Giardiasis

Giardiasis is an infectious bowel disease caused by Giardia lamblia, a one-celled parasite.


Causes/associated factors
G. lamblia infects people and certain animals, including dogs, cats, cattle, sheep, rodents and beavers. It's found worldwide, including all parts of the United States. Itater from contaminated mountain streams, lakes, rivers, etc. while traveling, camping or hiking
people who ingest contaminated recreational water (from lakes, swimming pools, hot tubs or wading pools, for example)
people who drink from shallow wells
international travelers and people who live in areas where drinking water comes from streams or rivers with inadequate water treatment
children in child care settings (the parasite can easily spread from caregivers who diaper infected children), as well as child care workers and family members who care for infected children
people living in a custodial institutional setting
people who engage in anal sex

Transmission
The parasite's active form, known as a trophozoite, lives inside the small intestine of the host. Its inactive form, known as a cyst, survives well in the environment, especially in cold water. The cysts may enter your body through contaminated food or water or through direct contact with infected feces. For example, the parasite may spread if you don't wash your hands after touching contaminated material (such as diaper pails, changing tables, bathroom fixtures or toys) or through anal sex.
As few as 10 to 25 cysts can cause an infection. Once the cysts are in your body, your stomach acid activates them, which releases the trophozoites. The trophozoites multiply in the small intestine. Before passing out of the body in your stool, they develop into more resistant cysts, which can survive for several months in water.

You're considered contagious as long as the parasite is in your system, even if you don't develop symptoms. If left untreated, this means you can pass G. lamblia in your stool for months. Also, developing giardiasis once does not completely protect you from another infection. In some cases, the infection can become chronic, causing recurrent symptoms for months or even years.

The incubation period (time from exposure until symptoms appear) averages from one to two weeks, but may last from three to 25 days. Giardiasis occurs more often during the summer in the United States, when water recreation is most common.


Signs/symptoms
Symptoms are often mild, if they even appear at all, and many people are unaware they've been infected. When present, symptoms can last from two to six weeks and may include:
sudden, explosive, watery, foul-smelling diarrhea
appetite loss
nausea
vomiting
gas or bloating
abdominal cramping or pain
rarely, mild fever
If the condition becomes chronic, loss of appetite and poor absorption of nutrients can lead to fatigue, weakness, weight loss and dehydration.


Diagnosis
The doctor will review your medical history and do a physical exam. The parasite can be identified through stool samples. Several samples taken over the course of a few days may be needed because the parasite can be difficult to diagnose. G. lamblia can also be detected through a sample of small intestine fluid, which may be taken through a tube that's passed from the nose into the stomach and upper intestine or by swallowing a specially designed string. Rarely, a biopsy of the intestines (taking a tissue sample for further evaluation in the lab) is done to identify the parasite.

Treatment
If you have no symptoms, treatment is not typically necessary. In most cases, your body will rid itself of the parasite within six weeks. However, your doctor may recommend treatment if you risk passing the infection to a pregnant woman or someone with a weak immune system. If you have symptoms, your doctor may prescribe a drug such as metronidazole, albendazole or furazolidone. If you have diarrhea, remember to drink plenty of fluids to prevent dehydration.

Complications
Children who have severe cases of giardiasis may experience impaired growth and development, especially if they were undernourished before the infection. For people who have weak immune systems, giardiasis may cause complications such as malabsorption, dehydration, weakness and electrolyte imbalances. (Electrolytes are substances that assist with the conduction of electrical impulses when dissolved in body fluids.) Chronic giardiasis is more likely to develop in people who have weak immune systems. Recently, severe giardiasis that's difficult to treat has been observed in people who have AIDS.

Pregnancy-specific information
Some of the more common drugs used to treat giardiasis are unsafe for the developing fetus, especially during the first trimester of pregnancy. If your symptoms are mild, your doctor may recommend delaying treatment until after delivery or at least until after the first trimester. If you need treatment, your doctor may prescribe a drug such as paromomycin or metronidazole. Be sure to remind the doctor you're pregnant before taking any medications.

Senior-specific information
Older adults are at higher risk for complications of diarrhea, such as dehydration. If you experience prolonged diarrhea, consult your doctor.

Prevention
To prevent infection, avoid contact with feces and potentially contaminated food and water. Remember that contaminated water may not look, smell or taste bad, including lake water, river water or other potentially contaminated water sources. Ensure safety of potentially contaminated drinking water by boiling it vigorously for one minute, filtering it or treating it with iodine or chlorine, which can be found in sporting goods stores or pharmacies. Carefully follow the package directions. Three minutes of vigorous boiling or disinfection with iodine after boiling for one minute is recommended at altitudes higher than 6,562 feet. (Water reaches its boiling point sooner at higher altitudes.) To filter water, use a filter with an absolute pore size of at least 1 micron or one that has been rated for cyst removal by the National Safety Foundation. Have well water tested for fecal substances if you suspect it may be contaminated.
In areas with potentially contaminated water, canned or bottled carbonated beverages (including water and soft drinks), beer, wine and beverages made from boiled water are considered safe. Be sure to avoid using ice cubes made from potentially contaminated water and drinking from unclean glasses or wet or dirty cans or bottles. (Drink straight from the can or bottle after wiping it clean and dry.)

Other preventive measures include washing your hands with soap and water before handling food and after using the toilet or changing diapers. Always wash and peel raw fruits and vegetables before eating. Finally, don't brush your teeth in potentially contaminated tap water or swallow bath or recreational water.