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.
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, 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 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 5 percent of the cases.
- The organisms in such cases make the gall bladder their habitat.
Communicable Disease- Hepatitis:
- Hepatitis is the inflammation of liver. It can be caused by viruses (five different viruses— termed A, B, C, D and E cause viral Hepatitis), bacterial infections, or continuous exposure to alcohol, drugs, or toxic chemicals, such as those found in aerosol sprays and paint thinners, or as a result, of an auto-immune disorder.
- Hepatitis results in either damage or reduction in the livers ability to perform life-preserving functions, including filtering harmful, infectious agents from blood, storing blood sugar and converting it into usable energy forms, and producing many proteins necessary for life.
- Symptoms seen in Hepatitis differ according to the cause and the overall health of the infected individual. However, at times, the symptoms can be very mild.
- The commonly seen clinical features are general weakness and fatigue, loss of appetite, nausea, fever, abdominal pain and tenderness.
- The main feature is the presence of jaundice (yellowing of skin and eyes that occurs when the liver fails to break-down excess yellow- coloured bile pigments in the blood).
- Depending on the progress and intensity, Hepatitis can be categorized as acute or chronic. In acute Hepatitis, clinical features often subside without treatment within a few weeks or months. However, about 5 percent of the cases go on to develop into chronic Hepatitis, which may last for years. Chronic Hepatitis slowly leads to progressive liver damage and cirrhosis.
- Hepatitis A is a self-limiting disease that is found all across the world.
- It is usually transmitted through oral ingestion of infected material (mainly water), but sometimes transmitted parenterally; most cases resemble the symptoms of a mild flu attack and jaundice is mild too.
- Hepatitis B is an acute vital disease. It primarily spreads parenterally, but sometimes orally as well.
- However, the main mode of spread is intimate contact and from mother to the new born.
- Fever, anorexia, nausea, vomiting are the initial symptoms, and they soon lead to severe jaundice, urticarial skin lesions, arthritis, etc.
- Some patients become carriers or even remain chronically ill, even though most patients recover in about three to four months.
- Hepatitis C is a viral disease commonly occurring after transfusion or parenteral drug abuse.
- It frequently progresses to a chronic form that is usually asymptomatic, but may involve liver cirrhosis.
- Hepatitis D or Delta Hepatitis is caused by the Hepatitis D virus.
- It usually occurs simultaneously with or as a super infection in case of Hepatitis B, thus increasing its severity.
- Hepatitis E is transmitted by the oral fecal route; usually by contaminated water.
- Chronic infection does not occur but acute infection may be fatal in pregnant women.
Communicable Disease- Jaundice:
- Jaundice, also known as icterus, is a condition, which is characterized by yellowish discolouration of the skin and whites of eyes. It is a symptom or clinical sign, not a disease by itself.
- The yellow colouration is caused by an excess amount of bile pigment known as bilirubin in the body. Normally, bilirubin is formed by the breakdown of haemoglobin during the destruction of worn-out red blood cells.
Communicable Disease- Leptospirosis:
- Leptospirosis is a disease caused by a type of bacteria and is associated with animals. It is more common in the tropical countries.
- The disease is also known as canefield fever; cani- cola fever, field-fever, mud fever, seven day fever and swineherd disease. Leptospirosis is caused by different strains of bacteria of the genus Leptospira.
- Of all the varieties that cause disease, Leptospira icterohaemorrhagiae is the most serious type.
- If not treated properly, it could lead to serious complications. Leptospirosis is a disease of animals that can spread to humans.
- Rats are the most common carriers. Soil contaminated with urine of infected animals can also transmit the disease to persons exposed to cattle urine, rat urine or to foetal fluids from cattle.
- Sewage workers, agricultural workers, butchers, meat inspectors, workers in contact with contaminated waters and veterinarians are generally at risk.
- Person to person transmission is not possible. Leptospirosis can spread due to contact with urine, blood or tissues from infected persons. The organisms enter the body through the breaks in the skin or through mucous membranes.
- The organisms can also be acquired by drinking contaminated water. Infection is commonly acquired by bathing in contaminated water.
- The organisms multiply in the blood and tissues of the body. Though the organism can affect any organ of the body, the kidney and liver are commonly involved. The incubation period is usually 10 days. It may vary from 2 to 20 days.
Communicable Disease- Diarrhoeal Diseases:
- The term gastroenteritis’ is most frequently used to describe acute diarrhoea. Diarrhoea is defined as the passage of loose, liquid or watery stools.
- These liquid stools are usually passed more than three times a day. The attack usually lasts for about 3 to 7 days, but may also last up to 10 to 14 days.
- Diarrhoea is a major public health problem in developing countries. Diarrhoeal diseases cause a heavy economic burden on health services.
- About 15 percent of all pediatric beds in India are occupied by admissions due to gastroenteritis.
