Protist and Fungal Infections: Malaria and Chalara Ash Dieback

Two infections, two kinds of pathogen

A pathogen causes disease in the organism it infects. Pathogens do not all belong to the same group: Chalara ash dieback is caused by a fungus and affects ash trees, while malaria is caused by protists and affects humans. The places each pathogen damages help explain the signs of disease.

Chalara ash dieback: leaves and bark

Chalara ash dieback is caused by the fungus Hymenoscyphus fraxineus. Infected ash leaves may blacken and wilt, then fall from the tree earlier than they normally would. This leaf loss reduces the tree’s leafy growth. Infection can also move into twigs and branches, where it produces dark lesions—patches of damaged bark. Shoots beyond the damage may die back, giving the disease its name.

A tree losing leaves in autumn is not, by itself, evidence of ash dieback. The combination of unhealthy leaves and bark lesions is more informative than leaf loss alone.

Malaria: liver and blood

Malaria is an infection caused by parasitic protists called Plasmodium. A parasite lives in or on another organism and gains resources from it. After entering a person, the malaria parasites infect liver cells and multiply there. They then enter the blood and infect red blood cells. As the parasites multiply, infected red blood cells rupture, damaging the blood and contributing to anaemia—a shortage of healthy red blood cells. The infection also damages the liver. Fever and chills are common symptoms, but the key affected parts to remember here are blood and liver.