9 Classifications of Communicable Diseases according to Nature of the Pathogen (2023)


Communicable diseases are classified into nine types according to the nature of the pathogen (causing agent). They are 1. Viral diseases, 2. Rickettsial diseases, 3. Mycoplasmal diseases, 4. Chlamydial dis­eases, 5. Bacterial diseases, 6. Spirochaetal diseases, 7. Protozoan diseases, 8. Helminthic diseases and 9. Fungal diseases.

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1. Viral Diseases:

1. Poliomyelitis or Polio (Infantile Paralysis):



Enter virus (Poliovirus)

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Modes of Transmission:


Polio virus usually enters the body via alimentary canal (faecal oral route) where it multiplies and reaches the nervous system through the blood stream.

Incubation Period:

7 to 14 days

Signs and Symptoms:


It produces inflammation of the nervous system. 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, chilliness, pain all over the body.

Prevention and Treatment:

There must be provided an adequate arrangement for proper disposal of urine and faeces of the patient, because they contain polio virus. Over­crowding of children in schools, playgrounds and cinema halls should be avoided. Polio is preventive. Polio vaccine is safe and effective. The first polio vaccine was prepared by Jonas Salk (1953). The killed virus is called “Salk Vaccine” and injected to develop immunity. Jonas Salk is called “father of polio vaccine”.

Sabin et al prepared an oral vaccine known as OPV (Oral Polio Vaccine).

2. Rabies (Hydrophobia):



Rabies virus.

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Symptoms and Modes of Transmission:


The virus is introduced in the body by the bite of rabid (mad) dogs usually. It can be injected by the bite of jackals, wolves, cats etc.,

Incubation period:

10 days to one year.

Signs and Symptoms:


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.

Prevention and Treatment:

There should be compulsory immunisation of dogs and cat population. All ownerless and stray dogs should be destroyed. Wound of the bitten person should be immediately washed with soap and water. After this give anti rabies vaccine to the patient. The pet should be watched for 10 days after it has bitten someone to make sure that it does not have rabies virus.

3. Viral Hepatitis:



It is commonly called jaundice. Viral hepatitis is the most important form of hepatitis. In early stage the liver is enlarged and congested. In later stage the liver becomes smaller, yellowish or greenish. The symptoms in early phase include— fever, anorexia, nausea, vomiting, epigastric discomfort, pains in muscles and joints. The urine is dark and stool is pale. Splenic enlargement is sometimes present.

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There are 6 types of viral hepatitis. These are Hepatitis A, Hepatitis B, Hepatitis C, Hepatitis D, Hepatitis E and Hepatitis G. These (except Hepatitis G) are given below in table form. There is no Hepatitis F.

Characteristic Features of Different Types of Hepatitis:

FeatureHepatitis AHepatitis ВHepatitis СHepatitis DHepatitis E
3. TransmissionFaecal oral RouteParenteral; (Blood, Needle, Body secretion, Placenta, Sexual contact)Parenteral; (Blood)Parenteral; (Blood, co-infection with ­ hepatitis B)Faecal oral Route
4. SymptomsFever, head­ ache, gastro intestinal disturbance, dark urine, jaundiceSimilar, to HAV but no headache. Severe liver damage, yellowish eyes, light coloured stools,Similar to HBV more likely to become chronicSevere liver damage, high mortality rateSimilar to HAV but pregnant women may have high mortality
5. Incubation Period2-6 weeks6 weeks-6 months2-22 weeks6-26 weeks2-6 weeks
6. VaccineHepatitis A virus vaccineGenetically modified vaccineNoHBV vaccine is protectiveNo
7. Chronic HepatitisNoneYesYesYesNo

4. 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 lies “doubled up” due to severe joint pains. Epidemics of chikungunya have occurred in many African countries.

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Mode of Transmission:

By the bite of Aedes aegypti mosquito. No vaccine is available.

Signs and Symptoms:

Its symptoms include sudden onset of fever, crippling joint pains, lymphadenopathy and conjunctivitis. Some show haemorrhagic manifestations. The fever is typically biphasic. Chikungunya has been reported from India.


Incubation Period:

Usually 3-6 days

Prevention and Treatment:

Preventive measures include elimination of mosquitoes and their eggs. Paracetamol is given to reduce fever, analgesic (drug that relieves pain) drugs such as aspirin for the joint pain. Bed rest and adequate fluid intake are also recommended.

5. Dengue Fever (Break-bone fever):


Dengue fever is caused by mosquito borne flavi-ribo virus.

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Mode of Transmission:

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

Incubation Period:

3 to 8 days

Types of Dengue Fever:


Two types of dengue fever are common: classical dengue fever and dengue haemorrhagic.

