I went to medical school and I'll offer an opinion. Bear in mind that I am far removed from infectious diseases at this point.

In medical school, the study of parasites is wrapped into a pathology course. Pathology usually covers infectious diseases, autoimmune diseases, cancer, etc. It is very extensive and includes every system of the body.

Within infectious diseases, the vast majority of the information is on bacteria and antibiotic resistance. This is where the scary stuff is. Eventually, we're going to lose the ability to kill certain types of bacteria. Let's hope we have some dramatic break throughs in antibiotics soon.

The study of viruses is an overview of how types of viruses invade, infect, reproduce, and kill cells. The medications we have against them basically slow or stop their reproduction long enough for our immune systems to ramp up against the virus.

For parasites, the study focuses on a few that are much more common in North America than others. Beyond those, the students learn only the basics of the rarer parasites that people might encounter traveling over seas or to less-developed areas. If someone wants to specialize in this field of medicine they would likely be involved in extensive research and intensive fellowship training.

Parasites depend on their ability to hide from your immune system, which they are very effective at doing. They can live years without causing any significant symptoms. When symptoms are present they can be vague and non-specific; stomach aches, fatigue, occasional diarrhea, weight loss, vitamin deficiencies... They can also cause dramatic symptoms which can be deadly.

It would be foolish to think that we have an adequate understanding of the microscopic things that are trying to kill us. This is why PhD doctors are the real geniuses. They need lots of funding but until saving humanity becomes extremely profitable they will have to continue begging the government.

Wash your hands.