Untitled Flashcards Set

Subclinical cases play a dominant role in maintaining the chain of infection in the community. Disease agent multiply in the host but does not manifest by S/S. Mild cases are more important sources of infection than severe cases Carrier is an infected person or animal that harbors a specific infectious agent in absence of discernible clinical disease and serves as a potential source of infection to others. Animal reservoirs • Humans are incidental hosts of many diseases of animal origin • Zoonotic disease - An infectious disease that is transmissible under natural conditions from vertebrate animals to humans. • Example - brucellosis (cows and pigs), anthrax (sheep), plague (rodents), tularemia (rabbits), and rabies (bats, dogs) West Nile encephalitis (birds), and monkey pox (prairie dogs). • HIV/AIDS, Ebola, SARS, COVID 19 considered to have animal origin. Environmental reservoirs • Plants, soil, and water in the environment are also reservoirs for some infectious agents. • Many fungal agents, such as those that cause histoplasmosis, live and multiply in the soil. • Outbreaks of Legionnaires disease are often traced to water supplies in cooling towers and evaporative condensers, reservoirs for the causative organism Legionella pneumophila. 1.5. Vectors Transmission from infectious agent to host can occur via vector. In this case the vector is neither the host nor the reservoir, rather they are the mode of transmission. Vector-borne diseases are infectious diseases that are caused by parasites, viruses and bacteria that are transmitted by vectors. Vectors are living organisms, typically blood-sucking insects, that act as carriers for disease-causing pathogens. Some of the most common vectors are: Mosquitoes can transmit Malaria, Dengue, Chikungunya, Zika, West Nile virus, Japanese encephalitis, Barmah Forest virus, Murray Valley encephalitis and Yellow Fever Ticks can transmit Lyme disease and tick-borne encephalitis Sandflies can transmit lesihmaniasis Triatomine bugs can transmit Chagas disease Natural History Determinants Natural, Social & Environmental History Determinants: Factors that influence health outcomes and disease progression.