You must have often heard of a disease being contagious. What exactly are contagious or communicable diseases? In the simplest terms, contagious diseases can be defined as diseases that can be transmitted from one person to the other by various means. Direct physical contact or coming in contact with the infected person's bodily secretions are the common ways a disease can be spread. On the other hand, some diseases and disorders require a special mode of transmission between the infected person and others. Contagious or communicable diseases can be classified according to their modes of transmission. Diseases spread through direct contact: Certain airborne diseases are spread through the droplets that are sprayed in the air when the person suffering from infection sneezes or coughs. Most of the respiratory diseases are spread in this fashion. For e.g., tuberculosis, bronchitis, diphtheria, croup, measles, scarlet fever, and whooping cough. Contagious skin diseases are also spread by direct contact. Sexually transmitted diseases: Sexually transmitted diseases can be spread by sexual intercourse. Some of these diseases are also transmittable from pregnant mother to her child. HIV/AIDS is an example of sexually transmitted disease. Diseases spread by the fecal-oral route: Certain diseases can be spread by the intake of contaminated food or water. Sometimes these diseases turn into pandemics when contamination occurs on a large scale. Diarrhea, cholera, and some types of gastroenteritis are the examples for the same. Diseases spread by insect vectors and pathogens: Most of the contagious diseases are spread by vector insects and pathogens found in a particular region. Malaria, meningitis, plague, typhus, tetanus, and yellow fever are the examples for the same. These diseases are usually found in tropical and sub tropical regions. The following is a list of the most deadly contagious or communicable diseases, that are reasons for deaths of millions of people all over the world.

• All lower respiratory infectious diseases
• HIV/AIDS
• Tuberculosis
• Malaria
• Measles
• Whooping Cough
• Tetanus
• Meningitis
• Hepatitis B

The following is an alphabetical list of highly communicable diseases. This is a non-exhaustive list. Athlete's foot: Also known as ringworm of the foot, it is a fungal infection of the foot. It spreads by direct contact (skin-to-skin) as well as indirect contact (coming in contact with contaminated objects). Bacterial meningitis: It is the infection or inflammation of the meninges of the brain and spinal cord caused due to bacteria. The bacteria can be spread from one person to other by coming in contact with bodily secretions. Chancroid: It is a sexually transmitted disease (STD) caused due to bacteria, characterized by sores in the genital region. It is spread by coming in contact with the open sores. Chickenpox: It is an infection caused due to herpes varicella-zoster virus. It is spread by coming in contact with a person suffering from it. Chlamydia: It is a sexually transmitted disease (STD) caused due to Chlamydia trachomatis bacteria. It spreads by sexual contact. Common cold: It is an infection of the upper respiratory tract caused by virus. It is easily spread from person to person. Conjunctivitis (Pink eye): It is an infection of the eye, caused due to viruses or bacteria. It is highly contagious and can be spread very easily. Crabs: Also known as pubic lice, crabs are parasites found in pubic hair in humans. It is a contagious sexually transmitted disease (STD). Croup: It is an infection of the trachea and larynx. It is contagious and can be easily spread by coming in contact with nasal secretions. Cryptosporidiosis: It is a gastrointestinal infectious disease caused by a parasite known as Cryptosporidium. It is extremely contagious. Diphtheria: It is the infection of upper respiratory tract (nose and throat) caused due to Corynebacterium diphtheriae. It is extremely contagious. Encephalitis: It is inflammation of the brain caused due to viral infection. It can be contagious in some cases. Flu (Influenza): It is a disease of the respiratory system caused due to viral infection. It is highly contagious and can be spread from one person to the other through airborne respiratory fluids. Giardiasis: It is intestinal infection caused by Giardia intestinalis. It is very contagious to people of all age groups. Gonorrhea: It is a sexually transmitted disease (STD), characterized by infection in the genitals. It is spread by sexual contact with the person suffering from the disease. Hepatitis: It is the inflammation of the liver caused due to infection. Hepatitis A, B, and C are contagious. Herpes: A group of diseases caused due to Herpes simplex virus (HSV). Genital herpes is contagious and is spread by sexual contact. HIV/AIDS: Acquired immunodeficiency syndrome (AIDS) caused by human immunodeficiency virus (HIV) is an immune system disease. It can be spread during sexual activity and from a mother to infant. HPV: HPV (human papillomavirus) infection causes warts in men and women. The infection is contagious and can be spread by sexual contact. Impetigo: It is a skin infection caused by bacteria, resulting in blisters and sores. It is highly contagious and be spread by direct close contact. Leprosy: It is a chronic skin infection caused by bacteria Mycobacterium leprae. It is not very contagious, but can be spread by frequently coming in contact with nasal secretions of people suffering from the disease. Measles: Also known as Rubeola, it is an infectious disease of the respiratory system caused by rubeola virus. It is highly contagious and can be spread very easily by coming in contact with people suffering