First Line Defence Mechanism By The Use Biology Essay


The multiplication, invasion, development and reproduction in host tissues by a disease causing microorganisms (pathogens) and the response of the host tissues to these disease causing microorganisms is called as infection. Bacteria, fungi and viruses are the common disease causing micro organisms which cause infection. Immune system of the host usually fights against the infections. Innate response of mammalian immune system reacts to the infections by inflammation. Drugs and pharmaceuticals usually help to over come the infections by controlling and limiting the pathogens and pathogenic activity.


Infections can be classified in multiple ways based on causative agent, locality of host organs, medical signs and symptoms.

Infection Classification based on Causative agents.

Bacterial Infection. (caused by Bacteria)

Fungal infection. (caused by Fungi)

Viral infection. (caused by Virus)

Infection Classification based on signs and symptoms.

Apparent infection. (Symptoms produced during infection.)

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In-apparent infection. (Does not produce obvious symptoms during infection.)

Infection Classification based on duration of time.

Acute infection. (Short period of time.)

Chronic infection. (Long time period.)

Immune system

Immune system of the human body protects against the pathogens which help to step away the infections. Innumerable numbers of micro organisms infect the organs throughout the life time of the hosts. These pathogens triggers the specific immune response called as antigen which helps the host to protect from infections and diseases. Defence mechanism of Immune system helps the hosts to over come these infections by several ways.

First line defence mechanism by the use of non-specific barriers.

Second line defence mechanism by the use of leucocytes (white blood cells)

Third line defence mechanism by the use of the specific immune response

First line defence mechanism

The skin, mucous membrane, hair, cilia, gastric juice, vaginal secretions, tears, cerumen, sweat and saliva are the common first line barriers which prevent all types of foreign particles to enter into the host. These barriers are non specific to the foreign particles. They are usually the outer covering or layer of the body.

Second line defence mechanism

When the pathogens and foreign particles infiltrate into the host they will enter into the systemic circulation. Granulocytes and agranulocytes are the white blood cells found in the blood circulation cause destruction to the pathogens and foreign particles before it cause the infection. These white blood cells are non specific to the pathogens as they use phagocytises mechanism to destroy the pathogens.

Third line defence mechanism.

After the pathogens overcome the non specific barriers third line of defence mechanism causes specific immune response to identify and destroy the pathogens. These specific antigens stimulate the antibodies to label the pathogens which help to prevent the infection by restricting the multiplication of pathogen by causing destruction to the pathogens.

World health organisations define the "infectious diseases are caused by pathogenic microorganisms, such as bacteria, viruses, parasites or fungi; the diseases can be spread, directly or indirectly, from one person to another. Zoonotic diseases are infectious diseases of animals that can cause disease when transmitted to humans". []

These infectious diseases further classified based on causative agents such as bacteria, fungi, viral and parasitic infectious diseases and based on the locality of the organ which is susceptible to infection.

E.g. dermatological infectious disease, ophthalmological infectious disease, etc

Ophthalmological infection

Eyes are the most sensitive parts in our body which can get infections easily. First line defence mechanism of eyes is totally depend on tears which secreted by lacrimal apparatus. When the foreign particles enter into the eyes lacrimal apparatus secrete high amount of tears to eliminate them. Any how its not have specificity to eliminate them. Due to this eye infections are common in the world which results to serious the cause "Blindness". Naturally eyes have several mechanisms to avoid infections, such as

Lids -physical protection

Tears- flushing action, lysozyme antibacterial activity, humoral immunoglobulin protection.

Low temperature-due to exposure to air.

World health organisation summarised from the Extrapolated data suggests that 38 million people are blind and 110 million people have low vision around the world. Further to that it suggests nearly 10 million people are blind due to the infectious diseases. This implies that twenty five percentage of world's blindness due to Ophthalmological infectious diseases.


Prevalence of Blindness (%)

Blindness Due to Infection (%)

Prevalence of Infectious Blindness (%)

No. of Blind Due to Eye Infection

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Established Market Economies





Former Socialist Economies of Europe





Latin America and the Caribbean















Middle-Eastern crescent





Other Asia and islands





Table i: Global Distribution of Blindness Due to Ocular Infection, WHO 2005

World health organisation and cross sectional survey based studies in united states be evidence for that the socioeconomic status play the key role to determine the ocular health.

