Giardia
Giardia is the most common cause of parasitic intestinal infections worldwide. In the US, approximately 20,000 cases are reported annually; it is estimated that there could be an annual incidence of 2 million.
Substantial genetic diversity exists within the species. A host is usually infected with food or drink contaminated with cysts, but contact with an infected individual can also transmit the disease. Outbreaks have occurred in institutions where people live close together, where sanitation facilities are poor, and among people who work around sewage or other contaminated areas. A high incidence is also found in immunocompromised people.
Some people may host large numbers of organisms but show no symptoms. When a host does get sick, they show a wide variety of symptoms. In the beginning, they may experience nausea, anorexia, low-grade fever, and chills, along with a sudden onset of explosive, watery, foul-smelling diarrhea. As the disease progresses, patients can have pain, malabsorption of fats and other substances, and weight loss. Occasionally, they may experience gallbladder involvement.
After the acute phase of the disease, patients may enter a chronic phase with intermittent episodes of loose stools, normal stools, and even constipation. They may experience abdominal distention, flatulence, and belching.
Dientamoeba
Infections with this organism are also seen worldwide, but are more common among pediatric populations. There is a general lack of knowledge of this organism, and its morphology can differ even within one individual, so it may well be underdiagnosed.
Since there is no cyst stage, the route of infection with Dientamoeba fragilis is not fully known. However, it is transmitted with helminth eggs such as Ascaris and Enterobius spp.
The most common symptoms include intermittent diarrhea, abdominal pain, nausea, and fatigue.
