Vaccination to prevent TB

Vaccine which is used against TB infection is BCG. The BCG vaccine contains a live but weakened form of Mycobacterium bovis, which is one of the bacterium that causes tuberculosis (see previous posts). The vaccine is known as BCG vaccine because a strain of bacterium known as Bacillus Calmette-Guerin is used in this process. The vaccine is used to prevent tuberculosis and works by stimulating the body’s immune response to the bacteria without actually causing the disease.

Prevention of TB

Several points should be kept in mind regarding prevention of TB (Tuberculosis) disease. The prevention of spreading the disease from infected to healthy individual is of utmost importance. The following points may be noted in order to achieve this gaol: -

#Early detection of TB, prompt isolation and immediate treatment of the patient.
#Educating health care workers/close members of the patient about TB
#Screening health care workers/close members of the patient for TB
#Implementing effective work practices including wearing proper respiratory protection
#Preventing the spread of infectious droplets into the air by using appropriate exhaust #ventilation
#Controlling the direction of air flow to prevent air contamination adjacent to the infectious source
#Diluting the air through general ventilation
#Cleaning the air through air filtration

Mycobacterium tuberculosis

Staining means coloring of the bacteria for proper viewing under the microscope. It is very important part of identifying TB bacteria. Mycobacterium tuberculosis (MTB) is a slow growing aerobic bacterium that divides in every 16 to 20 hours; this is extremely slow compared to other bacteria that have division times measured in minutes. In contrast, one of the fastest growing bacteria is a strain of E. coli that can divide roughly every 20 minutes. As MTB only has one phosphorlipid outer membrane, it is classified as Gram-positive bacteria. But if a Gram stain is performed, MTB either stains very weakly Gram-positive or does not retain dye, due to high lipid content of its cell wall. MTB is a small rod shaped bacteria (Bacillus), which can withstand weak disinfectants and can survive in a dry state for weeks. Normally the bacteria can only grow inside a host, so in vitro (outside host) culture of M. tuberculosis took a long time to develop, but is now a routine laboratory procedure. MTB is identified microscopically by its staining characteristics; it retains certain stains often being treated with acid solution & thus is classified as an “acid-fast bacillus” or AFB. This can also be visualized by fluorescent microscopy and by an auramine-rhodomine stain.

Treatment of TB

Treatment for TB uses antibiotics to kill bacteria. The two antibiotics most commonly used are rifampicin and isoniazid. However, these treatments are more difficult than the short courses of antibiotics used to cure most other bacterial infections as long periods of treatments (around 6 to 12 months) are needed to entirely eliminate mycobacterium from the body. Latent TB treatment usually uses a single antibiotic, while active TB disease is best treated with combinations of several antibiotics to reduce the risk of the bacteria developing antibiotic resistance. People with latent infections are treated to prevent them from progressing to active TB disease later in life. Treatment using rifampicin & pyrazinamide (often used) is also not always risk free. It may cause liver damage & death due to combination of these drugs.

What is microbiology?

Since I am writing on human disease, we have to deal a lot with microbes as infectious diseases are caused by microorganisms. So I am giving a small introduction about microbiology for clear understanding of common people.
Biology is the branch of science that deals with living organisms and microbiology is a part of biology. Microbiology deals with the microscopic organisms. They include bacteria, yeasts, molds, algae & protozoa. By microscopic it means that the organism can only be seen with the aid of microscope. If an object has a diameter of less than 0.1 mm, human eye cannot perceive it. In fact anything less than 1 mm cannot be properly perceived by our eye. So organisms, whose diameter falls below 1 mm, can be regarded roughly as microorganisms & fall under the domain of microbiology. For long these organisms were not known to human being for this reason. After the invention of microscope at early seventeenth century, this new world of biology has evolved and by far this is biggest community of life. In fact all the other groups of organisms (i.e. the macro world) together do not have the number or diversity and abundance as possessed by microorganisms.

Microscopes in the early stages were of two kinds - the first was simple microscope with a single lens of very short focal length consequently capable of high magnification (just like magnifying glasses of modern world). The second one was known as compound microscope with double lens system & hence completely displaced the simple one in modern world. But in early stages the compound microscopes were full of various optical defects render them less effective than simple microscope with very short focal length (although it is extremely difficult to produce a simple microscope with that short focal length). It takes a lot of skill to make such simple microscopes.

Now everybody may think that it is not possible to see bacteria or other microbes through naked eye. It is not possible to see a bacterium off course, but you can definitely visualize them when they are in clusters. The distinction of microbes as plants or animals are not very strong. Many of them specially the bacteria are closely resemble plants in many ways. So they can be seen as unicellular plants, but many of them has no similarity with plants or may have similarity with animals. Most of them are prokaryotes (has primitive cell) but many are eukaryotes (cells with prominent nucleus) as well. Microorganisms usually possess only one cell i.e. they are unicellular organisms. For their small size they have a very high ratio of surface area to volume, which is approximately 200,000 times greater than a similar ratio for an adult human being. They absorb nutrients through their body surfaces & have high metabolic rates & rapid rate of multiplication, which results in proliferation of a certain species in small time. This way they can affect an environment enormously in very short time. This particular aspect of microbes is very important in its interaction with higher organisms. This ability can be used very efficiently for detection of pollution in the environment or can be a detrimental factor while producing disease of mankind/other useful animals (but if the disease is against an organism harmful to human then it can be regarded as a beneficial issue also).