(a) Symptoms of Classical Dengue Fever:

(i) Abrupt onset of high fever,

(ii) Severe frontal headache,

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

(iv) Muscles and joint pains,


(v) Loss of sense of taste and appetite,

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

(v) Nausea and vomiting.

(b) Symptoms of Dengue Haemorrhagic Fever:

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.

No vaccine for Dengue fever is available.

Prevention and Treatment:

Mosquitoes and their eggs should be eliminated.

No specific therapy is available. Symptomatic care including bed rest, adequate fluid intake and analgesic medicine is recommended. Do not take aspirin and dispirin.

6. Common Cold/Rhinitis:


It is one of the most infectious human diseases caused by Rhino viruses. The viruses attack the nose and respiratory passage but not the lungs.

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Modes of Transmission:

The viruses are transmitted through inhalation of droplets from infected person or through contaminated objects (droplet infection).

Incubation Period:

3 to 7 days.

Signs and Symptoms:

The common cold is characterised by nasal congestion, exces­sive nasal secretion, very sore throat, cough, headache, etc.


Antihistamines and decongestants are used as drugs to treat common cold. No vaccine is available.

Other Viral Diseases of Humans:

2. Rickettsial Diseases:

These are caused by rickettsiae (the obligate intracellular parasites). The Rickettsiae were formerly considered closely related to viruses. Examples: Rocky Mountain Spotted Fever (RMSF), Rickettsial pox, trench fever, fever and epidemic typhus fever.

3. Mycoplasmal Diseases:

Mycoplasma are the smallest free living microorganism. They lack a rigid cell wall and hence they are one of the pleomorphics (having many shapes). They can produce filaments which resemble fungi mycelia hence their name (mykes- fungus and plasma – formed).

A typical Pneumonia Pathogen:

Mycoplasma pneumonia was discovered by Eaton in 1941.


It is by droplets of nasopharyngeal secretions.


The disease is characterised by scarcity of respiratory signs on physical examination, low fever, cough, headache.

Incubation Period:

1 to 3 weeks.


Tetracycline’s are the drugs of choice. Penicillin’s are of no use.

4. Chlamydial Diseases:

Chlamydia is also microorganisms that are intracellular parasites. Since the chlamydiae are obligate intracellular parasites, they were previously thought to be viruses. They are in between bacteria and viruses. Chlamydiae differ from viruses in having cell wall, both DNA and RNA and in multiplying by binary fission. Example: Trachoma

5. Bacterial Diseases:

1. Typhoid (Enteric fever):


Salmonella typhi.

Modes of Transmission:

Faecal oral route.

Typhoid Mary:

It is a classic case in medicine. Mary Mallon was a cook by profession and was a typhoid carrier. She continued to spread typhoid for several years through the food she prepared.

Incubation Period:

It is 1-3 weeks.

Signs and Symptoms:

There is high fever but pulse rate is low. The patient feels abdominal pain and passes frequent stools. Confirmed by Widal Test. Typhoid vaccine is available.


The patient is treated with antibiotics such as Terramycin and Chloromycetin.

2. Pneumonia:


Streptococcus pneumoniae and Haemophilus influenzae. Pneumonia is a serious disease of the lungs.

Modes of Transmission:

The disease spreads by sputum of the patient.

Incubation period:

1-3 days.

Signs and Symptoms:

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. No vaccine is available


Use of Penicillin, Streptomycin and Ampicillin.

3. Cholera:


Vibrio cholera.

Modes of Transmission:

Faecal Oral Route. Robert Koch (1843-1910) discovered cholera. John Snow (1913) was the first to demonstrate that cholera is transmitted by contaminated water.

Incubation period:

It varies from a few hours to 2-3 days.

Signs and Symptoms:

The patient starts passing stools frequently, which are white like rice water, and gets repeated vomiting. The disease can be diagnosed by the microscopic examination of the stool or the vomit when the typical comma-shaped cholera vibrio’s can be seen.


Rapid replacement of fluid and electrolytes is needed by oral rehydration- therapy. You can make your own oral rehydration solution (ORS) at home by adding one teaspoon of sugar and a pinch of salt to one quarter of water. Drugs tetracycline and chloramphenicol are used.

4. Tuberculosis (ТВ) or Koch’s Disease:


Mycobacterium tuberculosis.

Modes of Transmission:

The bacteria damage the tissues and release a toxin named tuberculin which produces the disease. It affects the lungs, lymph nodes, bones and joints.

Modes of infection includes infection by inhalation of droplets expelled by tubercular patients, infection of food and drink contaminated with bacteria of tuberculosis, milk from a tubercular cow, etc.

