Communicable diseases are categorized according to the type of pathogens like bacterial, viral, protozoans, helminthes etc.
I. Bacterial Disease
Highly communicable disease.
Caused by Vibrio cholera. It is transmitted by contaminated food, water, drinks (fomite transmission) through houseflies. It is an acute diarrhoeal disease characterised by vomiting, muscular cramps, anuria (no urine) & rapid dehydration.
Preventive measures include proper community sanitation, destruction of flies, purification of water by treatment with tropical chloride of lime (TCL) or chlorine, personal cleanliness, taking boiled water & heated food, avoiding eatables exposed to flies & dust, isolation of the patient, & health education. Most important antibiotics for cholera are tetracycline & chloramphenicol.
Inflammatory disease of lungs.
Caused by Streptococcus pneumoniae. It is characterised by sudden chill, chest pain, cough with rusty mucoid sputum, rapid shallow breathing & high temperature. In this the fluids collects in the alveoli & bronchioles due to which the lungs do not get sufficient air to support life. Pneumonia commonly occurs in old peoples.
Important drugs for pneumonia are – erythromycin, tetracycline & sulphonamide.
Acute infectious disease.
Caused by Salmonella typhi which is found in the intestine of human. Typhoid spreads through food, milk & water contaminated with intestinal discharges either directly or through flies & personal hygiene. Main symptoms are high fever, headache, diarrhoea, gastrointestinal disorder like ulceration of intestine, etc.
Control – Diagnosed by widal test.
– Antibiotics are ampicillin & chloramphenicol.
(d) Leprosy (Hansen’s disease):
Contagious chronic disease.
Caused by Mycobacterium leprae which lives in the endothelial cells of blood vessels & in the monocytes of blood. It affects mainly the peripheral nerves. It also affects the skin, muscles, the eye, bones, testes and internal organs.
Leprosy is clinically characterized by one or more of the following cardinal features:
(i) Hypopigmented patches
(ii) Partial or total loss of cutaneous sensation in the affected areas (the earliest sensation to be affected is usually light touch)
(iii) Presence of thickened nerves, and
(iv) Presence of acid-fast bacilli in the skin or nasal smears
The signs of advanced disease are striking: presence of nodules or lumps especially in the skin of the face and ears; ulcers; loss of fingers or toes; nasal depression, foot-drop, clawed toes and other deformities. Presence of lepromin in skin test indicates the appearance of leprosy.
Leprosy is of two types – tuberculoid leprosy (involves tuberculoid granuloses formed by aggregation of macrophages) & lepromatous leprosy (characterised by nodular aggregates of lipid laden macrophages, lepra cells).
Tuberculoid leprosy give positive test with lepromin while lepromatous leprosy is negative to lepromin test. Diamino diphenyl sulphone (DDS) is used for treating leprosy.
Incurable bacterial disease. Caused by Clostridium tetani which lives in the intestine of horses & other animals without doing any harm. Its infection is acquired by contamination of wounds with tetanus spores as these infected spores are abundant in the soil manure with animal dung.
Tetanus results in painful spasm (involuntary muscular contraction) of voluntary muscle and paralysis, which usually begin with jaw and neck muscles. This has led to the name “lockjaw”. The common symptoms -are stiffness of the jaw, difficulty in chewing and swallowing, fever, headache, and spasm of facial muscles. The disease is often fatal.
(f) Plague (also called black death):
Plague is primarily a disease of rat. It is caused by rod shaped non-motile bacterium Pasteurellal Yersinea pestis which is an endoparasite of gut of rat flea, Xenopsylla cheopsis. Rat flea is the ectoparasite of rat & mice. Its germs are also be transmitted from man by head louse (Pediculus) & bed bug (Cimex). Plague is of 3 types – (i) bubonic plague (ii) pneumonic plague (iii) septicemic plague.
(i) Bubonic plague is basically a blood disease in which bacteria multiply in the blood streams & localize in the lymph nodes, especially those of armpits, neck & groin. It is characterised by high fever, weakness, enlargement of lymph nodes (especially of armpit & groin), delerium, exhaustion & haemorrhages which turn black. The patient dies thereafter. Hence plague is also called Black Death.
(ii) Pneumonic plague is characterised by haemorrhage of bronchi & lungs. Pneumonic plague spreads from human to human (without ratflea) through droplets & fomites.
(iii) Septicemic plague is characterised by anaemia, fever, chill etc. leading to death within 2 days. Streptomycin injection & tetracycline are effective drugs against plague bacilli.
