Malaria is ‘an infectious disease characterized by cycles of chills, fever, and sweating, caused by a protozoan of the genus Plasmodium in red blood cells, which is transmitted to humans by the bite of an infected female anopheles mosquito’ (AHD). The word is pronounced [mə.ˈlɛ.ɹi.ə] in English and [ma.ˈla.ɾi̯a] in Spanish. English borrowed the word in the mid-18th century. The disease is ‘widespread in the tropical and subtropical regions that exist in a broad band around the equator. This includes much of Sub-Saharan Africa, Asia, and Latin America’ (WP). There were some 216 million cases of malaria in the world in 2016 worldwide, which resulted in some 731,000 deaths, about 90% of them in Africa. There several species of malaria causing parasites belonging to the genus Plasmodium (phylum Apicomplexa). P. falciparum is the most common and the one that accounts for the most deaths.
The name malaria comes from Italian phrase mala aria ‘bad air’, originally ‘denoting the unwholesome exhalations of marshes, to which the disease was formerly attributed’ (COED). The adjective mala ‘bad’ is cognate with Sp. mala (fem. of malo), ultimately from Lat. mala (fem. of malus, root: mal‑). The noun aria ‘air’ comes from Latin āerem, accusative of āēr, with metathesis of the second vowel, which is a loan from Ancient Greek ἀήρ (aḗr) ‘air’. Lat. āerem is also the source of patrimonial Sp. aire [ˈai̯.ɾe] and Eng. air [ˈɛ.əɹ], an early 14th century loanword from Fr. air ‘atmosphere, breeze, weather’ (Mod. Fr. air [ˈɛʀ]).
Another word for malaria in Spanish is paludismo, which has paludism as its English cognate. Sp. paludismo is a more common alternative to malaria than Eng. paludism is. The word is derived from the regular stem pălud‑ of Lat. pălus (gen.: pălūdis) ‘swamp, marsh, morass, bog, fen, pool’ (CTL). The word seems to have originated in French, created around 1869, as a variant of impaludisme, created in 1873. English and Spanish borrowed the word by the end of the 19th century. There is an adjective Eng. paludic ~ Sp. palúdico/a that is also much more common in Spanish than in English.
English has developed the adjective malarial out of the noun malaria, by means of the Latinate suffix ‑al, but Spanish has no such adjective and must use the phrase de malaria or else, the adjective palúdico derived from the noun paludismo, e.g. malarial mosquito = mosquito de la malaria or mosquito del paludismo (or just anofeles), and malarial fever = fiebres palúdicas.