Incubation period:

3-6 weeks (variable).

Signs and Symptoms:

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

Prevention and Treatment:

BCG vaccine gives protection against tuberculosis. When coughing, he/she should keep the handkerchief before his/her mouth. Tuberculosis is curable.

Isoniazid, Streptomycin and Rifampicin drugs are used to treat Tuberculosis.

6. Spirochaetal Diseases:

Spirochaetes are flexible, twisted round the long axis microorganisms. The characteristic feature is the presence of varying numbers of fine fibrils between the cell wall and cytoplas­mic membrane. Example: Syphilis.



Treponema pallidium

Mode of Transmission:

It is a sexually transmitted disease (STD) which is also known as venereal disease (VD). However, T. pallidium can be transmitted from an infected mother to the developing foetus across the placenta which is called congenital syphilis.

Incubation Period:

2 to 3 weeks


The symptoms of syphilis occur in four stages:

(i) Primary syphilis. A red painless ulcer called a chancre appears at the site of the spirochaete infection. In males this is usually the penis but in females it is often the vagina or the cervix,

(ii) Secondary syphilis. It includes fever, general enlargement of lymph nodes, a pink skin rash all over the body and joint pain,

(iii) Latent Syphilis. In this stage there is no sign and symptom of the disease,

(iv) Tertiary syphilis. It is characterized by tumour like masses called gummas. Tertiary syphilis may cause serious damage to the heart and blood vessels (Cardiovascular syphilis) or bones and skin.


VDRL test is done to detect the syphilis.


Penicillin is still the drug of choice for syphilis (all stages).

7. Protozoan Diseases:

1. Malaria:


Malarial parasite (= Plasmodium). Plasmodium has two hosts:

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(a) Female Anopheles Mosquito:

As the sexual phase of the malarial parasite occurs in the mosquito it is considered the definitive (= primary) host of malarial parasite.

(b) Human beings:

As the asexual phase of the malarial parasite occurs in man, it is considered the intermediate (= secondary) host. As the female Anopheles mosquitoes feed on blood, only they can serve as vector hosts (= carrier) of malarial parasites. The parasite does not harm the mosquito.

Historical Aspects:

Lancisi (1717) first suspected a relationship between swamp, ma­laria and mosquito. Laveran (1880) discovered that malaria is caused by protozoan parasite. In fact he discovered Plasmodium. He got Nobel Prize in 1907. His topic of discovery was “Role of Protozoans in Causing Disease”.

Golgi (1885) confirmed Laveran’s discovery by observing stages of Plasmodium malariae in human RBCs. In 1897 Sir Ronald Ross, a doctor who was born at Almora in India and he was in Indian Army, established that malarial parasite is transmitted by the bite of a female Anopheles mosquito. In 1902, he got Nobel Prize for this discovery. He worked in India.

Life Cycle of Plasmodium:

Life cycle of Plasmodium requires two hosts for completion, such a two host life cycle is called digenetic.

I. Life Cycle of Plasmodium in Man:

1. Infective stage of Plasmodium is sporozoite. When the mosquito bites another hu­man, sporozoites are injected with bite.

2. Parasites (sporozoites) reach the liver through blood.

3. The parasite reproduces asexually in liver cells, bursting the cell and releasing into the blood.

4. Parasites enter the red blood cells and reproduce asexually there bursting the red blood cells and causing cycles of fever and other symptoms. Released parasites infect new red blood cells.

5. Sexual stages (gametocytes) develop in red blood cells.

II. Life Cycle of Plasmodium in Female Anopheles mosquito:

1. Female mosquito takes up gametocytes with blood meal.

2. Fertilisation and development take place in the mosquito’s stomach.

3. The zygote elongates and becomes motile called ookinete.

4. The ookinete moves and bores through the wall of the stomach of female Anopheles mosquito. The ookinete changes to oocyst on the surface of the stomach.

5. Inside the oocyst, sporozoites are formed which are released in the body cavity of the mosquito.

6. Mature infective stages (sporozoites) move to different organs of the body cavity but many of them penetrate salivary glands of the mosquito.

7. When the female Anopheles mosquito bites a healthy person, the sporozoites are injected in his/her blood alongwith saliva.

Human Species of Plasmodium and Types of Malaria:

In human beings, malaria is caused by four species.

1. Plasmodium vivax:

It is most common in India. It is less common in Africa. Its incubation period is about 14 days. It causes Benign Tertian Malaria. Recurrence of fever is after every 48 hours (every third day). Recurrent attacks of fever are called paroxysms.

