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Essay on Infections. The below given essay will help you to learn about the following things: 1. Host Factors Contributing to Infection 2. Sources of Infection For Man 3. Modes of Spread of Infections 4. Basic Principles of Disease Transmission 5. Vectors and 6. Application to Nursing.
Essay # Host Factors Contributing to Infection:
Various host factors, affecting an individual or a community, contributing to the occurrence of the infection are:
1. Very young children and very old individuals are susceptible to infection, because of inadequate body defence mechanism.
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2. Malnutrition favours the incidence and severity of infection in poor community.
3. Metabolic diseases like diabetes and hormonal upsets due to corticosteroid therapy predispose to the infection.
4. Haematological disorder neoplasm and renal diseases resistance to infection.
5. Factors such as age, obesity, size of wound, wound drainage, duration of operation and length of stay before or after operation may affect the nosocomial infection (hospital acquired infection) caused by staphylococci and gram-negative bacilli.
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6. Acquired immunodeficiency syndrome (AIDS) Patients are highly susceptible to various infections.
7. Community factors affecting host resistance are the complex components of poverty (overcrowding, inadequate food, clothing and housing, hypothermia and poor personal hygiene).
8. Drug addiction and alcoholism may predispose to infection.
Essay # Sources of Infection For Man:
The term infection (Lax. infectio — to infect) signifies the sum of biological processes which take place in the human or animal body upon the penetration of pathogenic microorganisms in the host’s body by injuring body tissues and producing a reaction on the part of the host.
Source of infection is defined as the normal growth habitat of the microbes, e.g., a site in the body of the human or animal host. Objects contaminated with live or temporarily inactive microbes may be called vehicles or reservoirs of infection, not sources of infection.
Man Acquires Infection:
A. From outside sources, which is known as exogenous infection, e.g., from human patients with clinical infections, healthy human carriers of the pathogenic microorganisms.
B. Within the patient’s own body, the infection is said to be endogenous.
Exogenous Infections:
1. Patients:
Some microbial infections are acquired from sick patients with active infections (pulmonary tuberculosis, leprosy, whooping cough, syphilis, gonorrhea, measles, small pox, mumps and influenza).
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2. Healthy Carriers:
Healthy persons, though they carry many species of pathogenic microbes, sometimes show a subclinical infection and are commonly capable of disseminating these pathogenic microbes to other persons who will manifest the signs and symptoms of illness; they are then termed as carriers-, thus they are potential source of infection. Some infectious diseases are contracted from carriers much more frequently than from patients, e.g., streptococcal, staphylococcal, pneumococcal and meningococcal infections, diphtheria, typhoid fever, bacillary dysentery and poliomyelitis.
3. Convalescent carriers are persons in whom a limited, localised infection continues for a period of weeks or months after clinical recovery from a manifest infection.
4. Contact carriers are those persons who acquire the pathogen from a patient.
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5 Paradoxical carriers are those who acquire the infection asymptomatically from another carrier. If the carriage persists for more than an arbitrary period of time, e.g., one year in the case of typhoid infection, the person is called chronic carrier.
Endogenous Infections:
Endogenous infections may occur in carriers of potentially pathogenic organisms, when these previously harmless bacteria invade. Other surfaces or tissues in the carrier, e.g., Escherichia coli derived from the bowel, where it is harmless, may cause acute suppurative infection in the urinary tract; Staph, aureus from the nostrils may cause boil in the skin or infection in a wound; and pneumococci from the nasopharynx may cause bronchitis and bronchopneumonia. The source of endogenous infection is thus the site in a patient’s body (e.g., colon, skin or nasopharynx) where the organism grows harmlessly as a commensal.
Staphylococcal sepsis of the skin and wounds, which is mainly endogenous, may under certain circumstances become transmissible, as in hospital, where conditions may favour cross-infection between patients. Thus, the cross-infected patients suffer from exogenous infection.
However, patients with endogenous infections caused by organism of low virulence are not likely to infect other persons, e.g., patients with bronchopneumonia due to pneumococci of less virulence are not a danger to relatives, nurses or other patients and there is no need to isolate them from other patients in hospital.