(g) Tuberculosis (TB):
Tuberculosis is specific infectious disease caused by Mycobacterium tuberculosis. The disease primarily affects lungs and causes pulmonary tuberculosis. It can also affect intestine, meninges, bones and joints, lymph glands, skin and other tissues of the body.
During infection bacteria produce a toxin called tuberculin. The disease is usually chronic with varying clinical manifestations. The disease also affects animal like cattle; this is known as “bovine tuberculosis”, which may sometimes be communicated to man.
Pulmonary tuberculosis is the most common form of tuberculosis. Pulmonary tuberculosis is characterised by coughing, fever, chest pain, difficult breathing & blood in sputum (haemoptysis), meningitis (leads to coma).
Tuberculosis is transmitted by droplet infection and droplet nuclei generated by sputum (which is positive for pulmonary tuberculosis).
To transmit infection, the particles must be fresh enough to carry a viable organism. Coughing generates the largest number of droplets of all sizes.
Sputum, tuberculin (Mantoux test), X-ray and gastric analysis are carried out to diagnose tuberculosis.
BCG (Bacillus Calmette Guerin) vaccine gives considerable protection against the disease. Antituberculosis drugs are streptomycin, PAS (para amino salicylic acid), rifampicin, ethambutol etc.
(h) Pertussis/Whooping cough:
Pertussis is one of the most dangerous diseases of childhood & is caused by Bordetella pertussis. It affects respiratory passage resulting in their inflammation in association with cold, cough with the characteristic “whoop” (loud crowing inspiration) & mild fever in beginning leading to accumulation of mucous. Whooping cough is spread through droplet infection & direct contact.
Most effective antibiotic for whooping cough are erythromycin, ampicillin, chloramphenicol & streptomycin.
Vaccine for pertussis is available in the form of DPT (i.e., diphtheria, pertussis, tetanus) given to new-born at monthly interval.
Diphtheria, a respiratory disease common in children is caused by Corynebacterium diphtheriae. This disease affects the throat whose main symptom is suffocation. It is characterised by oozing of semisolid material in throat forming a tough membrane.
It is highly infectious & spread through droplet infection & direct contact. Antibiotics recommended in case of diphtheria are penicillin & erythromycin.
It is an acute infections disease caused by spare forming bacterium Bacillus anthracis. Anthrax is most common in agricultural regions where it occurs in animals. It most commonly occurs in wild and domestic lower vertebrates (cattle, sheep, goats, camels, antelopes and other herbivores), but it can also occur in humans when they are exposed to infected animals or tissue from infected animals. Anthrax infection can occur in three forms – cutaneous, inhalation and gastrointestinal.
Itchy bump that resembles an insect bite and develops into a vesicle and then a painless ulcer within 12 days with a characteristic black necrotic area in the centre.
Common cold which may progress to severe breathing problems and shock. It is usually fatal.
Acute inflammation of the intestinal tract with initial signs of nausea, loss of appetite, vomiting, fever, abdominal pain, severe diarrhoea.
If left untreated, anthrax in all forms can lead to septicemia and death. Anthrax is considered to be a potential agent for use in biological warfare.
Peptic ulcers are basically the eroded areas in the lining of stomach & duodenum which occurs due to excessive secretion of acid in gastric juice.
But now it is known that ulcers are due to attack of bacterium – Helicobacter pylori which explain why non-acid producing regions also develop gastritis & ulcers.
II. Viral Diseases:
(a) Influenza (also called flu):
Influenza is an acute respiratory tract infection caused by influenza virus. Influenza viruses are classified within the family Orthomyxoviridae.
There are three viral subtypes, namely influenza type – A, type – B & type-C. Both A & B type viruses are responsible for epidemics of disease throughout the world.
These three viruses are antigenetically distinct. Antigenic variability is highest in the influenza virus type A and less in type B, while it has not been demonstrated in type C. There is no cross immunity between them.
Therefore person infected with one type (if A) will not develop immunity for the other two type (B & C).
Major reservoir of influenza virus exists in animals & birds. It spread mainly from person to person by droplet infection or droplet nuclei created by sneezing, coughing or talking. The portal of entry of the virus is the respiratory tract.
Influenza causes inflammation of upper respiratory tract, nose, throat and eyes. It results in coryza (profound discharge of running nose), sneezing, sore throat, coughing, muscle pains, headache, chill and fever for 4- 5 days. Incubation period is 2-3 days. Vaccine available against influenza virus A.
