8.1 COMMON DISEASES IN HUMANS NEET

8.1 COMMON DISEASES IN HUMANS

• A wide range of organisms belonging to bacteria, viruses, fungi, protozoans, helminths, etc., could cause diseases in man. 
• Such disease causing organisms are called pathogens. Most parasites are therefore pathogens as they cause harm to the host by living in (or on) them. 
• The pathogens can enter our body by various means, multiply and interfere with normal vital activities, resulting in morphological and functional damage. 
• Pathogens have to adapt to life within the environment of the host. 
• For example, the pathogens that enter the gut must know a way of surviving in the stomach at low pH and resisting the various digestive enzymes. 
• A few representative members from different groups of pathogenic organisms are discussed here along with the diseases caused by them. 
• Preventive and control measures against these diseases in general, are also briefly described.

Typhoid: 

• Salmonella typhi is a pathogenic bacterium which causes typhoid fever in human beings. 
• These pathogens generally enter the small intestine through food and water contaminated with them and migrate to other organs through blood. 
• Sustained high fever (39° to 40°C), weakness, stomach pain, constipation, headache and loss of appetite are some of the common symptoms of this disease. 
• Intestinal perforation and death may occur in severe cases. 
• Typhoid fever could be confirmed by Widal test. 
• A classic case in medicine, that of Mary Mallon nicknamed Typhoid Mary, is worth mentioning here. 
• She was a cook by profession and was a typhoid carrier who continued to spread typhoid for several years through the food she prepared. 

Pneumonia 

• Bacteria like Streptococcus pneumoniae and Haemophilus influenzae are responsible for the disease pneumonia in humans which infects the alveoli (air filled sacs) of the lungs. 
• As a result of the infection, the alveoli get filled with fluid leading to severe problems in respiration. 
• The symptoms of pneumonia include fever, chills, cough and headache. In severe cases, the lips and finger nails may turn gray to bluish in colour. 
• A healthy person acquires the infection by inhaling the droplets/aerosols released by an infected person or even by sharing glasses and utensils with an infected person. 

Dysentery, plague, diphtheria, etc., are some of the other bacterial diseases in man. 

Common cold.

• Many viruses also cause diseases in human beings. 
• Rhino viruses represent one such group of viruses which cause one of the most infectious human ailments – the common cold. 
• They infect the nose and respiratory passage but not the lungs. 
• The common cold is characterised by nasal congestion and discharge, sore throat, hoarseness, cough, headache, tiredness, etc., which usually last for 3-7 days. 
• Droplets resulting from cough or sneezes of an infected person are either inhaled directly or transmitted through contaminated objects such as pens, books, cups, doorknobs, computer keyboard or mouse, etc., and cause infection in a healthy person. 

Malaria

• Some of the human diseases are caused by protozoans too. 
• You might have heard about malaria, a disease man has been fighting since many years. Plasmodium, a tiny protozoan is responsible for this disease. 
• Different species of Plasmodium (P. vivax, P. malaria and P. falciparum) are responsible for different types of malaria. 
• Of these, malignant malaria caused by Plasmodium falciparum is the most serious one and can even be fatal. Let us take a glance at the life cycle of Plasmodium. 
• Plasmodium enters the human body as sporozoites (infectious form) through the bite of infected female Anopheles mosquito. 
• The parasites initially multiply within the liver cells and then attack the red blood cells (RBCs) resulting in their rupture. 
• The rupture of RBCs is associated with release of a toxic substance, haemozoin, which is responsible for the chill and high fever recurring every three to four days. 
• When a female Anopheles mosquito bites an infected person, these parasites enter the mosquito’s body and undergo further development. 
• The parasites multiply within them to form sporozoites that are stored in their salivary glands. When these mosquitoes bite a human, the sporozoites are introduced into his/ her body, thereby initiating the events mentioned above. 
• It is interesting to note that the malarial parasite requires two hosts – human and mosquitoes – to complete its life cycle; the female Anopheles mosquito is the vector (transmitting agent) too.

Amoebiasis 

• Entamoeba histolytica is a protozoan parasite in the large intestine of human which causes amoebiasis (amoebic dysentery). 
• Symptoms of this disease include constipation, abdominal pain and cramps, stools with excess mucous and blood clots. 
• Houseflies act as mechanical carriers and serve to transmit the parasite from faeces of infected person to food and food products, thereby contaminating them. 
• Drinking water and food contaminated by the faecal matter are the main source of infection.

Ascariasis

• Ascaris, an intestinal parasite causes ascariasis. 
• Symptoms of these disease include internal bleeding, muscular pain, fever, anemia and blockage of the intestinal passage. 
• Toxins produced by Ascaris may interfere with protein digestion.
• Monogenetic- no intermediate host is required to complete the life cycle.
• The eggs of the parasite are excreted along with the faeces of infected persons which contaminate soil, water, plants, etc. 
• Egg is mammilated, oval in shape and has 3 layer (outer- protein, middle- chitinous, inner- esterified glycosides membrane)
• Embryonic development takes place only out side of the host body (at low temperature).
• Infective eggs can remain viable six years.
• The larva is called as Rhabtiform larva (Rhabtoid)
• The first stage larva is not infective.
• A healthy person acquires this infection through contaminated water, vegetables, fruits, etc.
• Drugs: albendazol, oil of chenopdium, santonin, antipar, tetrachloroethylene, alcopar, decaris, diethylcarbamazine.

Migrations

• Primary: intestinal wall>haepatic portal> liver> haepatic vein> heart> pulmonary artery> lungs
• secondary: lungs> bronchi> trachia> pharynx> gullet> oesophagous> stomach> intestine
• Aberrant migration: migrtion from luns to brain, spinal cord and eye

Elephantiasis or 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 mosquito (culex) vectors. 
• Nocturnal periodicity: the migration micro-filaria larvae from deeper blood vessels to the periferal blood vessels from 10 pm to 4 am. this is correspond to the nocturnal behavior of female culex mosquito. 

Some other Helminth Parasites 

Ringworms 

• Many fungi belonging to the genera Microsporum, Trichophyton and Epidermophyton are responsible for ringworms which is one of the most common infectious diseases in man. 
• Appearance of dry, scaly lesions on various parts of the body such as skin, nails and scalp are the main symptoms of the disease. 
• These lesions are accompanied by intense itching. 
• Heat and moisture help these fungi to grow, which makes them thrive in skin folds such as those in the groin or between the toes. 
• Ringworms are generally acquired from soil or by using towels, clothes or even the comb of infected individuals

Some disease and their tests-

Q/A:

• Write in brief about the following disease in context of the name of causative agent, sign & symptoms and  mode of transmission.
• Typhoid
• Amoebiasis
• ascariasis
• filariasis
• ring worm
• common cold 
• pneumonia 
• malaria 
• Write a brief note on common human disease.