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on 27 August 2013

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Transcript of Infection

The Epidemiology of Infection
is the invasion of a host organism's bodily tissues by disease-causing organisms, their multiplication, and the reaction of host tissues to these organisms and the toxins they produce.Infections are caused by infectious agents such as viruses, viroids, and prions, microorganisms such as bacteria, nematodes such as roundworms and pin worms,arthropods such as ticks, mites, fleas, and lice, fungi such as ringworm, and other macroparasites such as tapeworms.

Hosts can fight infections using their immune system. Mammalian hosts react to infections with an innate response, often involving inflammation, followed by an adaptive response. Pharmaceuticals can also help fight infections.

Vehicle Transmission
- involves pathogens riding along on supposedly clean components.
Spreading Infection
Source of Infection

The source of infection can be a person or an animal from which the infectious agent is secreted into the outer milieu and from there to individuals.

Direct Transmission
Indirect Transmission

Intravenous fluids
Examples of vehicles include:
Bodily fluids
Agents of disease (etiological agents)areas follows:
– parasitichelminths
In the process of spreading infection we must consider the characteristics of the following etiological agents:
– ability of agent to cause specific pathological condition in an organism

In addition, the following factors should also be considered:

1. Infection dose
– quantity of pathogenic agent that has penetrated into the organism

– malaria, leishmaniasis,
– dermatomycosis, histoplasmosis,
– rickettsiae, chlamydia,
– incompletevirus
– degree of pathogenicity of agents is determined by toxicity and invasiveness, both of the searevariable
– ability to harm organism by creating toxins
– ability to penetrate in to the tissues of organism, to stay there, to propagate events and undergo certain degree of development
2. Resistance to physical factors
- low or high temperatures and radiation
3. Ability to infect intermediary hosts or vectors
4. Ability to propagate out the organism
In certain circumstances the outer milieu can be the source of infection where the agent lives as asaprophyte(mycoses, legionllie)
A person can be
the source of infection in the following cases:
• During incubation period of disease
- in some infections the agent is secreted during the incubation period(Hep A, B). Careful consideration should be made of this patient as there infection is usually not known
• Sickperson
– in clinical, abortive, atypical, in apparent forms
• Convalescent
– secretion of these agents occur during convalescencei.e.as in pertussis
Diseases that can be transmitted from animals to persons are called
(anthrax, salmonella, brucellosis, Q-fever, tularaemia).
Animals can be source of infection in a similar way to persons.
Animals that can act as sources are sheep, goats, ducks, hens, pigeons, dogs, cats, deer, stags and small rodents.
Modes of Transmission
– when the individual comes into contact with the etiologic agent at transmission.
– when transmission source and host are mediated by a further factor.
- the skin or mucosa of the affected individual comes into contact with another individual(sexual intercourse, biting, scratching, and kissing). Most venereal diseases are transmitted this way.
By Droplet

- transmission through the air; when infectious agents are expelled from the upper respiratory airway of the source to the host who inhales them. Mainly acute respiratory infections are transmitted this way(influenza, parainfluenza).
- transmission of infection can occur from mother to fetus(rubella virus, HIV virus, cytomegalovirus, toxoplasmagondii, treponemapallidum)

– newborns can be infected by a number of agents during birth (streptococcigroup B, E-Coli, N.gonorrhoea)
By Contact
Mediated by contaminated objects
- infectious agent is transmitted by objects of daily domestic use(towels, handkerchief, combs, dishes, cutlery, etc.)

Transmission by Air
- usually from upper respiratory airways when a person sneezes, coughs, or speaks. These etiologic agents can be inhaled by another individual who may become infected.
Droplets larger than 100µ create contaminated dust when they fall to earth and dry out. This dust maybe breathed in and result in subsequent infection. This also may occur by dried pus.
Transmission by Alimentaryway

– point of entrance for this type of etiologic agent is through the digestive tract and occurs due to substances containing this agent (water, milk and most food stuffs.)

Transmission by Water
– occurs when the pathogenic germs get into the water supply; this can be due to interrupted sewage, leaking of waste water, waste water being carried to water flows or water basins. This type of transmission usually results in an explosive epidemic, the extent of which depends on how many people are supplied by that water. This occurs in abdominal typhoid fever, parathyroid fever, cholera, Hepatitis A, poliomyelitis, leptospirosis. The duration of survival of this agent within the water depends on the physical, chemical and biological
qualities of the water.
Transmission by Food/Food stuffs

– these can also lead to explosive epidemics as the food is
a perfectly suitable transport medium for the propagation of microbes and the production of their toxins. This is most often food of animal origin(meat, eggs), vegetable(manure by faeces), or fruit(used without peeling).