An acute infectious disease caused by a specific virus which has a prediliction for glandular and nervous tissue. Clinically, the disease is recognized by non-suppurative enlargement and tenderness of one or both the parotid glands, hence called parotiditis.
The causative agent, Myxovirus parotiditis is a RNA virus of the myxovirus family.
The disease is spread mainly by droplet infection and after direct contact with an infected person.
It is characterised by pain and swelling in either one or both the parotid glands but May also involve the sublingual and submandibular glands. Often the child complains of “ear ache” on the affected side prior to the onset of swelling.
There may be pain and stiffness on opening the mouth before the swelling of the gland is evident. Mumps may also affect the testes, pancreas, CNS, ovaries, prostate etc. Infection of testes may cause sterility. These are the secondary infection occur especially in adults which can be prevented by given antibiotics. In severe cases, there may be fever, headache and other constitutional symptoms which may last from 3-5 days.
The swelling subsides slowly over 1-2 weeks.
Vaccination is available as MMR.
(c) Measles (Rubeola disease):
It is an acute infectious eruptive viral disease of childhood (3-5 years old) caused by specific virus of the group myxoviruses. Basically it is caused by an RNA containing Rubeola virus/Polynosa morbillorum. Measles is the infection of respiratory tract & conjunctiva which is transmitted by contact, fomite & droplet methods.
In pre-eruptive stage (3-4 days), there is hoarseness, cough, sneezing and running nose or coryza due to inflammation of respiratory tract, redness or watering of eyes (conjunctivitis), loss of appetite and fever. Blue- white Koplick’s spots (with reddish base) appear opposite molar teeth in buccal cavity on third day.
Fourth day begins with itching, skin rash, small raised red spots (rubeola) in crescent shaped groups starting from back of ears, reaching forehead, face (bloated and blotchy) and then body. By 5-6th day the rashes begin to subside.
Incubation period is commonly 10 days from exposure to onset of fever & 14 days to appearance of rash. Antibiotics and vitamin A are given to prevent complications. Vaccination (MMR or Mumps, Measles and Rubella) is available which is given at the age of one. Prior to that the infant carries passive immunity from mother.
(d) General measles (Rubella):
Rubella or german measles is an acute childhood infection, usually mild, of short duration (approximately 3 days) and accompanied by low-grade fever, lymphadenopathy and a maculopapular rash. Infection in early pregnancy may result in serious congenital defects, including death of the foetus. It is caused by Rubella virus. Immunoglobin are useful & vaccination is provided as MMR.
(e) Small pox:
Small pox has been eradicated globally. Vaccine was first developed by Edward lenner.
(f) Chicken pox:
It is a contagious and fomite transmitted eruptive viral disease which is more common but less severe in children of up to 10 years and severe but rare in adults. It is caused by virus Varicella zoster with incubation period of 14-16 days.
Illness begins with slight fever, shivering and backache.”There are then prodromal (symptom that starts before the onset of an illness) or transitory rashes with crops to pinkish centripetal spots appearing first on trunk, forehead and face. Uneasiness, aches and high fever accompany each new crop.
Spots turns into fluid filled vesicles and then scabs in five days. Scabs fall off without leaving any mark. Use of boric acid, calamine and benzyl benzoate reduces itching and tendency to scratch. No drug, no vaccine. Antibiotics are given for covering any complication. Passive immunity is possible through immunoglobulins. Single attack gives lifelong immunity.
It is a highly infectious disease of infants & children. It may attack adult also.
It is caused by very small RNA virus containing Polio virus & transmitted through faeces, urine & nasal secretions contaminating food, water drinks either directly or through flies. This virus causes inflammation of grey matter of the spinal cord, inability of the head to bend forward, and stiffness of the neck. It also destroys motor nerve cells in the spinal cord. Muscles fail to work and shrink due to lack of nerve impulses.
This may cause paralysis of limbs in some cases. Hence called infantile paralysis. Paralysis is accompanied by high fever, headache, chilliness and pain all over the body.
Involvement of the laryngeal and pharyngeal muscles proves fatal. The virus enters the digestive tract with contaminated food and water and multiplies in the intestinal cells. It then passes into blood stream and lymphatic system, and finally reaches the spinal cord where it starts multiplication.
Oral vaccines are available (developed by Jonas Salk and Albert Sabin, 1940) to protect babies from polio attack. Public Pulse Polio Immunization Programme is organized in India for eradicating polio.
(h) Rabies (Hydrophobia):
Rabies is caused by RNA virus called Rabies virus (Lassa virus). Rabies virus is neutrotrophic i.e., damage motor neurons of brains. Rabies affects all warm blooded animals & is exclusively transmitted by the bites of carnivores. It is transmitted to human beings by biting/saliva of rabbit, dog, monkey, cats, etc.
