Final answer:
Alex's symptoms are indicative of a foodborne illness possibly caused by bacteria, viruses, or protozoan pathogens. Cholera is an example of a severe waterborne illness. Certain populations are more at risk and severe foodborne illness requires medical care.
Step-by-step explanation:
Based on the information provided, Alex's symptoms suggest that he is suffering from a foodborne illness, which can be caused by various pathogens such as bacteria, viruses, or protozoa. Some of the possible bacterial sources of foodborne illness include enterotoxigenic E. coli, Vibrio cholerae, Campylobacter jejuni, or Salmonella. Viral infections such as rotavirus or norovirus and protozoan infections from Giardia lamblia, Cryptosporidium parvum, or Entamoeba histolytica are also common causes. Among the diseases listed in the second example, Cholera is caused by contaminated water and is a serious foodborne and waterborne illness.
Specific populations, such as pregnant women, young children, older adults, and people with weakened immune systems due to conditions such as diabetes, liver disease, kidney disease, HIV/AIDS, or those undergoing chemotherapy or radiation treatment are more likely to develop severe symptoms from foodborne illnesses. While most people recover without medical intervention, severe cases do require medical attention.
In the scenario described where Terri becomes ill after drinking water from a stream, the most likely culprit is a protozoan infection. Considering the symptoms and the method of infection, Terri probably contracted the illness from a protozoa commonly found in untreated natural freshwater sources.