We have already studied many things about infectious diseases in previous articles. In this article, we shall study the treatment of infectious diseases

Acute Diseases:

An acute disease is a disease which lasts for just a short time but can begin rapidly and have intense symptoms. Example: Common cold, Influenza, malaria, cholera, etc.

Characteristics of Acute Diseases:

• The onset of the acute disease is usually abrupt and is from a single cause
• This type of disease develops quickly and worsens rapidly, such as an infection, trauma or injury.
• The symptoms and acute pain last for a few days only, and after healing of the patient, the symptoms disappear.
• Such diseases can be diagnosed and treated accordingly.
• Once treated these diseases generally do not have any long-term effect.
• There is a possibility that the healing may take place on its own. and the patient returns to normal within a few days.
• The disease usually isolated to one bodily area
• If the acute disease lasts longer than three months, it may lead to chronic disease.

Types of Acute Diseases:

• Common short-term infections: common colds, influenza, sore throat, acute sinusitis, ear infection, urine infection, etc.
• Severe diseases: pneumonia, bronchitis, encephalomyelitis.
• Physical injury: a cut, broken bone, muscle tearing, sprain, burn or trauma
• Organ failures: a heart attack or kidney failure

Treatment of Acute Diseases:

For minor illnesses such as the common cold medical treatment is not necessary. If the disease is a more serious, a medication and in some cases, a few days of hospitalization is required.

Information about these diseases is available easily and precise laboratory testing, medication, and surgical procedures are available. Hence most of the acute diseases can be treated and cured and the patient returns to normal life.

Chronic Diseases:

Chronic disease is a disease which is persistent. It lasts for a long period of time and might recur. Examples: asthma, arthritis, tuberculosis, cancer, arthritis, cardiovascular diseases, diabetes, etc.

Characteristics of Chronic Diseases:

• The onset of chronic disease is commonly gradual.
• This type of disease develops slowly and worsens slowly over a long period.
• The duration of chronic diseases is lengthy and indefinite.
• Diagnosis of chronic diseases is often uncertain and takes a long time and a lengthy process for an accurate diagnosis.
• Once treated these diseases can have long-term effect and possibility of recurrence is there.
• There is no possibility of auto-healing. A proper long medical treatment is required.
• There are multiple causes for diseases including generic and environmental.
• Chronic disease is the major cause of deaths.

Treatment of Chronic Disease:

Effective treatment of the chronic disease requires that the physician and patient work together on a long-term basis. The physician, observes symptoms over a period and interpret the condition, trend and the rate of change of the diseases in the patient.

Sign and Symptoms of Disease:

A symptom is any subjective evidence of disease, while a sign is any objective evidence of disease. Thus, a symptom is a phenomenon that is experienced by the individual affected by the disease, while a sign is a phenomenon that can be detected by someone other than the individual affected by the disease.

For examples, anxiety, pain, and fatigue are all symptoms can be experienced by individual suffering from the disease. While a bloody nose is a sign of injured blood vessels in the nose that can be detected by another person. Rashes, swelling of glands, change in colour of skin and eyes, oedema, etc. are other signs which give the doctor a good idea about diseases. For e.g. a yellowish colour of skin and eye can be due to hepatitis. Red sticky eyes are due to conjunctivitis, etc.

Symptoms:

When we suffer from a disease, we feel unwell because some part or parts of our body are not working normally. This indication of diseases can be perceived by us only. These indications are called symptoms. Each infectious disease has its own specific signs and symptoms. General signs and symptoms common to a number of infectious diseases include fever, diarrhoea, fatigue. muscle aches, coughing.

A patient has to tell the symptoms to the doctor because the doctor cannot see or feel them. Symptoms only indicate that the patient is suffering by diseases but they do not indicate what disease.

Diagnosis of Infectious Diseases:

Diagnosis means a process of identifying the disease from symptoms and signs. Apart from knowing symptoms and observing signs, a doctor may measure temperature, blood pressure, the bodyweight of the patient.

The doctor on this basis of initial diagnosis may prescribe some initial tests like complete Blood Check (CBC), urine routine, stool routine, blood and urine sugar level, etc. to narrow the possible diagnostic options and choose initial treatments.

Treatment of Infectious Diseases:

For Reducing Symptoms:

This treatment is done only for the comfort of the patient because this treatment does not cure diseases but reduces symptoms. For e.g., If the patient is suffering from pain can be given a painkiller. The painkiller does not remove the cause of the pain or treat the diseases but reduces the perception of pain. Similarly, a cough syrup clears the respiratory tract but does not act on the cause of the infection.

