common diseases in human

HEALTH

The term health is very frequently used by everybody. How do we define if?

Health does not simply mean 'absence of disease' or 'physical fitness'.

It could be defined as a state of complete physical, mental and social well-being.

When people are healthy, they are more efficient at work.

This increases productivity and brings economic prosperity.

Health also increases longevity of people and reduces infant and maternal mortality.

Balanced diet, personal hygiene and regular exercise are very important to maintain good health.

Yoga has been practised since time immemorial to achieve physical and mental health.

Awareness about diseases and their effect on different bodily functions, vaccination (immunisation) against infectious diseases, proper disposal of wastes, control of vectors and maintenance of hygienic food and water resources are necessary for achieving good health.

DISEASE

When the functioning of one or more organs or systems of the body is adversely affected, characterised by various signs and symptoms, we say that we are not healthy, i.e., we have a disease.

Diseases can be broadly grouped into infectious and non-infectious.

Diseases which are easily transmitted from one person to another, are called infectious diseases.

Infectious diseases are very common and every one of us suffers from these at sometime or other.

Some of the infectious diseases like AIDS are fatal.

Among non-infectious diseases, cancer is the major cause of death.

Drug and alcohol abuse also affect our health adversely.

The disease can be defined as a disorder of the mind or body.

This term covers varied conditions leading to deviation of the human body from the normal course or deviation from the normal health.

Thus disease is opposed to health.

From time immemorial diseases have been a prime concern of man.

Early man thought that diseases were caused by evil spirits, hence cure consisted of pacifying the evil spirits with the help of charms and magic.

Hippocrates (B.C. 460-359), the great Greek physician was the first to separate medicine from religion and superstition.

He gave description of disease symptoms and emphasized the need for good diet, fresh air and rest.

He also described that human body has natural tendency to defend itself against diseases.

Pathogen. It is an organism which is capable of producing a disease.

The ability of the pathogen to gain entrance and produce symptoms of disease is called pathogenicity.

Virulence is the degree of pathogenicity of a pathogen in the host body.

Pathogens are biological agents including bacteria, fungi, viruses, mycoplasma, protozoans, helminths, etc.

Parasite is the organism which lives at the expense of the other organism called host for obtaining food and shelter.

A parasite may cause disease in the host.

Infection is the interaction between the host and the parasite having a competition for superiority.

The disease occurs when the parasitic organism is able to win.

The infection or transmission may occur by contact, through air, through food and water, insect bite or by contaminated materials.

The researches in parasitology described causative organisms (parasites) of diseases.

Our knowledge of human parasities developed after the invention of microscope in 1835.

Categories of Diseases

The diseases can be broadly divided into two groups congenital and acquired diseases.

(i) Congenital Diseases : They occur since birth and may result from metabolic disorder or defect in development.

(ii) Acquired Diseases : They develop after birth and can be further divided into two main categories

(i) Communicable diseases which rapidly spread from one person to another, they include infectious diseases, and

(ii) Non-communicable diseases which do not spread from person to person, they include all other acquired diseases.

COMMUNICABLE DISEASES

The infectious diseases rapidly spreading from person to person are called communicable diseases.

The communicable diseases can be categorised on the basis of different aspects.

On the basis of transmission they may be divided into (i) transmitted through air, (ii) through food and water, (iii) through insect bite, and (iv) transmitted by contact.

On the basis of causative organism or pathogen these diseases may be categorised into bacterial, viral, protozoic, helminthic and fungal diseases.

DISEASES CAUSED BY VIRUSES

1. Common cold:

One of the most infectious human ailment.

It is caused by Rhino viruses.

They infect the nose and respiratory passage but not the lungs.

The common cold is characterised by nasal congestion and discharge, sore throat, cough, headache, tiredness, hoarseness etc. for 3 to 7 days.

2. Influenza:

It is commonly known as "Flu" and is highly infectious.

It causes fever and pain all over the body and affects the nose, throat and air passages as in common cold.

