This course is a comprehensive review of pathogenic bacteria, fungi, parasites, and viruses. Emphasis is on epidemiology, pathogenesis, diagnosis, prevention, and treatment. Bacterial diseases include pertussis, sexually transmitted infections (STIs), Lyme disease, tuberculosis, leprosy, typhus, and legionnaire’s disease. Medical mycology is explored with emphasis on fungal diseases such as dermatophytoses. The section on parasites includes amoebae, malaria, round worms, and tapeworms. The final section of the course is a comprehensive review of viral diseases, including smallpox, herpes, polio, influenza, measles, mumps, rubella, hepatitis, rabies, and HIV. Risks to travelers as well as preventive measures are discussed. The laboratory includes bacteriological staining exercises, examination of parasites, and cultivation of fungi. Important public health aspects, including immunizations, are discussed whenever relevant.