Diseases like influenza do not have a cure. In this case, a medication which reduces the aches and fever are prescribed.

For Elimination of Disease:

The agents causing infectious diseases are viruses, bacteria, fungi, protozoan, parasites, and worms. They differ from each other in many ways. A single drug cannot kill them all.  Hence in such treatment doctor has to focus on each type of infectious agent separately.

Biochemical Pathway: A number of biochemical processes going on inside the living cell. During these biochemical processes energy and some chemical substances are produced. The energy and the substances produce are essential for the proper life function of the cell.  Scientists study the biochemistry of the infectious agent to find out which of these processes can be attached by the drug. The drug should be such that it should not harm the biochemical processes of the human being or animal to whom the drug is administered.

Antibiotics: Antibiotics are the drugs which are used for curing of diseases produced by bacteria. There is a wide range of antibiotics which attack different processes and structure in bacteria to kill them or to stop their growth. Antibiotic Penicillin stops the production of a compound needed for making cell wall in bacteria. The cell content of bacteria grows but the cell was is prevented from expanding due to unavailability of the material for it and under pressure from internal content, the cell bursts and the bacteria is killed. Other types of antibiotics act on other processes in bacteria such as protein synthesis.

Antibiotics Do Not Work on Viruses:

Viruses are not cells. They are genetic material inside protein cover.   They do not have cytoplasm or cell organelles, hence no biochemical processes occur in the. To multiply they enter the cell of a living organism (hos).

Viruses use resources of the host to produce their copies. Antibiotics act on biochemical processes of the infecting agent. As the biochemical processes are absent in viruses, there is no effect of antibiotics on viruses.

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In this article, we shall study the use of microbes as biocontrol agents and biofertilizers.

Microbes as Biocontrol Agents:

Chemical insecticides and pesticides are toxic and extremely harmful, to human beings and animals. These chemicals pollute the environment (soil, groundwater), fruits, vegetables, and crop plants. Our soil is also polluted due to the use of weedicides to remove weeds. To avoid this pollution and environmental degradation, biocontrol methods are used in place of chemicals. Biocontrol refers to the use of biological methods for controlling plant diseases and pests.

Microbial Pesticides:

In agriculture, there is a method of controlling pests that relies on natural predation rather than introduced chemicals. In this method, pests are kept in check, and not totally eradicated. Thus the food chains not disturbed e.g. Ladybird and Dragonflies useful to get rid of aphids and mosquitoes. Microbes used are either pathogens or predators or parasites on the pests. As it is natural predation it is not harmful.

An example of microbial biocontrol agent Bacillus thuringiensis (Bt) used to control butterfly caterpillar. They are available in sachets as dry spores, mixed with water and sprayed on plants. Fruits of these plants are eaten by insect larvae. In the gut of the larvae, the toxin is released and the larvae get killed. The bacterial disease will kill the caterpillars, but leave other insects unharmed. Now Bt toxin genes introduced into plants, which makes them resistant to insect pests. e.g. Bt cotton.

A biological control being developed for use in the treatment of plant disease is the fungus Tungus Trichoderma. Trichoderma species are free-living fungi that are very common in the root ecosystems. They are effective biocontrol agents of several plant pathogens.

Groups of Biocontrol Agents:

Pathogen: Bacteria

• Bacillus thuringiensis (Bt)
• Host range: Caterpillars (larvae of moths and butterflies). larvae of Aedes, black flies, some adult beetles, wax moths etc.

Pathogen: Fungi

• Beauveria bassiana
• Host range: Aphids, mealy bugs, mites, whiteflies, etc.

Pathogens: Protozoans

• Nosema locustae
• Host range: Grasshoppers, caterpillars, some corn borers and crickets.

Pathogen: Viruses

• Nucleopolyhedrovirus or NPV
• Host range: Gypsy moths and caterpillars

Microbial Herbicides/ Weedicides:

Pathogenic fungi as mycoherbicides:

• Phytopthera palmivora
• Alternaria crassa
• Fusarium sp.

Pathogenic bacteria as mycoherbicides:

• Pseudomonas sp.
• Xanthomonas sp.
• Agrobacterium sp.

Microbes as Biofertilizers:

The use of the chemical fertilizers to meet the ever-increasing demand for agricultural produce has contributed significantly to the pollution. Hence switching to organic farming is essential. Biofertilizers are organisms that enrich the nutrient quality of the soil. The main sources of biofertilizers are bacteria, fungi, and cyanobacteria.