2. Plasmodium falciparum:

It is common in certain parts of India. It is the greatest killer of human beings over most parts of Africa and else where in tropics. Its incubation period is about 12 days. Recurrence of fever is after every 48 hours (every third day). It causes Malignant (=Aestivo-autumnal or Pernicious or Cerebral or Tropical) Tertian Malaria.

3. Plasmodium malariae:

It is common in tropical Africa, Burma, Sri Lanka and parts of India. It is less common in India. This was the species of malarial parasite discovered by Laveran. This is the only species which can also infect other primates. Its incubation period is 28 days. Recurrence of fever is after 72 hours (every 4th day). It causes Quartan Malaria.

4. Plasmodium ovale:

This is the rarest of the four species which infect man. It is mostly found in tropical Africa. It is usually not seen in India. Its incubation period is about 14 days. It causes Mild Tertian Malaria.

Pigment granules (dots) in the cytoplasm of infected RBCs in four Species of Plasmodium:

P. vivaxP. falciparumP. malariaeP. ovale
Schuffner’s dotsMaurer’s dotsZiemann’s dotsJame’s dots

Symptoms of Malaria:

The patient displays symptoms of malaria fever after a period of 14 days from infectious bite. Early restlessness, less appetite and slight sleeplessness are followed by muscular pains, headache and a feeling of chilliness. In response to chills the body temperature starts rising and may reach 106°F at the height of fever. The patient sweats a lot and the temperature steadily goes down to normal, till the next attack takes place after 48 hours.

Control of Malaria:

Malaria is widely spread disease in India. There is separate anti­malaria department of the government which controls malaria through National Malaria Eradication Programme (NMEP).

(a) Treatment of the patient:

Quinine, the oldest drug for malaria, and other drugs are also used for this purpose. Quinine is extracted from the bark of the cinchona tree which is mostly growing in West Indies, India, Sri Lanka, Java and Peru. Other anti-malarial drugs are paludrine and Primaquin, Chloroquinine, Camoquin and Comoprima. Now malaria is also being treated with sulpha drugs such as sulphadoxin, dapsone, etc.

(b) Prevention of Infection:

Ducks, larvivorous fish like Gambusia, some adult insects like dragon flies, insectivorous plants such as Utricularia, are the natural enemies of mos­quito larvae and pupae as they feed upon them. These may be introduced in the water containing the larvae and pupae.

2. Amoebiasis (= Amoebic Dysentery; Enteritis):


Entamoeba histolytica


It is monogenetic (single host life cycle, i.e., humans).


Lamble (1859) discovered Entamoeba histolytica. Losch (1875) discov­ered its pathogenic nature.


The pathogen lives in the large intestine of humans. It is more commonly found in males than females. Presence of chromatoid bodies is the characteristic of the cysts of Entamoeba hystolytica.

Modes of Transmission:

(i) Faecal oral route,

(ii) Sexual transmission,

(iii) Vectors such as flies, cockroaches, etc.

Incubation Period:

2 to 4 weeks or more.

Mode of Infection:

The cyst passes unaltered through the stomach. The cyst wall is resistant to the action of the gastric juice but is digested by the action of trypsin in the intestine. Thus active parasites are liberated from the cyst into the intestine where it starts normal life. E. histolytica eats red blood corpuscles. Tetranucleate cyst is infective stage.

E. histolytica is dimorphic, i.e., occurs in two forms larger harmful magna form and smaller harmless minuta form.


Presence of Charcot-Leyden crystals made up of protein, normally found in the cytoplasm of eosinophil’s. Presence of chromatid bodies is the characteristic of E. histolytic.

Incubation Period:

It varies in humans but is generally 4 or 5 days.


In amoebic dysentry (amoebiasis) the patient passes blood alongwith the faeces and feels pain in the abdomen.

Prevention and Treatment:

Symptomatic treatment includes the use of Metronidazole and Tinidazole.

3. Giardiasis (= Diarrhoea):

It is caused by a zooflagellate protozoan named Giardia intestinalis. Giardia was discoverd by Leeuwenhoek in his own stools in 1681. It is the first human parasitic protozoan known. It lives in the upper parts (duodenum and jejunum) of human small intestine. It absorbs nourishment from the food passing through intestine, grow and multiply through binary fission.

The large number of parasites interferes with digestion and absorption of food. This causes epigastric pain, abdominal discomfort, diarrhoea, headache and sometimes fever. The diseases caused by Giardia are popularly known as giardiasis or diarrhoea (watery and frequent stools).

4. Trypanosonaiasis:

It includes African Trypanosomiasis and American Trypanosomiasis.