Ophthalmological infectious diseases stays on a global concern as it cause a huge burden to the growth of the countries. Proper sanitation and health care can reduce Infection and infectious diseases from the world.

As per Indian scenario, infectious blindness is a common factor. One fourth of the blindness in India is caused by ocular infections. The prevalence rate of infectious blindness is quite high than the other countries due to poor sanitation, inadequate health care systems, lack of knowledge among the people related to infections and unsteady government setup. Environment plays a significant role in ocular infections as pathogenic micro organism can survive in tropical climatic zones.

Ophthalmological infectious diseases

Ophthalmological bacterial infectious diseases.

Bacteria are the causative agent / pathogen of these diseases, which cause severe infectious conditions result to blindness. Before the invention of antibiotics these diseases are the major contributing factor to increase the prevalence of infectious blindness. Bacterial Conjunctivitis, Blepharitis, acute and Chronic Dacryocystitis, Endopthalmitis, Corneal ulcer / Ulcerative keratosis, Canaliculitis, Hordeola/ Chalazia, Opthalmia Neonatum, Periorbital Cellulitis, Trachoma, bacterial Uveitis/Iritis and etc.

Bacterial Conjunctivitis.

Infection in conjunctiva by bacterial pathogens result to the inflammation of conjunctiva is called as bacterial conjunctivitis. It's very common in developing countries during the monsoon season.


Predisposing factors

Poor hygienic and sanitation conditions, dirty habits, flies, hot and dry climate are the predisposing factors which help the pathogen to highly contagious.

Causative organisms

Haemophilus influenzae, Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pneumonia, Streptococcus pyogenes, Pseudomonas pyocyanea, Moraxella lacunate, Neisseria meningitides and Neisseria gonorrhoeae.

Corynebacterium diphtheria - presently it became very rare case.

Mode of infection.

Exogenous mode of infection can occur via close contact ( water and air borne infection), through a vector like flies and through material transfer. (e.g. towels , handkerchiefs)

Local spread can happen by infected lacrimal sac, nasopharynx and eye lids.

Endogenous infection can take place in very rare cases from systemic blood infection


Pathology of bacterial conjunctivitis hangs on in four responses. The responses usually varies depend upon the causative pathogen and severity of inflammation.

Vascular response. - Increase in permeability and congestion of conjunctiva capillaries and vessels.

Cellular response. - Exudation of inflammatory cells like polymorphonuclear cells into conjunctival sac and conjunctiva substantia propria.

Conjunctival tissue response. - The superficial degeneration of epithelial cells make the conjunctiva oedematous, Which increase the goblet cells mucin secretion.

Conjunctival discharge. - Severe inflammation and diapedesis of red cells happen during this response.


Embarrassment and alien body sensation because of inflammation.

Trouble to tolerate the light (photophobia)

Discharge of mucopurulent from eyes.

Lid sticking sensation during sleep.

Minor blurring vision because of mucous.

Coloured halos prism effect in some patients.

Fiery red eye appearance.

Swelling of conjunctiva.


Topical antibiotics

Broad spectrum antibiotics are used to treat bacterial conjunctivitis. Chloramphenicol, gentamycin and framycetin eye drops and ointment are widely used to treat this infection. if the subject will not show proper response to these antibiotics ciprofloxacin, ofloxacin or gatifloxacin antibiotic eye drops will be used to treat this bacterial conjunctivitis.

Irrigation of conjunctival sac

Frequent eye wash with clean water will help to remove deleterious materials.

Dark goggles

To reduce the symptomatic photo phobia

No bandage

Exposure of eyes to the air will help to reduce the temperature of conjunctiva which inhibit the growth of bacteria, thus bandaging of eyes will put a stop to discharge elimination.

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No steroids

Steroids will induce the corneal ulcers which flare up the bacterial growth.

