even produce appendicitis, cholecystitis, pancreatic and liver absesses. They can cause peritonitis, if they penetrate a typhoid ulcer. Adult worm may reach the esophogus and larynx and can cause asphyxia. Rarely, hypersensitivity to the antigen may occur. Fever, urticaria, angioneurotic edema, wheezing, and conjunctivitis can be seen in such patients.
Lab Diagnosis
Demonstration of Eggs.
Adult worm.
Peripheral smear for Eosinophilia.
X- ray, Barium study and USG.
Treatment
Mebendazole and Albendazole are effective. Pyrantel Palmoate, Piperazine Citrate are also effective.
Prevention
Proper sanitation, Washing of hands before eating food, Avoiding consumption of uncooked vegetables and fruits grown in soil.
ENTEROBIOUS VERMICULARIS
Enterobious vermicularis:- (Other names: Threadworm, Pinworm)
E. vermicularis is distributed worldwide. It is more prevalent in temperate climate.
Characteristic Features
E.vermicularis exists in two forms—adult and larvae. Adults habitate in Appendix, Caecum. The male worm measures 2 to 5 mm × 0.1 to 0.2 mm. It has a coiled tail with a single spicule. The female worm measures
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8 × 13 mm × 0.3 to 0.5 mm. The posterior thread of its body is pointed like a pin. The gravid worm has egg filled uteri occupying the entire body. The female E. Vermicularis worm in oviparous. Eggs are colorless (not bile stained). They are Plano-convex and measure about 55 µm × 30 µm. Eggs contain a larva.
Life Cycle
It has a simple life cycle. Humans are the only host. The infective form of E.Vermicularis is the embryonated egg. Transmission is faecooral. Eggs hatch in the intestine to release the larvae. The larvae develops into mature forms. The male fertilized female and dies. The female worm migrate around the anal region and lays upto 10,000 eggs. The larvae present in the eggs develop fully in 6 hours. Such mature eggs are infertile. E. vermicularis eggs can reinfect the same host (autoinfection) or infect a different host (Fig. 33.19). They migrate through the anus upto caecum to develop them.
The eggs on the perianal region contaminate the under garments and the bedding. These contaminated clothes can transmit the infection. The life cycle of E. Vermicularis completes in one month.
Fig. 33.19: Egg of E. vermicularis
Clinical Features
Perianal pruritis is the characteristic feature of Enterobiosis. Itching is worst at night. Excoriation and secondary bacterial infection may occur. In females they cause vulvovaginitis, salphingitis and pelvic or peritoneal granuloma. Another surgical complication of pin worm is appendicitis (acute or chronic).
Laboratory Diagnosis
1.Demonstration of eggs or adult worms in faeces.
2.Perianal swab can be used for demonstration of eggs.
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3.Eggs can otherwise be demonstrated by applying transparent cellophane tape in the perianal region which is subjected for microscopy.
4.NIH (National Institute of Health ) swab can be used for screening the eggs.
Treatment
Mebendazole, Pyrantal palmoate.
Household contacts should be screened and treated as well.
ANCYLOSTOMA DUODENALE
Ancylostoma Duodenale
Characteristic features: A. duodenale exist in 2 forms. Adult and Larval forms. Adults live in the small intestine (jejunum). They are reddish brown in color. A.duodenale is curved with concavity on the dorsal aspect. The anterior end is bent dorsally, hence the name Hookworm. The mouth of A.duodenale has 4 pointed teeth (2 on the dorsal side and 2 on the ventral side. Life span of an adult worm is about 6-8 years. The adult male measures 8 × 0.4 mm. Its posterior end has a conspicuous umbrella like copulatory bursa having 2 copulatory spicules. The bursa has 3 membranous lobes. These lobes supported by fleshy layers. The adult female measures 10 × 0.6 mm. The vulva opens ventrally at the junction of the middle and posterior thirds of the body. The female worm is oviparous and lays 10,000 eggs to 20,000 eggs per day that pass along the faeces. Eggs are oval and measure 60 × 40 Micro meters. They are colorless (not bile-stained) with a thin transparent hyaline shell membrane (Fig. 33.20). The ovum present inside is usually segmented with 4 blatomers. Freshly passed eggs are not infectious. Further development of eggs occurs in soil. These eggs hatch to produce rhabditiform larvae. The rhabditiform larvae develop into filariform larvae which is the infective form.
Fig. 33.20: Egg of A. duodenale
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Life Cycle
Human is the only host. The infective filariform larvae enters human by penetrating the skin especially in bear footed walkers.They invade the blood stream to reach lungs. In lungs they penetrate through the capillaries to reach alveoli. From here the larvae ascend the bronchial tree, trachea, larynx and pharynx. Then they crawl over the epiglottis and are swallowed with saliva. On reaching jejunum, they attach to the mucosa and grow into adults in 3-4 weeks. The eggs are passed in the feaces after 3-4 weeks and develop in the soil. Rhabditiform larvae hatch out from the eggs in about 48 hours. They moult twice to develop into the infection filariform larvae to complete the cycle.