Essay # Modes of Spread of Infections:
A variety of mechanisms can spread respiratory and alimentary infections from host to host, while a single mechanism, for which the parasite is specially adapted, can spread venereal and arthropod-borne blood infections:
1. Respiratory Infection:
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The causative microbes are disseminated into the environment in masses of infected secretion, e.g., secretion transferred from the nose or mouth on floors, handkerchiefs, cups, spoons or secretions expelled in spitting or blowing the nose; they are also discharged to a less extent in the droplet spray produced by sneezing, coughing and speaking, but in normal breathing, they are very rarely disseminated.
The secretion contaminates handkerchiefs, clothing, bedding, floors, furniture’s and household articles (fomites) which may act as vehicles or reservoirs of infection. It dries in dust, most kinds of respiratory microbes may remain alive for several days, even for several months, if protected from direct sunlight, e.g., tubercle bacilli, diphtheria bacilli, streptococci, staphylococci and small pox virus.
(a) Infection may be passed to the recipient by contact, either:
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(i) Direct contact, i.e., touching of bodies as in handshaking, kissing and contact of cloth, or
(ii) Indirect contact, e.g., contaminated eating utensils, door handles, towels; the recipient may transfer the microbes from contaminated fingers to his sore or mouth.
(b) Infection may be dust-borne by inhalation of air-borne infected dust particles. The infected numerous dust particles are disseminated into the air from the skin and clothing during normal body movements; from dried contaminated handkerchiefs during its use, from bed sheets while bed making, from floor during sweeping and walking, and from furniture while dusting.
The larger infected dust particles may settle within a few minutes on the floor and other exposed surface, e.g., skin, clothing, wounds and surgical supplies; whereas the smaller dust particles remain air-borne for up to 1 to 2 hours and may be inhaled into the recipient’s nose, throat, bronchi, lung alveoli. Within the room of its origin, air-borne infection is very common and dangerous; but its spreading to other rooms in the same building is rare.
(c) The third least important means of respiratory infections is droplet spray, except in the case of the pathogens that are rapidly killed by drying, e.g., meningococcus, whooping cough bacillus, measles and common cold viruses.
Sneezing, coughing, speaking and other forceful expiratory activities expel a spray of droplets derived from the saliva of the anterior mouth which is infected with small numbers of pathogenic microbes from the nose, throat, lungs.
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Numerous droplets are expelled, but only a few are infected. The large droplets (over 0.1 mm. in diameter) fly forwards and downwards from the mouth to the distance of a few feet (about 1 meter), they reach the floor or body surfaces (eye, face, mouth and clothing) or the persons standing in front of the other person producing the spray, within a few seconds.
These particles cannot be inhaled. Measles, chicken pox and dog distemper are common viral infections spread by the larger droplets. The small droplets (below 0.1 mm. in diameter) evaporate immediately to become minute solid residues or “droplet nuclei” (mainly 1 to 10 µ m in diameter) which remain air-borne and may be inhaled into the nose, throat, lung. Few of the droplet nuclei are infected with pathogenic microbes. Measles, chicken-pox, and dog distemper are common viral infections spread by the droplet nuclei.
2. Mucous Membrane, Skin Wound, Discharges and Burn Infections.
Gonococcal ophthalmia caused by gonococci and inclusion blenorrhoea caused by sub-group-A of chlamydia may be acquired from the infected genital tract of the mother, when the mucous membrane of eyes of new born infants gets infected as the infant passes down the infected birth canal. Leptospira excreted in the urine of the infected animals enter the human body through the skin, similarly larvae of schistosoma and ankylostoma penetrate the skin.
The superficial infections may be acquired by (a) contact with infected hands, clothing or other articles, (b) by exposure to the deposition of contaminated droplet spray, pathogenic streptococci and staphylococci derived from respiratory tract are important causes of wound and burn infections; if pathogenic staphylococci are disseminated from pus discharge, they may cause infection of broken skin and burn wound.