It leads to encephalitis, fear of water (hence called hyrophobia), high fever, severe headache, spasm of throat & chest leading to death. Characteristics cytoplasmic inclusions called Negri bodies found in many neurons help in: rapid diagnosis.
Vaccine against rabies was developed by Louis Pasteur.
Hepatitis is the viral infection of liver causing their inflammation. It is accompanied by loss of appetite, nausea, whitish stool, but orange brown urine & jaundice which occur due to bilirubin released from damaged liver cell.
Hepatitis is of two types – (i) Hepatitis A (epidemic jaundice) or (ii) Hepatitis B (serum hepatitis):
(i) Hepatitis A is more common in children & young adult with incubation period of 2-6 weeks.
(ii) Hepatitis B occurs at any age with incubation period of 6 weeks to 6 months.
About 80% liver cancer is believed to be due to hepatitis B.
Infection of infectious hepatitis spread from persons to persons by faecal oral route. Contamination of water and food may cause epidemic. Serum hepatitis spreads by transfusion of contaminated blood & blood products.
Personal cleanliness, boiled water, properly heated cooked/cleaned food articles and control of flies are required in period of epidemic. Vaccine is available.
(j) Dengue fever (Break bone fever):
Dengue fever is an acute tropical frequently epidemic viral disease of humans which is caused by RNA containing dengue virus. It is transmitted by bite of female tiger mosquito Aedes aegypti during day time. Two types of dengue fever are: (i) classical dengue fever & (ii) dengue haemorrhagic fever.
(i) Classical dengue fever (break bone fever) is more severe in adults & characterised by mild conjunctivitis, high fever, backache, retro-orbital pain (pain behind the eye ball) etc.
(ii) Dengue haemorrhagic fever is a fatal form with nausea, headache, vomiting, abdominal pain etc. Preventive measures are same as for malaria.
(k) Yellow fever:
Yellow fever caused by an arbovirus is a haemorrhagic disease transmitted by the infected Aedes aegypti. Symptoms of yellow fever are headache, fever, vomiting, rupture of veins in kidneys, spleen, liver, etc. In severe cases, the skin of the sufferer becomes yellow from jaundice, hence the name yellow fever. Max Theilder in 1951 got Nobel Prize for the development of vaccine for yellow fever.
Trachoma is an eye disease which is caused by Chlamydia trachomatis (a primitive prokaryote).
It is transmitted by direct contact, fomite & flies. Trachoma is characterized by inflammation & discharge from eyes & ulceration of cornea & conjunctiva resulting in blindness. Chlamydia trachomatis are obligatory intracellular parasite & are larger than virus.
III. Protozoan Disease:
Types of protozoan diseases are – malaria, amoebiasis, kala- azar, trypanosomiasis etc. (a) Malaria (means bad air) It is the most common protozoan diseases caused by the infection with parasites of the genus Plasmodium & transmitted to man by certain species of female Anopheles mosquito.
Malaria is characterised by recurring rigors lasting 6-10 hours. There are three stages:-
(i) Cold stage: Chill & shivering.
(ii) Hot stage: Temperature rises to 100°C.
(iii) Sweating stage: There is perspiration & gradual fall in temperature.
Malaria results in anaemia, toxaemia & splenomegaly (enlarged spleen).
The Life Cycle of the Plasmodium:
Plasmodium completes its life cycle in two phases and two hosts: asexual phase in the human host and sexual phase in the female Anopheles mosquito host. Man and mosquitoes are regarded secondary (intermediate) host and primary (final) host respectively.
A. Infected (carrying sporozoites) female Anopheles mosquito bites a person.
B. Plasmodium sporozoites enter the bloodstream and travel to the liver.
C. They divide repeatedly, and new spores called merozoites emerge and infect red blood cells
D. Some merozoites in the blood develop into special cells called gametocytes.
E. When a female Anopheles bites the infected person, it ingests these gametocytes.
F. In the mosquito’s digestive system, the sperm and egg combine to form a zygote.
G. The zygote divides repeatedly to form more sporozoites (Infective stage)
H. The sporozoites migrate to the salivary glands of the mosquito. When the insect bites another person, the life cycle begins again
Control: Two types: offensive & defensive.
Offensive measures: The offensive measures can be taken against both the organisms (mosquitoes and malarial parasites) involved in malaria.
