Protozoa Dr. Fontanilla 25 Jan 2011

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1 Protozoa Dr. Fontanilla 25 Jan 2011 PROTOZOA - was once a phylum name - currently used colloquially as a common noun - refers to a number of phyla Protozoa consist of a single cell - many species contain more than one nucleus during all or portions of their life cycles. Protozoa like fungi, plants and animals are described as eukaryotes: the genetic material, DNA which is carried on well-defined chromosomes contained within a membranebound nucleus PARTS & STRUCTURES o Plasma membrane: like all cells, the bodies of protozoa are covered by plasma membrane o Pellicular microtubules: or fibrils may course beneath the plasma membrane kinetoplastid flagellates: microtubules underlie a flexible membrane. trypanosome and trichomonas: adjoining membranes have, a fibrous connection between them such as that Between the body and undulating membrane. o Mitochondria amoeba: branched tubular cristae flagellates: a single, large body ciliates: arranged as elongated sausageshaped structures o Golgi Apparatus (dictyosome) flagellates: large and/or multiple parabasal bodies in association with kinetosomes, the basal bodies o Locomotor Organelles Protozoa move by 3 basic types; 1. pseudopods (amoeba) 2. flagella (flagellates) 3. cilia (ciliates) * some amoebas possess both flagella and pseudopods transformation from flagellated to ameboid cell occurs in response to enviromental conditions and is a recognized life-cycle event Pseudopodia - temporary extensions of the cell membrane and are found in amoebas as well as in a variety of cell types - movement by means of pseudopodia is a complex form of protoplasmic streaming involving protrusion of the cell, adhesion to substrate and subsequent contraction. Cilia - structurally similar to flagella; with a kinetosome and an axoneme composed of two central and nine peripheral microtubules - appear to beat regularly, with a back-and-forth stroke in a two-dimensional plane Flagella (undulipodia) - slender whip like structures - composed of a central axoneme and an outer sheath that is a continuation of the cell membrane - the axoneme consists of nine peripheral and one central pair of microtubules. - The axoneme arises from a kinetosome (basal body) which is similar to centrioles of other eukaryotic cells - the flagellum may also be bent back along and loosely attached to the lateral cell surface forming a finlike undulating membrane (an adaptation in a viscous environment)

2 - a dark staining body, the kinetoplast found near the kinetosome ENCYSTMENT - Many protozoa can secrete a resistant covering and enter a resting stage cyst - Conditions favoring encystment involve some adverse environment events such as food deficiency, dessication, increased tonicity, decreased oxygen concentration or ph or temperature change. - During encystment, a cyst wall is secreted. - During excystation, there is return to a favorable environment. **in coccidians the cystic form is an oocyst which is formed after gamete union and in which multiple fission occurs (sporogony) with cytokinesis to produce sporozoites. Amoeba: temporary Ciliates: permanent; cytostome o Excretion: of indigestible material Ciliates: cytopyge CLASSIFICATION - Protozoa have been divided traditionally on the basis of their means of locomotion, although this character is no longer believed to represent genuine relationships: o Flagellates (e.g. Giardia lamblia) o Amoeboids (e.g. Entamoeba histolytica) o Sporozoans (e.g. Plasmodium) Apicomplexa Microsporidia o Ciliates (e.g. Balantidium coli) CILLIATES Phylum Ciliophora Subphylum Intramacronucleata Class Litostomatea Order Vestibulifera Genera: Balantidium Balantidium coli EPIDEMIOLOGY - Largest protozoan parasite of humans - Common in tropical zones; present throughout temperate climates also - Primarily a parasite of pigs; some strains adapted to other hosts including humans MORPHOLOGY: o Trophozoites: - oblong - 30 μm to 150 μm long x 25 μm to 120 μm wide o Cysts: - commonly found in stools - spheroid or ovoid - 40 μm to 60 μm in diameter FEEDING & METABOLISM - Protozoa lacking chloroplasts are all heterotrophic get energy from complex carbohydrates and nitrogen from amino acids o Mouth parts:

3 cyst trophozoite LIFE CYCLE o Habitat: - cecum and colon of humans and pigs and many other mammals - not readily transmissible from one species to another; require a period of time to adjust to flora of new host - when able to adapt, becomes a serious pathogen; especially when intestinal mucosa is previously damaged The host most often acquires the cyst through ingestion of contaminated food or water. Following ingestion, excystation occurs in the small intestine, and the trophozoites colonize the large intestine. The trophozoites reside in the lumen of the large intestine of humans and animals, where they replicate by binary fission, during which conjugation may occur. Trophozoites undergo encystation to produce infective cysts. Some trophozoites invade the wall of the colon and multiply. Some return to lumen and disintegrate. Mature cysts are passed with feces. o PATHOLOGY - Under ordinary conditions, trophozoites feed, ingesting particles through a vestibulum and cytostome - Sometimes produces a proteolytic enzyme that digests intestinal epithelium hyaluronidase - Ulcers produced are similar to amebic ulcers flask shaped Cysts are the parasite stage responsible for transmission of balantidiasis. Most cases of Balantidium coli infection are asymptomatic. If possible, asymptomatic individuals should still be treated in order to halt further transmission of the disease. Many people clear the infection spontaneously without treatment. Infected individuals usually respond well to treatment using one of the aforementioned regimens. If left untreated, Balantidiasis can become chronic. Persistent diarrhea can lead to high fluid loss and dehydration. Intestinal perforation or abdominal bleeding can lead to death. o TREATMENT & CONTROL

4 - DOC: tetracycline - Alternatives: metronidazole and iodoquinol - proper hygiene especially those handling hogs cyst trophozoite FLAGELLATES Phylum Retortamonada Class Retortamonadea Order Retortamonadida Genera: Chilomastix Retortamonas Class Diplomonadea Order Enteromonadida Genus: Enteromonas Order Diplomonadida Genus: Giardia Phylum Parabasalia Class Trichomonada Order Trichomonadida Genera: Monocercomonidae Dientamoeba Trichomonidae - Trichomonas Chilomastix mesnili EPIDEMILOGY - Occurs worldwide - Lives in the cecum and colon of humans, monkeys and pigs - Considered non-pathogenic, but often occurs with other parasites that are pathogenic - Transmission is by ingestion of cysts LIFE CYCLE MORPHOLOGY o Cyst: - Cyst stage occurs especially in formed stools - thick walled μm to 10.0 μm long and pear or lemon shaped - has a single nucleus o Trophozoite: - Pyriform in shape - Posterior end is drawn out into a blunt point - longitudinal spiral groove occurs in the surface of the body - the sunken cytosomal groove is prominent near the anterior end - four flagella, one longer than the others emerge from the anterior end - one flagellum is very short and delicate, curving back into the cytostome where it undulates - the large nucleus is located anteriorly The cyst stage is resistant to environmental pressures and is responsible for transmission of Chilomastix. Both cysts and trophozoites can be found in the feces (diagnostic stages). Infection occurs by the ingestion of cysts in contaminated water, food, or by the fecal-oral route (hands or fomites). In the large (and possibly small) intestine, excystation releases trophozoites. Chilomastix resides in the cecum and/or colon; it is generally considered a commensal whose contribution to pathogenesis is uncertain. Animals may serve as a reservoir for Chilomastix.

5 Retortamonas intestinalis EPIDEMIOLOGY - Retortamonas intestinalis is considered nonpathogenic. - The presence of trophozoites and/or cysts in stool specimens can however be an indicator of fecal contamination of a food or water source, and thus does not rule-out other parasitic infections. MORPHOLOGY o Cyst - ovoid or pyriform - measure 4-7 µm long by 3-5 µm wide. - Mature cysts contain a single nucleus, with a compact central karyosome and varying amounts of peripheral chromatin. - The fibril associated with the cytostome may be been seen in close proximity to the nucleus. o Trophozoite - ovoid or pyriform in shape - measure 4-10 µm long by 3-8 µm wide. - possess two flagella, one directed anteriorly and one extending posteriorly. - A cytostome is present at the anterior half of the trophozoite and is bordered by a fibril. - The single, spherical nucleus is located at the anterior end and contains a small karyosome and a fine layer of peripheral chromatin. Cyst trophozoite LIFE CYCLE Both cysts and trophozoites of Retortamonas intestinalis are shed in feces. (diagnostic stages) Infection occurs after the ingestion of cysts in fecal-contaminated food or water, or on fomites. In the large (and possibly small) intestine, excystation releases trophozoites. Retortamonas resides in the large intestine, where it is regarded as a commensal and is not known to cause disease. Giardia duodenalis ( Giardia lamblia / Giardia intestinalis) EPIDEMIOLOGY - Was first discovered in 1681 by Anton van Leeuwenhoek in his own stools - Cosmopolitan in distribution but mostly in warm climates - Most common flagellate of the digestive tract Causes Giardiasis is caused by the ingestion of infective cysts. Person-to-person transmission, often associated with poor hygiene and sanitation, is a primary means of infection.