(i) African Trypanosomiasis (African Sleeping Sickness):

Its pathogens are trans­mitted by bite of tse tse fly (Glossima palpalis and G. morsitans). The pathogens are found in blood but later enter the cerebrospinal fluid and migrate to the brain. The patient becomes lethargic and uncounscious.

Because of it the disease is called sleeping sickness. African Trypanosomiais is of two types (a) Gambian Trypanosomasis (West African Sleeping Sickness) caused by Trypanosoma gambiense and (b) Rhodesian Trypanosomiasis (East African Sleeping Sickness) caused by Trypanosoma Rhodesiense.

(ii) American Trypanosomiasis (American Sleeping Sickness or Chagas Disease):

Chagas disease occurs rarely in the United States and Mexico but is more common in South America particularly Brazil. Its pathogen is Trypanosoma cruzi which is transmitted by “kissing bugs” (triatomids).

The bugs pass the infectious parasites in the faeces. The infec­tious parasites enter the host through damaged skin or mucous membrane. The parasite is found in blood. The patient becomes lethargic. In Chagas disease other symptoms are fever, cardiac dilation, digestive tract damage, enlargement of spleen, etc.

5. Leishmaniasis or Kala-azar (Dum-Dum Fever):

It is caused by Leishmania donovani. The parasite is transmitted by Phlebotomus argentipes (sandfly). Its symptoms are continuous fever, anaemia, enlargement of liver, spleen, etc.

6. Trichomoniasis (Vaginitis, Leucorrhoea):

It is caused by Trichomonas vaginalis. It lives in the vagina of women. The symptoms of this diseases are burning sensation, itching and frothy discharge. In males the parasite produces irritation in urethra. Its transmission is through sexual act.

7. Balantidiasis (= Balantidium Dysentery):

It is caused by Balantidium coli. This parasite lives in the human large intestine (colon). It feeds on human red blood corpuscles, tissue fragments, undigested food and bacteria. It also undergoes cyst formation. Cysts are passed out in the host’s faeces. Infection occurs by ingesting cysts with food and water.

Balantidium coli invades mucous membrane of the colon by secreting an enzyme hyaluronidase. The parasite causes ulcers in the human colon and diarrhoea but may also lead to severe dysentery. Ciliary dysentery can be prevented by protecting food articles from dust and flies that carry cysts of Balantidium coli.

8. Helminthic Diseases:

These diseases are caused by flat worms and round worms.

Platyhelminths (Flatworms) and Nematodes (Round worms) constitute the Helminths.

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(a) Diseases Caused by Flat Worms:

DiseasePathogenSite of InfectionMode of InfectionSecondary HostEffect
1. FasciolopsiasisFasciolopsis buski – The Intestinal FlukeSmall Intetine of manMetacercariae on water plantsSegmentina or Planorbis (snails)Intestinalinflammation,ulcer,


2. SchistosomiasisSchistosoma haematobium (Blood fluke)Portal and mesenteric veins of manCercariae in water penetrate the skin when come in contactBulinus orMelania(snails)Urinogenitalschistoso­miasis
3. TaeniasisTaenia solium (Pork tape­worm)Small Intestine of manBy eating ill cooked measly porkPigTaeniasis(intestinaldisorders)
4. TaeniasisTaenia saginata (Beef tape­worm)Small Intestine cooked of manBy eating ill cooked beefCattleIntestinal disorders & anaemia
5. CysticercosisIt is more danger­ous than taeniasisCysticercus (larva of tape­worm)Ingestion of eggs or onchospheres reach the stomach from intestine by antiperistalsis of intestine where onchospheres (larvae) develop into cysticerci (larvae). From stomach cysti­cerci reach the eyes and brainIngestion of eggs of tapeworm or they reach lower part of digestive tract and develop into cysticerci & reach the eyes and brainManIn the eye cysticercus can cause blindness & in the brain it can cause epilepsy
6. Hydatid DiseaseEchinococcus granulosus (Dog tape­worm or Hydatid worm)In the intestine of dogs, cats, foxes and manBy playing with pet dogs.Man, sheep, goat, pig and catThe parasite liberates toxins which have harmful effect on the body & brain of the host

Diseases Caused by Nematodes (Round Worms):

1. Ascariasis:


It is caused by Ascaris lumbricoides.

Host and Infection:

Ascaris is an endoparasite of the small intestine of human beings. 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. Second stage juvenile— also called embryonated egg, is infective stage. There is no secondary host in the life cycle of this parasite.

