Coccidians

• Coccidians


  • Live intracellularly
  • Possess a structure called the APICAL COMPLEX, by means of which they attach to and penetrate host cells
• Phases of coccidians


  • Sexual sporogonic phase
  • Asexual schizogonic phase
• Many parasites in this group have acquired great prominence due to their frequent association with HIV infection
• Forms of Toxoplasma gondii

  • Trophozoite/ Tachyzoites
  • Tissue cyst
  • Oocyst

  
• Trophozoites/ Tachyzoites


  • Crescent-shaped, with one end pointed and the other end rounded
  • Stains well with Giemsa, cytoplasm appearing azure blue and the nucleus red

  
• Endogony (internal budding)


  1. Invade any nucleated cell and replicate within cytoplasmic vacuoles

  2. Two daughter trophozoites are formed
• Tachyzoites


  Rapidly proliferating trophozoites in acute infection
• Tissue cyst


  • Resting form
  • Chronic stage
  • Brain (MC site), skeletal muscles and various other organs
• Bradyzoites


  Slowly multiplying parasites within the tissue cyst
• Oocyst


  • Develop only in definitive hosts
  • Oval
  • Surrounded by thick resistant wall
• Oocyst sporulation


  In the soil with formation of two sporocysts, each containing four sporozoites
• Hosts


  • Definitive hosts: Cats and other felines, in which both sexual and asexual cycles take place
  • Intermediate hosts: Man and other mammals, in which only the asexual cycle takes place
• Toxoplasma gondii infection is asymptomatic
• Clinical manifestations


  Become apparent when the immune system is suppressed (old age, drug-induced immunosuppression after organ transplantation, AIDS)
• Common manifestations in immunocompromised patients

  • Encephalitis
  • Retinochoroiditis, lymphoreticular hyperplasia with enlargement of posterior cervical LN, hepatitis, splenomegaly, pneumonia, extramedullary hematopoiesis, failure to gain weight
• Congenital toxoplasmosis


  • Stillbirth and abortion
  • Chorioretinitis, epileptic seizures, jaundice, hydrocephaly, microcephaly
  • Death of infected newborn babies is usually due to anemia with pneumonia
• Toxoplasma diagnosis


  • Examination of tissue imprints stained with Giemsa
  • Tissue sections can be processed and stained with hematoxylin and eosin
  • Serodiagnostic methods – detect antibodies against T. gondii
  • Seroconversion to a positive titer or a four-fold increase in titers
  • Sabin-Feldman methylene blue dye test
• Sabin-Feldman methylene blue dye test


  • Very sensitive and specific but requires maintenance of live organisms in the laboratory
  • Based on specific inhibition of the staining of trophozoites by alkaline methylene blue dye
• Other Toxoplasma tests


  • Indirect hemagglutination test
  • Indirect fluorescent antibody test
  • Enzyme linked immunosorbent assay
  • PCR
• Cryptosporidium hominis


  Formerly known as C. parvum anthroponotic genotype or genotype 1
• Cryptosporidium hominis in immunocompetent host

  • Self-limiting diarrhea for 2-3 weeks
  • Abdominal pain, anorexia, fever, nausea, weight loss
• Cryptosporidium hominis in immunocompromised host


  • Severe, progressive, and may become life-threatening diarrhea
  • Bile duct and gallbladder may become heavily infected → acute and gangrenous cholecystitis
  • Respiratory infections → chronic coughing, dyspnea, bronchiolitis, pneumonia
• Intestinal villi blunted, leading to malabsorption and excessive fluid loss. Death in disseminated infections.
• Cryptosporidium diagnosis


  • Sheather's sugar flotation
  • Formalin ether/ ethyl acetate concentration technique
  • Kinyoun's modified acid fast stain
• Other Cryptosporidium specimens


  • Intestinal biopsy material
  • Sputum
  • Transbronchial and bronchoalveolar lavage
• Cyclospora cayetanensis


  • First thought to be member of cyanobacteria (originally called a cyanobacterium-like body)
  • Photosynthesizing organelles
  • Autofluorescing particles characteristic of blue green algae
• Cyclospora cayetanensis symptoms


  • Initial symptoms: malaise, low grade fever (12-24 hrs after exposure)
  • Chronic and intermittent watery diarrhea
  • Alternating constipation
  • Other symptoms: fatigue, anorexia, weight loss, nausea, vomiting, abdominal pain, flatulence, bloating and dyspnea
• Cyclospora diagnosis


  • Direct microscopic examination of fecal smears under high magnification
  • Concentration techniques
  • Acid fast-staining (Kinyoun's stain)
  • Safranin staining and microwae heating
  • PCR (differentiate Cyclospora from closely related Eimeria species)
• Cytoisospora belli in immunocompetent host

  • Asymptomatic or may present as a self-limiting gastroenteritis
  • Severe diarrhea, fat malabsorption may occur in severe infection
  • Low-grade fever, anorexia, vomiting, general body malaise, weight loss, flatulence
  • Stools usually contain undigested food, mucus, Charcot-Leyden crystals
• Cytoisospora belli in immunocompromised host

  • Self-limiting enteritis to severe diarrheal illness resembling cryptosporidiosis, giardiasis, cyclosporiasis
  • Mucosal bowel biopsy: flattened mucosa, damaged villi
  • Lamina propria with lymphocytes, plasma cells, eosinophils
• Cytoisospora belli diagnosis


  • Demonstration of oocyts in the feces by direct microscopy or formalin ether/ ethyl actetate concentration
  • Zinc sulfate
  • Sugar flotation
  • Modified Ziehl-Neelsen method (granular red color against green background)
  • Phenol-auramine staining
  • Iodine staining
  • Acid fast stain (Kinyoun's stain, auramine-rhodamine stain)