The disease is caused by various types of influenza viruses (e.g., Myxovirus influenzae).

It starts with fever, headache, sore throat, cold with sneezing and pain all over the body with restlessness.

In neglected cases, complications like pneumonia, bronchitis and ear infections may develop.

There is no vaccine at present which can give protection against all types of influenza viruses as each epidemic is of a different type.

3. Small Pox (Variola) :

It is highly infectious disease starting with high fever, chill, backache and headache, followed by appearance of rash on the third day of illness.

The rash appears first on the face, then on the rest of the body.

It is more on the face and limbs and less on the trunk.

The rash starts as small reddish spots which change into papules.

These in turn change into small vesicles containing clear fluid.

Vesicles change into pustules.

Finally, a scab is formed and it falls off by the third week.

These scabs leave deep pits or scars known as pock marks.

Many children become blind and develop discharge from the ear.

This disease is caused by a small pox virus named Variola virus (ds DNA virus).

The virus is present in the oral and nasal discharges of the patients and is ejected during the acts of coughing, sneezing, fomites etc., and infects the healthy people.

Vaccination against small pox is one of the best preventive remedies available today.

This was discovered by Edward Jenner in 1798.

Small-pox has been eradicated from India.

4. Chicken Pox (Varicella) :

It is a mild but highly infectious disease causing slight slight fever and a rash which undergoes changes into vesicles, pustules and finally a dark brown scab which falls off leaving no scar unlike smallpox.

The rash comes out in crops and with each fresh crop, there may be slight fever again.

The rash first appears on the trunk and there are more lesions on the trunk than on the face and limbs.

The disease is caused by a virus of chicken-pox named Varicella zoster which is passed out in the discharges of the respiratory tract of an infected person directly as droplets or through contaminated articles used by the patient.

Vaccination against chicken-pox is now available.

The most common late complication of chicken-pox is shingles caused by reactivation of varicella zoster.

5. Measles (Rubeola Disease) :

Measles is a highly infectious disease causing fever, inflammation of the air passages and a rash all over the body.

It attacks especially the children below the age of 5 years and those who have escaped may be attacked even in the later life.

It is caused by Rubeola virus (RNA virus) which is passed out in the secretions of nose and throat of the infected persons as droplets or in articles soiled by these secretions.

The disease starts with catarrh' of the nose and throat, and fever.

The eyes are red and watery, and the face is flushed.

The rash which is slightly pinkish in colour appears first on the back of the ear and face, and spreads downwards on the body.

6. Mumps (Infectious Parotitis):

It is infectious disease causing fever, difficulty in opening the mouth and painful swelling of the parotid glands which lie just below the lobe of the ears.

It is caused by Paramyxovirus (RNA virus), which comes out in the saliva of the infected person.

The patient should take complete bed rest till the swelling subsides in order to avoid complications.

Usually, there are no complications, but in some cases there may be pain and swelling of the testes (orchitis) or pain in the abdomen.

7. Poliomyelitis:

This disease was called infantile paralysis.

But it is now known that the disease may occur at any age.

This disease spreads mainly through intestinal discharges.

It may also spread through contaminated food or drink and by flies or other insects that may contaminate food or drink.

Polio virus (ss RNA) usually enters the body via alimentary canal where it multiplies and reaches the nervous system (spinal cord) through the blood stream.

Its incubation period is 7-14 days.

It produces inflammation of the nervous system.

The earliest sign of this disease is involvement of the central nervous system causing inability to bend the head forward.

Stiffness of the neck is an important sign. Paralysis starts following the weakness of particular skeletal muscles.

The attack of paralysis begins with high fever, headache, chills, pain all over the body.

If muscles of larynx and pharynx are involved it proves fatal.

Within two to three days the paralysis reaches its maximum.

There is no sure cure for polio.

The patient should be kept isolated.

He should be given complete rest.

