Second National Communications Graph 11 shows annual typhoid fever data that suggest a constant presence of the disease; cases usually peak at the start of the year. Graph 12. Annual Trends of vector-borne diseases, NESSS, 1989 - 2007 Dengue fever Malaria 60,000 50,000 Number 40,000 30,000 20,000 10,000 0 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 As seen in Graph 12, there is an upward trend of dengue fever cases over the last 20 years. Peaks occur every 3 to 4 years and may suggest the dominance of a different type of dengue strain or combination of strains. Annual malaria data suggest constant presence of the disease; monthly analysis show peaks during the months of May to June as seen in Graph 13. Graph 13. Monthly Trend of Malaria cases, NESSS, 2000 - 2006 40