(a) Offensive measures against mosquitoes: Mosquitoes can be destroyed by the following methods:-
(i) Drain off or fill up all ditches, ponds and pools with earth so that the mosquitoes may not find water to breed.
(ii) If the above places are too large to be drained off or filled up, sprinkle kerosene oil or solution of DDT on water so that the mosquito larvae and pupae may not breathe fresh air and may die of suffocation.
(iii) Cover the drains or make underground drains to eliminate breeding grounds of mosquitoes.
(iv) Clear the sluggish drains and water courses of aquatic vegetation to speed up the water flow. This will sweep the eggs, larvae and pupae to sewers or rivers and seas where they may perish.
(v) Spray suitable insecticides, such as DDT and BHC, in and around the human habitations to kill the adult mosquitoes. The latter can also be killed or driven out of the houses by fumigation with sulphur.
(vi) The adult mosquitoes can also be avoided by removing unnecessary vegetation from and around the houses.
Offensive measures against parasites of malaria:
(i) Originally, quinine derived from the bark of a Peruvian tree Cinchona was used.
(ii) These days’ synthetic drugs chloroquine phosphate and primaquine are used.
(iii) More effective than these is daraprim. It is slow in action, but, in due course of time, kills the parasites both in the blood and the liver, and also in the mosquito that feeds on the blood of an infected person.
The defensive measures include the precautions by which we protect ourselves from mosquitoes without killing them. These are summarised below –
(a) Apply some insect-repellent (mosquito oil or cream) to the exposed parts of the body at night so that mosquitoes do not bite).
(b) Screen all habitations from mosquitoes with wire-gauze over doors, windows and ventilators.
(c) Build houses on high sites away from swamps and vegetation to avoid mosquitoes.
(b) Kala azar (Leishmaniasis):
Kala azar is caused by Leishmania donovani. It is spread by sandfly (Phlebotomus) & characterised by enlarged spleen & liver with high fever. Kala azar is also known as dum dum fever.
Leishmania braziliensis causes espundia with ulcers appearing first on legs later on throat, nose etc. Oriental sore is caused by L. tropica.
(c) Ciliary dysentry (Balantidiasis):
Ciliary dysentry is caused by a ciliated protozoan named Balantidium coli. The latter inhabits the human large intestine (colon). Also seen in pigs and monkeys. In pigs they are non-pathogenic. It reproduces asexually by transverse binary fission and sexually by conjugation. The latter is followed by cyst formation. Cysts pass out in the host’s faeces.
Infection occurs by ingesting cysts with food and drinks. Balantidium coli causes ulcers in the colon and invades mucous membrane by secreting an enzyme hyaluronidase. This generally results in diarrhoea, but may also lead to severe or fatal dysentery. Protection of food articles from dust and flies, that may carry cysts, can prevent human infection. Tetracycline or iodoquinol are effective treatments.
IV. Helminthic Diseases:
Helminthes are multicellular parasites which causes many disease in man. It consists of roundworms & flatworms. Helminthes diseases are transmitted through dirty hands, contaminated soil and food. Types of diseases are ascariasis, ancylostomiasis, filariasis, taeniasis etc.
Tapeworm infection can also occur by taking improperly washed vegetables and water contaminated with the tapeworm capsules. Thus, the vegetarians can also get tapeworm infection. The capsules release embryos which may reach eyes or brain, develop into larvae, called cysticerci that encyst. The cysts so formed may cause blindness or epilepsy like symptoms and prove fatal. Another species, T. saginata, called beef tapeworm, causes taeniasis in beef- taking humans. Its intermediate hosts are cattle.
Other diseases caused by helminthes:
Enterobius vermicularis (Oxyuris):
Called as the pinworms, found in large intestine and appendix, causes anal itching, appendicitis, nervous problem. No intermediate host. Transmission is direct by contaminated food. Causes: Enterobiasis.
Dracunculus medinensis (Guinea worm):
These are found in the subcutaneous tissues of body. Causes: Guinea worm disease, characterised by blisters on skin. “Like small pox it is considered to be an extinct disease in India.
Loa Loa (The eye worm):
Found in the subcutaneous tissues of eyes, causes conjunctivitis.
Found in the human intestine, cause muscular pains and pneumonia or Trichiniasis, transmitted by eating infected pork.
Trichuris trichura (whip worm):
Found in the caecum and appendix, causes anaemia, bloody stools and pain.
Causes schistostomiasis (also called Bilharzia). Transmitted by snail. Found in urinary bladder, blood vessels & caused itching rashes aches, fever & eosinophilia.