- In India, diarrhoeal diseases are a major public health problem among children under the age of 5 years. In health institutions, up to a third of total pediatric admissions are due to diarrhoeal diseases.
- Diarrhoea related diseases are a significant cause of mortality in children less than five years of age. Incidence is highest in the age group of 6 to 11 months.
- The National Diarrhoeal Disease Control Programme has made a significant contribution in averting deaths among children less than five years of age.
Communicable Disease- Amoebiasis:
- Amoebiasis is an infection caused by a parasite ‘Entamoeba Histolytica. The intestinal disease varies from mild abdominal discomfort and diarrhoea to acute fulminating dysentery.
- Extra intestinal amoebiasis includes involvement of the liver (liver abseess), lungs, brain, spleen, skin, etc.
- Amoebiasis is a common infection of the human gastrointestinal tract. It has a worldwide distribution.
- It is a major health problem in the whole of China south-east and west Asia and Latin America, especially Mexico. It is generally agreed that amoebiasis affects about 15 percent of the Indian population. Amoebiasis has been reported throughout India.
Communicable Disease- Cholera:
- Cholera is an acute diarrhoeal disease caused by V. Cholera (classical or El T). It is now commonly due to the El T or biotype.
- The majority of infections are mild or symptomatic. Epidemics of cholera are characteristically abrupt and often create an acute public health problem.
- They have a high potential to spread fast and cause deaths. The epidemic reaches a peak and subsides gradually as the ‘force of infection declines.
- Often, when time control measures are instituted, the epidemic has already reached its peak and is waning.
Communicable Disease- Brucellosis:
- Brucellosis is one of the major bacterial zoonoses, and in humans is also known as undulent fever, Malta fever or Mediterranean fever.
- It is occasionally transmitted to humans by direct or indirect contact with infected animals.
- The disease may last for several days, months or occasionally, even years.
- Brucellosis is both a severe human disease and a disease of animals with serious economic consequences. Brucellosis is a recognized public health hazard that is found the world over.
- It is endemic wherever cattle, pigs, goats and sheep are raised in large numbers. The important endemic areas for Brucellosis exist in Mediterranean zones, Europe, Central Asia, Mexico and South America. Animal Brucellosis has been reported from practically every state in India.
- However, no statistical information is available about the extent of infection in humans in various parts of the country.
- The prevalence of human Brucellosis is difficult to estimate. Many cases remain undiagnosed either because they are not apparent, or because physicians in many countries are unfamiliar with the disease.
Communicable Disease- Hookworm Infection:
- Hookworm infection is defined as: ‘any infection caused by Ancylostoma or Necator’.
- They may occur as single or mixed infections in the same person through various factors, which have to be prevented. Hookworm infection is widely prevalent in India.
- Necator americanus is predominant in south India, and Ancylostoms duodenal in north India. Recently, another species, A. ceylanicum has been reported from a village near Calcutta.
- The heavily infected areas are found in Assam (tea gardens).
- West Bengal, Bihar, Orissa, Andhra Pradesh, Tamil Nadu, Kerala and Maharashtra. More than 200 million people are estimated to be infected in India.
- It is believed that 60 to 80 percent of the population of certain areas of West Bengal, Uttar Pradesh, Bihar, Orissa, Punjab, and the eastern coast of Tamil Nadu and Andhra Pradesh are infected with hookworms.
Communicable Disease- Influenza:
- Influenza is an acute respiratory tract infection caused by influenza virus of which there are three types—A, B and C.
- All known pandemics were caused by influenza A strains, due to various factors. Influenza is found all over the world.
- It occurs in all countries and affects millions of people. Outbreaks of influenza A occur virtually every year. Major epidemics occur at intervals of two to three years, and pandemics at intervals of about 10 to 15 years.
- The first pandemic during the present century occurred in 1918-19, which affected an estimated 500 million people and killed more than 20 million.
- In India alone, over six million people died during this pandemic. This pandemic was caused by what is now known as the swine influenza virus.
- Recent pandemics occurred in 1957-58 owing to the influenza A (H2N2) and in 1968 owing to the influenza A (H3N2).
- Outbreaks of influenza B also occur annually with epidemics occurring at intervals of407 years. Influenza brought on by the type C virus occurs sporadically as small outbreaks.
- The unique features of influenza epidemics are the suddenness with which they arise, and the speed and ease with which they spread.
- The short incubation period, a large number of subclinical cases, a high proportion of susceptible population, short duration of immunity, and an absence of cross-immunity, all contribute to its rapid spread.
- The fate of the virus during inter-epidemic periods is also known. Possible explanations include transmission of virus to extra-human reservoirs (pigs, horses, birds. etc.,) latent infection or continuous transfer from one human to another. This explains the occurrence of sporadic cases.
