Viral disease:The most common viral disease is viral fever.Much more diseases like mumps,measles and rubella are also caused by viruses.Chicken pox,HIV,SARS and Ebola are viral diseases that have been spreading now-a-days.Viruses cannot exist on their own and for survival they need to spread to another host. This is because the original host may either die or eliminate the infectionViral diseases can be prevented from spreading by vaccinations and the most successful of these is the small pox vaccine that has completely eradicated the disease in 1980. It is hoped that several other viruses, such as polio and measles, will follow.Bacterial disease:Tuberculosis and Pneumonia caused many deaths that are causes by bacteria.It leads to many infections that affect human skin,food poisoning and much more Pathogenic bacteria also cause infections such as tetanus, typhoid fever, diphtheria, syphilis and Hansen's disease.People who have healthy immune systems can often fight off a tuberculosis infection after breathing in Mycobacterium tuberculosis bacteria. .Protozoan disease:Malaria is a deadly disease once,which is caused by plasmodium.It is transmitted by mosquitoes and affect human RBC.Sleeping sickness ia also another problem.while many medical advances have been made to safeguard against infection by pathogens, through the use ofvaccination, antibiotics, and fungicide, pathogens continue to threaten human life. Social advances such as food safety, hygiene, and water treatment have reduced the threat from some pathogens.Fungal disease:Ringworm and athelte's foot are fungal diseases.These diseases affect major part of skin. Life-threatening fungal infections in humans most often occur in immuno compromised patients or vulnerable people with a weakened immune system, although fungi are common problems in the immuno competent population as the causative agents of skin, nail or yeast infections.