Microorganisms
Microscopic organisms, commonly known as microorganisms or microbes, are found all around us and even inside our bodies. The category ‘Microbes’ includes a massive range of organisms including bacteria, fungi, viruses, algae, archaea and protozoa. Some of these, such as bacteria and fungi, are well known, but others such as archaea much less so.
The vast majority of microbes on the earth pose no real threat to humans, plants or animals; in fact they actually work alongside humans to make world go round, aiding decomposition, decay and even helping us to digest our food. However, there are some microorganisms which negatively impact our lives, causing illness, bad odours and damaging products and surfaces. Some of the names we regularly hear in the media are Salmonella, E.Coli, MRSA, Malaria and Bird flu.
common bacteria
The types of bacteria prevalent in an environment are determined by several factors. However, bacteria are found in every habitable place on earth. They survive in soil, rocks, oceans, volcanoes, and even arctic snow. Some have been found living in or on other organisms including plants, animals, and humans. The common types of bacteria found in buildings are not harmful when in low numbers. However, just like with mold, elevated levels of bacteria particularly the gram negative type are potentially a health hazard.
Some types of bacteria in buildings are brought in with occupants and with outdoor air. Others are human-gut-associated bacteria such as Lactobacillus, Staphylococcus and Clostridium. These types of bacteria are most common in bathroom environment. Research has shown that the types of bacteria in a building are also influenced by the type of ventilation, i.e., mechanically or naturally ventilated. For example, naturally ventilated buildings are associated with more plant- and soil-associated bacteria while mechanically ventilated buildings are likely to be dominated by human-associated bacteria.
Virus
Virus, an infectious agent of small size and simple composition that can multiply only in living cells of animals, plants, or bacteria. The name is from a Latin word meaning “slimy liquid” or “poison.”
The earliest indications of the biological nature of viruses came from studies in 1892 by the Russian scientist Dmitry I. Ivanovsky and in 1898 by the Dutch scientist Martinus W. Beijerinck. Beijerinck first surmised that the virus under study was a new kind of infectious agent, which he designated contagium vivum fluidum, meaning that it was a live, reproducing organism that differed from other organisms. Both of these investigators found that a disease of tobacco plants could be transmitted by an agent, later called tobacco mosaic virus, passing through a minute filter that would not allow the passage of bacteria. This virus and those subsequently isolated would not grow on an artificial medium and were not visible under the light microscope. In independent studies in 1915 by the British investigator Frederick W. Twort and in 1917 by the French Canadian scientist Félix H. d’Hérelle, lesions in cultures of bacteria were discovered and attributed to an agent called bacteriophage (“eater of bacteria”), now known to be viruses that specifically infect bacteria.
The unique nature of these organisms meant that new methods and alternative models had to be developed to study and classify them. The study of viruses confined exclusively or largely to humans, however, posed the formidable problem of finding a susceptible animal host. In 1933 the British investigators Wilson Smith, Christopher H. Andrewes, and Patrick P. Laidlaw were able to transmit influenza to ferrets, and the influenza virus was subsequently adapted to mice. In 1941 the American scientist George K. Hirst found that influenza virus grown in tissues of the chicken embryo could be detected by its capacity to agglutinate (draw together) red blood cells.
A significant advance was made by the American scientists John Enders, Thomas Weller, and Frederick Robbins, who in 1949 developed the technique of culturing cells on glass surfaces; cells could then be infected with the viruses that cause polio (poliovirus) and other diseases. (Until this time, the poliovirus could be grown only in the brains of chimpanzees or the spinal cords of monkeys.) Culturing cells on glass surfaces opened the way for diseases caused by viruses to be identified by their effects on cells (cytopathogenic effect) and by the presence of antibodies to them in the blood. Cell culture then led to the development and production of vaccines (preparations used to elicit immunity against a disease) such as the poliovirus vaccine.
Scientists were soon able to detect the number of bacterial viruses in a culture vessel by measuring their ability to break apart (lyse) adjoining bacteria in an area of bacteria (lawn) overlaid with an inert gelatinous substance called agar—viral action that resulted in a clearing, or “plaque.” The American scientist Renato Dulbecco in 1952 applied this technique to measuring the number of animal viruses that could produce plaques in layers of adjoining animal cells overlaid with agar. In the 1940s the development of the electron microscope permitted individual virus particles to be seen for the first time, leading to the classification of viruses and giving insight into their structure.
Advancements that have been made in chemistry, physics, and molecular biology since the 1960s have revolutionized the study of viruses. For example, electrophoresis on gel substrates gave a deeper understanding of the protein and nucleic acid composition of viruses. More-sophisticated immunologic procedures, including the use of monoclonal antibodies directed to specific antigenic sites on proteins, gave a better insight into the structure and function of viral proteins. The progress made in the physics of crystals that could be studied by X-ray diffraction provided the high resolution required to discover the basic structure of minute viruses. Applications of new knowledge about cell biology and biochemistry helped to determine how viruses use their host cells for synthesizing viral nucleic acids and proteins.
Logic originally dictated that viruses be identified on the basis of the host they infect. This is justified in many cases but not in others, and the host range and distribution of viruses are only one criterion for their classification. It is still traditional to divide viruses into three categories: those that infect animals, plants, or bacteria.