In modern classification of living kingdom bacteria has been placed separately. There are three groups —- Archea, Bacteria and Eukaryota. Archea & Bacteria are definitely microorganisms. But some of the eukaryotes are also microbes as they are unicellular. All the bacteria have prokaryotic cell, whereas the eukaryotes have eukaryotic cell. Archea have something common of both bacteria and eukaryota.

Confirmatory test for TB

If any person has positive TB skin test or QHT - G test then some additional tests should be performed for confirmation of TB infection. These usually include a chest x - ray & test of the phlegm coughed up by the patient. This is done because pulmonary TB is most common & it is highly contagious unlike other forms of TB. If these tests show negative results then one should go for other types of TB. For this purpose blood & urine samples of the patient will be tested. If one has active TB disease then he/she should start taking medicines as directed by the physician. One should also keep in mind that to treat TB one has to take medicine for at least 6 months even if the symptoms are no longer existing (i.e. have to complete the course). Otherwise the TB bacteria will develop resistance against the drugs, as latent asymptomatic form may still exist in the patient’s body if the course of medicine is not followed.

New findings in Malaria

Malaria is one of the most important infectious disease in human history. To eliminate Malaria, countries must treat their entire population, even asymtomatic adults. But there's rarely enough money and medicine for developing nations to do that. So Doctors focus their energies on the young people who are clearly ill. Adults who have developed some level of immunity to malaria end up as reservoirs for parasites, continuing to spread the illness without ever feeling sick.

QuantiFERON TB Gold or QFT G Test

QFT - G is a blood test is another very useful test to find TB infection. The QFT - G test measures the response t TB proteins when they are mixed with a small amount of blood collected from the patient. But the problem is that there are very few clinics, which actually offer this test. The test requires only one visit to the clinic instead of two in case of TB skin test.

Resistance of Malaria parasite against Chloroquine

Malaria was treated with quinine in the past. Recently Chloroquine (a derivative of quinine) is used effectively especially against Plasmodium falciparum. But recently Plasmodium falciparum (the deadliest of all) developed resistance against chloroquine. Malaria can be easily prevented using good health-care infrastructure. So there may be no requirement of drugs in 1st World Countries. But in third world countries like India the disease is treated primarily through chemotherapy. So scientists are searching for new drugs and also want to explore the reason behind resistance development. Recently $ 1.5 million grant is sanctioned from National Institute of Health (NIH) USA for this purpose. So we may hope something interesting in the coming year.

TB Skin Test

Today we will know about TB skin test. This test is a very good test for detection of TB infection. In that process a small amount of testing fluid (called tuberculin or PPD) is injected just under the skin on the underside of forearm. Actually tuberculin contains anti-antibody of TB bacteria. An infected person will have antibody against TB bacteria produced by immune system. So presence of antibody (against TB bacteria) confirms TB infection. After 2 – 3 days, there will be a swelling in the arm where tuberculin was injected. A positive reaction will result in more swelling due to the allergic reaction between the two antibodies. So by measuring the swelling a trained person can tell whether the person has TB infection or not.

If anyone has any question or insight regarding this feel free to ask and share.

Nine eleven and Malaria

Here I want to share another astonishing fact regarding Malaria. Do you know that malaria is responsible for 1 - 3 million deaths a year (mostly in sub-Saharan Africa), and this is equal to the death toll from the attacks of 9/11 every 8 to 24 hours. Think of it. More facts will follow.

Diagnosis of TB

Diagnosis of TB may be difficult due to the difficulty in culturing the slow growing organisms in Laboratory. So other methods besides culturing have to be employed. Medical history, chest X-ray & physical examinations are required for correct diagnosis. Currently two tests 1) The TB skin test & 2) QuantiFERON - TB Gold (QFT-G) test are employed to identify both Active & Latent form of the disease.

Testing for TB

As a precaution one should get tested for TB when one feels so. One should get tested if he/she has: -

Ø Spent time with a person having TB disease or suspected to have TB disease.

Ø HIV infection or any other immunosuppressed condition.

Ø Latent TB disease

Ø Gone to country/returned from a country with high active TB disease

Ø Gone to some areas where TB is common (homeless shelters, migrant camp, prison, hospitals etc.)

Ø Injected illegal drugs.

Mode of transmission of TB

Mode of transmission of TB is through air from infected to non-infected person when infected persons cough or sneezes. Each sneeze contains approximately 40,000 of infectious droplets (i.e. droplets containing TB bacteria) and when nearby person breath in these droplets they may become infected. The bacteria after entering a healthy individual settle in the lungs and grow and thus infection starts in the lungs of a new individual. From there they can be transmitted to other parts of the body (kidney, spine & brain) through blood and infect those organs.

One should keep in mind that though TB in lungs or throat is highly contagious that in other parts of the body are usually not. So people should be aware of the fact that person with Active lung TB (there is another Latent form of TB that I will discuss later) can spread the germ and hence family members, friends and co-workers of TB patients are the most susceptible persons to have TB.