Bacterial Biofertilizers:

The nodules on the roots of leguminous plants formed by the symbiotic association of Rhizobium. These bacteria multiply in the root and fix atmospheric nitrogen into organic forms, which is used by the plant as a nutrient. The specific Rhizobium is specific for a particular plant. e.g pea plant (Rhizobium leguminosarum) and for bean plant (Rhizobium phsaeoli).

Other bacteria can fix atmospheric nitrogen while free-living in the soil (examples Azospirillum and Azotobacter), thus enriching the nitrogen content of the soil.

Cyanobacterial Biofertilizers:

Cyanobacteria are autotrophic microbes many of which can fix atmospheric nitrogen. They are free-living, filamentous and may be aquatic or terrestrial. e.g. Anabaena azollae, Nostoc, Oscillatoria, Aulosira, Tolypothrix, etc. These blue-green algae have specialized cells called heterocytes which help in the fixation of nitrogen. In paddy fields, cyanobacteria (mainly Anabaena azollae, Nostoc) serve as an important biofertilizer.

Fungal Biofertilizers:

Fungi like mycorrhiza can also form symbiotic associations with plants. Many members of the genus Glomus form mycorrhiza. e.g. Ectomucorrhiza and Endomucorrhiza. The fungal symbiont in these associations absorbs phosphorus from soil and passes it to the plant.

Ectomycorrhizae form mycelium outside the root in the form of the mantle. It increases the surface area of the root. Due to which there is an increase in the uptake of water and nutrients. Due to which overall rate of growth of plant increases.

Endomicorrhizae grow in between and within the cortical cells of roots. The fungal hyphae penetrate the cells and form vesicles or finely branched arbuscles. Hence they are called Vesicular Arbuscular Mycorrhizae or VAM. Due to their presence, the plant can grow easily in the less irrigated land.

This association increases the resistance to root-borne pathogens, tolerance to salinity and drought and increase in plant growth and development.

Biodegradable Plastic:

Biodegradable plastic, like polyhydroxy butyrate (PHB) is being produced commercially by fermentation with the bacterium Alcaligenes eutrophus. Production of PHB can be easily achieved in tree plants like populous, where PHB can be extracted from leaves. Its production cost is high compared to synthetic plastics.

Edible vaccines:

The genes encoding the antigenic proteins of viruses and bacteria can be isolated from the pathogens and expressed in plants. such transgenic plants or their tissues producing antigens can be eaten for vaccination/immunization. Hence they are called edible vaccines.

The expression of such antigenic proteins in crops like banana and tomato are useful for immunization of humans since banana and tomato fruits can be eaten raw. Example: cholera and hepatitis B vaccine.

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Communicable diseases are those diseases which 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. They are spread by pathogens like viruses, bacteria, fungi, protozoa, helminths, and certain arthropods, etc.

The possible connection between living organisms and disease (cause of communicable diseases) was first proposed by Italian physician Fracastorius in 1546. He proposed that syphilis is caused by virus Contaginum vivam through live contact. Louis Pasteur and Robert Koch (1876-85) proposed the Germ Theory of Disease (related to communicable diseases). Which states that “The germ theory of disease states that certain diseases are caused by specific germs or infectious agents”.

Koch collected rod-shaped anthrax bacteria from farm animals that had died of the disease and used them to infect healthy mice. He also carried out a control experiment, using exactly the same method but substituting the anthrax bacilli with blood from healthy farm animals. The anthrax-infected mice developed the disease and died, but the control mice remained healthy: Koch now had clear evidence that the anthrax bacteria had caused the disease.

The Reservoir of Infection:

Any person, animal, plant, soil or substance in which an infectious agent normally lives and multiplies is called the reservoir of infection. The reservoir typically harbors the infectious agent without injury to itself and serves as a source from which other individuals can be infected.

The infectious agent primarily depends on the reservoir for its survival. It is from the reservoir that the infectious substance is transmitted to a human or another susceptible host.

The soil is a reservoir of Clostridium tetani. Air is a reservoir of bacterial cysts of tuberculosis, diphtheria, the virus of measles and mumps and other diseases causing bacteria. Food and water are reservoirs for the cyst of cholera, typhoid, Entamoeba histolytica and helminths like Taenia, Ascaris, and Wuchereria, etc. Carriers or vectors are those living organisms that spread pathogens from an infected person to healthy person but themselves are not affected. Vectors are the organisms that transmit disease but itself remains uninfected and disease-free. Carriers are the organisms that transmit disease itself are infected but remain disease-free.

Carriers of Communicable Diseases:

How Pathogens Cause Disease?

