Diseases caused by micro-organisms and worms

Microorganisms causing diseases

 Very minute living organism not seen without the aid of microscope are callec microorganisms. There are numerous microorganism but ones which concern us are germs o disease causing microorganisms (called pathogens). They are found almost everywhere in nature (in air, water and soil), on the surface of objects and living organisms, within the living organisms.  

 Viruses causing diseases

 Pathogenic microorganisms are viruses, many bacteria, certain fungi and some protozoan. Viruses cause disease in living cells and are the smallest disease causing particles known. They are only visible under electron microscope. 

Virus in humans

Chickeimox, measles, poliomyelitis, the common cold, mumps, influenza and AIDS are a few diseases caused by viruses. 

Bacteria causing diseases

 Bacteria are larger than viruses and are visible under the ordinary light microscope. All of the bacteria are not pathogens. Some of the diseases caused by bacteria include boils, food poisoning, whooping coughs, cholera, diphtheria, typhoid, bacillary dysentery, TB etc. 

Protozoa causing diseases

 Protozoa are single-celled organisms which vary in size and shape. 
Very few of them cause disease in humans. Some common diseases caused by protozoa are malaria, amoebic dysentery, some types of ulcers in large intestine, etc. Fungi 

 Fungi causing diseases

  Very few fungi are responsible for causing human diseases. Most of the fungi are multi-cellular but some are unicellular. Their mode of nutrition is saprotrophic but very few of them are human parasites. 
Common fungal human diseases are Ring Worm, Athlete’s foot, histoplasmosis, candidia (thrash) etc. 

Ring Worm (fungal disease)

 Ring Worm is a skin disease caused by fungus. The disease is spread by spores of the fungus which are passed from one individual to another by personal contact or by contact with clothing since the fungus can grow on clothing or other personal objects.
 Hyphae of the fungus penetrate the outer layers of the skin and grow in the normal way. 
The red patch as it spreads, causes intense itching. As the fungus grows, the center loses its colour to normal leaving a circular red patch which is darker at the edge. The name ‘ring worm’ is given because of this appearance. 

Athlete’s Foot (fungal disease)

Athlete’s foot is also a fungal disease. 
It is sort of ringworm of the foot. Fungus attacks soft skin between the toes and in bad cases spreads over the whole foot. The skin peels off leaving very sore patches. Infected floors and mats spread the problem. Worms Some common parasitic worms are round worms, thread worms, liver fluke and tapeworms. 
Ascaris is a common roundworm. It is 20-30 cm long and is pinkish white in colour. These worms live in the small intestine of man and move freely. The major symptoms of the disease are abdominal pain, dyspepsia, anxiety, nausea, and coughing. The eggs of Ascaris are excreted in soil along with feces. These eggs can enter another person, due to unhygienic conditions. 
When these eggs reach small intestine, they develop into new worms and cause disease. This disease is more common in children as compared to adults and children are source of its spread. In this disease, as the worms feed on the food of the patient, that is why patient suffers from malnutrition. 

Thread Worms causing diseases

 Thread worms are very small only some inch long. Both male and female worms live in the colon of human beings. At night the female descends the colon and lays her eggs in the folds of skin about the anus. This causes intense itching, if the anus is scratched, the eggs stick to the fingers and thus transferred to the mouth or deposited on cutlery and household utensils. 
The eggs also become attached to the clothing and the bedding. When these articles are shaken, the eggs are dispersed in the air and may be breathed in. The eggs pass to the stomach and to the large intestine and develop into adult Thread worms. 
Children are mainly affected by these worms. Drugs can be given to get rid of worms. 

Liver Fluke (Platyhelminthes)

Liver fluke

 

The fluke are flat worms. They are the parasites of both man and animal. All flukes require at least two hosts to complete their life cycle. One of the fluke is liver fluke. It lives in and feeds in the liver of the human beings, where it causes much damage. 
The eggs of the fluke pass out in the faeces of infected person and thus they may come to the freshwater. Snails living in the freshwater eat the eggs. The eggs develop and form larva in the snails. The larva Mevelops into small creature with a tail. At this stage they leave the snail and swim into water and seek a fresh host. Their next host is freshwater fish. The embryos penetrate the skin and enter the muscles of the fish. In the muscles the embryo form a hard protective layer and become cysts. 
These cysts are very hard and are only destroyed by a thorough cooking of the fish. When partially cooked fish is eaten by man, the cysts arrive in the stomach and there they develop. From the stomach the parasites pass to the liver, where they grow to adult flukes. 
The adult flukes are both male and female, they come together and fertile eggs are produced and the cycle is repeated Drugs for the treatment are available but the best way is to improve sanitation. Infected man Eggs in feces Poorly cooked fish Eggs develop in embryos Cyst develops in stomach Embryos escape from snail Embryo forms cyst in fish’s muscles Fluke lives in liver enter through Embryos fish’s skin Cyst not destroyed swimming in freshwater Freshwater snail Tapeworms (Taenia solium) Flat worms are largest organisms to parasitize human beings. They are called flat worms because of their flattened bodies.

Tapeworms 

 All tapeworms are parasites and require at least two hosts to complete their life cycle. Tapeworms have a small head on which suckers and sometimes hooks are present to attach them to their host’s intestine. Their length varies from few centimeters to 10 meters and their body is made of segments called proglottids. They are hermaphrodite i.e. each proglottid has both sexes. The life cycle of tapeworm involves two hosts. 
Primary host is the one in which the adult tapeworm lives and reproduces. And secondary host is an animal, which is eaten by the primary host For example beef tape worm’s primary host are humans and secondary host is cattle. If the sewage disposal conditions are not proper, tape worm eggs may be eaten by a cow while grazing.
 Because of the digestive juice of cow in the gut, larvae come out of the eggs which then find their way into the muscular tissues. There they remain unchanged for several years. If the partially cooked cow meat of infested cow is eaten by humans the larvae are activated by digestive juices, where they manage to attach the intestinal wall with their suckers or hooks. There the larvae develop into adult  tapeworms. 

After fertilization sex organs disappear and are replaced by thousands of microscopic proglottids. At this stage proglottids drop from the tape worm and pass out of the host’s body with faeces . 

Housefly as a Vector of disease 

Housefly is a mechanical vector. It feeds on decaying matter and dung which is rich source of germs causing typhoid fever, typhus, cholera, dysentery, tuberculosis and anthrax along with some tapeworm and roundworm eggs. 
As flies feed their feet, bodies and digestive system becomes contaminated with germs and eggs. If the flies then settle on human food, the germs and eggs are deposited on the food. By eating this contaminated food persons become ill. Mosquitoes as Vectors Mosquito is a biological vector because the pathogen which is responsile for causing the disease under goes a cycle of development in it.
 Mosquito is a vector for transritting malaria and yellow fever. In case of malaria, pathogen is a protozoan Plasmodium. Plasmodium uner goes two stages in its life cycle, one in man and one in the mosquito. In man, the parasite enters irough the bite of an infected female Anopheles mosquito. 
One stage of its life cycle is completed in man, as a result gametocytes are formed, which are sucked along with blood by a mosquito. Second stage of its life cycle is completed in mosquito The mosquito in its life cycle is an intermediary host. Without this interrediary stage, the disease would not be passed from patient to healthy person.