Route of the Parasite / Juveniles and Moulds Fertilized eggs —> Out with host faeces —> First stage juvenile in egg— also called Rhabditiform larva (First mould) —> 2nd stage juvenile— also called embryonated egg (infective juvenile in egg) —> Embryo­nated egg swallowed by man with food —> 2nd stage juvenile becomes free in human intestine —> 2nd stage juvenile bores through intestinal wall into blood capillaries —> Heart -> 3rd stage juvenile in lung alveoli (2nd mould) —> 4th stage juvenile in lung alveoli (3rd mould) —> Bronchioles (4th stage juvenile) —> Bronchi —> Trachea —> Pharynx —> Intestine (4th mould) —» Young worms.


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 indigestion, diarrohea and vomiting.

Treatment and Prevention:

The disease can best be treated by administering antihelminthic drugs such as oil of chenopodium, Alcopar, Bendex, Dewormis, Zental, etc. Mebendazole is the drug of choice. The parents should see to it that their children do not take to the habit of eating soil.

2. Filariasis (Elephantiasis):


Filariasis is caused by a number of worms. But in India only two types of worms are responsible and are called Wuchereria bancrofti and W. malayi.


The infestation is transmitted by female Culex mosquitoes from one individual to the others. The worms live in the lymphatic system.


This disease is characterised by the swelling of the legs and scrotum. The disease is, therefore, commonly known as elephantiasis due to its resemblance to a leg of an elephant.


Albendazole with Diethylcarbamazine (DEC- hetrazan) is the commonly used drug.

(b) Other Diseases Caused by Round Worms:

DiseasePathogenSite of InfectionMode of InfectionEffect
1. Ancylosto­miasisAncylostomaduodenale(Hookworm)Small IntestineLarvae bore through the skin of feetItching and Inflamma­tion of skin, anaemia, mental & physical deficiency
2. Enterobiasis (Oxyuriasis)Enterobius vermicularis (Pin worm)Caecum & Colon appendixBy swallowing eggs with foodAnal itching, appen­dicitis, nervous trouble
3. TrichinellosisTrichinellaspiralis(Trichina worm)Encysted larvae in striated muscles, adults in intestineBy eating half cooked infected porkMuscular pain, pne­umonia
4. DracunculiasisDracunculus medinesis (Guinea worm)SubcutaneoustissueTaking infected Cyclops with waterUlcers, diarrhoea, asthma, giddiness
5. TrichuriasisTrichuristrichiura(Whipworm)Caecum and ap­pendixBy taking eggs with foodAbdominal pain, anaemia, bloody stools
6. Loiasis(Eye worm disease)Loa Loa (Eye worm)Subcutaneous tissue of eyesBy bite of infected deerfly (Chrysops)Conjunctivitis

9. Fungal Diseases:

These are caused by fungi. Fungi had been discovered as causative agents of human diseases earlier than bacteria. Study of fungal diseases in humans is called Medical Mycol­ogy.

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The fungal diseases of man are either mycoses (caused by infection of fungi) or toxicoses (caused by toxic fungal metabolites). The term myco refers to a fungus and osis or iosis means condition.

Ringworm or Tinea:

A long time ago people believed that worms lived in the scaly ring, hence the name the ringworm or tinea.


Fungi belonging to genera Trichophyton, Epidermophyton and Microsporum are responsible for ringworm or tinea in man.

Mode of Infection:

The infection is generally acquired from soil or by using towels, clothes or even the comb of infected persons.

Effects of three Genera:

Effects of three genera Trichophyton, Epidermophyton and Microsporum are given below.

(i) Trichophyton:

Trichophytons infect skin, hair and nails. T. rubrum is the most common species infecting man.

(ii) Epidermophyton:

It attacks the skin and nails but not the hair, e.g., E. floccsum.

(iii) Microsporum:

It infects the hair and skin but usually not the nails, e.g., M. canis.


Griseofulvin (orally) and Miconazole (topically).

Some Types of Tinea or Ringworm (According to the Affected Parts):

(i) Tinea pedis (athletes’foot) is ringworm of the foot. Drug Tolnaftate is used to cure the athlete’s foot,

(ii) Tinea capitis- ringworm of the scalp,

(iii) Tinea cruris— involvement of the groin and perineum,

(iv) Tinea barbae- involvement of the bearded areas of the face and neck.

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  • HIV / STDs / Hepatitis.

What are the classifications of communicable diseases? ›

Communicable diseases may be classified by a variety of methods: by clinical syndrome, mode of transmission, methods of prevention (e.g., vaccine preventable), or by major organism classification, that is, viral, bacterial, fungal, and parasitic disease.

What is pathogenic disease Class 9? ›

Pathogens are microorganisms that have the potential to cause infectious diseases. Viruses, bacteria, protozoans and fungi are all potential pathogens. A pathogen is simply defined as an organism that has the potential to cause infectious diseases in its host.