6 Diaper changing and inadequate hand washing are risk factors for transmission from infected children. Children attending day care centers, as well as day care workers, have a higher risk of infection secondary to fecal-oral transmission. Water-borne transmission is responsible for a significant number of epidemics in the United States, Venereal transmission occurs through fecaloral contamination. Food-borne epidemics have been reported, most commonly secondary to contamination by infected food-handlers. Pets frequently harbor Giardia in their GI tracts, but they are not thought to be a significant cause of outbreaks in humans MORPHOLOGY o Cyst - cysts are oval to ellipsoid and measure 8-19 µm (average µm). - Mature cysts have 4 nuclei, while immature cysts have two. - Nuclei and fibrils are visible in both iodine-stained wet mounts and trichromestained smears. o Trophozoite - pear-shaped and measure micrometers in length - Rounded at the anterior end and pointed at the posterior end - dorsoventrally flattened and convex on the dorsal surface - the flattened ventral surface bears a concave, bilobed adhesive disc when applied to host cell responsible for the remarkable ability to adhere to host cells - Has 4 pairs of flagella anterior, posterior, ventral, caudal - has a pair of large, curved, transverse, dark-staining median bodies lies behind the adhesive disc; function is obscure - with 2 nuclei behind the lobes of the adhesive discs LIFE CYCLE Cysts are resistant forms and are responsible for transmission of giardiasis. Both cysts and trophozoites can be found in the feces (diagnostic stages). Infection occurs by the ingestion of cysts in contaminated water, food, or by the fecaloral route (hands or fomites).

7 in the small intestine, excystation releases trophozoites (each cyst produces two trophozoites). trophozoites multiply by longitudinal binary fission, remaining in the lumen of the proximal small bowel where they can be free or attached to the mucosa by a ventral sucking disk. Encystation occurs as the parasites transit toward the colon. The cyst is the stage found most commonly in nondiarrheal feces. Because the cysts are infectious when passed in the stool or shortly afterward, person-toperson transmission is possible. PATHOLOGY - Strains differ in pathogenicity and response to treatment - Many cases are asymptomatic - Some people are more sensitive than others - Some acquire protective immunity - The parasite does not lyse host cells but feeds on mucus secretions - A dense coating of parasites on the microvilli interferes with absorption of fat and other nutrients - The stool is fatty but never contains blood - In infected individuals, there is a marked increase in mucus production, diarrhea, dehydration, intestinal pain, flatulence, and weight loss TREATMENT & CONTROL - Treatment is not usually recommended for asymptomatic individuals. - However, treatment may be warranted to prevent the spread of infection if a patient is a household contact of a pregnant woman, an immunocompromised individual (especially in the setting of hypogammaglobulinemia), or a child in a day-care or other setting who might transmit infection to others - Quinacrine or metronidazole Dientamoeba fragilis MORPHOLOGY - Traditionally considered a member of the ameba family; but moves by pseudopodia instead of flagella - Only trophic stage exist - Size is from 12 μm in diameter - ectoplasm is somewhat differentiated from endoplasm - a single, broad pseudopodium is usually present - food vacuoles contain, bacteria, yeast, starch granules, and cellular debris - About 60 % contain 2 nuclei arrested telophase - the endosome is eccentric, sometime fragmented or peripheral in the nucleus -

8 LIFE CYCLE - it is found especially in tartar around the teeth or in defects of carious teeth. - Cannot survive passage through the digestive tract - Transmission is direct, by kissing or common use of eating or drinking utensils Lives in the large intestines, especially in the caecal area Feeds mainly on debris traditionally considered a harmless commensal but lately shown to cause diarrhea, abdominal pain and anal pruritus may be responsible for many unknown etiology of diarrhea probably transmitted by fecal-oral route and transmission via helminth eggs (e.g., Ascaris, Enterobius spp.) has been postulated TREATMENT - The drug of choice is iodoquinol. - Paromomycin,tetracycline, (contraindicated in children under age 8, pregnant and lactating women) or metronidazole can also be used. TRICHOMONADS Trichomonas tenax EPIDEMIOLOGY - World wide in distribution - protozoan that lives as a commensal in the mouth feeding on microorganisms and cellular debris MORPHOLOGY: - All species of trichomonas have only trophic stage - oblong in shape - 5 μm to 16 μm long by - 2 μm to 15 μm wide - there are 4 anterior flagella with a fifith flagellum curving back along the margin of an undulating membrane along its length Trichomonas vaginalis EPIDEMIOLOGY - Cosmopolitan in distribution - Found in the reproductive tracts of men and women - Higher prevalence among persons with multiple sexual partners or other venereal diseases. MORPHOLOGY - Trophozoites of Trichomonas vaginalis are pyriform and 7-30 µm long. - somewhat larger than Trichomonas tenax - They have five flagella: four anteriorly directed flagella and one posteriorly along the