Different pathogens act in different ways. Some produce a poisonous substance called toxins. While other invade cells or tissues and produce toxin. The disease symptoms appear only after the lapse of some time, during which period the microbes multiply rapidly. The period between the infection and the appearance of signs of a disease is called the incubation period. The symptoms may be fever, headache, nausea, and vomiting in the body of the host.

Bacteria:

Bacteria stick to a certain cell type. They are able to colonize or penetrate the cell’s surface. If the host is immune to the bacteria due to previous exposure or vaccination, these organisms may not be able to cause disease. The person’s immune system detects their presence and eliminates them. Penetrating the cell surface can result in the destruction of the cell or will allow the bacteria to move inside the cell. Once colonized or inside a cell, bacteria often produce toxins: poisonous substances that cause disease.

However, if there is an imbalance in the host (non-immune), the bacteria is virulent. Small numbers are capable of causing illness, If there is exposure to large numbers of microbes that can paralyse or overcome the immune system, and the host is a nutritious target, then disease may result. Bacteria tend to be less tissue-specific and non-discriminatory than viruses and can cause a variety of infections once they have invaded the host.

Bacteria cause pneumonia,  tetanus, tuberculosis and cholera.

Viruses:

They must invade a cell (its host) to reproduce.  If the host is immune to the virus due to previous exposure or vaccination, these organisms may not be able to cause disease. The person’s immune system detects their presence and eliminates them. However, if there is an imbalance in the host (non-immune), the microbe is virulent.  once inside a cell, bacteria often produce toxins: poisonous substances that cause disease. The host cell burst. Thus there is multi-killing of cells. Viruses cause diseases such as common cold, measles, and influenza.

• Lytic Infections: The virus enters a cell, uses the cell’s resources to make copies of itself, and causes the cell to burst, releasing more virus to the organism. e.g. Common Cold, Influenza
• Lysogenic Infections: A virus integrates its DNA into the DNA of the host cell, forcing the host cell to replicate the viral DNA with every regular DNA replication. e.g. HIV, Hepatitis B.

The mass killing of cells can cause a wide range of diseases. The intestinal cells reproduce rapidly any infection of these cells does not last long and no permanent damage is done. e.g. Stomach Flu and Rotavirus

The viral infection of neurons, which cannot be replaced can cause permanent damage including paralysis e.g. Encephalitis and Viral Meningitis

The viral infection of immune system cells can disable a person’s ability to defend itself against pathogens. e.g. Lupus and HIV

Fungi:

Fungi thrive in warm, moist environments. Microscopic fungi normally colonize dead skin and hair. Occasionally the fungus can invade the skin or can be inhaled, causing infection through the release of toxins. e.g. Athlete’s Foot, Jock Itch, Ringworm. Fungi not only produce diseases but they attack food surfaces.

Protists:

Protists commonly invade the bloodstream (Malaria and African Sleeping Sickness) or the intestines (Dysentery). Protists are large enough that the body tries to fight them off, causing illness. Protists can release waste that causes a severe reaction or infection.

Nutrients meant for the host are used by the protist, and any disease related to lack of nutrients may occur. Protozoa cause malaria and amoebic dysentery.

Worms:

Animals generally get worms by ingesting their eggs, which then mature inside the warm, nutrient-rich body. Worms latch onto a tissue and consume cells and nutrients intended for the host, often leading to nutrient deficiency. Some worms burrow into tissue and cause infection in the host.

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Microbes are omnipresent i.e. they exist everywhere: in soil, air, water and also in the human body and the bodies of plants and other animals! They also exist in places where no other life-form exists. Bacteria, fungi, protozoa, viroids are examples of microorganisms. The general presumption is that the microbes are harmful to us because some of them cause diseases to both plants and animals including humans. However, there are many microorganisms, who are useful to us in many ways. In this article, we shall study the use of microbes in household activities.

Edible mushrooms are cultivated and consumed as food worldwide. Algae are used as thickening agents and in ice creams. They are nutritionally important in vegetarian diets. Yeasts are used as a common flavoring agent of food and for food production. Bacteria are used to produce dairy products like cheese and yogurt.

Fermentation:

The process of anaerobic respiration in which the complex molecules incompletely brakes into simple ones by the microbial action is called fermentation. There are many types of fermentation that are distinguished by the end products formed from pyruvate or its derivatives. The two fermentations most commonly used by humans to produce commercial foods are ethanol fermentation (used in beer and bread) and lactic acid fermentation (used to flavor and preserve dairy and vegetables). While there are a number of products from fermentation, the most common are ethanol, lactic acid, carbon dioxide, and hydrogen gas (H₂). These products are used commercially in foods, vitamins, pharmaceuticals, or as industrial chemicals. 

