Protozoans (blood And Tissue Flagellates)

BLOOD AND TISSUE FLAGELLATES Trypanosoma cruzi  The etiologic agent of Chagas disease or American trypanosomiasis.  Carlos Chagas  intracellular parasite, w/ myocytes (particularly myocardial tissues) and cells of the RES being the most heavily infected cells.  Other tissues infected: skin, gonads, interstitial mucosa, and placenta.  reduviid bugs (Triatoma, Panstrongylus, and Rhodnius) vectors  Four stages of development: 1.Amastigote 2.Promastigote 3.Epimastigote 4.Trypomastigote  In humans: ® trypomastigotes - bloodstream ® amastigotes - tissue cells.  Vectors: ® amastigote, epimastigote, and promastigote – midgut; ® metacyclic trypomastigote appear - hindgut  stained specimens: trypomastigotes (C-shaped, U- or S-shaped w/ a prominent kinetoplast)  trypomastigote of T. cruzi do not multiply in the bloodstream

of inoculation.  Chagomas, furuncle-like lesions  Romańa’s sign - conjunctiva  Rarely, acute infection à inflammation of the heart muscle or the brain and lining around the brain.  Following the acute phase, most infected people enter into a prolonged asymptomatic form of disease (called "chronic indeterminate") during which few or no parasites are found in the blood.  Complications of chronic Chagas disease:  heart rhythm abnormalities à sudden death  a dilated heart that doesn’t pump blood well;  dilated esophagus or colon à difficulties with eating or passing stool.  People w/ suppressed immune systems (AIDS or chemotherapy), Chagas disease can reactivate with parasites found in the circulating blood.

Diagnosis  Thick and thin blood smears - acute phase of infection  CSF, tissue samples, or lymph  only in the first two months of acute disease can T. cruzi trypomastigotes be seen in film.  concentration methods (microhematocrit), blood culture and PCR  2 diff serologic tests (WHO recommendation)

Treatment  nifurtimox and benznidazole à severe side effects  Other drugs: allopurinol, itraconazole – side effects – progression to cardiomyopathy  Newer drugs: triazole derivatives and cruzipain inhibitors - currently under development Prevention and Control  Vector control and blood transfusion regulations  Spraying of insecticide  use of insecticide-treated bed nets  house improvements to prevent vector infestations Trypanosoma brucei gambiense Trypanosoma brucei rhodesiense Mode of Transmission     

Bite of infected vector blood transfusions organ transplantation Transplacentally laboratory accidents

Pathogenesis  Chagas disease: acute and chronic phase - focal or diffuse inflammation of the myocardium. - Cutaneous manifestations w/ a localized inflammatory reaction at or near the site

 Human African trypanosomiasis (HAT) - African sleeping sickness, a highly fatal disease.  3rd spp. T. brucei brucei - affects wild and domestic animals  MOT: bite of the blood-sucking tsetse fly (Glossina spp.) feeding from an infected mammalian host, mechanical methods (accidental needle pricks, other blood-sucking insects), mother-to-child infection through the placenta T. brucei gambiense  Western and central regions of sub-Saharan Africa  Primarily affects humans; dogs, pigs, and sheep - reservoir hosts.  chronic type of sleeping sickness; 95% of all HAT cases. T. Brucei rhodesiense

 East Africa  primarily a zoonosis of cattle and wild animals; humans accidental hosts  acute and rapidly fatal form of sleeping sickness; accounts 5% of HAT cases.  Only the epimastigote and trypomastigote forms - T. brucei complex Trypomastigote:  Polymorphic, either typical slender forms, and short, stumpy forms; flattened and fusiform in shape, 14 – 33mm in length by 1.5 – 3.5 mm in width.  body tapers anteriorly and is blunt posteriorly  centrally located nucleus contains a large central karyosome  Presence of undulating membrane, single flagellum that runs along the edge of the undulating membrane and becomes free anteriorly.

