immunity questions

Question 1

A person has a 1 in 500 probability of being infected by chloroquine-resistant strain of malarial parasite and 1 in 500 probability of being infected by a proguanil-resistant strain. Use a calculation from these figures to explain why scientists are ‘increasingly looking at combinations of drugs’

Answer 1

• 1/500 x 1/500 = 1/250,000
• 1 in 250 000 people are infected by resistant strain when drugs are combined.
• there is a longer immunity provided by the drug