An adequate arrangement for proper disposal of urine and faeces of the patient must be provided because they contain polio virus.

Overcrowding of children in schools, playgrounds and cinema should be avoided.

Polio is preventable. Polio vaccine is safe and effective.

Now-a-days multiple vaccines are used against polio, diphtheria, whooping cough and tetanus simultaneously.

Concept Builder

Pulse Polio is an Immunization campaign established by the Government of India in 1994 to eradicate poliomyelitis (Polio) in India by vaccinating annually all children under age five against poliovirus.

Every child (0-5 years of age) receives a dose of Oral Polio Vaccine (OPV), a live, attenuated virus which colonises the gastrointestinal tract.

This virus competitively inhibits the wild, disease-causing poliovirus.

Not only does this prevent pernicious infection in the host, it precludes transmission of the wild poliovirus to other hosts.

Since poliovirus cannot survive outside a host for more than two weeks, theoretically it would be eradicated, resulting in the eradication of poliomyelitis.

The campaign proved to be successful and the incidence of poliomyelitis in India has decreased dramatically.

Nevertheless, critics charge that the campaign has seriously encroached on other essential public health services at times when health care resources were minimal.

8. Trachoma:

It is caused by Chlamydia trachomatis.

Trachoma is a chronic inflammatory disease of the eye affecting the conjunctiva and cornea.

It is characterised by development of granules.

Its common symptoms are inflammation, pain and watering of the eye.

It can lead to blindness.

Infection spreads by direct contact, by use of handkerchiefs, towels, pillows of the patient.

9. Rabies (Hydrophobia) :

It is caused by a virus named as Rhabdo virus.

It is introduced in the body by the bite of rabid (mad) dogs usually.

It can be injected by the bite of jackels, wolves, cats etc., Incubation period is from 10 days to one year.

Fear of water is the most important characteristic symptom of this disease.

Other symptoms are saliva from the mouth, severe headache, high fever, alternating periods of excitement and depression, inability to swallow even fluids due to choked throat.

The virus destroys the brain and spinal cord. Rabies is 100% fatal.

There should be compulsory immunisation of dogs and cat population.

10. Dengue fever:

Dengue fever is caused by a RNA containing Arbovirus (Arthropod borne virus) of ffavivirus group which also causes yellow fever (not found in India).

Thus, the virus which causes dengue fever is a mosquito borne flavi-ribo virus.

The virus of dengue fever is transmitted by the bite of female Aedes aegypti (mosquito).

Incubation period is 3-8 days.

Two types: classical dengue fever and dengue haemorrhagic fever are known to occur.

Symptoms of Classical Dengue Fever are

(i) Abrupt onset of high fever.

(ii) Severe frontal headache.

(iii) Pain behind the eyes which worsens with eye movement.

(iv) Muscles and joint pain.

(v) Loss of sense of taste and appetite.

(vi) Measles like rash over chest and upper limbs.

(vii) Nausea and vomiting.

Symptoms of Dengue Haemorrhagic Fever are symptoms similar to classical dengue fever except the following

(i) Bleeding from the nose, mouth, gums and skin bruising.

(ii) Severe and continuous stomach pains.

(iii) Frequent vomiting with or without blood.

(iv) Pale cold or clammy skin.

(v) Excessive thirst (dry mouth).

(vi) Rapid weak pulse.

(vii) Difficulty in breathing.

(viii) Restlessness and constant crying.

If there is fever consult the doctor at once, take paracetamol tablets on the advice of doctor.

Don't take Aspirin and Dispirin.

Do cold sponging if fever is high.

Give plenty of liquids to the patient.

Rush the patient to the hospital if there is bleeding from any part of the body or if the patient becomes unconscious.

No vaccine for Dengue fever is available.

Eliminate mosquito breeding places by covering small water containers, water tanks, changing the water of cooler every week, and where Aedes mosquito breed.

Wear clothes which cover arms and legs.

Do not allow children to play in shorts and half sleeved clothes.