Communicable Disease- Filariasis:
- It is caused by a parasite, which belongs to the nematode family Filariasis. According to WHO reports, an estimated 751 million people are at ‘risk’ for infection, and 120 million have actually been infected.
- The public health problem of lymphatic filariasis is greatest in China, India and Indonesia. These three countries account for about two-thirds of the estimated world total of persons infected.
Filarial Problem in India:
- Filariasis is a major public health problem in India. There are an estimated six million attacks of acute filarial disease per year, and at least 45 million persons currently have one or more chronic filarial lesions.
- Heavily infected areas are found in Uttar Pradesh, Bihar, Andhra Pradesh, Orissa, Tamil Nadu, Kerala and Gujarat.
- The infection is acquired from a person who has filariasis. The maximum infectivity is when the organisms are circulating the blood.
- The largest number appears in the blood at night time, and retreats from the blood stream during the day. Their usual habitat is in the lymph nodes.
- The mosquito feeds on such a person and acquires the filarial parasite. The filarial organism is transmitted when the mosquito bites a person. The parasite is deposited near the site of puncture.
- It passes through the punctured skin or may penetrate the skin on its own and finally reach the lymphatic system. Filariasis affects all age groups.
Communicable Disease- Tuberculosis:
- Tuberculosis remains a worldwide public health problem, particularly in the Third World countries. Tuberculosis is India’s biggest public health problem. An estimated that 5, 00,000 deaths annually are reported due to this disease, while a similar number of persons get cured.
- The population in the Third World countries like India is exposed to tuberculosis. The disease, however, does not develop in everyone who is exposed. Poor nutrition, overcrowding, low socio-economic status, are more likely to develop the disease.
- The prevalence of people who are infected is about 30 percent of the population. The prevalence of infection is more common in the younger population.
- The vast majority of cases are to be found in rural and semi-urban areas, where more than 80 percent of the country’s population lives. In urban areas, tuberculosis is found more frequently in slum-dwellers and lower socio-economic groups than in well-off groups
Current Burden of Non-Communicable Diseases in India
- Non communicable diseases are the one which are of long duration and slow in progression. As per World health organization, NCDs account for total 53% of all deaths in India. Most of the burden is attributed by cardiovascular diseases (24%), followed by respiratory diseases (11%), other NCDs (10%) and Injuries (10%).
- According to a report presented by world economic forum and Harward School of public health, the prevalent NCDs in India are CVDs, chronic respiratory diseases, Diabetes, and cancer.
- Cancer is one the leading cause of death in India with 28 lac cases at a point of time and 10 lac new cases taking place very year. The burden of cancer is expected to rise in the country due to the effects of tobacco, demographic transitions and increase in the life expectancy.
- Diabetes is another leading NCD in the nation. Estimated total number of people suffering with diabetes is 40.9 million in India and by 2025 it is expected to increase up-to 69.9 million. Diabetes accounts for 1.09 lakh deaths in a year.
- Hypertension is a major risk factor for cardiovascular diseases. Hypertension is directly responsible for 57% of all stroke deaths and 24% of all coronary heart disease deaths in India. The cases of CVDs are expected to rise up to 741 lacs in 2015.
- Chronic obstructive pulmonary disease is responsible for high rate of mortality and morbidity across the world. In 2010, almost 24 million adults over the age of 40 in India had COPD. It is expected to increase to 32 million by 2020.
- The other conditions which contribute to the burden of non-communicable diseases are mental health conditions (schizophrenia, depression & bipolar disorder) and musculoskeletal disorders (Rheumatoid arthritis, osteoarthritis & gout).
- The non-communicable diseases are emerging due to the risk factors associated with it. The main risk factors which are associated with NCDs are tobacco use, harmful use of alcohol, lack of physical activity and poor diet.3Table 2&3 shows the risk factors(Behavioral & Metabolic respectively) associated with noncommunicable diseases and their prevalence.
- In addition to the above said risk factors for NCDs; Globalization and urbanization has also contributed to its burden. It has caused the nutritional transition in the country because of the availability of the commercial food. One another important factor causing the rise in NCDs is change in demographic profile of the country.
- A study conducted by Joy Kumar Chakma & Sanjay Gupta on“Lifestyle and Non-Communicable Diseases: A double edged sword for future India” showed that In India, 53% of the deaths in 2008 were due to NCDs (WHO). The cardiovascular diseases (CVDs) alone account for 24 percent of all deaths.
- The anticipated cumulative loss of national income due to NCDs mortality for India for 2006-2015 will be USD237 billion. By 2030, this productivity loss is expected to double. These major NCDs can be prevented through effective interventions by undertaking the lifestyle related modifiable risk factors.
- Total deaths (in thousands) caused by non-communicable diseases as per WHO (2008) estimates are 2967.6 and 2273.8 among males and females respectively. NCD deaths under the age of 60 years are 35.0% (Males) and 32.1% (Females).