Anti-inflammatory and analgesic drugs

Usually give mild pain relief to the sensitive subjects and reduce the symptomatic complaints. (E.g. paracetomol, ibuprofen)


Its one of the most common eye disease which affects the lid margins by causing chronic inflammation. Its further divided into four sub types such as seborrhoeic blepharitis, ulcerative blepharitis, and meibomitis and mixed blepharitis (seborrhoeic and staphylococcal) Seborrhoea of scalp and dandruff is the common allied factor which induces the blepharitis disease condition. During this disease condition, abnormal secretions of natural lipids by the gland of zeis are usually split into irritating fatty acid by Corynebacterium acne. Further to that staphylococcal bacterial infection on the lid margins makes the blepharitis as a chronic disease as it start from the childhood and may lead till all over the life time.


Predisposing factors

Dandruff, Chronic conjunctivitis and Dacryocystitis, a chronic staphylococcal infection.

Causative organisms

Corynebacterium acne, staphylococcal coagulase positive strain bacteria.

Mode of infection.

Infection in eye lids by close contact (air borne and water borne bacterial strains) and material contact (e.g. towels, pillow covers)


Abnormal secretions of natural lipids by the gland of zeis are usually split into irritating fatty acid by Corynebacterium acne during blepharitis disease condition.

Coagulase positive staphylococcal bacterial infection on the lid margins makes chronic inflammation.


Whitish material Deposition in the margin of eye lids.

Mild uneasiness

Irritating sensation


History of falling eye lashes.

Mild lacrimation and watering of eyes.


Gluing of cilia.


Trichiasis, Poliosis



Balanced diet

Healthy and balanced diet will improve the disease condition.

Topical antibiotic and steroid combination

Topical application of ointments with the combination of antibiotics and steroids.

Removal of crusts

Oral antibiotics (e.g. Erythromycin, tetracycline)

Anti inflammatory drugs. ( e.g. ibuprofen)


Bacterial infection in Lacrimal sac which cause the blockage to the lacrimal sac resulting the inflammation is called as Dacryocystitis. Congenital Dacryocystitis and adult Dacryocystitis are the two forms affect the lacrimal sac of the eyes.

Congenital Dacryocystitis / Dacryocystitis Neonatorum.

These types of lacrimal sac inflammation usually affect the new born infants.


Predisposing factors

Nasolacrimal duct congenital blockage, membranous occlusion, existence of epithelial debris

Causative organisms

Staphylococci, pneumococci and streptococci bacteria.

Mode of infection.

Epiphora, After one week of birth it can occur resulting copious mucopurulent discharge.


Blockage of secretions in the lacrimal sac due to congenital blockage in the nasolacrimal duct.


Swelling of the lacrimal sac area.

Purulent discharge


Regurgitation test

Pressure over the lacrimal sac is used eliminate the discharge the purulent from lower punctum.

Massage over the lacrimal sac area and topical antibiotics.

Pressure over lacrimal sac increase the hydrostatic pressure which helps to unlock the membranous occlusions.

Lacrimal syringing (irrigation) with normal saline and antibiotic solution.

Irrigation increases the hydraulic pressure to wash out the membranous occlusions.

Probing of NLD with Bowman's probe.

Probing will performed under general anaesthesia without affecting the canaliculus.

Intubations with silicone tube.

Dacryocystorhinostomy (DCR) operations.

Adult Dacryocystitis.

Acute and chronic form of adult dacryocystitis may occur, however acute dacryocyctitis is not common than chronic form.


Predisposing factors

Age - more widespread between the age of 40 to 60 years.

Sex - female (80%) affected more due to narrow lumen bony canal.

Race - common in Whites than Negros.

Heredity - facial configuration like length and wide of bony canal play indirect role.

Socio-economic factor- rare in higher socio economic status people.

Hygiene - poor personal hygiene increase the risk.

Causative organisms

Staphylococci, pneumococci, haemolyticus, streptococci and Pseudomonas pyocyanea.

Mode of infection.

Direct contribution from the adjacent infected make-up

Such as: paranasal sinuses, surrounding bones and dental abscess or caries teeth in the upper jaw.