PROTOZOA AND HEMOFLAGELLATES

• Amebae or Amoeba


  Specifically referring to the parasitic protozoan Entamoeba histolytica, which causes amebiasis
• Amebiasis


  • Spectrum ranging from asymptomatic colonization to severe manifestations such as amebic colitis and life-threatening abscesses
  • Disease may occur months to years after exposure
  • Previously thought to infect 10% of the world's population, 2 morphologically identical but genetically distinct and apparently non pathogenic Entamoeba species are now recognized as causing most asymptomatic cases
• Parasitic amoebas


  Exemplified by Entamoeba histolytica, manifest as the primary agents responsible for amebiasis, a disease prevalent in tropical regions characterized by substandard sanitary conditions
• Infection


  Typically occurs via ingestion of contaminated food or water containing amoebic cysts, leading to a spectrum of symptoms ranging from mild diarrhea to severe abdominal pain and bloody stools, with potential complications including liver abscesses
• Diagnosis challenges


  • Due to morphological similarities between E. histolytica and other non-pathogenic amoebas, necessitating careful microscopic examination of stool samples for accurate identification
• Treatment


  Involves antimicrobial medications, such as metronidazole, to eradicate the parasite
• Prevention strategies


  Center on improving sanitation and hygiene practices, particularly in endemic areas, and advocating for safe water supply and food preparation techniques
• Common parasitic amoebas


  • Entamoeba histolytica
  • Entamoeba dispar
  • Entamoeba moshkovskii
• Entamoeba histolytica


  Causes most symptomatic diseases
• Entamoeba moshkovskii


  Pathogenicity is unclear
• Transmission


  Spread via the oral-fecal route, with infected cysts often found in contaminated food and water. Rare cases of sexual spread have also been reported
• Immune response to amoebic infection

  1. Involves both innate and adaptive immunity systems, with innate immunity being crucial to the rapid immune response triggered following parasite invasion

  2. Patterns of molecular recognition associated with pathogens (PAMPs) on E. Histolytica cause innate immune cells to generate chemokines and pro-inflammatory cytokines, which draw additional immune cells to the infection site

  3. Adaptive immunity is triggered to manage and eradicate the infection, with resistance against amoebic invasion mostly dependent on CD4+ T cells and the synthesis of antibodies, especially IgA
• Intestinal amoebiasis


  • The most common form of amoebiasis, which can cause abdominal pain, diarrhea (including bloody), flatulence, and weight loss
  • Once ingested, the cysts pass through the stomach and reach the small intestine, where they undergo excystation, releasing trophozoites
  • E. histolytica can infect individuals without causing symptoms, leading to asymptomatic colonization and the shedding of cysts in feces
  • Intestinal amoebiasis can progress to severe complications such as colitis or fulminant colitis, characterized by severe inflammation and ulceration of the colon
• Extra-intestinal amoebiasis


  E. histolytica can also cause extra-intestinal amoebiasis, such as hepatic amoebiasis which presents as an abscess in the liver, leading to symptoms such as right upper quadrant abdominal pain, fever, and hepatomegaly
• Invasive disease


  • In rare, severe cases, the parasite can invade the intestinal mucosa, leading to amoebic dysentery characterized by bloody diarrhea, abdominal cramps, and tenesmus, or even amoebic sepsis, a life-threatening condition associated with multi-organ failure
  • Entamoeba histolytica trophozoites invade the intestinal mucosa, causing tissue damage and inflammation. They can penetrate the mucosal layer, leading to ulceration and sometimes hemorrhage
• Asymptomatic colonization


  • Numerous factors, including the host's nutritional health, immunological system, and concurrent illnesses, might affect the disease symptoms of amoebiasis
  • Prevention of complications and reduction of amoebiasis-related morbidity and death are dependent on early diagnosis and adequate treatment
  • Entamoeba dispar, a morphologically similar species, colonizes the human gut but does not have invasive potential like Entamoeba histolytica and does not cause tissue invasion or spread to other organs
• Diagnosis and treatment


  1. Amoebiasis may be diagnosed when E. histolytica is seen in your stools (faeces) after a stool sample is sent to the laboratory and examined under a microscope

