Infection -The lodgement and multiplication of a parasite in or on the tissue of a host is known as infection.

 

         INFECTION

Infection

The lodgement and multiplication of a parasite in or on the tissue of a host is known as infection.

Infection can be occur by various ways such as

Primary infection - initial infection with a parasite is called primary infection.

Reinfection - subsequent infection with the same parasite in same host is known as reinfection.

Secondary infection - when the primary infection lowers the resistance of the host and the latter get infection with another organisms is known as secondary infection.

Cross infection - when a patient already suffering from a disease acquires a new infection is known as cross infection.

Nosocomial or Hospital infection - when cross infection is acquired during his stay in the hospital is known as nosocomial or hospital infection.

Physician induced infection - when the infection is acquired during therapeutic or investigative procedures is known as iatrogenic or physician induced infection.

Subclinical infection - when the clinical symptoms of an infection are not apparent is known as subclinical infection.

Latent infection - after infection, parasite remain in a latent or hidden form for some time and it proliferates and produced clinical disease when the host resistance is lowered is known as latent infection.

SOURCES AND RESERVOIR OF INFECTION

Pathogens are either endogenous or exogenous. Endogenous are arising from the host's own flora and exogenous arising from the an external source. Reservoir of infection is the pathogen existence in human or animal population or environment and from which pathogen can be transmitted.

Endogenous infections

It is also known as autoinfection. For example, normal flora present inside the body, usually non pathogenic but occasionally they may led to infection.

Exogenous infections

Infections arise from outside the body, so it is referred to as exogenous.

Few source of exogenous infection are

1.      Human

2.      Animal

3.      Insects

4.      Environment

Human as carrier

Source of human infection comes from patient or carrier.

Patients - patients are ill persons from them infections may acquired.

Carrier - a carrier is a person who harbours the pathogens without suffering from it. Types of carrier are

1.      Healthy carrier - people harbours the pathogen but never suffered from the disease.

2.      Convalescent carrier - people recovered from the disease but continues to harbour the pathogen on his body.

3.      Temporary carrier - when carrier state lasts for less than six months in the individual.

4.      Chronic carrier - when carrier state lasts for years or may be for the life of the patient.

5.      Paradoxical carrier - person acquires the organisms from another carrier.

6.      Contact carrier - person acquires the organisms from the patient.

 Animal

Animals are source of infections. Infections in animals may be asymptomatic and serve as reservoir for human infections are known as reservoir hosts.

Infectious diseases transmitted from animals to man are known as zoonoses.

 

 

Diseases caused from animals

Diseases	Pathogen	Reservoir hosts	Transmission
Viral Disease
Rabies Tickborne encephalitis	Rhabdoviridae Flaviviridae	Animal species wild animals	Bite of diseased animals Ticks
Bacterial Disease Brucellosis	Brucella	Cattle, pig, goat.	Animals milk and dairy products
Lyme Disease Plague	Borrelia Yersinia pasties	Wild rodents Rodents	Ticks Contact with diseased animals
Q fever	Coxiellaburnetii	Sheep, goat, cattle	Dust, milk or diary products.
Enteric salmonellosis	Salmonella enterica	Pig, cattle, poultry	Meat, milk, eggs
Protozoan disease Toxoplasmosis Cryptosporidiosis	Toxoplasma gondii Cryptosporidium	Cat, sheep, pigs Cattle	Oral, prenatal Ingestion of oocysts
Helminthic Disease Echinococcosis Taeniasis	Echinococcus Taenia	Dog, fox Cattle, buffalo, pigs	Ingestion of eggs Ingestion of metacestodes with meat
Anthropoid Disease Pseudo scabies	Sarcoptes spp.	Dog, cat, pig	Contact with diseased animals

 

Insects

Insects transmitting pathogens are known as vectors. Thus insects act as a source of a number of human and animal infections. Few examples for insects are mosquitoes, ticks, mites, flies and lice. Vectors are of two types. They are mechanical vectors and biological vectors.

Mechanical vectors -  vectors which carry the organisms on their legs, wings and body and transmit them to the food which act as a source of infections. e.g salmonellosis and shigellosis (Domestic fly).

Biological vectors - vectors carry pathogens undergo multiplication or developmental changes with or without multiplication inside their body. Biological vectors are classified into three types

1.       Propagative vector

2.       Cyclo-Propagative vector

3.       Cyclo-Developmental vector

Anthropod transmitting disease

Insects	Disease
Flies	Typhoid and paratyphoid fever, diarrhea, dysentery, cholera, gastroenteritis, amoebiasis.
Ticks	Spotted fever, Q fever, relapsing fever.
Mosquitoes	Malaria, filariasis, yellow fever, dengue, chikungunya fever, rift valley fever.
Louse	Epidemic typhus, relapsing fever, trench fever.
Ratflea	Bubonic plague, endemic typhus.
Mites	Scrub typhus, rickettsia pox, scabies.
Cockroaches	Typhoid, diarrhea, dysentery.

 

Environment

Environment is the major source of infection. Environment includes soil, water and food. Soil contain organisms such as Clostridium, Bacillus, roundworms, hookworms and few fungal species. These pathogens causes disease to the pathogens. Water also found with different pathogens such as Salmonella, Shigella, Vibrio, Polio, Hepatitis and larvae of worms. Food contain organisms causing food poisoning, gastroenteritis, diarrhea and dysentery.