Contagious Diseases

A contagious disease is a subset category of transmissible diseases, usually infections or some non-infection diseases, which are transmitted to other persons, either by physical contact with the person suffering the disease, or by casual contact with their secretions or objects touched by them or airborne route among other routes.
Non-contagious infections, by contrast, usually require a special mode of transmission between persons or hosts. These include need for intermediate vector species (mosquitoes that cause malaria) or by non-casual transfer of bodily fluid (such as transfusions, needle sharing or sexual contact). They can also be inherited from parents or caused by environmental or behavioral factors.
The boundary between contagious and non-contagious infectious diseases is not perfectly drawn, as illustrated classically by tuberculosis, which is clearly transmissible from person to person, but was not classically considered a contagious disease. In the present day, most sexually transmitted diseases are considered contagious, but only some of them are subject to medical isolation.

Global infectious disease surveillance
Increased movements of people, expansion of international trade in foodstuffs and medicinal biological products, social and environmental changes linked to urbanization, and deforestation are all manifestations of the rapidly-changing nature of the world we live in. Add to that the rapid adaptation of microorganisms, which has facilitated the return of old communicable diseases and the emergence of new ones, and the evolution of antimicrobial resistance, which means that curative treatments for a wide range of parasitic, bacterial and viral infections have become less effective, and a communicable disease in one country today is the concern of all.

Worldwide, infectious diseases are the leading cause of death of children and adolescents, and one of the leading causes in adults.
Three of the top ten causes of death, or sixteen percent of all deaths each year, are from infectious diseases . Most of these deaths are in low- and middle-income countries and are attributable to preventable or treatable diseases such as diarrhea, lower respiratory infections, HIV/AIDS, tuberculosis, and malaria. While significant advances have been made in interventions to prevent and treat most of these diseases, those interventions are often unavailable to the populations most in need.

The Response
Over the past century, the public health community has enjoyed periodic major successes in the control and elimination of infectious diseases. In one of public health's greatest victories, smallpox was eradicated in 1977. The smallpox effort was aided by committed medical and political leadership, an inexpensive vaccine that was relatively simple to administer, and a strong surveillance system that allowed rapid detection and containment of outbreaks.
Between 2000 and 2006, global measles incidence decreased by 91%, and incidence of Chagas Disease in Latin America decreased by over 70% from 1983 to 2000. More recently, the effort to eradicate Guinea worm (dracunculiasis) has accelerated and is now close to completion.
However, the global polio eradication program, intended for completion by 2000, has fallen victim to political and civil unrest in Nigeria, Afghanistan, Pakistan and India.

Annual Deaths (in millions)
Disease                            Deaths
Respiratory Infections       3.9
Malaria                            1.3 - 3.0
HIV/AIDS                       2.5
Diarrheal Diseases           1.8
Tuberculosis                    1.7
Neglected Tropical          0.5