  2. If you have no symptoms but are found to have E. histolytica in a stool (faeces) specimen, it is usually advised that you should be treated with medication to kill the parasite

  3. The medicines diloxanide furoate and paromomycin are commonly used

  4. Treatment is advised because you can still pass on the infection to others even if you have no symptoms, and you may still develop symptoms at a later stage
• Giardia lamblia


  • Causes diarrheal disease worldwide, prevalent in developing countries and responsible for waterborne outbreaks in the US
  • Transmission occurs through contaminated water or food, and tourists are at risk in certain regions
  • Its life cycle involves cysts and trophozoites, with infection initiated by ingesting cysts
  • Trophozoites cause symptoms in the small intestine before forming cysts in the jejunum and excreting them in feces, completing the transmission cycle
  • Both cysts and trophozoites in feces are immediately infective, with cysts surviving for months in the environment
  • Trophozoites multiply in the small intestine and can live freely or attach to the mucosa, with encystation occurring as they move toward the colon, leading to cyst passage in feces
• Trichomonas vaginalis


  • A preventable and curable sexually transmitted protozoan that infects the urogenital tract
  • Although the majority of infections are asymptomatic, more than 50% of women with Trichomonas vaginalis infection have vaginal discharge and about 10% of men have urethritis
  • The parasite is transmitted during oral, vaginal and anal sex, and in some rare instances during delivery
  • Symptomatic women can have vaginal discharge (yellow in colour), which may appear purulent. Other symptoms include a red and sore vagina. The person with the infection can also feel pain during intercourse and urination
  • Trichomonas vaginalis is treatable and curable. People who suspect they may have trichomoniasis should speak to their healthcare provider. Treatment often requires metronidazole (first choice) or tinidazole administered orally
• Chilomastix mesnili


  • A non-pathogenic microorganism found in the gastrointestinal tract of primates, including humans
  • It typically resides in the cecum and colon and is commonly associated with but does not directly cause parasitic infections
  • Despite its non-pathogenic nature, C. mesnili can often be detected alongside other parasite infections
  • Its morphology includes two main life forms: trophozoites and cysts
  • Although non-pathogenic, C. mesnili can lead to misdiagnosis, potentially resulting in unnecessary or withheld treatment, due to its resemblance to other pathogenic species
• Enteromonas hominis


  • A flagellate present in the human gastrointestinal tract, often mentioned in conjunction with other intestinal flagellates such as Chilomastix mesnili and Trichomonas hominis
  • The cultivation of Enteromonas hominis from stool samples was achieved through a culture method, but the stained smears were insufficiently clear to confirm the diagnosis of the living forms within the culture
  • Cultivation of Enteromonas hominis was facilitated using a medium known as ovomucoid, previously utilized for the growth of other intestinal flagellates
• Retortamonas intestinalis


  Considered nonpathogenic, but its presence in stool specimens can be an indicator of fecal contamination of a food or water source, and thus does not rule-out other parasitic infections
• Dientamoeba fragilis


  • A flagellate protozoan parasite found in the human gastrointestinal tract
  • Despite historical controversy surrounding its life cycle and pathogenicity, numerous reports link it to human illness
  • First observed in 1909 and described in 1918, D. fragilis was initially thought to be an amoeba but later recognized as an ameboflagellate
  • Shares morphological similarities with Histomonas meleagridis, a parasite of turkeys
  • The discovery of its transmission via the eggs of Heterakis, a cecal worm of chickens and turkeys, shed light on its life cycle
  • Electron microscopy studies have further classified D. fragilis as an ameboflagellate closely related to Histomonas and Trichomonas spp.
• Zoological classification of flagellates

  • Phylum: Sarcomastigophora
  • Subphylum: Mastigophora
  • Class: Kinetoplastidea
  • Order: Trypanosomatida
  • Family: Trypanosomatidae
• Flagellates


  • Unicellular microorganisms and a part of the protozoa group, characterized by having one or more flagella, a hair-like whip organelle
  • There are many different types of flagellates, with two main categories being phytoflagellates and zooflagellates
  • Phytoflagellates are green and plant-like creatures that use photosynthesis to produce food, while zooflagellates are colorless and animal-like
  • Both phytoflagellates and zooflagellates can be found in ponds, lagoons, and even shallow puddles, but parasitic zooflagellates live inside the intestines or bloodstream of a host and can cause harmful diseases like giardiasis
• Phytoflagellates