9 outer membrane of the undulating membrane. - The large nucleus is usually located at the wider, anterior end and contains many chromatin granules and a small karyosome. - The cytoplasm also contains many granules, but these are often not seen in Giemsa-stained specimens. LIFE CYCLE Trichomonas vaginalis resides in the female lower genital tract and the male urethra and prostate, where it replicates by binary fission. The parasite does not appear to have a cyst form, and does not survive well in the external environment. Trichomonas vaginalis is transmitted among humans, its only known host, primarily by sexual intercourse. o PATHOGENESIS - Some strains are of low pathogenicity; asymptomatic individuals - Some strains cause intense inflammation with itching and a copious white discharge (leukorrhea) - in men infection is usually asymptomatic although there may be an irritating urethritis or prostatitis o TREATMENT - Treatment should be implemented under medical supervision, and should include all sexual partners of the infected persons. - The drugs of choice for treatment are metronidazole and tinidazole; - therapy is usually highly successful. Strains of Trichomonas vaginalis resistant to both drugs have been reported. Pentatrichomonas hominis EPIDEMIOLOGY - Next to Giardia duodenalis and Chilomastix mesnili it is the most common intestinal flagellate of humans - Pentatrichomonas hominis is considered nonpathogenic. - The presence of trophozoites in stool specimens can however be an indicator of fecal contamination of a food or water source, and thus does not rule-out other parasitic infections. MORPHOLOGY - Similar superficially to T. tenax and T. v - size is 8 μm to 20 μm by 3 μm to 14 μm - 5 anterior flagella are present in most specimens - The fifth flagellum originates and beats independently of the others

10 - a recurrent, 6 th flagellum continues as a long, free flagellum past the posterior end of the body Epimastigote - Basal body anterior of nucleus, with a long flagellum attached along the cell body. Trypomastigote - Basal body posterior of nucleus, with a long flagellum attached along the cell body. These names are derived from the Greek mastigmeaning whip, referring to the trypanosome's TRYPANOSOMA All trypanosomes are heteroxenous Heteroxenous: during one stage of their lives they live in the blood and/or fixed tissues of all vertebrate classes and during other stages they live in the intestines of bloodsucking invertebrates. They are called hemoflagellates: laboratory culture media usually must contain blood Various species pass through amastigote, promastigote, epimastigote and/or trypomastigote stages whip-like flagellum. Trypanosomes are divided into two broad groups, based on the characteristics of their development in the insect hosts Section Salivaria: the species develops in the anterior portion of the digestive tract of the insect host Section Stercoraria: the species develops in the vector s hindgut Amastigote - Basal body anterior of nucleus, with a short, essentially non-functional, flagellum. Promastigote - Basal body anterior of nucleus, with a long detached flagellum. Trypanosoma brucei (Section Salivaria) Trypanosoma brucei 3 subspecies; morphologically indistinguishable Trypanosoma brucei brucei Trypanosoma brucei gambiense Trypanosoma brucei rhodesiense