Clinical Features
A duodenale cause ancyclostomiasis or hookworm diseases. Most hookworm infections are asymptomatic. Symptomatic infections are either due to larvae or adults. Larvae produce maculo-papular dermatitis (ground itch) at the site of the skin penetration. Larvae migrating through the lungs can sometime produce pneumonitis. This pulmonary disease (loeffler pneumonia) is rarely seen in hookworm disease. Adult worm may produce epigastric pain, diarrhoea and vomiting.
The most important and serious manifestation of hookworm infestation is microcytic hyphochromic anaemia (Iron deficiency anaemia). The adult worm sucks blood at the site of attachment in the intestine. A single worm sucks about 0.2 ml blood per day. Development of virus deficiency anaemia is related to the chronicity of the infections. Malnourished individuals also have hypoproteinemia.
Laboratory Diagnosis
1.Finding the eggs in the faeces.
2.Stool concentration methods like Format Ether and Zinc Floatation techniques can be used.
3.Peripheral smear and hemoglobin assay.
Treatment
Mebandazole, Pyrantel palmoate or albendazole can be used. Supplemental Iron to correct anemia.
Prevention and Control
Prevention of soil pollution with human faces. Adequate foot wear.
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TRICHIURIS TRICHIURA (WHIPWORM)
This worm is moist and warm climates.
Characteristic Features
It exists in 2 forms: adult and larvae. The adults live in caecum and appendix of human like E. vermicularis.
They are pinkish white and have a whip like shape. Hence called as whip worm. The anterior three - fifths is thin, elongated and coiled. The posterior two - fifths is thick and fleshly resembling the handle of a whip. The adult worm lives for several years. The male is 30-40mm long. Its posterior end is coiled ventrally and has a simple sheathed spicule. Adult female is 4050 mm long. The posterior end is blunt and round. The female worm is oviparous. They lay about 5000 eggs per day. The eggs are oval shaped and measure 50 mm × 25 mm in size (Fig. 33.21). Mucous plugs project from both the poles. The eggs are bile stained. When passed in faeces the eggs contain unsegmented ovum. At this stage they are not infertile to human. Development of eggs occur in soil. The infertile larvae develops within the egg in 3 - 4 weeks.
Fig. 33.21: Egg of Trichiuris trichiura
Life Cycle
Man is the only host. The infective form is the egg containing the larvae. Man gets infection by ingesting the embryonated eggs along with food and water. The eggs hatch in small intestine and grow into adult worm. They migrated to caecum and appendix. The fertilized female lays eggs that pass along with the faeces. The entire process of acquiring infection to passage of eggs takes 3 months.
Clinical Features
T. trichiura causes Trichiuriasis. Infections may result in abdominal pain, bloody diarrhea. T.trichiura can cause anemia, malnutrition and growth retardation. Appendicitis and rectal prolapse may occur rarely.
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Laboratory Diagnosis
Demonstration of characteristic Eggs with mucous plugs on both poles Demonstration of adult worm in faeces.
Treatment
Mebandazole or Albendazole.
STRONGYLOIDS STERCORALIS
S stercoralis infections seen world wide.
Characteristic Features
Strongyloids stercoralis exists in adult and larval form. Adult males are not demonstrated in the humans because they are eliminated from bowel by the time females live in the mucosa of the small intestine. They measure 2.5 mm × 0.04 to 0.05 mm. The female S. stercoralis worm is ovoviviparous. The eggs have a thin shell and measure about 55µm × 30µm. The eggs are laid in the tissues. A rhabditiform larvae hatches out immediately and move to the lumen of the intestine and passed with the faeces. They measure about 200 × 300 µm × 15µm. They are actively motile.
Life Cycle
Humans acquire Strongyloids following contact with faecally contaminated soil or by autoinfection. The infective form are the filariform larvae that penetrate intact skin or mucous membranes. After penetration, the larvae travel through the blood stream to the lungs, where they break into alveoli, ascend the bronchial tree, crawl over the epiglottis and are swallowed to reach the small intestine. Female lays eggs and the eggs hatch within the intestinal mucosa to release rhabdtiform larvae either passed with the faeces to the soil or develop into filariform larvae lead to auto infection by penetrating the mucosa or the perianal skin.
Rhabditiform larvae that have reached the soil can develop into 2 ways. They can mature into infective filariform larvae or develop into free living adult males and females.
The male fertilizes the female and eggs are laid in the soil. Rhabditiform larvae develop into filariform larvae and thus the cycle is repeated.
Clinical Features
Most cases of Strongyloidiasis are asymptomatic. Recurrent utricaria is the most common cutaneous manifestation. Migrating larvae (larva currens) produces a pruritic, raised, erythematous lessin that advances along the course of migration. Migrating larvae also produce hemorrhagic lesions in the lungs.