3. Venereal Infections:
The diseases transmitted exclusively by sexual intercourse are called venereal diseases, since the causative agents, e.g., Treponema pallidum and Neisseria gonorrhoeae are highly susceptible to lethal effects of drying, they are to be transmitted only by sexual contact. Gonococcus which causes vulvovaginitis in young girls may be acquired, under unhygienic conditions, from the common use of towels and bathing facilities.
This is non-venereal spread of infection in young girls. Sub-group A of chlamydia (Lymphogranuloma Venereum – LGV) infection is transmitted by sexual contact. Acquired immunodeficiency syndrome (AIDS) caused by Human immunodeficiency virus (HIV) can be transmitted through sex — commonly by homosexuality.
4. Alimentary Tract Infections:
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Persons with intestinal infection may disseminate the pathogenic microbes in excreta. These microbes are transmitted in various ways, the so-called faecal-oral routes, leading to their ingestion by the recipient, e.g., Salmonella typhi. Most of the intestinal pathogens are not much resistant to drying, they may die within a few hours, they may survive on cloth, or in dust for several days. They are more likely to be spread by moist vehicles (water or food) in which they may survive for several weeks.
(a) Water-Borne Infections:
May occur when faeces contaminate a water supply, e.g., river or well, which is used without purification for drinking purpose. In typhoid and cholera, water is the common vehicle of infection and the infecting dose may be small. Water is supplied to the citizen by the municipality after purification.
Purification, which renders the water non-infective, is carried out on a large scale by storage, filtration and chlorination. Small amounts of water required for drinking purpose may be treated by boiling or by the addition of hypochlorite tablets.
(b) Hand Infections:
The hands of the nurses can get infected while attending the patients and touching the bed pans. Similarly the hands of the carrier can be contaminated with bacteria contained in the faeces. Such persons may contaminate the foodstuffs, eating utensils, wash basins, towels, door handles and other fomites (inanimate objects). A recipient may eat contaminated food or put in his mouth the contaminated utensils or may pick up the microbes on his fingers and then transfer them into his mouth.
(c) Food-Borne Infections may occur through:
(i) A carrier handling the food (food as a vector of disease;
(ii) Preparation of the food in utensils contaminated by handling or washing in contaminated water;
(iii) Files alighting on the food after feeding on infected faeces. Enterotoxins may be produced on the food contaminated by bacteria during their growth in favourable conditions, e.g., Staph, aureus and Clostridium botulinum.
These preformed enterotoxins are prerequisites for bacterial food poisoning, whereas food-borne infections may result from the ingestion of only a few pathogenic microorganisms, e.g., Sh. dysenteries which liberate enterotoxin.
5. Urine:
Typhoid bacilli are excreted in the urine and feces, similarly leptospirae are excreted by animals through the urine and enter the mucous membrane and skin.
6. Arthropod-Borne Infections:
In systemic infection, the causative microbes are present in large number in blood, so they may be transmitted to other individuals by blood sucking arthropods such as mosquito (malaria, filaria, yellow fever); flea (plagues- louse (epidemic typhus fever); mite (scrub typhus) and tsetse fly (trypanosomiasis).
7. Laboratory Infections:
Laboratory workers may occasionally become infected from artificial cultures or infected diagnostic or necropsy materials collected from patients or experimental animals. Brucella, rickettsia and Pasteurella tularensis especially cause laboratory infections; while other organisms (tubercle bacilli, anthrax bacilli, pathogenic leptospires, borreliae, freshly isolated typhoid, dysentery bacilli, psittacosis organisms and serum hepatitis virus) should be handled very carefully.
The pipetting of infected liquids by mouth leading to their accidental ingestion is certainly a danger of laboratory infections. Accidental self-inoculation with a syringe may take place or the conjunctiva may be sprayed when the needle becomes loosened from a syringe during an injection.
Many laboratory procedures (the expulsion of liquid from a pipette or the use of the mechanical blenders, the centrifugation of tubes bearing traces of liquid on their rim) or drop separated from an inoculation loop may cause laboratory infections, when working particularly with pathogens which may cause air-borne infection such as tubercle bacilli, thus it is necessary that all these procedures should be carried out within a especially ventilated protective cabinet or inoculation hood.