Use mosquito repellents, repellent cream and sleep in mosquito-net.

11. Chikungunya:

It is caused by Chikungunya virus.

This virus was first isolated from human patients and Aedes aegypti mosquitoes from Tanzania in 1952.

The name 'Chikungunya' is derived from the native word for the disease in which patient walks "doubled up" due to severe joint pain.

Its symptons include sudden onset of fever, crippling joint pain, lymphodenopathy and conjuctivitis.

Some show haemorrhagic manifestations.

No vaccine is available.

DISEASES CAUSED BY BACTERIA

1. Cholera:

This is an acute infectious disease caused by Vibrio cholerae.

These may get into a healthy person with contaminated food and water.

The patient starts passing stools frequently, which are white like rice water, and gets repeated vomiting.

Since, a large quantity of fluid and salts are rapidly lost through stools and vomit, therefore, the most important dore treatment is to replace the lost fluid and salts equally rapidly.

Rapid replacement of fluid and elecrolytes is done by oral rehydration-therapy.

2. Typhoid:

It is an infectious disease caused by Gram negative bacterium called Salmonella typhi which is a non-spore forming bacillus.

Typhoid germs are contracted from food or drink contaminated with excreta from carriers or patients.

The spread is facilitated by poor environmental hygiene. Immunity following the infection is not sufficient to prevent relapse.

A large number of organisms have to be ingested by healthy person to suffer from typhoid.

Smaller number may produce the disease if the organisms are very virulent or if the resistance of the host is poor.

The acid in stomach destroys Salmonella that is ingested. Hence, patients having achlorhydria (no acid in stomach) or who take large amounts of antacids to neutralise the acid in stomach suffer more often from typhoid.

The normal intestinal flora produces short chain fatty acids which are lethal to Salmonella.

When this is reduced by antibiotics, the patient is more prone to typhoid.

Salmonella that cause enterocolitis after ingestion, invade the mucosal cells and multiply within them.

They do not penetrate beyond lamina propria and multiply in the lymphoid tissues (Peyers patches) of the small intestine.

Inflammatory changes occur with accumulation of leucocytes.

Enterotoxin liberated by the bacteria may form abscess which may burst causing ovoid ulcers.

This may cause haemorrhage and if the ulcer reaches the serosa, perforation occurs leading peritonitis.

The infection is usually localised in the small intestine and colon.

The incubation period is usually 12-72 hours but may be up to 2 weeks.

(i) Nausea, vomiting and an early chill are common initially followed by colicky abdominal pain and diarrhoea of watery, green, offensive stools.

(ii) Blood mixed with stool and high fever may occur if there is involvement of colon.

Symptoms may subside within a week or two.

There is clinical syndrome characterised by fever, headache, cough, splenomegaly and leucopenia.

This is called enteric fever.

The fever is continuous in type which rises in a step-wise manner.

Diagnosis is done by Widal test which determines the agglutinins against the antigen.

The test is usually positive in the 2^nd week of the disease.

The concentration of agglutinins must keep on rising with time to suggest the disease.

The treatment involves use of antibiotics, antipyretics and rest. TAB vaccine is useful against typhoid.

Special care must be taken to ensure that persons who are engaged as cooks or work in eating establishments are not 'carriers' of this disease who can keep spreading this disease through food .

A classical example of typhoid carrier recorded in history was Mary Mallon who was a cook.

3. Diphtheria:

This disease is caused by Corynebacterium diphtheriae usually affecting children upto five years of age.

It maystart as sore throat, chills with mild fever, sometimes vomiting and headache.

Throat and or tonsils show a grey membrane which may spread down and cause hoarseness and difficulty in breathing.

Nose may be affected giving rise to a blood-tinged nasal discharge from one nostril.

If the disease is not treated early and properly, the toxin produced by the germs affects the heart and the nervous system, and proves fatal.

The most important preventive measure-against this disease is that all babies should be, immunised within the first six weeks of birth using DPT vaccine.