Fermentation of dough is done for making dosa, idli. CO₂ produced in the process gets trapped in gluten and makes idli puffy. Microorganisms involved in the process are Bacillus Candida, Saccharomyces cerevisiae. For making bread the microbe used in Baker‘s yeast (Saccharomyces cerevisiae). Toddy is made from the sap of palm using the process of fermentation.

The products obtained in the dairy industry by microbe activities are cheese, yogurt, buttermilk, paneer. Microbes used are species of Streptomyces, Penicillium, Lactobacillus

Bread Making:

The flour, salt, and yeast are mixed. Then the oil and water are mixed with it. The dough is kneaded until the dough becomes smooth. Then the dough is allowed to ferment overnight. The dough is moulded into balls and put on a baking tray. The oven is preheated to 220˚C and the balls are baked for 25-30 minutes until they turn golden brown, Then they are allowed to cool on wire mesh.

Cheese Making:

The process is used in cheese making (eg. Swiss cheese by Propionibacterium sharmanii, Roquefort cheese by fungi). Different varieties of cheese are known by their characteristic texture, flavour, and taste, the specificity coming from the microbes used. The bacterium Propionibacterium sharmanii is used in ‘Swiss cheese’ to give it its characteristic holes by producing a large amount of carbon dioxide. ‘Roquefort cheese’ is ripened by growing certain fungi on them to give them their specific flavour.

Curd Making:

The increased acidity causes the milk proteins (casein) to tangle into solid masses or curds. Milk that has been left to sour (raw milk alone or pasteurized milk with added lactic acid bacteria) will also naturally produce curds.

A small amount of curd added to the fresh milk as inoculum or starter contains millions of LAB, which at suitable temperatures multiply, thus converting milk to curd. During growth, the LAB produces acids that coagulate and partially digest the milk proteins. The microorganism involved is Lactobacillus Lactic acid Bacteria (LAB). The process increases nutritional value. It checks disease-causing microbes in our stomach. It increases Vitamin B₁₂

Yogurt Making:

Milk contains the sugar lactose. and some bacteria will ferment lactose to produce lactic acid. Yogurt is produced by batch culture, where pasteurized milk has the bacteria Lactobacillus bulgaricus and Streptococcus thermophilus added to it. The mixture is maintained at a temperature of around 40°C. The bacteria will produce lactic acid by respiration, and this lowers the pH. When it reaches a target the product is harvested.

Microbes as the Source of Food:

With the continuous rise in the global population, the demand for food has also increased. The conventional methods of agriculture and animal husbandry are not sufficient to fulfill the nutritional requirements of the growing population. This resulted in malnutrition due to deficiency of protein in food.

Some microbes or their fruiting bodies are directly used as a source of food. The microorganisms utilize the carbon and nitrogen present in these materials and convert them into high-quality proteins which can be used as a supplement in both human and animal feed.  They are rich in protein. Single-cell protein (SCP) is the protein extracted, or the cells themselves, from cultivated microbial biomass. The microbes involved are bacteria, fungi, and algae. SCP has high protein content. They can be grown on waste products such as whey, which makes it more of an economically- feasible protein source.

SCP can be obtained from bacteria (Bacillus subtilis), fungi (Candida and Saccharomyces cerevisiae), algae (Chlorella).  Bacterial sources of SCP are Pseudomonas fluorescens, Lactobacillus, Bacillus megaterium. The fungal sources of SCP are Aspergillus fumigatus, Aspergillus niger, Rhizopus cyclopean. Yeasts used as source of SCP are Saccharomyces cerevisiae, Candida tropicalis, Candida utilis. The algal sources of SCP are Spirulina sps, Chlorella pyrenoidosa, Chondrus crispus.

Mushrooms:

Fungus like mushrooms and truffles (bacidomycetes) are directly used as food. They are sugar-free, fat-free. They have low-calorie value. They are rich in proteins, vitamins, minerals, and amino acids. Some common edible mushrooms are white button mushroom (Agaricus bisporus), Paddy straw mushroom (Volvariella Volvacea), Oyster mushroom (Pleurotus florida). Toadstools are poisonous mushrooms.

Algae, which include seaweeds and other aquatic plants, contain chlorophyll and require carbon dioxide and continuous sunlight. Those without chlorophyll, particularly yeasts and fungi, show more promise for commercial production.

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