zahuatl.

valla Totomoniztli, inic micque nicā tlaca: in itoca vei çavatl = there came an illness of pustules of which many local people died; it was called "the great rash" [smallpox].
(Mexico City, sixteenth century)
James Lockhart, We People Here: Nahuatl Accounts of the Conquest of Mexico, Repertorium Columbianum v. 1 (Los Angeles: UCLA Center for Medieval and Renaissance Studies, 1993), 180.

¶ xi calli xihuitl 1529 años ypan in çahuatl momanaco totomonihuac = The year Eleven House, 1529. At this time smallpox prevailed; there were blisters.
Codex Chimalpahin: Society and Politics in Mexico Tenochtitlan, Tlatelolco, Culhuacan, and Other Nahuatl Altepetl in Central Mexico; The Nahuatl and Spanish Annals and Accounts Collected and Recorded by don Domingo de San Antón Muñón Chimalpahin Quauhtlehuanitzin, eds. and transl. Arthur J. O. Anderson and Susan Schroeder (Norman: University of Oklahoma Press, 1997), vol. 1, 236, 237.

cenca miequintin yc momiquillique yn pipiltzitzinti. yn inpilhuã timacehualtin. yhuan ҫan no yhui yn inpilhuan españolestin. yhuan yn inpilhuan tliltique. ҫan mochtin neliuhtiaque yn momiquilique. yhuan cequintin ye huehueỹtin tlaca. ynic momiquillique ҫahuatl = Very many children of us commoners died of it, and likewise children of Spaniards and children of blacks; all died mixed together [without distinction], as well as some adults who died of smallpox (central Mexico, 1609)
Annals of His Time: Don Domingo de San Antón Muñón Chimalpahin Quauhtlehuanitzin, James Lockhart, Susan Schroeder, and Doris Namala, eds. and transl. (Stanford: Stanford University Press, 2006), 156–7.

"1693. Calxihuitl niman huala zahuatl sarampion mochi tlacatl ozahuatic miec omomiquili (p. 764)" = "1693. House year. Then a pox, the measles, broke out. Many people got the pox; a lot of them died." (Anales de Puebla y Tlaxcala, no. 1, part 2, 1519–1697)
Frances Krug, "The Nahuatl Annals of the Tlaxcala-Puebla Region," ch. 2, p. 92, Ph.D. Dissertation draft written in the 1980s, with transcriptions and translations approved by James Lockhart. This quote from Krug may suggest that zahuatl and measles were the same thing for that tlacuilo. (SW)

Krug's dissertation also includes a list or quotes about zahuatl, with the nouns: "huey zahuatl," "zahuatzintli," "zahuatl," "çahuatl," "zahuatli," and "teozahuatl," and verbs about it: "omozahuahuique," "zahuatic." One wonders whether "teozahuatl" suggests some role of religion (Nahua or Christian?) in bringing on the illness (SW).
Frances Krug, "The Nahuatl Annals of the Tlaxcala-Puebla Region," ch. 5, pp. 42–44, Ph.D. Dissertation draft written in the 1980s, with transcriptions and translations approved by James Lockhart.

za man onpa nimozcalti yn niya yquac oquizqui vey zavatl at oya yexivitl = ni mas ni menos que ahi creci, yo, ya estaba cuando paso lo de la gran epidemia de la viruela que duro tres años (Tlaxcala, 1567)
Catálogo de documentos escritos en náhuatl, siglo XVI, vol. I (Tlaxcala: Gobierno del Estado de Tlaxcala y el Archivo Histórico del Estado de Tlaxcala, 2013), 193. Cited by SW.

quito testigo yn oquizqui uey zavatl at ymacuilxiuh yocyoc quipix Agustin niman ya vitz yn nican Tlaxcalan = dijo el testigo, le dio la gran epidemia de la viruela, yo tenia cinco años cuando lo tuvo Agustin, despues ya vino aqui a Tlaxcala (Tlaxcala, 1567)
Catálogo de documentos escritos en náhuatl, siglo XVI, vol. I (Tlaxcala: Gobierno del Estado de Tlaxcala y el Archivo Histórico del Estado de Tlaxcala, 2013), 198. Cited here by SW.

Çahuatepitzin = Viruela pequeña (Tlaxcala, 1662–1692)
Juan Buenaventura Zapata y Mendoza, Historia cronológica de la Noble Ciudad de Tlaxcala, transcripción paleográfica, traducción, presentación y notas por Luis Reyes García y Andrea Martínez Baracs (Tlaxcala and México: Universidad Autónoma de Tlaxcala, Secretaría de Extensión Universitaria y Difusión Cultural, y Centro de Investigaciones y Estudios Superiores en Antropología Social, 1995), 140–141.

yn iquac mochiuh huey çahuatl = Entonces ocurrió la viruela grande (Tlaxcala, 1662–1692)
Juan Buenaventura Zapata y Mendoza, Historia cronológica de la Noble Ciudad de Tlaxcala, transcripción paleográfica, traducción, presentación y notas por Luis Reyes García y Andrea Martínez Baracs (Tlaxcala and México: Universidad Autónoma de Tlaxcala, Secretaría de Extensión Universitaria y Difusión Cultural, y Centro de Investigaciones y Estudios Superiores en Antropología Social, 1995), 132–133.