from the disease. Meningococcemia: It is infection of the blood caused by Neisseria meningitides bacteria. It is not very contagious, but can be spread by being in contact. Molluscum contagiosum: It is viral skin infection caused by molluscum virus. It is very contagious and can be spread through direct contact. Infectious mononucleosis: Also known as glandular fever, kissing disease or simply mono, it is an infectious disease caused due to Epstein-Barr virus. It can spread by being in close contact with people suffering from the disease. MRSA (Staph) infection: It is caused by MRSA bacteria, which is resistant to many antibiotics. It can be spread by being in contact with people suffering from it or by touching contaminated objects. Mumps: It is an infectious viral disease, characterized by painful swelling in the face. It can spread by coming in contact with nasal fluids of the person suffering from it. Nongonococcal urethritis: It is inflammation of the urethra caused due to causes other than gonorrhea. It is a contagious disease. Pelvic inflammatory disease: It is the infection of the female genital tract caused due to bacteria. Although the disease in itself is not contagious, the organisms causing it are contagious. Plantar warts: It is a condition caused due to human papillomavirus (HPV), characterized by warts on soles of foot. It is contagious but does not spread through direct contact. Poliomyelitis: It is a condition caused due to the contagious poliovirus. The virus enters human body through contaminated food. Ringworm: It is an infectious skin disease caused due to fungus. It can spread on coming in direct contact with humans or animals suffering from it. Roseola infantum: It is a viral infection, characterized by skin rash. It is mildly contagious. Rubella (German measles): It is an infection caused by rubella virus. The infection is contagious a couple of days before the symptoms appear. Scabies: It is a skin disease caused by Sarcoptes scabiei mites. Direct contact from one person to the other results in spreading this disease. Scarlet fever: It is an infectious disease caused due to bacteria. It is characterized by a reddish skin rash. It is very contagious and can spread by coming in contact with nasal fluids of the person suffering from it. Shigellosis: It is an infectious intestinal disease caused due to Shigella bacteria. It is highly contagious and can be transmitted by being in contact with contaminated things. Smallpox: It is an infectious disease caused by Variola, characterized by blisters on face, legs, and arms. The disease is spread by direct contact. Strep throat: It is an infectious disease caused due to Streptococcus bacteria. The infection can spread through direct contact. Swine flu: It is an infectious respiratory disease caused due to H1N1 flu virus. It is very contagious and its mode of transmission is similar to influenza. Syphilis: It is a sexually transmitted disease (STD) caused by bacteria. The disease spreads by sexual contact. Tonsillitis: It is the inflammation of the tonsils caused due to viral or bacterial infection. It can be contagious or not contagious (depending on the cause). Trichomoniasis: It is a sexually transmitted disease (STD) caused by Trichomonas vaginalis. It spreads by sexual contact. Tuberculosis (TB): It is an infectious disease caused by Mycobacterium tuberculosis bacteria. It is contagious and can spread if a healthy person comes in contact with the air contaminated with TB bacteria. Viral gastroenteritis: As the name suggests, it is an intestinal infection caused by virus. It is contagious and easily transmitted from one person to the other. Viral laryngitis: It is the inflammation of the larynx (voice box) by virus. It is contagious and can spread like common cold. Whooping cough (Pertussis): It is an infectious respiratory disease caused due to Bordetella pertussis bacteria. It spreads by coming in contact with nasal secretions of a person suffering from this disease. Today there are fewer deaths occurring due to contagious diseases as compared to previous century due to improved medicines and vaccinations. There are certain things a person should follow in order to prevent these diseases. ➡ Consult the doctor to get the disease diagnosed and to know whether it is contagious or not. If yes, look out for safety measures as early as possible. ➡ If a family member suffers from a transmittable diseases, he/she should avoid close contact with other members of the family, specially babies and older people. ➡ People should avoid sharing of daily use articles like toothbrushes, handkerchiefs, towels, etc. Washing hands and maintaining hygiene can help in preventing some communicable diseases to a great extent. ➡ Similarly, if you are planning a picnic or a vacation in tropical regions, it is essential to check out the weather conditions as certain diseases are prevalent in certain climatic conditions. Have thorough information about the contagious diseases found there and get vaccinated against the same. Sometimes, it is simply best to avoid visiting such places. ➡ Today effective vaccinations are available for most of these diseases. Infants and old people should be specially vaccinated on regular intervals as they are more prone to these diseases. ➡ One should try to prevent spread of sexually transmitted diseases by following safe sex practices. Avoid having sex with multiple partners and also undergo a regular medical checkup to prevent the spread of sexually transmitted diseases (STD). As a concluding note, one should remember that the prevention of contagious or communicable diseases is possible to a great extent by vaccinations and proper awareness. Take care!