4. Whooping Cough (Pertussis) :

It is a highly infectious disease of young children causing inflammation of the respiratory passages with severe attacks of cough.

It is caused by Bordetella pertussis which comes out while coughing from the discharges of the nose and throat of the patient.

It spreads by direct inhalation of droplets from the patient or the carrier, or by the articles freshly soiled by the discharges.

The cough becomes troublesome, especially at night.

Face becomes red during coughing.

These repeated bouts of violent cough end in a whoop.

Whooping sound is produced due to rushing in of air during deep inspiration at the end of a bout of cough.

The child usually vomits and there is frothy discharge from his mouth and nose.

The disease can be prevented by immunising all infants with whooping cough vaccine which is available singly or in combination as triple vaccine (i.e., DPT).

5. Pneumonia:

This disease is caused by Diplococcus pneumoniae.

Pneumonia is a serious disease of the lungs.

Lymph and mucus collect in the alveoli and bronchioles of the lungs so that the lungs do not get sufficient air.

Therefore, proper exchange of gases does not take place in the alveoli.

It usually lowers body resistance.

Infection spreads by sputum of the patient.

Breathing rate increases with high grade fever. Common in children below age of 5 years.

6. Tetanus (Lock Jaw) :

It is caused by Clostridium tetani.

The first indications of this disease are irritability and restlessness, the neck becomes stiff and there is difficulty in chewing and swallowing.

Subsequently spasms of muscles of the jaw and face take place and thus "Lock Jaw" occurs.

There is a severe pain.

It is often a fatal disease.

The toxin affects 'voluntary muscles' mainly.

Tetanus organisms live in the intestine of horses and other animals without doing any harm.

The spores, are therefore, abundant in the soil manufactured with animal dung.

Spores may survive for 60 or more years in contaminated soil.

On entering the body by way of wounds, the spores release active bacteria.

The latter multiply and secrete powerful exotoxin into the tissue and blood.

The exotoxin known as Tetanospasmin brings about tetanus.

Anti tetanus serum (ATS) injection should be administered in case of an injury.

7. Plague:

This disease is characterized by high fever and a bubo (painful swelling) in the groin or the armpit.

Plague is caused by Yersinia pestis, a deadly bacterium.

It is primarily a disease of rodents but it accidently affects man.

It goes from rat to rat through the rat fleas.

But when the rats die of plague, the fleas leave the dead rat and if any man is round about, they bite him and accidently inject into his blood some plague germs.

In its typical form the bubonic plague is not transmitted from one man to the other, but always from a rat to one or more men.

Concept Builder

When a person is bitten by an infected flea or is infected by handling an infected animal, the plague bacteria move through the bloodstream to the lymph nodes.

The lymph nodes swell, causing the painful lumps ("bubos") that are characteristic of bubonic plague.

Other symptoms are fever, headache, chills, and extreme tiredness.

Some people have gastrointestinal symptoms.

If bubonic plague goes untreated, the bacteria can multiply in the bloodstream and produce plague septicemia (septicemia plague), severe blood infection.

Signs and symptoms are fever, chills, tiredness, abdominal pain, shock, and bleeding into the skin another organs.

Untreated septicemia plague is usually fatal.

Pneumonic plague, or plague pneumonia, develops when the bacteria infect the lungs.

People with plague pneumonia have high fever, chills, difficulty breathing, a cough, and bloody sputum.

Plague pneumonia is considered a public health emergency because a cough can quickly spread the disease to others.

Untreated pneumonic plague is usually fatal.

8. Tuberculosis (TB) :

It is also called Koch's disease.

It a caused by Mycobacterium tuberculosis.

The bacteria damage the tissues and release a toxin named tuberculin which produces the disease.

It affects the lungs, lymph nodes, bones and joints.

Incubation period is quite variable.

