The World Health Organisation (WHO) says global warming could lead to a major increase in insect-borne diseases in Britain and Europe, as northern Europe becomes warmer, ticks—which carry encephalitis and lyme disease and sandflies which carry visceral leishmaniasis are likely to move in. However, malaria has always been a common threat in European past, with the last epidemic occurring in the Netherlands during the 1950s. In the United States, Malaria has been endemic in as much as 36 states (including Washington, North Dakota, Michigan and New York) until the 1940s. By 1949, the country was declared free of malaria as a significant public health problem, after more than 4,650,000 house DDT spray applications had been made.