What are the pathogens of communicable diseases? ›

Pathogens that cause infectious diseases are viruses, bacteria, fungi, parasites and, rarely, prions. You can get infectious diseases from other people, bug bites and contaminated food, water or soil.

What are top 10 communicable diseases? ›

The diseases below are among them.
  • MRSA.
  • Pertussis.
  • Rabies.
  • Sexually Transmitted Disease.
  • Shigellosis.
  • Tuberculosis.
  • West Nile Virus.
  • Zika.

What are the 8 common communicable diseases? ›

Some examples of the communicable disease include HIV, hepatitis A, B and C, measles, salmonella, measles, and blood-borne illnesses. Most common forms of spread include fecal-oral, food, sexual intercourse, insect bites, contact with contaminated fomites, droplets, or skin contact.

What is communicable disease Class 9 short answer? ›

What is a communicable disease? A communicable disease is one that is spread from one person to another through a variety of ways that include: contact with blood and bodily fluids; breathing in an airborne virus; or by being bitten by an insect.

What are the 11 communicable diseases? ›

Quick Links
  • Campylobacter Infection.
  • Hepatitis A.
  • Hepatitis B.
  • Hepatitis C.
  • Novel Coronavirus (COVID-19)
  • Influenza (Flu)
  • Measles.
  • Meningococcal Disease.

What are communicable diseases Class 8 with examples? ›

  • Communicable diseases are transmitted from an infected person to a healthy person via air, water, food, or direct contact.
  • Examples: Common cold, Cholera, Chickenpox, Tuberculosis.

What are the classification of diseases Class 9? ›

Similarly, diseases are caused by different microorganisms and can be classified as diseases caused by bacteria, fungi, viruses etc. Some diseases are also caused by multicellular organisms such as worms.

How does pathogen spread disease Class 9? ›

Touching an infected person, or their body fluids such as saliva, blood, sweat, urine, etc. transfer the infections to a healthy person, e.g. chickenpox, measles, etc. Touching the objects or areas touched by an infected person can transfer the infection to a non-infected person and cause diseases.

What are the classification of pathogens? ›

Pathogen types. There are different types of pathogens, but we're going to focus on the four most common types: viruses, bacteria, fungi, and parasites.

What are the five types of communicable pathogens? ›

There are five main types of pathogens:
  • Bacteria. Bacteria are microscopic pathogens that reproduce rapidly after entering the body. ...
  • Viruses. Smaller than bacteria, a virus invades a host cell. ...
  • Fungi. There are thousands of species of fungi, some of which cause disease in humans. ...
  • Protists. ...
  • Parasitic worms.
Aug 21, 2020

What are the 7 pathogens? ›

Infectious diseases are caused by pathogens, which include bacteria, fungi, protozoa, worms, viruses, and even infectious proteins called prions.

What are the 10 communicable diseases PDF? ›

  • Diarrhoeal diseases.
  • Bacillary dysentery.
  • Cholera.
  • Typhoid fever.
  • Poliomyelitis.
  • Acute Lower Respiratory Infections.
  • Measles.
  • Tuberculosis.

What are the 10 common noncommunicable diseases? ›

What are the 10 non communicable diseases?
  • Cancer.
  • Diabetes.
  • Heart disease.
  • Chronic lung disease.
  • Alzheimer's Disease.
  • Hypertension.
  • Asthma.
  • Mental health ailments.

How many communicable diseases are there in the world? ›

Viral infections occur due to infection with a virus. Millions of different viruses may exist, but researchers have only identified about 5,000 types to date.

Which one of the following is a communicable disease Class 9? ›

Examples of communicable diseases are chicken pox, dengue, common cold, malaria, etc.

What is non-communicable disease class 9? ›

Non-communicable Disease Definition: The diseases which are not transmitted from one person to another are known as non-communicable diseases (NCD). These are typically some of the allergies, nutrient deficiencies etc. For example, cardiovascular diseases, diabetes, cancer, etc.

What are communicable and non-communicable diseases Class 9? ›

Communicable diseases are the diseases which passes from one individual to another individual. They are generally caused by some bacteria, viruses or any other pathogens. For example, malaria, AIDS etc. Non-communicable diseases are the diseases which does not spread from one person to another person.

What is acute disease class 9? ›

A disease which occurs suddenly and lasts only for a short amount of time is defined as an acute disease.

What are the 8 non communicable diseases? ›

Explore data on NCDs, risk factors, injuries and violence, and public policies on NCDs in ENLACE data portal
  • Alcohol.
  • Breast cancer.
  • Breastfeeding and complementary feeding.
  • Cancer.
  • Cardiovascular diseases.
  • Cervical Cancer.
  • Chronic kidney disease.
  • Diabetes.