8. Congenital Transmission:
Serum hepatitis virus can be transmitted from the infected pregnant mother through the placenta to the fetus. Similarly, human immunodeficiency virus (HIV) can be transmitted through placenta to the new born.
Congenital Malaria is Comparatively Rare:
The intrauterine transmission of malaria is well established. The congenital malaria is very common in non-immune infected mothers. It is also believed the passage of the parasite to the fetus occurs only when the placental barrier has been injured.
Congenital toxoplasmosis results from the congenital infection in infants and young children. It usually appears as a form of encephalitis, accompanied by chorioretinitis, hydrocephalus or microcephaly, mental retardation and convulsions. The infection passes from the mother through the placenta late in pregnancy when neutralisation of antibodies cannot take place. The child is usually born jaundiced with purpuric or maculopapular rash, enlarged liver and spleen.
Congenital trypanosomiasis in man is possible but is rare; a case was reported in a child born of an infected mother, in Germany, who died less than three months after birth, because of proven trypanosomiasis. Later, two more proven congenital infections in infants were reported.
Congenital Filariasis:
The microfilariae of Wuchereria bancrofti may pass from the infected pregnant mother to the new born through the placental filter.
Essay # Basic Principles of Disease Transmission:
Portals of entry and portals of exit are two basic principles of disease transmission:
1. Portals of Entry:
Normally, microorganisms enter into the body through certain routes and cause the infection; but they cannot gain entrance through other abnormal portals of entry:
(a) Cuts or abrasions of the skin (e.g., bites of arthropods or animals);
(b) Mucosa of respiratory tract (nose, throat, lungs), eyes and mouth, gastrointestinal, genitourinary tracts are the most important common portals of entry.
Abnormal Portals of Entry:
If harmless saprophytic microorganisms are introduced parenterally into the brain or into the peritoneal cavity by a hypodermic needle, they set up the rapid fatal infection. Many organisms can cause the infection if they enter only through their obliogate portals of entry. Thus, dysentery bacilli can produce severe bacillary dysentery, if they are consumed through water or food; if they are rubbed into the skin wound, they will not initiate any infection. Severe, even fatal infections (abscess, boil, carbuncle), can be produced if staphylococci are rubbed in the skin; if swallowed, they are ineffective. Some organisms can enter through any portal.
Path of Organisms in the Body:
From the sites (portals of entry) of infection, organisms may pass into the blood stream and initiate a secondary (metastatic) infection in internal organs (i.e., in the meninges of the brain and spinal cord — meningitis).
When the enteric pathogens (typhoid bacilli, dysentery bacilli, Vibrio cholerae) are swallowed, they enter the stomach unaffected temporarily by gastric juice (especially in the presence of food), they set up ultimately gastro-intestinal infection.
The respiratory pathogens locate in or on tonsils, throat (Streptococci, diphtheria bacilli, whooping cough bacilli) may cause the infection, if they pass down into the lungs, they may produce pneumonia (Pneumococci) and tuberculosis (tubercle bacilli). The organisms (Treponema pallidum, gonococci) find their portals of entry through genital mucosa.
2. Portals of Exit:
The pathway by which organisms leave the body of one patient to another patient or healthy individual to initiate the infection is known as Portals of exit.
Vectors:
Vectors may be animate or inanimate:
(a) Inanimate Vectors may be the food, discharges (faeces, saliva, pus), water, bandages, dressings, instruments, bedding, eating utensils and other inanimate objects (fomites) contaminated with infectious discharges.
(b) Animate Vectors are generally arthropods or mammals: Female anopheles mosquito is the vector for malaria; vectors of rabies are dogs or other mammals. Other animate vectors are the hands (very common) of the patients, nurses, doctors and patient’s relatives coming in contact with an infectious patient or his fomites.
Since man cannot be disinfected with Dichloro Diphenyl Trichloroethane (DDT) or muzzled and put on a leash, he himself may be regarded as one of the most dangerous vector of the diseases (e.g., man is the only significant living vector of AIDS, poliomyelitis, measles and syphilis and he is the most frequent live vector of human tuberculosis).