Virtually all plant viruses are transmitted by insects or other organisms (vectors) that feed on plants. The hosts of animal viruses vary from protozoans (single-celled animal organisms) to humans. Many viruses infect either invertebrate animals or vertebrates, and some infect both. Certain viruses that cause serious diseases of animals and humans are carried by arthropods. These vector-borne viruses multiply in both the invertebrate vector and the vertebrate host.
Certain viruses are limited in their host range to the various orders of vertebrates. Some viruses appear to be adapted for growth only in ectothermic vertebrates (animals commonly referred to as cold-blooded, such as fishes and reptiles), possibly because they can reproduce only at low temperatures. Other viruses are limited in their host range to endothermic vertebrates (animals commonly referred to as warm-blooded, such as mammals).
Diseases – Communicable diseases, Endemic diseases
Top 10 Causes of Death (Source: WHO World Health Statistics 2012)
- Ischemic heart disease 12 %
- Chronic obstructive pulmonary disease 11%
- Stroke 9%
- Diarrheal disease 6%
- Lower respiratory infections 5%
- Preterm birth complications 4%
- Tuberculosis 3%
- Self-inflicted injuries 3%
- Falls 3%
- Road injuries 2%
Communicable diseases
- Communicable diseases continue to be a major public health problem in India.
- Many communicable diseases like tuberculosis, leprosy, vector borne diseases like malaria, kalaazar, dengue fever, chikungunya, filariasis, Japanese encephalitis, water-borne diseases like cholera, diarrhoeal diseases, viral hepatitis A & E, typhoid fever, leptospirosis, etc and other viral infections are endemic in the country.
- In addition to these endemic diseases, there is always a threat of new emerging and re-emerging infectious diseases like nipah virus, avian influenza, SARS, novel H1N1 influenza, hanta virus etc.
- Local or widespread outbreaks of these diseases result in high morbidity, mortality and adverse socio-economic impact.
The most common diseases which are endemic in India are as follows:
Communicable Disease- Malaria:
- Malaria is a very common disease in developing countries. The word malaria is derived from the word ‘mal-aria meaning bad air.
- Ronald Ross first discovered the transmission of malaria by mosquitoes, while he was working in India (Secunderabad, AP) in 1897. Malaria is one of the most widespread diseases in the world.
- Each year, there are 300 to 500 million clinical cases of malaria, 90 percent of them in Africa alone.
- Among all infectious diseases, malaria continues to be one of the biggest contributors to disease burden in terms of deaths and suffering.
- Malaria kills more than one million children a year in the developing world, accounting for about half of malaria deaths globally.
- The risk of getting malaria extends to almost the entire population in India (almost 95 percent).
- The following states that have the highest number of malaria cases are Madhya Pradesh, Maharashtra, Orissa, Karnataka, Rajasthan, Assam, Gujarat and Andhra Pradesh.
Communicable Disease- Typhoid:
- Typhoid fever is an acute, systemic infection presenting as fever with abdominal symptoms, caused by Salmonella typhi and paratyphi.
- Before nineteenth century, typhus and typhoid fever were considered to be the same. Enteric fever is an alternative name for typhoid. Salmonella typhi and paratyphi colonise only humans.
- The organisms are acquired via ingestion of food or water, contaminated with human excreta from infected persons.
- Direct person-to-person transmission is rare. Typhoid is a global health problem. It is seen in children older than the age of one.
- Outbreak of typhoid in developing countries results in high mortality. The recent development of antibiotic resistant organisms is causing much concern.
- Typhoid fever is more common in the tropics. It tends to occur in places, where the sanitation standards are poor. A bacterial organism called salmonella typhi causes typhoid fever.
- Salmonella paratyphi can also cause fever and abdominal symptoms. The disease caused by both these entities is called enteric fever.
- The disease presents with a typical, continuous fever for about three to four weeks, relative bradycardia with abdominal pain (due to enlargement of lymph nodes in the abdomen), and constipation.
- Geographical Distribution Worldwide, typhoid fever affects about six million people with more than 6, 00,000 deaths a year.
- Almost 80 percent of cases and deaths occur in Asia, and most others in Africa and Latin America. Among Asian countries, India probably has a large number of these cases.
- Indian Statistics Typhoid fever is endemic in India.
- Health surveys conducted by the Central Ministry of Health in the community development areas indicated a morbidity rate varying from 102 to 2,219 per 1, 00,000 population in different parts of the country.
- A limited study in an urban slum showed 1 percent of children up to 17 years of age suffer from typhoid fever every year.
- Carriers of Typhoid Fever Typhoid infection is mainly acquired from persons who are carriers of the disease.
- Carriers are the people who continue to excrete salmonella through their urine and feces a year after an attack of typhoid. A chronic carrier state develops in about 2 to 23.7 24.8 41.5 48.3 47.8C117.2 448 288 448 288 448s170.8 0 213.4-11.5c23.5-6.3 42-24.2 48.3-47.8 11.4-42.9 11.4-132.3 11.4-132.3s0-89.4-11.4-132.3zm-317.5 213.5V175.2l142.7 81.2-142.7 81.2z"/> Subscribe on YouTube