Many deadly diseases appeared late in Scandinavia; for example, the first recorded smallpox epidemic (variola) in Iceland was in 1241, arriving via the area of Denmark. Smallpox wasn't really a severe problem in Europe until the start of the Crusades (just at the end of the Viking Age), when returning crusaders brought the disease home with them. ("The History of Smallpox and its Spread Around the World". Ch. 5. Smallpox and its Eradication. Eds. Frank Fenner, Donald A. Henderson, Isao Arita, Zdeněk Ježek and Ivan Danilovich Ladnya. Geneva: World Health Organization. pp. 209-244. http://whqlibdoc.who.int/smallpox/9241561106.pdf)
Similarly, typhus ("spotted fever", Rickettsia prowazekii) doesn't seem to have spread throughout Europe until 1489, when Spanish soldiers who fought the Turks in Cyprus brought the disease to Spain. (James G. Olson. Epidemic Typhus: A Forgotten But Lingering Threat". Ch. 5. Emerging Infections 3. Eds. W.M. Scheld, W.A. Craig, and J.M. Hughes. Washington D.C.: ASM Press. 1999. pp. 67-72.)
Cholera is believed to have originated in the subcontinent of India. The disease may have been described by the Greek physician Hippocrates (460-377 BC), but the great cholera pandemics didn't occur until the 19th c. (Antonis A. Kousoulis. "Etymology of Cholera". Emerg Infect Dis. March 2012).
Prior to the scientific understanding of bacteria, and illness that could spread amongst people or animals could be considered "a plague". Hard evidence as to what diseases may have infected people in Viking Age Scandinavia are spotty. Tuberculosis, endemic in bovine populations, can be shown to have affected both humans and livestock in Viking Age Scandinavian settlements via the evidence of bone lesions.
Leprosy probably spread to Scandinavia during the Viking Age, when large numbers of slaves from Ireland were imported. Leprosy was known in Ireland as early as the 7th c. and widespread in Ireland by the 10th c. Certainly, both the Gulaþing Law and Borgarþing Law state that "a promise of marriage is not binding if one of the partners was found to be leprous". (Thomas M. Vogelsang. "Leprosy in Norway". Medical History 9:1 (Jan. 1965). pp 29-35. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1033440/pdf/medhist00156-0037.pdf)