Infections of Natural Focus
- these are infections occurring in certain localities characterized by:
- animals that act as servoir for infection(small rodents)
- vectors(transmitters)which act as a reservoir on animals and can transmit infection to further hosts
- flora & fauna(biocenosis) which create a milieu for animal and vectors that act as a reservoir or infection

– instruments and equipments used by medical personnel
Transmission by inoculation
Viruses such as Hepa B & C, cytomegalovirus, HIV
may introduce the etiologic agent into host(injections,
transfusions, operations, blood plasma).
infection can be spread by this way as
cannosocomial infections.
Depending on their size droplets smaller than 100µ stay in the air for a shorter or longer period of time. Smaller droplets get dry immediately and can remain in the atmosphere for a longer period of time. Due to their size they may infiltrate alveolus resulting in decreased effect of ciliary epithelium. The smaller the droplet the further it may be carried from source of infection.
This type of transmission occurs in respiratory infections(acute respiratory disease, exanthematic disease, pertussis, diphtheria, pulmonary tuberculosis). It may also occur in dermatological diseases(staphylococci), alimentary disease(oxyuriasis) and even in the transmission of zoonoses (tularaemia, anthrax).
Contamination of food that is off animal origin occurs
when cause is due to endogen contamination occurring intravitally in animals(salmonella),
(b) secondarily
when preparing various foods, the dishes and cooking instruments used are contaminated or due to dirty contaminated hands of personnel
preparing the food.
Milk and milk products can be primarily
contaminated by zoonotic agents(bovine tbc, foot and mouth disease, Q-Fever, tickencephalitis, brucellosis).
Eggs are contaminated both primarily and secondarily by salmonella. Highly dangerous are cold meal products(mayonnaise) and confectionary products in which raw eggs are used. To ensure safety of eggs from salmonella contamination yous hould boil them for 8-10 minutes.
Meat products can also be contaminated both primarily and secondarily, mostly in meals prepared from grinded meat, blood, intestinal(salmonella, trichinella, and toxoplasma). Meats that are not sufficiently
smoked or warmed can endanger persons
with botulism.
– mediation of agent can be by various
kinds of arthropods and can be as follows:

Transmission Transmissive(vector-born)
• Biological
– the agent propagates in the vector and undergoes a part of its development cycle. Can be transmitted in a trans ovarian way. It is mediated by arthropods that live on humanor animal blood(malaria, trypanosomiasis, leishmaniosis, arbo virus, tularemia, rickettsiosis, plague, recurrent typhoid fever,
Q- Fever).
• Mechanical
– the surface of an insect
may be infected when it comes into contact with faeces(synantropic flies, cockroach), upon contact with food the pathogenic germs can be transmitted. Salmonella and enterovirus may be transmitted by this method:
- tetanus spores, anaerobic clostridium, some types of mycoses.
Transmission by Contaminates Soil
 Microorganisms(etiologic agent)
– certain qualities such as virulence, size of infection dose, resistance of agent of infection to outer and inner milieu can express influences on process of infection.
Individual - Host
 Macroorganisms(person)
– receptiveness or resistance is decided through a number of factors:
1. Character and degree of immunity
2. Age and time of infection
3. State of nourishment
4. Presence of other diseases
5. Infection by several agents at the same time
6. Personal habits(smoking, alcohol,
dependence on medicines,
psychological factors
like depression, belief, will)

Three basic groups of mechanism
come into effect at the defense of organism: non-specific resistance,
non-specific immunity, gained
specific immunity.

Non-specific resistance
– based on the inborn protective factors of an individual. These include physical(mechanical) barriers such as surface of cilia or non-disturbed epithelium surfaces, and biochemical barriers such as HCL in stomach, genetic and hormone cellular effects.
Gained specific immunity
– conditioned by previous etiologic agent or its antigens. It is divided between humoral (antibodies) and cellular (mediated by T-lymphocytes).
Non-specific immunity(natural)
– includes the processes conditioned by the previous etiologic agent who work independently and are not specific(phagocytosis, complement system, lysozyme, interferon, inflammatory processes).
Prepared by: Ivana Grace Sayco and Krissa Pauline Czari Palabrica
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