11 Tsetse flies are now restricted to continental Africa. About half of Africa is infested: some 10.4 million square kilometres in all. Trypanosoma brucei gambiense The etiologic agents of African Sleeping sickness - chronic form of sleeping sickness. - found in west central and central Africa - vector: G. palpalis and G. tachinoides which inhabit the riverine areas in western and central Africa - reservoir: found mostly in domestic pigs, cattle, and dogs, although there is evidence that antelopes in certain areas may also carry the parasite. - Man-fly-man transmission is hence more common in west and central Africa. Asymptomatic persons can carry the parasites in their blood for long periods and could be continuously infective for the vectors. The genus includes about 30 species and subspecies. Most of these are not associated with transmission of sleeping sickness, although many transmit animal trypanosomiasis to game and domestic livestock. Members of the genus Glossina are divided conveniently into three groups which are often given subgeneric status. These divisions are: (1) the fusca group (=subgenus Austenina), (2) the palpalis group (= subgenus Nemorhina) (3) the morsitans groups (= subgenus Glossina s.s.) Trypanosoma brucei brucei A blood stream parasite of native antelopes and other African ruminant Produces a disease called Nagana Humans are not susceptible Trypanosoma brucei rhodesiense acute form of sleeping sickness found in central and east central Africa vector: G. morsitans, G. palllidipes, G. swynnertoni -which inhabit the open savannah of eastern Africa reservoir: Wild game mammals (bushbuck, hartebeest, lion, hyena) as well as cattle the more virulent of the two, is thus maintained in the most resistant reservoirs, resulting in continuous selection of aggressive strains. During a blood meal on the mammalian host, an infected tsetse fly (genus Glossina) injects metacyclic trypomastigotes into skin tissue. The parasites enter the lymphatic system and pass into the bloodstream. Inside the host, they transform into bloodstream trypomastigotes, are carried to other sites throughout the body, reach other blood fluids (e.g., lymph, spinal fluid), and continue the replication by binary fission. The entire life cycle of African Trypanosomes is represented by extracellular stages. The tsetse fly becomes infected with bloodstream trypomastigotes when taking a blood meal on an infected mammalian host. In the fly s midgut, the parasites transform into procyclic trypomastigotes, multiply by binary fission, leave the midgut, and transform into epimastigotes.

12 The epimastigotes reach the fly s salivary glands and continue multiplication by binary fission. The cycle in the fly takes approximately 3 weeks. Humans are the main reservoir for Trypanosoma brucei gambiense, but this species can also be found in animals. Wild game animals are the main reservoir of T. b. rhodesiense. Domestic and wild cycles of Gambian and Rhodesian types of African sleeping sickness (A) in West Africa, riverine tsetse flies ( palpalis group) living in the bush transmit the Gambian forms to humans (man-fly cycle) and sometimes to domestic animals, particularly pigs. (B) In East Africa, morsitans group tsetse flies of the open savannah transmit the Rhodesian form to various mammals, mainly antelopes, and to humans. The Gambian cycle can result in an epidemic.

13 PATHOGENESIS Symptoms The clinical features of Gambian and Rhodesian disease are the same, however they vary in severity and duration. Rhodesian disease progresses more rapidly and the symptoms are often more pronounced. The symptoms of the two diseases are also more pronounced in Caucasians than in the local African population. Classically, the progression of African trypanosomiasis can be divided into three stages: 1. Bite reaction (chancre) - A non-pustular, painful, itchy chancre forms 1-3 weeks after the bite and lasts 1-2 weeks. It leaves no scar. 2. Parasitemia (blood and lymphoid tissues) - Parasitemia and lymph node invasion is marked by attacks of fever which starts 2-3 weeks after the bite and is accompanied by malaise, lassitude, insomnia headache and lymphadenopathy and edema. - Painful sensitivity of palms and ulnar region to pressure (Kerandel's sign) may develop in some Caucasians. - Very characteristic of Gambian disease is visible enlargement of the glands of the posterior cervical region (Winterbottom's sign). o Swollen nodes at the base of the skull o especially in the neck, groin and legs - Febrile episodes may last few months as in Rhodesian disease or several years as in Gambian disease. - Parasitemia is more prominent during the acute stage than during the recurrence episodes. 3. CNS stage - The late or CNS stage is marked by changes in character and personality. - lack of interest and disinclination to work, - avoidance of acquaintances, - morose and melancholic attitude alternating with exaltation, - mental retardation and lethargy, - low and tremulous speech, - tremors of tongue and limbs, - slow and shuffling gait, altered reflexes, etc. - Males become impotent. - There is a slow progressive involvement of cardiac tissue. - The later stages are characterized by drowsiness and uncontrollable urge to sleep. - The terminal stage is marked by wasting and emaciation. - Death results from coma, intercurrent infection or cardiac failure. African trypanosomes express a glycosylphosphatidyl inositol (GPI)-anchored variant-specific surface glycoprotein (VSG) as a protective coat. - During infection, large amounts of VSG molecules are released into the circulation. - Their interaction with various cells of the immune system underlies the severe infection-associated pathology. - Recent results have shown that anti-gpi vaccination can prevent the occurrence of this pathology. The surface of the trypanosome is covered by a dense coat of molecules of Variable Surface Glycoprotein (VSG). This coat enables an infecting T. brucei population to persistently evade the host's immune system, allowing chronic infection. The two properties of the VSG coat that allow immune evasion are: 1. Shielding - the dense nature of the VSG coat prevents the immune system of the mammalian host from accessing the plasma membrane or any other invariant surface epitopes (such as ion channels, transporters, receptors etc.) of the parasite. 2. Periodic antigenic variation - the VSG coat undergoes frequent genetic modification - 'switching' - allowing variants expressing a new VSG coat to escape the specific immune response raised against the previous coat.

