Introduction to Infectious Diseases

Infectious diseases are clinical diseases caused by pathogenic microbial agents – pathogenic bacteria, pathogenic viruses, fungi, multicellular parasites, protozoa, and aberrant proteins (prions). These pathogens cause diseases in humans, animals, and plants. The following are the five human infectious diseases classified according to the causative pathogenic microbial agents:

Bacterial infectious diseases

Not all bacteria are harmful. Your bowels, mouth, and skin are in fact full of them. Many bacteria are even helpful – thay help you digest the foods you eat and guard against some infectious organisms. The problems are the bacterias that make harmful chemicals acting like poisons or acids.

Here are examples of human diseases caused by bacteria: bacterial meningitis, anthrax, brucellosis, botulism, cat scratch disease, campylobacteriosis, diphtheria, cholera, gonorrhea, epidemic typhus, legionellosis, impetigo, leptospirosis, leprosy, lyme disease, listeriosis, rheumatic fever, melioidosis, nocardiosis, MRSA infection, plague, pertussis, psittacosis, pneumococcal pneumonia, Rocky Mountain Spotted Fever, Q fever, Scarlet Fever, salmonellosis, syphilis, shigellosis, trachoma, tetanus, tularemia, tuberculosis, typhus, urinary tract infections, and typhoid fever.

Viral infectious diseases

Viruses are sub-microscopic infectious agents that can’t grow outside a living host cell. Viruses often damage the cells, causing the disease. In addition, some viruses trigger uncontrollable growth of cells and produce cancers.

Here are examples of human diseases caused by viruses: AIDS, AIDS related complications, common cold, chickenpox, Colorado tick fever, cytomegalovirus infection, ebola hemorrhagic fever, dengue fever, foot and mouth disease, herpes simplex, hepatitis, influenza, herpes zoster, measles, Lassa fever, infectious mononucleosis, Marburg hemorrhagic fever, norovirus, mumps, progressive multifocal leukencephalopathy, poliomyelitis,rubella, rabies, smallpox, SARS, viral gastroenteritis, viral encephalitis, viral pneumonia, viral meningitis, yellow fever, and West Nile disease.

Parasitic infectious diseases

Parasitic infectious diseases are responsible for the high rate of human mortality and morbidity, and certainly contribute largely to mortality and morbidity among animals as well.

Here are examples of human diseases caused by parasites: amoebiasis, African trypanosomiasis, babesiosis, ascariasis, clonorchiasis,Chagas Disease, cysticercosis, cryptosporidiosis, dracunculiasis, diphyllobothriasis, enterobiasis, echinococcosis, fasciolopsiasis, fascioliasis, free-living amoebic infection, filariasis, giardiasis, hymenolepiasis, gnathostomiasis, Kala-azar, isosporiasis, malaria, leishmaniasis, myiasis, metagonimiasis, pediculosis, onchocerciasis, scabies, pinworm infection, taeniasis, schistosomiasis, toxoplasmosis, toxocariasis,trichinosis, trichinellosis, trichomoniasis, trichuriasis, and trypanosomiasis.

Fungal infectious diseases

Fungal infectious diseases are caused by a type of fungus that thrivs in warm and moist areas of the skin such as in the scalp, in the groin, between the fingers or toes, and on those parts of the body where skin folds. Here are examples of human diseases caused by fungi: tinea pedis, histoplasmosis, coccidioidomycosis, candidiasis, cryptococcosis, blastomycosis, and aspergillosis.

Prion infectious diseases

Prions cause neurodegenerative diseases characterizd by such symptoms as dementia, convulsions, ataxia (oordination and balance dysfunction), and personality or behavioral changes. Here are examples of human diseases caused by prions: Bovine spongiform encephalopathy, transmissible spongiform encephalopathy, Kuru-Fatal Familial Insomnia, Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker syndrome, and Alpers Syndrome.