**5. Clinical aspects**

The clinical manifestations, course, and duration of *Giardia* infections are variable. In that way, infections may be self-limited or persistent, asymptomatic, or symptomatic. Usually, most patients remain asymptomatic, but when signs and symptoms occur and acute disease is established, manifestations happen normally in travelers and in outbreaks, and they are characterized by diarrhea, nausea, anorexia, dehydration, flatulence, eructation, distention, abdominal cramping, and weight loss. Contradictorily, fever and vomiting are uncommon [7, 13, 20].

The first signs of infection appear after 6–15 days. Most symptomatic infections resolve spontaneously; however, sometimes, hospitalization is required when infections have longterm consequences and do not respond to the normal treatment. Chronic *Giardia* infections are reported frequently in nonendemic areas and also could result in irritable bowel syndrome, food allergies, arthritis, aphthous ulcers, or chronic fatigue syndrome after resolution [3, 10–12].

In some cases, if acute symptoms are not treated on time, they can develop into a chronic stage, which can affect all age groups but children are at higher risk, in whom *Giardia* infections have been associated with lower serum level of zinc, iron, and vitamins (A, B12, and folate); despite similar anthropometric indicators among infected and uninfected individuals in early childhood, the failure to thrive and poor cognitive function are characteristics in them. Furthermore, the loss of lactose is common and can persist for some weeks after treatment, which is why it is necessary to be distinguished in symptomatic patients from relapse or reinfection. In extreme cases, malabsorption and weight loss are severe and mimic sprue [1, 2, 8].

A typical scenario is a mildly to moderately ill person who grumbles of a raised number of urgent loose stools, with flatus, cramping, anorexia, and weight loss. There may even be periods when the person feels better only to relapse and then become noticeably worse. Finally, after some days to several weeks, the person will seek medical help. Similar to other causes of infectious diarrheas, symptoms can carry on after successful treatment and evolve into irritable bowel syndrome and chronic fatigue, even 6 years after the infection. Infrequently, *Giardia* is also found in biliary and pancreatic ducts and can cause cholecystitis and pancreatitis, and other localizations reported are the urinary tract, gastric mucosa, and colonic and ileal mucosa. Extraintestinal manifestations and long-term consequences are unusual, but a series of sporadic cases documented them in a third of the patients. The signs can include rash, reactive arthritis, eye complaints, and cognitive deficiencies [1, 2, 9, 10, 20].