Symptoms of pulmonary (lungs) tuberculosis are fever, cough, blood containing sputum, pain in the chest and loss of weight, excessive fatigue, failure of appetite, rise of temperature in the evening, hoarseness of throat, night sweating and rapid pulse.

BCG vaccine gives considerable protection against tuberculosis.

Concept Builder

DOTS (Directly Observed Treatment, Short course chemotherapy) is a strategy to ensure cure by providing the most effective medicine and confirming that it is taken.

It is the only strategy which has been documented to be effective Worldwide on a program basis.

DOTS ensures that patients take medicines regularly until they are cured.

During the intensive phase of treatment, a health worker or other trained person watches as the patient swallows the drug in his presence.

During the continuation phase, the patient is issued medicines for one week of which the first dose is taken in presence of health worker or other trained person issuing the drugs.

The consumption of medicine in the continuation phase is also checked by return of the empty multibilister combipack when the patientcomes to collect medicine for the next week.

Sputum microscopy is done at defined intervals during treatment to monitor the patients progress toward cure.

9. Leprosy (Hansen's Disease) :

This disease is caused by Mycobacterium leprae, which was discovered by Hansen.

Symptoms of leprosy include appearance of light coloured patches on the skin, thickening of the nerves, partial or total loss of sensation in the affected parts of the body.

These are accompanied by fever, pain, ulcers and skin eruptions.

Deformities of toes and fingers may also develop.

The bacilli leave the body in nasal discharge, from the throat during coughing, sneezing and even speaking and through broken skin lesions.

The patient is treated with DDS (diamino diphenyl sulphone).

DISEASE SPREAD BY PROTOZOA

1. Malaria

Of all the communicable diseases caused by protozoa, malaria is the most destructive for man. Malaria is widespread in the tropics and subtropics and also in certain areas of the temperate zones.

Malaria was earlier thought to be caused by foul gases emanating from marshes, hence the disease was named malaria (Italian, mala = bad, aria = air).

The term malaria was given by Maculoch (1837).

A French army doctor Charles Laveran (1880) discovered malaria parasite (Plasmodium vivax and P. malariae) in the RBC of malaria patient.

Stephens discovered P. ovale and Welch discovered P. falciparum. Lancisi suspected that malaria occurs where mosquito are found.

Richard Pfeiffer (1892) explained that some blood sucking insects are involved in transmission of malaria.

Scottish doctor Patrick Manson (1894) suggested that mosquito has some role in transmission of malaria.

A doctor in Indian Army Sir Ronald Ross (1897) established relationship between mosquito and malaria.

On 29^th August, 1897 Ronald Ross discovered the oocysts of Plasmodium on the stomach of female Anopheles mosquito.

Hence 29^th August is observed as the Mosquito day.

For his valuable discovery Ronald Ross was awarded the Noble Prize of medicine in 1902.

The life history of malaria parasite in female Anopheles mosquito was studied by B. Grassi (1917).

A. Bignami and G. Bastianelli.

Erythrocytic schizogony in the RBC of man was studied by Golgi (1885).

E. Shortt (1948) reported development of malaria parasite in the liver of man.

The detailed monograph of malarial parasites was written in 1996 by P.C.C. Garnham and their fine structure has been reviewed by M. Rudzinska (1969).

Malaria is a common tropical disease caused by a protozoa Plasmodium through the bite of female Anopheles mosquito.

There are mainly four types of Plasmodium infection causing malaria as follows:

1. Plasmodium falciparum (Malignant tertian malaria)

2. Plasmodium vivax (Benign tertian malaria)

3. Plasmodium malariae (Quartan malaria)

4. Plasmodium ovale (Mild tertian malaria)

When an infected mosquito bites an individual, its saliva, rich in parasites (sporozoites) is injected.

The sporozoites enter the circulation and then the liver (pre-erythrocytic phase).

It multiplies in the liver cells forming merozoites.

After 5-9 days, the merozoites enter the red blood cells (erythrocytic phase) forming trophozoites which subsequently mature to become schizonts.

