lecture 15- Protozoa, toxoplasma and cryptosporidium Flashcards
where was toxoplasma first isolated from?
an African desert rodent Ctenofactylus gundi
what are some characteristics of Toxoplasma gondii?
- one of the most common human infections found throughout the world
- obligate intracellular parasites
- has a very low intermediate host specificity and will probably infect almost any mammal
- has also been reported in birds, and most recently in fish
- infects almost all tissues
- causes the disease, toxoplasmosis
- in most healthy humans, the disease is asymptomatic
where is toxoplasma gondii found the most?
higher prevalence in central america
what animal is toxoplasma gondii most frequently found in?
stray cats
how is one infected by toxoplasma gondii?
consumption of raw or undercooked meat that has been contaminated by the parasite
what is the economic impact of toxoplasma gondii?
devastating economic impact on the countries who export livestock.
leading cause of abortion in sheep and goats.
cattle are less affected.
what are the 2 hosts involved in the cycle of T. gondii?
- the definitive host= domestic and wild cats
- the intermediate host= most species of warm-blooded animals including birds, mice, squirrels, rabbits, cattle, pigs, sheep, and humans
what are the two phases of T. gondii life cycle?
- the intestinal phase
- the extra-intestinal phase
the intestinal phase occurs in cats only
the extra-intestinal phase occurs in all infected animals
how are cats infected by T. gondii?
- eating oocyst in cat feces or:
2. eating intermediate host (bird or mouse) containing bradyzoites
oocysts, sporozoites, and bradyzoites penetrate the…
small intestinal cell and develop into trophozoites that then undergo schizogony and develop into merozoites which re-invade the small intestinal cell and turn into gametocytes
toxoplasmosis is commonly transmitted from … to …
cats to humans
what type of reproduction does the parasite undergo in the intermediate/reservoir host?
asexual reproduction
what are the three infective forms of toxoplasma gondii?
- oocysts
- tachyzoites
- bradyzoites (tissue cysts)
where are oocysts shed?
in the feces of the cat
how long do infected cats shed oocysts for?
1-2 weeks
how long is it until oocysts are infective after being shed from the cat?
oocysts sporulate and only become infective after 1-5 days
the oocyst contains…
two sporocysts, each of which contain four sporozoites
what is the potential of oocyst survival?
have the potential to remain viable for many years
what is the significance of tachyzoites?
- mark the acute phase of infection
- invade all nucleated cells and occur in groups
- rapid multiplication and cell lyses
- rapidly growing stage observed in the early stage of infection
what are bradyzoites?
slowly growing trophozoites that are in tissue cysts.
They occur as a circular mass in body cells
what is the significance of bradyzoites?
they mark the chronic phase of infection, are resistant to low pH and digestive enzymes during stomach passage, and released into the intestine and are highly infective if ingested
what are ways humans can become infected with T. gondii?
- eating raw or undercooked meat of animals harboring tissue cysts
- consuming food or water contaminated with oocysts from cat feces or by contaminated environmental samples
- blood transfusion or organ transplantation (both rare)
- transplacentally from mother to fetus
prevention of T. gondii:
- wash hands and countertop thoroughly after preparing raw meat and fish
- thoroughly cook meat
- wash and/or peel fruits and vegetables
- clean litter box daily
- feed cat commercial dry food, never raw meat
- cover outdoor sandboxes
toxoplasmosis in cats
asymptomatic in adult cats. acute infections result in numerous intestinal lesions that can kill kittens (rare)
toxoplasmosis in humans
the clinical course is benign and self-limited; symptoms usually resolve within a few months to a year
mild fever, sore muscles swollen glands and lymph nodes
when is the fetus at risk for T. gondii infection?
if the mother acquires the infection for the first-time during gestation.
only if a woman receives her first exposure to toxoplasmosis while pregnant, is the fetus at risk
what are the effects of congenital toxoplasmosis on the fetus?
- abortion
- stillborn
- severely handicapped mentally and/or physically
the risk of infecting the fetus is related to the …
gestation at which it is acquired
the risk of passing the infection to the unborn baby is greatest in …
the third trimester, at 60-70%
common defects of congenital toxoplasmosis:
- chorioretinitis
- intra-cerebral calcifications
- hydrocephaly /microcephaly
what is the least common lesion in congential taxoplasmosis?
hydrocephalus
what is the most common disease from congenital toxoplasmosis?
ocular disease
diagnosis of T. gondii
- serological testing - ELISA tests
measure IgG and IgM levels - amniotic/spinal fluid isolation and culture of parasite
- direct detection by microscopy and PCR
what is the most reliable serological testing method for T. gondii?
Sabin-Feldman dye test
when is treatment recommended for T. gondii?
for people with serious health problems (HIV, immunocompromised)
what are the medications prescribed for T. gondii?
- pyrimethamine
- sulfadiazine
- spiramycin
- clindamycin
How does T. gondii alter the behavior of its rodent host?
alter the behavior such that mice have no reaction to areas where there is cat urine. Loss of fear toward cat urine. Normally, healthy mice avoid these areas
observations of T. gondii behavior change support …
manipulation hypothesis
what is cryptosporidium?
a zoonotic protozoan parasite (apicomplexan)
what organ does cryptosporidium primarily infect?
the small intestine
what disease does cryptosporidium cause?
cryptosporidiosis
what are outbreaks of cryptosporidium associated with?
drinking water, food, swimming pools and lakes, hospitals, HIV/AIDS wards, pediatric hospitals
distribution of cryptosporidium
prevalence lower in developed countries, and higher in developing countries
what is the infective stage of cryptosporidium?
oocysts - in the environment
what is the vegetative stage of cryptosporidium?
sporozoites
how is cryptosporidium transmitted?
fecal-oral route via the oocyst stage
cryptosporidium transmission increases with:
- person-to-person contacts
- person-to-animal contacts
- water/food borne
- using water for drinking or recreational purposes
cryptosporidium- groups at risk
- workers
- vets
- farmers
- medical personnel
- day care centers - social factors
- family
- children (day care)
- pet owners
- travelers
- drinking non-filtered water - immunodeficient
symptoms of cryptosporidium
stomach cramps, pain, watery diarrhea, dehydration, weight loss, vomiting, fever
how long are immuno-competent individuals infected for from cryptospordium?
1 - 2 weeks
how long are immunodeficient individuals infected for from cryptosporidium?
months, even years
pathology of cryptosporidium?
resides at the apical surface of intestinal epithelial cells and does not invade deeper layers of the human gastrointestinal mucosa
causes a classical immune response to infectious agents
diagnosis of cryptosporidium?
- microscopy with an acid fast-stained stool smear
- ELISA
- PCR
treatment of crptosporidium?
- no treatment
- no vaccine
what are cryptosporidium oocysts resistant to?
- chlorine
- can live a long time in sea-water
what are cryptosporidium oocysts susceptible to?
drying and UV portion of sunlight
prevention and control of cryptosporidium?
- water purification and filtration
- education
- wash hands frequently
- minimize contact with young animals
- drink bottled water when travelling abroad
