Describe one method used to control the spread of malaria by targeting its vector and explain what it does.
Explain why developing an effective vaccine for malaria has been difficult.
Another way of preventing malaria is by taking drugs, such as chloroquine, but resistance to these drugs among certain species of the malarial parasite is increasing. New drugs are being developed. A laboratory investigation was carried out to find out the effect of a new drug on two strains of the malarial parasite $\textit{Plasmodium falciparum}$. The results are shown in Fig. 4.1. With reference to Fig. 4.1, compare the effect of increasing the concentration of the drug on the chloroquine-resistant and chloroquine-sensitive strains of $\textit{P. falciparum}$.
When a person is infected with the Human Immunodeficiency Virus (HIV), they become more vulnerable to infection by the malarial parasite. Fig. 4.2 shows maps of Africa produced by the WHO. Fig. 4.2a gives the percentage of the population in each country testing positive for HIV. Fig. 4.2b gives the percentage increase in malaria as a result of HIV infection in each country.
Explain how the information in Fig. 4.2 supports the idea that HIV infection is linked with susceptibility to malaria.
Suggest how HIV infection may have led to more malarial infections in these countries.