14 Infectivity of Trypanosoma brucei rhodesiense to humans is due to its resistance to a lytic factor present in human serum. EPIDEMIOLOGY AND CONTROL Transmission of trypanosomiasis involves four interacting organisms: the human host, the insect vector (Glossina sp.) the pathogenic parasite and the domestic and wild animal reservoirs. Glossina sp. (Tsetse fly) - efficient vectors and are responsible for linking these organisms - any reduction of their numbers should lead to significantly reduced transmission and hence contribute to elimination and the sustainability of control efforts Current vector control interventions involve the use of insecticides either through 1. sequential aerosol spraying technique (SAT); 2. ground spraying 3. insecticide-treated targets or insecticidetreated animals live baits 4. use of traps 5. Sterile Insect Technique (SIT) - most efficient and cost-effective method Some of the interventions conducted in the past such as bush clearing (tsetse habitat destruction) or elimination of wild animals (tsetse reservoir hosts) have been discarded for ecological and environmental concerns Odor baited traps and screen impregnated with insecticide and appropriate attractive colours have been used in many countries to effectively suppress tsetse population by 99%. - These artificial bait methods are cheaper than ground and aerial spraying but communities and governments cannot deploy them on sustainable bases, as they are labor and management intensive. The Sterile Insect Technique (SIT) is another approach to reduce Tsetse fly population. - This technique is based on the fact that females mate only once in their lifetime, thus any mating with a sterile male will prevent females from giving birth to any offspring. - SIT consists in rearing a large numbers of laboratory male Tsetse flies which are irradiated and subsequently released in the wild to compete with wild (naturally occurring) males so that females inseminated by them produce no offspring. Trypanosoma cruzi (Section Stercoraria) Depending on its host environment, the organism occurs in three different forms. a. Trypanosomal (trypomastigote) form - found in mammalian blood, is 15 to 20 microns long and morphologically similar to African trypanosomes. b. Crithidial (epimastigote) form - found in the insect intestine. c. Leishmanial (amastigote) form - found intracellularly or in pseudocysts in mammalian viscera (particularly in

15 myocardium and brain), is round or oval in shape, measures 2-4 microns and lacks a prominent flagellum. American trypanosomiasis (Chagas disease) - widespread in the American Continent chiefly among small wild mammals (enzootic sylvatic cycle) - Human Chagas disease constitutes a more recent situation, in which bio-ecological and socioeconomic factors leave rural poor populations of South and Central America in contact with the sylvatic cycle, where the parasite is transmitted by natural vectors of the infection. - Public Health standpoint: the importance of Chagas disease remains correlated to this socalled "domestic" cycle, not only because millions of human beings are involved but also because all the available control measures are directed against it. - In endemic areas it is closely associated with typical "social" diseases such as: o malnutrition o diarrhea o tuberculosis o other parasitic disease - originally prevalent in Latin America - spread to other continents attributed to urbanization - most important mode of transmission of T. cruzi to humans and other mammals: ingestion of feces of infected triatomines - Vectors: Insects from order Hemiptera, family Reduviidae and subfamily Triatominae o colonize poorer quality rural houses, where colonies of hundreds of individuals o (or even thousands) can be found Other species: strictly inhabitants of different wild ecotopes and never invade houses, thus not representing any problem for the man - Between the two polar categories there is yet an important number of sylvatic species which leave their natural habitat and invade the domestic space and eventually transmit the parasite to man and/or domestic mammals. - ancient sylvatic cycle of Chagas disease involves the interaction between wild vectors and hosts in different natural ecotopes of American Continent o ecological balance between the parasite and its vectors or hosts - parasitism seems not to harm triatomines or wild reservoirs - Domestic cycle due to: o o human-vector contact, involving the colonization of artificial ecotypes by the invertebrate vector (triatomines) a series of social and ecological modifications in the environment parasitism can cause important damage in the vertebrate hosts, with high degrees of morbidity and mortality frequently detected among infected people - The interaction between domestic and sylvatic cycles occurs as a product of different factors, the majority of them dependent on human behavior. - Two good examples that demonstrate the influence of ecological and social factors in human Chagas disease are: a. Its absence among Indian populations in the forest of central Brazil, where wild infected vectors and mammalian hosts co-exist, but where the natural environment is preserved by native culture. b. absence of human cases (only 3 have been detected) in the USA, where the prevalent triatomines have a very small capacity to colonize dwellings and where the social process did not produce huts or