The erythrocytic merozoites are discharged into the blood stream when the red cells degenerate.

This results in an attack of malarial fever.

The red cells are destroyed by the spleen which enlarges and some of the merozoites continue to develop in the liver (exo-erythrocytic phase) causing a relapse.

This phase is absent in life cycle of P. falciparum.

Some of the merozoites for unknown reasons do not form schizonts but develop into male and female gametocytes.

During the mosquito bite, these gametocytes are ingested.

They fertilise in mosquito's stomach and develop into sporozoites which localise in the salivary glands of the mosquito.

These sporozoites enter the human blood stream on a subsequent mosquito bite and thus complete the cycle.

The onset may be insidious with abdominal pain, nausea, dry cough and malaise. Rarely it may be acute and with fever and chills.

In the early stage, fever may be persistent for several days but soon it develops into a synchronous periodicity.

A classical attack of fever has a chill, rise in temperature to 40-41QC headache and myalgia.

This is followed by several hours of profuse sweating and fall in temperature.

In vivax and ovale malaria these paroxysms occur every 48 hours (benign tertian) whereas in malariae, it occurs every 72 hours (quartan).

In falciparum malaria, the temperature is usually persistently elevated or may progress to 48 hour cycle (malignant tertian malaria).

These cycles may be repeated in case of benign tertian malaria due to exo-erythrocytic phase.

Liver is moderately enlarged and tender.

Spleen is often palpable in acute attack.

It is soft to firm and occasionally tender.

Rarely jaundice may occur.

Malarial parasites may be visible on the peripheral smear examination.

Malarial parasites can also be demonstrated on bone marrow examination and by splenic puncture.

Treatment of Malaria includes drugs like Daraprim Chloroquine & Quinine (derived from the bark of Cinchona tree).

2. Amoebiasis

Amoebiasis is caused to man by a protozoan Entamoeba histolytica.

This is also known as amoebic dysentery.

Entamoeba histolytica was first discovered by Lambl (1859).

Friedrick Losch, a Russian zoologist in 1875, rediscovered this protozoan in the faeces and intestinal ulcers of dysentery patient and succeeded in transferring it to puppies.

Entamoeba histolytica is a microscopic endoparasite of man and is commonly found harbouring the lumen of the upper part of the large intestine i.e. the colon.

It invades the mucosa and sub-mucosa of the intestinal wall and causes amoebic dysentery or amoebiasis.

The trophozoites of the parasite make their way deep by eating through mucosa of the intestinal wall.

Here they multiply by binary fission and spread rapidly outward to form flask-shaped ulcers containing cellular debris, lymphocytes, blood corpuscles and bacteria.

This causes the formation of abscesses in the intestinal wall.

The penetration into the sub-mucosa by the trophozoites is made possible by histolysis as well as cytolysis.

The mechanism involves the dissolution and necrosis of tissues and cells by a proteolytic enzyme of the nature of histolysin secreted by the trophozoites themselves.

As the sub-mucosa is eroded by the trophozoites the ulcers burst and the blood capillaries rupture.

The blood and the ulcer contents pour into the lumen of the intestine and pass to outside with stool.

This characterises the amoebic dysentery or amoebiasis.

The stool of a dysenteric person is usually acidic and consists of swarms of Entamoebae as well.

Person suffering from amoebic dysentery has repeated blood-mixed, slimy and foul-smelling motions.

Sometimes, the trophozoites make their way through the blood circulation, into the brain, liver, spleen, lungs and gonads.

Here also they destroy the tissues and cause formation of abscesses (cavities containing pus).

Within the liver, the trophozoites cause severe lesion affecting the metabolic activities.

Formation of abscesses in brain usually proves fatal.

It mainly occurs by ingestion of tetranucleated cysts in food or drinks.

Diagnosis, consists of microscopical detection of trophozoites or cysts in faecal smears.

The presence of white, stone-shaped 'Charcot-Leydon' crystals in faeces suggest the E. histolytica infection.

