Other mycobacteria such as Mycobacterium bovis, Mycobacterium africanum, Mycobacterium canetti and Mycobacterium microti can also cause tuberculosis, but these species do not usually infect healthy adults. Mycobacteria stain positive with special dyes and are referred to as acid-fast bacteria (AFB).
Tuberculosis most commonly attacks the lungs but can also affect the central nervous system, the lymphatic system, the circulatory system, the genitourinary system, bones, joints and even the skin.
Scanning electron micrograph of M. tuberculosis Thin section transmission electron micrograph of M. tuberculosis
How does a person get TB? A person can become infected with tuberculosis bacteria when he /she inhales minute particles of infected sputum from the air. The bacteria get into the air when someone who has a tuberculosis lung infection coughs, sneezes, shouts, or spits. People who are nearby can then possibly breathe the bacteria into their lungs. TB is not infected by just touching the clothes or shaking the hands of someone who is infected.
Tuberculosis is spread by aerosols created by coughing or sneezing.
The risk factors for acquiring TB include close-contact situations, alcohol and drug abuse, and certain diseases (for example, diabetes, cancer, and HIV) and occupations (for example, health-care workers). The occurrence of HIV has been responsible for an increased frequency of tuberculosis. Control of HIV in the future, however, should substantially decrease the frequency of TB.
TB can remain in an inactive (dormant) state for years without causing symptoms or spreading to other people. When the immune system of a patient with dormant TB is weakened, the TB can become active (reactivate) and cause infection.
Most common symptoms - fatigue, fever, weight loss, coughing, and night sweats. If the infection in the lung worsens, then further symptoms can include coughing, chest pain, coughing up of sputum (material from the lungs) and/or blood, and shortness of breath. If the infection spreads beyond the lungs, the symptoms will depend upon the organs involved.
When the inhaled tuberculosis bacteria enter the lungs, they can multiply and cause a local lung infection (pneumonia). The local lymph nodes associated with the lungs may also become involved with the infection and usually become enlarged.
Rounded, focal nature of the granulomas x-ray film shows the cavities in the patient's right upper lung lobe.
Disease Diagnosis: skin tests, chest x-rays, sputum analysis (smear and culture), and PCR tests S kin tests - Tine test and the Mantoux test / PPD (purified protein derivative) test. In each of these tests, a small amount of purified extract from dead tuberculosis bacteria is injected under the skin. Negative skin test-no infection. Raised and reddened area around the site of the test injection after about 48 to 72 hours –Infected After the PPD is injected intracutaneously, a small wheal appears on the forearm. Positive TB skin test is marked by an area of reddish induration of 17mm. It is the induration (firm bump) that is gently palpated that determines the size, not the area of redness. Infected person expected to mount an immune response in the skin containing the bacterial proteins.
A person with a positive skin test, a normal chest x-ray and no symptoms most likely has only a few TB germs in an inactive state and is not contagious. Inactive tuberculosis may be treated with an antibiotic, isoniazid (INH), to prevent the TB infection from becoming active.
Bacille Calmette Guerin (BCG) is a vaccine used. Prepared from a strain of the attenuated (weakened) live Mycobacterium bovis .
Active TB is treated, usually successfully, with INH in combination with one or more of several drugs, including rifampin, ethambutol, pyrazinamide, and streptomycin.
Drug-resistant TB is a serious, as yet unsolved, public-health problem, especially in Southeast Asia, the countries of the former Soviet Union, Africa, and in prison populations. Poor patient compliance, lack of detection of resistant strains, and unavailable therapy are key reasons for the development of drug-resistant TB
Causative agent: Virus
ss RNA, approximately cylindrical in shape (bullet-like shape) Family-Rhabdoviridae EM of rabies virus
Rabies is a viral neuroinvasive disease that causes acute encephalitis (inflammation of the brain) in mammals. In non-vaccinated humans, rabies is almost invariably fatal after neurological symptoms have developed, but prompt post-exposure vaccination may prevent the virus from progressing.
Longitudinal and cross-sectional schematic view of rabies virus
Diagnosis may be made by a variety of diagnostic techniques, including PCR testing of cerebrospinal fluid, viral culture and serology.
Micrograph with numerous rabies virions (small dark-grey rod-like particles)
Soon after, the symptoms expand to slight or partial paralysis, anxiety, confusion, agitation, abnormal behavior, terror can be observed. The production of large quantities of saliva and tears coupled with an inability to speak or swallow. This can result in "hydrophobia", where the victim has difficulty swallowing, shows panic when presented with liquids to drink, and cannot quench his or her thirst. The patient "foams at the mouth" because they cannot swallow their own saliva for days and it gathers in the mouth until it overflows. Death almost invariably results two to ten days after the first symptoms.
Any mammal may become infected with the rabies virus. Infected bats, monkeys, raccoons, foxes, cattle, dogs or cats provide the greatest risk to humans. The virus is usually present in the nerves and saliva of a symptomatic rabid animal. Transmission may occur by a bite or via an aerosol through mucous membrane. Transmission between humans is extremely rare, although it can happen through transplant surgery or, even more rarely, through bites or kisses. After a typical human infection by bite, the virus enters the peripheral nervous system. It then travels along the nerves towards the central nervous system. Once the virus reaches the brain, it rapidly causes encephalitis.
Post-exposure immunization Treatment after exposure/ post-exposure prophylaxis / "P.E.P.“ Highly successful in preventing the disease if administered promptly, within six days after infection. Step 1- immediately washing the wound with soap and water, which is very effective at reducing the number of viral particles. Step 2- Patients receive one dose of immunoglobulin and five doses of rabies vaccine over a twenty-eight day period. The first dose of rabies vaccine is given as soon as possible after exposure, with additional doses on days 3, 7, 14, and 28 after the first. Patients that have previously received pre-exposure vaccination do not receive the immunoglobulin, only the post-exposure vaccinations. Pre-exposure immunization Domestic dogs and cats are required to be vaccinated. A pre-exposure vaccination is also available for humans, most commonly given to veterinarians and those traveling to regions where the disease is common. Rabies can be prevented by vaccination, both in humans and other animals.