Life Cycle  follows the same pattern w/ T. cruzi.  In humans, T. brucei lives in the blood, in the reticular tissue of lymph and spleen, and the CSF.  trypomastigotes multiply by longitudinal binary fission

Pathogenesis  T. b. gambiense sleeping sickness - months or years after initial infection.  T. b. rhodesiense sleeping sickness - weeks after infection.  initial lesion begins w/ a local, painful, pruritic, erythematous chancre located at the bite site, progressing into a central eschar, and resolving after 2 to3 weeks.  This trypanosomal chancre is more common in Gambian sleeping sickness.  Gambian trypanosomiasis - posterior cervical lymph nodes are enlarged, non-tender, and rubbery in consistency (Winterbottom’s sign).  after 1-2 years - evidence of central nervous system involvement, with personality changes, daytime sleepiness with nighttime sleep disturbance, and progressive confusion  Other neurologic signs, such as partial paralysis or problems with balance or walking may occur, as well as hormonal imbalances.  T. b. rhodesiense infection (East African sleeping sickness) progresses rapidly.  In some patients, a large sore (a chancre) will develop at the site of the tsetse bite.  fever, headache, muscle and joint aches, and enlarged lymph nodes within 1-2 weeks of the infective bite  Some people develop a rash.  After a few weeks of infection, CNS involvement à mental deterioration and other neurologic problems.  Death ensues usually within months.

Diagnosis  body fluid or tissue microscopy  parasite load in T. b. rhodesiense infection is substantially higher than the level in T. b. gambiense infection.

 T. b. rhodesiense parasites - found in blood, lymph node fluid or in fluid or biopsy of a chancre.  Serologic testing - not used, since microscopic detection is straightforward.  microscopic examination of lymph node aspirate from a posterior cervical node.  often difficult to detect T. b. gambiense in blood  Concentration techniques and serial examinations  All patients diagnosed with African trypanosomiasis must have their cerebrospinal fluid examined to determine whether there is involvement of the central nervous system, since the choice of treatment drug(s) will depend on the disease stage.  WHO criteria for central nervous system involvement include increased protein in cerebrospinal fluid and a white cell count of more than 5.  Trypanosomes can often be observed in cerebrospinal fluid in persons with second stage infection.

Treatment  Pentamidine - T. b. gambiense infection  other drugs (suramin, melarsoprol, eflornithine, and nifurtimox) used to treat African trypanosomiasis are available in the U.S. only from the CDC.  Once CNS involvement occurs, intravenous melarsoprol is the drug of choice for both types sleeping sickness.  A second-line drug, nitrofurazone, is used, in cases of melarsoprol treatment failure.  Tsetse flies live near the banks of rivers and streams,  Cattle and game animals such as antelopes - reservoir hosts

Prevention and Control  no vaccine or drug for prophylaxis against African trypanosomiasis.  minimizing contact with tsetse flies  Other helpful measures include: 1.Wear long-sleeved shirts and pants of medium-weight material in neutral colors that blend with the background environment. **Tsetse flies are attracted to bright or dark colors, and they can bite through lightweight clothing.** 2.Inspect vehicles before entering - flies are attracted to the motion and dust from moving vehicles 3.Avoid bushes - tsetse fly is less active during the hottest part of the day but will bite if disturbed. 4.Use insect repellent - Permethrin-impregnated clothing and insect repellent have not been proved to be particularly effective against tsetse flies, but they will prevent other insect bites that can cause illness.  Control of African trypanosomiasis rests on two strategies: reducing the disease reservoir and controlling the tsetse fly vector.  Because humans are the significant disease reservoir for T. b. gambiense, the main control strategy is active case-finding through population screening, followed by treatment of the infected persons that are identified.  Tsetse fly traps - sometimes used as an adjunct

 Reducing the reservoir of infection is more difficult for T. b. rhodesiense, since there are a variety of animal hosts.  Vector control is the primary strategy in use - done with traps or screens, in combination with insecticides and odors that attract the flies

Leishmania

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 Leishmaniasis - found in parts of the tropics, subtropics, and southern Europe.  classified as a Neglected Tropical Disease (NTD).  caused by infection with Leishmania parasites spread by the bite of Phlebotomine sand flies Forms:  cutaneous leishmaniasis - causes skin sores  visceral leishmaniasis - affects several internal organs (usually spleen, liver, and bone marrow).  sandflies Phlebotomus (Old World) and Lutzomyia (New World) - insect vector  Dogs - primary reservoir in urban areas; rodents - reservoirs of both urban and rural areas.  Leishmania spp. produces amastigotes intracellularly in the mammalian hosts, and promastigotes in the hindgut, midgut, and proboscis of the insect vectors.

2. Diffuse cutaneous leishmaniasis (DCL) 3. Mucocutaneous leishmaniasis (MCL) 4.Visceral leishmaniasis (VL)  symptoms manifested is often compared to leprosy, where the localized CL is similar to tuberculoid leprosy, and DCL is similar to lepromatous leprosy.  The immune response of the host against the infection depends on Leishmania-specific Th1-type CD4+ T-cells, macrophages, and cytokines  other factors: genetics, nutritional status, and environmental factors may affect the outcome of infection.