16 similar artificial ecotopes favorable to vector colonization. o A peridomestic cycle T. cruzi is accepted by some authors and constitutes an intermediate situation in which infected triatomines and domestic reservoirs circulate around human houses. - The Triatominae (kissing bug) o subfamily of Reduviidae (commonly known as assassin bugs) o suck vertebrate blood (strictly hematophagous) o o mainly restricted to the New World, in contrast to the other 30 or so reduviid subfamilies (over 6,000 described species) that prey on invertebrates and are distributed worldwide Within the subfamily, genera Triatoma, Rhodnius, and Panstrongylus contain species of bugs that are especially important vectors of Trypanosoma cruzi, the agent of Chagas disease in humans. Symptoms Chagas' disease can be divided into three stages: the primary lesion, the acute stage, and the chronic stage. - The primary lesion, chagoma, appearing at the site of infection, within a few hours of a bite, consists of a slightly raised, flat non-purulent erythematous plaque surrounded by a variable area of hard edema. - usually found on: o face o eyelids o cheek o lips o conjunctiva o but may also occur on the abdomen and limbs

17 - Primary chagoma on the face: o enlargement of the pre- and post- auricular and the submaxillary glands on the side of the bite - Infection in the eyelid -> unilateral conjunctivitis and orbital edema (Romaňa's sign) o is the most common finding Chronic Stage: Since most acute stage cases are asmptomatic and are left undiagnosed, ~10-20% of victims develop a chronic disease. They alternate between asymptomatic remission periods and relapses characterized by symptoms seen in the acute phase. o o o Cardiac arrhythmia COMMON Abnormal function of hollow organs heart esophagus colon Cardiac changes include: myocardial insufficiency cardiomegaly disturbances of atrio-ventricular conduction Adams-Stoke syndrome disturbances of peristalsis lead to megaesophagus and megacolon Acute Stage: 7-14 days after infection - characterized by o restlessness o sleeplessness o malaise o increasing exhaustion o chills o fever o bone and muscle pains o Other manifestations: cervical, axillary and iliac adenitis hepatomegaly erythematous rash acute myocarditis general edematous reaction associated with lymphadenopathy VERY FREQUENT: diffuse myocarditis, sometimes accompanied by serious pericarditis and endocarditis o in children: meningo-encephalitis coma o Death in 5-10 percent of infants o Hematologic examination reveals lymphocytosis and parasitemia Pathological effects of acute phase Chagas' disease result from direct damage to infected cells Destruction of the autonomic nerve ganglions significant sequelae in later stages

18 Immune mechanisms, both cell mediated and humoral, involving reaction contribute to pathogenesis T. cruzi stimulates both humoral and cell mediated immune responses. Antibody has been shown to lyze the organism, but rarely causes eradication of the organism, perhaps due to its intracellular localization. Cell mediated immunity may be of significant value. While normal macrophages are targeted by the organism for growth, activated macrophages can kill the organism. Unlike T. brucei, T. cruzi does not alter its antigenic coat. Antibodies directed against heart and muscle cells have also been detected in infected patients contributes to autoimmune reaction in the pathogenesis of Chagas' disease Infection causes severe depression of both cell mediated and humoral immune responses. Immunosuppression may be due to induction of suppressor T-cells and/or overstimulation of macrophages. DIAGNOSIS Demonstration of the causal agent -> diagnostic procedure in acute Chagas disease almost always yields positive results can be achieved by: Microscopic examination: a. of fresh anticoagulated blood, or its buffy coat, for motile parasites; and b. of thin and thick blood smears stained with Giemsa, for visualization of parasites. Isolation of the agent: a. inoculation in culture with specialized media (e.g. NNN, LIT); b. inoculation into mice; and c. xenodiagnosis, where uninfected triatomine bugs are fed on the patient's blood, and their gut contents examined for parasites 4 weeks later. TREATMENT The most effective drugs kill only extracellular protozoa Nifurtimox and Benznidazole - Somewhat effective in curing acute infections - Require long treatment duration - With significant side effects - Patients remain seropositive even after disappearance of parasites in the blood LEISHMANIA Like trypanosomes - heteroxenous - part of life cycle in sandflies promastigote - remainder of life cycle in vertebrate tissues - only amastigotes are found - known as Leishmania-Donovan (L-D) bodies Mammal most commonly affected: - humans, dogs and rodents ETIOLOGY Several species of Leishmania are pathogenic for man: L. donovani - visceral leishmaniasis (Kala-azar, black disease, dumdum fever) L. tropica (L. t. major, L. t. minor and L. ethiopica) - cutaneous leishmaniasis (oriental sore, Delhi ulcer, Aleppo, Delhi or Baghdad boil)

