Pathogenic fungi cause a variety of diseases in humans and livestock. Aspergillosis, most commonly caused by Aspergillus fumigatus, kills some 600,000 people per year, mostly those with already weakened immune systems.[51] Pneumocystis causes pneumonia, again mainly in people with weakened immune systems.[52] Candida yeasts are the agents of Candidiasis, causing infections of the mouth, throat, and genital tract, and more seriously of the blood.[53] Ringworm is a skin infection that infects some 20% of the human population; it is caused by some 40 different fungi.[53]