  Have many characteristics in common with typical algae, some containing chlorophyll and various accessory pigments and having a photosynthetic type of nutrition, although many exhibit heterotrophy or mixotrophy
• Zooflagellates


  • Assimilate organic material by osmotrophy (absorption through the plasma membrane) or phagotrophy (engulfing prey in food vacuoles)
  • The zooflagellate's flexible pellicle is sufficiently thin in certain genera to permit pseudopodial projections
  • Zooflagellates exhibit a considerable variation in form, and they may be free-living, symbiotic, commensal, or parasitic in humans and other animals and in certain plants
• Phytoflagellates


  • Use photosynthesis to produce food
  • Can be found in ponds, lagoons, and shallow puddles
  • Thrive where there are large amounts of soluble food
• Zooflagellates


  • Colorless and animal-like
  • Can be free-living, symbiotic, commensal, or parasitic
  • Assimilate organic material by osmotrophy or phagotrophy
  • Have a flexible pellicle that permits pseudopodial projections
  • Exhibit considerable variation in form
• Parasitic zooflagellates


  • Live inside the intestines or bloodstream of a host
  • Can cause harmful diseases like giardiasis
• Phytoflagellates


  • Have many characteristics in common with typical algae
  • Some contain chlorophyll and accessory pigments, have photosynthetic nutrition
  • Some exhibit heterotrophy or mixotrophy
  • May obtain nutrients by photosynthesis, absorption, or ingestion of food particles
• Trypanosomes


  • Flagellated protozoa with one or more whip-like flagella
  • Crucial for their motility and navigation through bodily fluids and tissues
  • Have a complex life cycle involving both vertebrate hosts and invertebrate vectors
  • Many are bloodstream parasites dwelling primarily in the blood circulation of their hosts
• Trypanosomes exhibit remarkable variability in morphology, ranging from elongated and slender forms to more rounded and stumpy shapes
• Trypanosomes are responsible for several debilitating diseases in humans and animals, including African trypanosomiasis, Chagas disease, and nagana in livestock
• Trypanosomes


  • Employ sophisticated mechanisms of antigenic variation to evade the host immune response
  • Exhibit extensive genetic diversity, contributing to their ability to adapt to different host environments and evade drug treatments
• Diagnosis of trypanosome infections can be challenging due to their variable morphology, low parasitemia levels, and the need for specialized laboratory techniques
• Leishmania


  • A genus of parasitic protozoa causing leishmaniasis, a vector-borne disease transmitted by infected sandflies
  • Affects humans and animals, prevalent in tropical regions
  • Symptoms range from mild skin lesions to severe visceral or mucocutaneous manifestations, potentially fatal if untreated
  • Treatment involves anti-parasitic medications, with control measures targeting sandfly bites and improving access to diagnosis and treatment
• Malaria and babesiosis


  • Significant vector-borne diseases transmitted by different species of parasites
  • Malaria, caused by Plasmodium species and transmitted by Anopheles mosquitoes, is a global health concern
  • Babesiosis, caused by Babesia species and transmitted through the bite of infected ticks, poses a threat mainly in temperate regions
  • Both diseases require prompt diagnosis and treatment to prevent adverse outcomes
• Coccidia


  • Microscopic, spore-forming, single-celled parasites that infect the intestinal tracts of animals
  • Infection with these parasites, known as coccidiosis, can cause disease in humans and various animals
  • Most coccidia are species-specific, except for Toxoplasma gondii, which can infect all mammals
  • Infection typically occurs through consumption of undercooked meat or poor hygiene when handling cat waste
• Microsporidia


  • Unicellular, obligate intracellular, spore-forming eukaryotes classified among the protists
  • As parasites, they have been reported from every major group of animals from other protists to mammals and man
  • Economically and medically important, can be found in terrestrial, marine, and freshwater ecosystems
  • Consist of over 200 genera and approximately 1,300 species producing benign to lethal infections
  • All share the diagnostic and unique resistant spore, which contains a polar filament complex that begins the life cycle by injecting the spore contents into a host cell