Treatment of amoebic dysentery is not very difficult but the permanent cure is sometimes hard to achieve as relapses do occur.

For temporary relief, an alkaloid Emetine is effective.

A synthetic derivative called Dehydroemetine, is equally effective.

The most significant advance in the treatment of amoebiasis has been the use of Metronidazole and Tinidiazole as an amoebicide.

It is very active against both intestinal and extra intestinal amoebiasis.

Prevention of infection is entirely a matter of hygiene, both personal as well as municipal.

3. Giardiasis (= Diarrhoea)

Also known as 'Backpacker disease' because travellers are some of the most vulnerable to this disease.

It is caused by a zooflagellate protozoan named Giardia intestinalis.

It is the first human parasitic protozoan known.

It lives in the upper parts (duodenum and jejunum) of human small intestine.

It is found all over the world.

The parasites perch over the living cells of intestinal wall by means of their adhesive discs.

They absorb nourishment from the food passing through intestine, grow and multiply through binary fission.

The large number of parasites interfere with digestion and absorption of food.

This causes epigastric pain, abdominal discomfort, diarrhoea, headache and sometimes fever.

The disease caused by Giardia is popularly known as giardiasis or diarrhoea (watery and frequent stools).

 

DISEASE CAUSED BY HELMINTHES

1. Ascariasis:

It is caused by Ascaris lumbricoides which is cosmopolitan in distribution.

It is an endoparasite of the small intestine of human beings, but also infects the pigs and cattle.

It is more common in the children, because the latter are generally in the habit of eating soil and clay, which may be infected by the eggs of Ascaris.

The food of the worm consists of semi-digested food of the host, the blood and the fluid of the alimentary canal of the host.

The worm ingests the food with the help of suctorial pharynx.

There is no secondary host in the life cycle of this parasite.

Since a large number of adult Ascaris worms normally infest a single host, they obstruct the intestinal passage and thereby cause abdominal discomforts, like colic pains.

The patient may also suffer from impaired digestion, diarrhoea and vomiting.

In children, where the ascaris infection is quite common, mental efficiency is affected and body growth is retarded.

The disease can best be treated by administering antihelminthic drugs such as oil of Chenopodium, Alcopar, Bendex, Dewormis, Zental, etc.

Since the main source of infection is the pollution of soil, water, vegetables, therefore utmost care should be taken in the dispersal of human faecal matter.

Vegetables as a rule, should be washed properly before eating.

The parents should see to it that their children do not take to the habit of eating soil.

2. Filariasis:

Wuchereria (W. bancrofti and W. malayi), the filarial worms cause a slowly developing chronic inflammation of the organs in which they live for many years, usually the lymphatic vessels of the lower limbs and the disease is called elephantiasis or filariasis.

The genital organs are also often affected, resulting in gross deformities.

The pathogens are transmitted to a healthy person through the bite by the female Culex mosquito vectors.

DISEASE CAUSED BY FUNGI

The dermatophytes are a group of closely related fungi.

These infect the skin hair and nails and cause a variety of clinical conditions collectively called as dermatophytoses or tinea or ringworm.

Dermatophytes include three genera:

Trichophyton. It infects skin, hair and nails.

Microsporum. It attacks the hair and skin but usually not the nails.

Epidermophyton. It infects the skin and nails but not the hair.

Thus main symptoms of the disease are appearance of dry, scaly lesions on various parts of the body such as skin, nails and scalp.

These lesions are accompanied by intense itching.

In Tinea cruis or dhobie itch, the groin and the perineum are involved.

In Tinea barbae, the bearded areas of the face and neck are involved.

Tinea pedis or athletes's foot is the ring worm of foot and Tinea capitis is the ringworm of the scalp.

Heat and moisture help these fungi to grow in the skin folds such as those in the groin or between the toes.

The infection of ringworm is usually acquired from soil or by using towels, clothes or comb of infected persons.