Who discovered pathogen class 9? ›

Discovered by: Dr Robert Koch, a German physician and microbiologist was the first person to discover the disease causing microorganisms, also called the pathogens.

How many categories of pathogen are there? ›

Types of pathogens. The different types of pathogens that invade the human body and cause health issues include viruses, bacteria, fungi, protozoa, and helminths (parasitic worms). Viruses: They are microscopic infectious agents that are smaller than bacteria.

What are the 10 pathogens? ›

The characteristics of the most common pathogenic bacteria (Bacillus cereus, Campylobacter jejuni, Clostridium botulinum, Clostridium perfringens, Cronobacter sakazakii, Esherichia coli, Listeria monocytogenes, Salmonella spp., Shigella spp., Staphylococccus aureus, Vibrio spp.

What are pathogens Class 9 Brainly? ›

Answer: a bacterium, virus, or other microorganism that can cause disease.

What are the 7 ways pathogens spread? ›

Understanding how diseases spread makes them easier to control and prevent.
  • Airborne transmission. ...
  • Respiratory (droplet) transmission. ...
  • Sexually transmitted diseases (STDs) ...
  • Animal or insect transmission. ...
  • Food or water transmission. ...
  • Health care transmission.

What are pathogens Name any two Class 9? ›

Disease causing microorganisms are called pathogens. These include viruses, bacteria, fungi, protozoans and worms.

What are the 6 main pathogens? ›

They list “The Big 6” pathogens (Norovirus, Nontyphoidal Salmonella, Salmonella Typhi, E. coli, Shigella, and Hepatitis A) as being highly infectious, able to cause severe disease in small quantities, and each will be featured individually in this series of articles.

What are the big 6 pathogens? ›

The US Food and Drug Administration (FDA) has identified six serogroups, known as the “big six”: E. coli O26, O45, O103, O111, O121, and O145.

What are the top 10 non communicable diseases? ›

  • Acid Reflux.
  • ADHD.
  • Allergies.
  • Alzheimer's & Dementia.
  • Bipolar Disorder.
  • Cancer.
  • Crohn's Disease.
  • Chronic Pain.

What are the 20 common diseases? ›

Common Infectious Diseases
  • Chickenpox.
  • Common cold.
  • Diphtheria.
  • E. coli.
  • Giardiasis.
  • Infectious mononucleosis.
  • Influenza (flu)

How many communicable diseases are there? ›

Since they are spread through contact, they are known as communicable diseases. According to medical records, there are over 20,000 diseases that affect millions of individuals each year. This article will discuss communicable diseases, their characteristics, types, symptoms, and how to prevent them.

What are non communicable diseases Class 9? ›

Non-communicable Disease Definition: The diseases which are not transmitted from one person to another are known as non-communicable diseases (NCD). These are typically some of the allergies, nutrient deficiencies etc. For example, cardiovascular diseases, diabetes, cancer, etc.

What are the causes of diseases Class 9? ›

They are usually caused by microorganisms called pathogens (fungi, rickettsia, bacteria, viruses, protozoans, and worms). When an infected person discharges bodily fluids, pathogens may exit the host and infect a new person (sneezing, coughing etc). Examples include Cholera, chickenpox, malaria etc.

What are the 10 major diseases? ›

The 10 most dangerous diseases in today's society
  1. Ischemic heart disease, or coronary artery disease. ...
  2. Stroke. ...
  3. Lower respiratory tract infections. ...
  4. Chronic Obstructive Pulmonary Disease. ...
  5. Tracheal, bronchial and lung cancer. ...
  6. Diabetes. ...
  7. Alzheimer's disease and other dementias. ...
  8. Dehydration due to diarrhea.

What are the 10 leading causes of diseases? ›

Leading Causes of Death
  • Heart disease: 695,547.
  • Cancer: 605,213.
  • COVID-19: 416,893.
  • Accidents (unintentional injuries): 224,935.
  • Stroke (cerebrovascular diseases): 162,890.
  • Chronic lower respiratory diseases: 142,342.
  • Alzheimer's disease: 119,399.
  • Diabetes: 103,294.

What are the 10 communicable diseases for kids? ›

Common Childhood Communicable Diseases
  • Chicken Pox (Varicella) Exclude if child has a fever. ...
  • Common Colds. Exclude if child has a fever. ...
  • Conjunctivitis (Pink-eye) ...
  • Diarrhea. ...
  • Fifth's Disease (Parvovirus B19) ...
  • Hand, Foot and Mouth Disease. ...
  • Hepatitis A. ...
  • Hepatitis B.


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