CRYPTOSPORIDIOSIS
A 34-year old Hispanic man
with a history of HIV infection is admitted to the hospital. His CD4 cell count is 18 (a normal count is
from 500-1200), and he complains of pain in the upper right abdomen, nausea,
fever and vomiting. What opportunistic
infection has taken hold in his body?
How can it be diagnosed? Can
anything be done for him? (see below for
answers!)
Life Cycle Cryptosporidiosis and
HIV/AIDS Glossary References and Links
What is it?
Cryptosporidiosis,
or “crypto,” is an enteric
disease caused by a protozoa. Crypto is found all over the world. Prevalence rates in Europe and North America
range from 1-6%, while rates in Asia and Africa are as high as 20%. It can affect both humans and animals (crypto
infections have been found in up to 150 different species), mainly causing
watery diarrhea. Other symptoms include
abdominal pain, and sometimes fever, malaise, nausea, vomiting, and loss of
appetite. Symptoms usually occur two to
ten days after infection, but it is important to note that many crypto
infections may be asymptomatic. The most
common animal reservoir is cattle, although crypto has been detected in
reptiles, birds, and insects.
Picture from Medical Journal of Australia
website
(http://www.mja.com.au/public/issues/dec2/lemmon/lemmon.html)
Is it serious?
Although
crypto is usually cleared by the immune system, it can be life-threatening for
people suffering from severe immunodeficiencies, such as AIDS.
It also disproportionately affects children from underdeveloped
countries. Chronic crypto infection has
been linked with impairments in physical fitness and reduced cognitive
abilities. Sadly, children with
persistant diarrhea enter a vicious cycle of malnutrition of decreased
nutritional status and further diarrheal illnesses.
How is it transmitted?
Crypto
is normally a zoonotic
infection spread by contaminated water, although food-borne and
person-to-person infections have been documented. Many outbreaks can be traced to water run-off
carrying animal waste. Endemic transmission
usually occurs through contamination of public water sources, such as beaches
and pools. It is only in large outbreaks
that contamination of the drinking water supply has been implicated. Food-borne transmission has only been
reliable documented in one case.
Person-to-person transmission is much more frequent, often occurring in
nursing homes and day care centers.
Crypto has a very low infectious dose (amount needed to establish
infection in the host), ranging from 9 to 1000 oocysts, depending on the species of
parasite.
How does a doctor diagnose
an infection?
The most widely used diagnostic test is the
modified acid-fast or Kinyoun stain. It
is used to detect Cryptosporidium in
stool samples. Several immunofluorescent
assays are also available, which test for antibodies to the parasite in the
blood. Some pharmaceutical companies
have produced rapid-result commercial assays, which are moderately successful
(~75% detection rate). Polymerase chain
reaction (PCR) techniques might also prove to be effective in diagnosing
infection.
Picture from Johns Hopkins website
(www.med.jhu.edu/IDAIDS/
qmaker/scan4.gif)
Why is it a threat to public health?
Crypto
is a serious issue for two reasons:
current water purification methods are ineffective at removing the
parasite from drinking water, and there is no effective therapy to treat
cryptosporidium infection.
How can transmission be prevented?
People
should wash their hands regularly as the most effective means of preventing
transmission. Immunocompromised
individuals should peel, wash, and cook all vegetables thoroughly. They may also wish to boil or filter drinking
water.
And what about our sick patient?
This
man has a cryptosporidium infection which will be diagnosed by one of the
assays mentioned above. His doctor will
attempt to reconstitute his immune system with a HAART regimen, which will hopefully clear
the parasite from his system. Otherwise,
only supportive care to replenish lost fluids and to prevent wasting is
available.
Timeline
1976—The first two
human cases of cryptosporidiosis are reported.
1984—The first
reported waterborne outbreak of crypto is attributed to fecal contamination of
a public artesian well in Texas.
1993—A crypto
outbreak in Milwaukee, Wisconsin sickens 400,000 people and causes over 100
deaths. It is traced to a contaminated
water supply.
1996—A food-bourne
outbreak occurs in the Northeast U.S. It
is determined that unpasteurized apple cider was contaminated during
processing.
Created by: Rebecca Hammon
Stanford University
May 2003