Exercises: Infectious and non-infectious diseases

Explain the fundamental difference between an infectious disease and a non-infectious disease, and classify the following into the two groups: flu (influenza), diabetes, tuberculosis, asthma, measles, high blood pressure (hypertension).

Name the four main types of agents that cause infectious diseases (viruses, bacteria, fungi and protozoa) and cite one disease caused by each type.

In the diagram, a sick person (left, surrounded by microorganisms) can transmit their infection to a healthy person (right) along three routes labelled with ?. Write the name of the transmission route that each path represents and give an example of a disease for each one.

A class of 24 pupils goes on a field trip and the next day 6 classmates fall ill with gastroenteritis after sharing sandwiches. Calculate what percentage of the class fell ill, explain which transmission route is the most likely, what hygiene measures would have prevented it, and why not everyone who ate necessarily fell ill.

Antibiotics cure bacterial infections, but are useless against flu or the common cold. Explain why, taking into account which agent causes each type of disease, and reason what danger there is in taking non-prescription antibiotics "just in case".

Cardiovascular diseases are non-infectious, yet they are closely related to lifestyle habits. Explain which modifiable risk factors favour them and propose four preventive measures that a young person can adopt.

A patient who has been prescribed antibiotics for 8 days for bacterial pharyngitis decides to stop taking them on the fourth day because they no longer have a fever or pain, arguing: "If I already feel fine, the fewer pills I take, the less my body will get used to the medication and the better it will respond in the future." Identify the two scientific errors in their reasoning (one regarding which organism resistance acts upon and another about what happens to the population of bacteria still remaining in their throat) and justify, in terms of natural selection, why stopping the treatment early increases the risk of a relapse with bacteria that are harder to eliminate.

In a flu outbreak at a school with $400$ students, $60$ become infected in the first week. Without preventive measures, the number of weekly infections doubles; with measures (hand hygiene, ventilation, and staying at home with symptoms), it only increases by half each week. Calculate how many new infections there would be in the second week in each scenario, compare the evolution of the outbreak in both cases, and reason why it is said that the measures "flatten the curve" even if they do not prevent all infections.

Two identical twin sisters share a genetic mutation that increases the risk of developing a certain type of cancer. One of them states: "Since the cause is in our DNA, our fate is sealed: we will get sick no matter what we do with our lifestyle, and what is more, our flatmates could catch it if they live with us." Refute both parts of her statement by distinguishing between genetic predisposition and environmental triggering factor, and justify why cancer is not considered an infectious disease even though there are external agents (such as tobacco or certain viruses) that promote its onset.