Diseases are of various types.Presently the whole world is facing many new viral diseases such as Aids,Hepatitis,dengue etc. The global prevalence of dengue has grown dramatically in recent decades. The disease is now endemic in more than 100 countries in Africa, the Americas, the Eastern Mediterranean, South-east Asia and the Western Pacific. South-east Asia and the Western Pacific are most seriously affected. Before 1970 only nine countries had experienced DHF epidemics, a number that had increased more than four-fold by Some 2500 million people — two fifths of the world's population — are now at risk from dengue. WHO currently estimates there may be 50 million cases of dengue infection worldwide every year. In 2001 alone, there were more than reported cases of dengue in the Americas, of which cases were DHF. This is greater than double the number of dengue cases which were recorded in the same region in 1995.

Dengue is an arbovirus disease caused by any one of four closely related viruses that do not provide cross-protective immunity; a person can be infected as many as four times, once with each serotype. Dengue viruses are transmitted from person to person by the Aedes aegypti mosquito in the domestic environment. Periodic epidemics have occurred in the Western Hemisphere for over 200 years. In the past 20 years, however, dengue transmission and frequency of epidemics have increased greatly in most tropical countries of the American region. As this has occurred, dengue hemorrhagic fever (DHF) has emerged and produced epidemics in many countries of the region.

Dengue is transmitted to people by the bite of an Aedes mosquito that is infected with a dengue virus. The mosquito becomes infected with dengue virus when it bites a person who has dengue or DHF and after about a week can transmit the virus while biting a healthy person. Dengue cannot be spread directly from person to person.

Dengue fever is characterized by the rapid development of a fever that may last from five to seven days with intense headache, joint and muscle pain and a rash. The rash develops on the feet or legs three to four days after the beginning of the fever. The hemorrhagic form of dengue fever is more severe and associated with loss of appetite, vomiting, high fever, headache and abdominal pain. Shock and circulatory failure may occur. Untreated hemorrhagic dengue results in death in up to 50 percent of cases.

Fortunately, DHF/DSS can be effectively managed by fluid replacement therapy, and if diagnosed early, fatality rates can be kept below 1%. It is very important, that physicians and other health care providers learn to recognize this disease. Once a person acquires dengue, the key to survival is early diagnosis and appropriate treatment. To manage the pain and fever, patients suspected of having a dengue infection should be given acetaminophen preparations rather than aspirin, because the anticoagulant effects of aspirin may aggravate the bleeding tendency associated with some dengue infections Tropical Diseases I INTRODUCTION Microsoft ® Encarta ® Encyclopedia © Microsoft Corporation. All rights reserved.

There is no vaccine for preventing dengue. The best preventive measure for residents living in areas infested with Aedes aegypti is to eliminate the places where the mosquito lays her eggs, primarily artificial containers that hold water. Items that collect rainwater or are used to store water (for example, plastic containers, 55- gallon drums, buckets, or used automobile tires) should be covered or properly discarded. Pet and animal watering containers and vases with fresh flowers should be emptied and scoured at least once a week. This will eliminate the mosquito eggs and larvae and reduce the number of mosquitoes present in these areas. For travelers to areas with dengue, a well as people living in areas with dengue, the risk of being bitten by mosquitoes indoors is reduced by utilization of air conditioning or windows and doors that are screened. Proper application of mosquito repellents containing 20% to 30% DEET as the active ingredient on exposed skin and clothing decreases the risk of being bitten by mosquitoes. The risk of dengue infection for international travelers appears to be small, unless an epidemic is in progress