Which of the following diseases can be caused by pathogens in water?

Giardiasis is an illness caused by the parasite Giardia intestinalis, which can be found in the water supply, especially in untreated water from rural or wilderness areas. This pathogen can contaminate drinking water through fecal matter, leading to infections in individuals who ingest it. Symptoms of giardiasis include diarrhea, abdominal cramps, and nausea, illustrating how waterborne pathogens can directly affect water quality and human health.

In contrast, although influenza is a viral infection that affects the respiratory system and can sometimes be associated with water (for instance, in cases of general hygiene practices), it is primarily transmitted person-to-person and not directly through contaminated water sources. Heart disease is a chronic condition influenced by a variety of factors including genetics, lifestyle choices, and environmental conditions, rather than being caused by pathogens in water. Allergies are immune responses to specific allergens and don’t stem from waterborne pathogens. Therefore, giardiasis is distinctly related to waterborne pathogens, making it the appropriate choice.