Cutaneous Leishmaniasis  The most common form of the disease; caused by:  L. tropica – dry or urban oriental sore  L. major – moist or rural oriental sore  L. mexicana – chiclero ulcer, usually affecting the ears.  incubation period - 2 weeks to several months.  erythematous papule or nodule, called an “ oriental button” produced at the inoculation site ® lesion is raised edges and a central crater ® papule forms a violaceous ulcer as it enlarges in size  The lesion may heal spontaneously after a few months, leading to disfiguring scar.

Diffuse Cutaneous Leishmaniasis Causal agent  21 of 30 species that infect mammals.  L. donovani complex with 2 species (L. donovani, L. infantum [also known as L. chagasi in the New World])  L. mexicana complex with 3 main species (L. mexicana, L. amazonensis, and L. venezuelensis)  L. tropica; L. major; L. aethiopica; and the subgenus Viannia with 4 main species (L. (V.) braziliensis, L. (V.) guyanensis, L. (V.) panamensis, and L. (V.) peruviana).  The different species are morphologically indistinguishable, but they can be differentiated by isoenzyme analysis, molecular methods, or monoclonal antibodies.

 Also called anergic or lepromatous leishmaniasis, ® characterized by a localized, non-ulcerating papule, eventually developing numerous diffuse satellite lesions that affect the face and extremities.  This type of leishmaniasis may be initially diagnosed as lepromatous leprosy.

Mucocutaneous Leishmaniasis  Results in person infected w/ L. braziliense.  Involvement of the mucous membranes of the nasal and oral cavities results in nasal stiffness, discharge, epistaxis, and destruction of the nasal septum.  This disfiguration is often called espundia.  Progression into the pharynx and larynx may threaten the airway passage, and may lead to dysphonia, dysphagia, and even aspiration pneumonia.

Visceral Leishmaniasis  Known as Kala azar  disseminated parasitosis primarily caused by L. donovani complex: L. donovani, L. chagasi, and L. infantum.  affects several internal organs (usually spleen, liver, and bone marrow) and can be life threatening.  The illness typically develops within months (sometimes as long as years) of the sand fly bite.  fever, weight loss, enlargement (swelling) of the spleen and liver, and low blood counts—a low red blood cell count (anemia), a low white blood cell count (leukopenia), and a low platelet count (thrombocytopenia).

Pathogenesis 4 categories of leishmaniasis: 1. Cutaneous leishmaniasis (CL)

Diagnosis

 microscopic demonstration of Leishmania from lesion and tissue scraping, aspirates, or biopsy.  Giemsa and H & E stains are often used in microscopic and histologic samples, and the demonstration of amastigotes confirms the diagnosis of leishmaniasis.  leishmania skin test (Montenegro skin test) - exposure to the parasite; it is usually positive in cases of CL and MCL, but is negative in cases of DCL and Kala azar.  Immunologic assays: ELISA and rk39 antigen dipstick test - high sensitivity and specificity for VL in certain immunocompetent patients populations  Direct agglutination, urine antigen assays, and newer techniques such as flow cytometry and molecular diagnostic modalities (PCR, RFLP analysis) are also being used.  The PCR RFLP analysis may be used to identify the species of Leishmania.

Treatment  Antimony compounds – primary pharmacologic treatment.  Amphotericin B – is the drug of choice in cases of failure using antimony compounds.

Prevention and Control  No vaccines or drugs to prevent infection are available.  The best way for travelers to prevent infection is to protect themselves from sand fly bites.  To decrease the risk of being bitten, follow these preventive measures:  Avoid outdoor activities, especially from dusk to dawn, when sand flies generally are the most active. When outdoors (or in unprotected quarters):  Minimize the amount of exposed (uncovered) skin.  To the extent that is tolerable in the climate, wear longsleeved shirts, long pants, and socks; and tuck your shirt into your pants.  Apply insect repellent to exposed skin and under the ends of sleeves and pant legs.  Follow the instructions on the label of the repellent.  The most effective repellents generally are those that contain the chemical DEET (N,N-diethylmetatoluamide). When indoors:  Stay in well-screened or air-conditioned areas.  Keep in mind that sand flies are much smaller than mosquitoes and therefore can get through smaller holes.  Spray living/sleeping areas with an insecticide to kill insects.  If you are not sleeping in a well-screened or airconditioned area, use a bed net and tuck it under your mattress.  If possible, use a bed net that has been soaked in or sprayed with a pyrethroid-containing insecticide.  The same treatment can be applied to screens, curtains, sheets, and clothing (clothing should be retreated after five washings).  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), and migrate to the proboscis