Answer to Case 683: Cryptosporidium sp. oocysts
The following OUTSTANDING discussion is from our guest author, Hadel Go, a third year medical student with a strong interest in clinical parasitology.
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We received some excellent feedback! Thank you all
for leaving comments on the blog, on Twitter, and on LinkedIn.
Yes, these are Cryptosporidium oocysts. These
protozoans can be identified by their size and consistent red color on modified
acid-fast staining of stool samples. They can also be diagnosed from H&E
stained tissue biopsies (see images here: Cryptosporidium,
parasitewonders.com), but nucleic acid amplification
tests (NAATs) and immunofluorescence microscopy have the greatest
sensitivity and specificity. The two main species that cause infection in
humans are C. parvum and C. hominis, although several others are
also capable. Species identification requires molecular methods like NAAT and/or
sequencing.
Transmission is fecal-oral through food and water
contaminated by stool from an infected person or animal. Some examples include
swallowing pool water, eating unwashed fruits/vegetables from unsafe farms where produce is contaminated with feces containing oocysts (@StephenTristam on Twitter noted a strong association with farming
communities), handling infected farm animals especially calves (@KevKeel brought up
infections among vet students!), caring for an infected person, engaging in
anal sexual contact (as mentioned by @RA_MLS), and touching your mouth with
contaminated hands.
Cryptosporidiosis will present with explosive watery
diarrhea, stomach pain, nausea, vomiting and fever 2-10 days after acquiring
the parasite as seen in our 4-year-old case patient. These are self-limiting in
most immunocompetent individuals. Replenishing fluids and electrolytes to
prevent dehydration is usually sufficient. The infection is mainly concentrated
in the small intestine, but complications can lead to malnutrition and wasting
due to malabsorption or severe dehydration especially in babies.
Immunocompromised patients such as people with
HIV/AIDS, inherited immune diseases, or on immunosuppressive drugs can progress
to severe chronic infection which may become fatal. The respiratory tract can also
be affected (respiratory cryptosporidiosis) resulting in a persistent cough.
Nitazoxanide is the FDA approved treatment for
diarrhea caused by Cryptosporidium in immunocompetent patients ≥ 1 year
of age. However, as Idzi P. mentioned in the comments, “efficacy in
immunocompromised patients is not yet clear… for patients with HIV,
anti-retroviral therapy (to improve immune status) could resolve the symptoms.”
Prevention is essential: practice good hygiene, wash
hands often, do not swallow water when swimming, only drink filtered or treated
water/ice especially when traveling or camping, practice safe sex, do not
consume undercooked meat or unpasteurized milk/apple cider, wash your fruits
and veggies. To avoid recurrent outbreaks, please do not go swimming if you
have diarrhea or within two weeks of resolution of symptoms.
The differential diagnosis is a protozoa in the same
family - Cyclospora cayetanensis (discussed in Case 457). It causes cyclosporiasis which presents similarly
and can be differentiated from Cryptosporidium species by measuring the
oocysts. Their location within enterocytes also varies; see photos from Case 343. The table below compares the two:
|
Cryptosporidium parvum |
Cyclospora cayetanensis |
Oocyst
size |
4-6
μm |
7.5-10
μm |
Acid-fast
staining |
Red
staining (can be variable) |
Often
variable staining |
Autofluorescence
under UV |
No
(as pointed out by Idzi P.) |
Yes |
Location
in enterocyte |
Replicates
outside the cytoplasm just below the cell membrane |
Replicates
within the cytoplasm |
Transmission |
Oocysts
are immediately infectious leading to massive outbreaks |
Person-person
transmission unlikely because sporulation can take weeks and occurs in the
soil. |
DID YOU KNOW?
- Each sporulated oocysts contains 4 sporozoites.
- Cryptosporidium is resistant to chlorine treatments alone due to their
protective outer shell.
- Ultraviolet light and boiling are effective ways to inactivate this protozoan.
- Cryptosporidium parvum oocysts are commonly found in young calves 1-4
weeks old.
- Cryptosporidium zoonotic infection can occur from sheep, cows, pigs,
rodents and other animals.
LIFE CYCLE (3 developmental stages in bold)
1.
Oocysts (thick-walled spore, infective form) are shed in
stool and ingested by host
2.
Excystation releases sporozoites which parasitize
epithelial cells of the GI tract
3.
Meronts undergo asexual multiplication within the brush
border
4.
Gamonts are produced from sexual multiplication
a.
Microgamonts = male; these rupture releasing
microgametes
b.
Macrogamonts = female
5.
Microgametes fertilize macrogamonts forming a zygote
6.
Zygotes give rise to two types of oocysts
a.
Thin-walled oocysts cause autoinfection
b.
Thick-walled oocysts are excreted into the
environment
TAXONOMY
Domain: Eukaryota
Clade: SAR
Infrakingdom: Alveolata
Phylum: Apicomplexa
Order: Eucoccidiorida
Family: Cryptosporidiidae
More information:
1. Parasites - Cryptosporidium (also
known as "Crypto") | Cryptosporidium | Parasites | CDC
2. CDC - DPDx -
Cryptosporidiosis Life Cycle
Thanks to Idzi P. for sharing the following articles
about the 1993 outbreak in Milwaukee, WI (the largest known outbreak affecting
~400,000 people):
1. A Massive
Outbreak in Milwaukee of Cryptosporidium Infection Transmitted through the
Public Water Supply | NEJM
2. Costs of
Illness in the 1993 Waterborne Cryptosporidium Outbreak, Milwaukee, Wisconsin
4 comments:
Fabulous lesson! Thank you for pulling into one place all this valuable information!
Thanks for this excellent review!
Another superb résumé Hadel!
Chapeau bas!
Another superb résumé Hadel!
Chapeau bas!
(That anonymous one before was me too)
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