What are infectious diseases?
An infectious disease is a clinically evident disease resulting from the presence of pathogenic microbial agents, including pathogenic viruses, pathogenic bacteria, fungi, protozoa, multicellular parasites, and aberrant proteins known as prions. These pathogens are able to cause disease in animals and/or plants.

Infectious pathologies are usually qualified as contagious diseases (also called communicable diseases) due to their potentiality of transmission from one person or species to another. Transmission of an infectious disease may occur through one or more of diverse pathways including physical contact with infected individuals. These infecting agents may also be transmitted through liquids, food, body fluids, contaminated objects, airborne inhalation, or through vector-borne spread.

How the Infectious Diseases are classified?
Human infectious diseases grouped by causative agent and alphabetically arranged.

Viral infectious diseases
AIDS – AIDS Related Complex – Chickenpox (Varicella) – Common cold – Cytomegalovirus Infection – Colorado tick fever – Dengue fever – Ebola hemorrhagic fever – Hand, foot and mouth disease – Hepatitis – Herpes simplex – Herpes zoster – HPV – Influenza (Flu) – Lassa fever – Measles – Marburg hemorrhagic fever – Infectious mononucleosis – Mumps – Norovirus – Poliomyelitis – Progressive multifocal leukencephalopathy – Rabies – Rubella – SARS – Smallpox (Variola) – Viral encephalitis – Viral gastroenteritis – Viral meningitis – Viral pneumonia – West Nile disease – Yellow fever

Bacterial infectious diseases
Anthrax – Bacterial Meningitis – Botulism – Brucellosis – Campylobacteriosis – Cat Scratch Disease – Cholera – Diphtheria – Epidemic Typhus – Gonorrhea – Impetigo– Legionellosis – Leprosy (Hansen's Disease) – Leptospirosis – Listeriosis – Lyme disease – Melioidosis – Rheumatic Fever;MRSA infection – Nocardiosis – Pertussis (Whooping Cough) – Plague – Pneumococcal pneumonia – Psittacosis – Q fever – Rocky Mountain Spotted Fever (RMSF) – Salmonellosis – Scarlet Fever – Shigellosis – Syphilis – Tetanus – Trachoma – Tuberculosis – Tularemia – Typhoid Fever – Typhus– Urinary Tract Infections

Parasitic infectious diseases
African trypanosomiasis – Amebiasis – Ascariasis – Babesiosis – Chagas Disease – Clonorchiasis – Cryptosporidiosis – Cysticercosis – Diphyllobothriasis – Dracunculiasis – Echinococcosis – Enterobiasis – Fascioliasis – Fasciolopsiasis – Filariasis – Free-living amebic infection – Giardiasis – Gnathostomiasis – Hymenolepiasis – Isosporiasis – Kala-azar – Leishmaniasis – Malaria – Metagonimiasis – Myiasis – Onchocerciasis – Pediculosis – Pinworm Infection – Scabies – Schistosomiasis – Taeniasis – Toxocariasis – Toxoplasmosis – Trichinellosis – Trichinosis – Trichuriasis – Trichomoniasis – Trypanosomiasis

Fungal infectious diseases
Aspergillosis – Blastomycosis – Candidiasis – Coccidioidomycosis – Cryptococcosis – Histoplasmosis – Tinea pedis

Prion infectious diseases
transmissible spongiform encephalopathy – Bovine spongiform encephalopathy – Creutzfeldt-Jakob disease – Kuru–Fatal Familial Insomnia–Alpers Syndrome

Diagnosis of Infectious Diseases

Diagnosis of infectious disease is nearly always initiated by medical history and physical examination. More detailed identification techniques involve the culture of infectious agents isolated from a patient. Culture allows identification of infectious organisms by examining their microscopic features, by detecting the presence of substances produced by pathogens, and by directly identifying an organism by its genotype. Other techniques (such as X-rays, CAT scans, PET scans or NMR) are used to produce images of internal abnormalities resulting from the growth of an infectious agent. The images are useful in detection of, for example, a bone abscess or a spongiform encephalopathy produced by a prion.

1. Microbial culture

2. Microscopy

3. Biochemical tests

4. Molecular Diagnostics

www.nlm.nih.gov/medlineplus/infectiousdiseases.html

Please visit the websites to read more about the Gene Based Diagnosis