19 L. braziliensis (also, L. mexicana and L. peruviana) - etiologic agents of mucocutaneous leishmaniasis (espundia, Uta, chiclero ulcer) Cutaneous Leishmaniasis Caused by: - Leishmania tropica - Leishmania major Found in West Central Africa, the Middle East and Asia Minor into India These 2 different species are found in different localities and have different reservoir and intermediate hosts. Vector: - Sandflies of the genus Phlebotomus - intermediate hosts and vectors - When a fly takes blood meal containing amastigotes, parasites multiply in the midgut and then move to the pharyn - Sandfly saliva contain low molecular weight compound and peptides that serve as vasodilators and facilitate infection LIFE CYCLE Transmitted by the bite of infected female phlebotomine sandflies sandflies inject the infective stage (i.e. promastigotes) from their proboscis during blood meals Promastigotes phagocytized by macrophages and other types of mononuclear phagocytic cells. Progmastigotes transform in these cells into the tissue stage of the parasite (i.e. amastigotes), which multiply by simple division and proceed to infect other mononuclear phagocytic cells. Parasite, host, and other factors affect whether the infection becomes symptomatic and whether cutaneous or visceral leishmaniasis results. Sandflies become infected by ingesting infected cells during blood meals. In sandflies, amastigotes transform into promastigotes, develop in the gut - in the hindgut for leishmanial organisms in the Viannia subgenus - in the midgut for organisms in the Leishmania subgenus Promastigotes migrate to the proboscis.

20 Organism (L. tropica) multiplies locally producing of a papule, 1-2 weeks (or as long as 1-2 months) after the bite Papule gradually grows to form a relatively painless ulcer - center of the ulcer encrusts while satellite papules develop at the periphery - ulcer heals in 2-10 months, even if untreated but leaves a disfiguring scar Disease may disseminate in the case of depressed immune function. Sores can change in size and appearance over time. - often end up looking somewhat like a volcano, with a raised edge and central crater - scab covers some sores - can be painless or painful - Some people have swollen glands near the sores (for example, in the armpit if the sores are on the arm or hand). - short axoneme, the last of which is rarely visible by light microscopy Organisms reside in macrophages of the host and can be found throughout the body. Mucocutaneous Leishmaniasis Caused by Leishmania braziliensis - Produces a disease known as espundia, uta, mucocutaneous leishmaniasis - Found in vast area between central Mexico and northern Argentina Caused by Leishmania donovani - found in northwest Africa LIFE CYCLE AND PATHOGENESIS similar to L. Tropica except that the promastigotes reproduce in the hindgut of the sandfly DIAGNOSIS scrapings from the side of an ulcer smeared on a slide and stained with Wright s or Giemsa stain - will show parasites in endothelial cells and monocytes, even if they cannot be found in circulating blood Amastigotes of Leishmania are spherical to ovoid and measure 1-5 µm long by 1-2 µm wide. - possess a large nucleus - a prominent kinetoplast

21 VISCERAL LEISHMANIASIS PATHOGENESIS clinically L. donovani infections may range from asymptomatic to progressive progressive type: Fully-developed Kala-azar incubation period 2-4 months begins slowly with low grade fever and malaise followed by progressive wasting and anemia, protusion of the abdomen from enlarged liver and spleen finally death in 2-3 years the immediate cause of death often is invasion of secondary pathogen NOTE: THIS TRANS IS REALLY TEXTY BECAUSE DR. FONATNILLA S PPT IS ACTUALLY NOT IN SUMMARIZED FORM. MOST PARTS ARE IN PARAGRAPH (ESP THOSE SLIDE AT THE LATTER PART), WE TRIED TO CONDENSE SOME SECTIONS THOUGH WITHOUT DISTORTING THE IDEA. DOC ALSO SAID HER PART IN THE EXAM WILL BE COMING FROM HER POWERPOINT ONLY. Godbless to all! For I know the plans I have for you, declares the Lord, declares the Lord, plans for welfare and not for evil, to give you a future and a hope. Jeremiah 29:11 (ESV) May we all trust God even more this season, despite of our preparedness, or the lack of it. He is mighty to save! May God s peace be upon everyone! Chill and relax lang!

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