An important aspect of infection prevention and control (IPC) is the identifying and breaking the chain of transmission. To do this, we need a good understanding of the interaction of agent, host, and environment in aiding transmission of diseases, and also acting as reservoirs.
Introduction
A reservoir is any one or more populations or habitats that are linked epidemiologically, where the disease can persist indefinitely and from which infection spreads to the designated target group. The reservoir of an infectious agent is its typical home, where it develops, replicates, and survives. The environment, animals, and people are examples of reservoirs. The source from which an agent is moved to a host could be the reservoir or it could not be.
For instance, dirt serves as a reservoir for Clostridium botulinum, but inadequately canned food containing spores of the bacteria is the primary cause of botulism diseases. Many infectious agents infect many host species, particularly those that lead to new illnesses. Controlling multihost pathogen reservoirs is frequently essential to the successful management of disease.
Human Reservoirs
Human reservoirs exist for numerous prevalent infectious illnesses. Several respiratory pathogens, measles, mumps, streptococcal infection, and some sexually transmitted illnesses can spread directly from person to person without the need for an intermediary. Following the identification and isolation of the final human case, naturally occurring smallpox was eradicated because humans were the only known reservoir for the smallpox virus.
Human reservoirs might or might not exhibit disease symptoms. As was previously said, an individual with an undetectable infection who can spread the pathogen to other people is considered a carrier. Healthy, asymptomatic, or passive carriers are persons who carry the infection but never show any symptoms. Those who can spread the agent during the incubation phase prior to the onset of clinical disease are known as incubatory carriers. Those who have recovered from their sickness yet are still able to spread to others are known as convalescent carriers.
People who carry a disease for months or even years after their initial infection, such as the typhoid fever-causing Salmonella Typhi or the Hepatitis B virus, are known as chronic carriers. Mary Mallon, sometimes known as Typhoid Mary, was a well-known chronic asymptomatic carrier of Salmonella Typhi. She accidentally infected scores of people while working as a cook in New York City and New Jersey in the early 1900s. She was then put in isolation on an island in the East River, where she passed away 23 years later.
Because carriers do not recognize their infection and so do not take extra efforts to stop transmission, they frequently spread disease. On the other hand, those with symptoms who are conscious of their condition might be less likely to spread infection because they are either too ill to leave the house, take preventative measures to lessen the spread of the sickness, or are receiving therapy that controls it.
Animal Reservoir
Diseases that have their reservoirs in animals can also affect humans. Animals to animals are the primary carriers of many of these diseases, with humans serving as unintentional hosts. An infectious disease that can spread naturally from vertebrate animals to humans is referred to as zoonosis. The following zoonotic illnesses have long been known: tularemia in rabbits; brucellosis in cows and pigs; anthrax in sheep; plague in rodents; trichinellosis/trichinosis in swine; and rabies in bats, raccoons, dogs, and other mammals. Two recent zoonoses to appear in North America are monkeypox (affecting prairie dogs) and West Nile encephalitis (affecting birds). Although the animal hosts of many recently found infectious diseases in humans, such as HIV/AIDS, Ebola, and SARS, are unknown, it is believed that these diseases originated in animals.
Environmental Reservoir
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. Fomites and inanimate objects are increasingly being identified as forms of temporary reservoirs for infectious agents.
Conclusion
A reservoir is any one or more populations or habitats that are linked epidemiologically, where the disease can persist indefinitely and from which infection spreads to the designated target group. When all means of transmission between target and nontarget populations have been eliminated, the presence of an infection within the target population is considered to be confirmed. Effective control of disease can be achieved with limited understanding of potentially complex reservoir infection dynamics when treatments within target populations are the only means of control.