Banana bunchy top virus causes this disease. The infected plant shows extremely stunted growth. Leaves become short and narrow. Affected leaves are crowded in a rosette like fashion (bunch of leaves) at the top of the plant. Chlorosis and curling of the leaves also occur. Diseased plants should immediately be uprooted and burnt to avoid further infection.
Emerging viral infections( in human beings)
Recent examples of emerging viral infections in different regions of the world include ebola virus, HIV, dengue, hemorrhagic fever, lassa fever, Rift valley fever, SARS.
HIV belongs to a group of viruses called retroviruses. It infects the T4 lymphocytes known as helper cells which form the main line of body immune system. HIV kills the T4 lymphocytes and the resulting depletion of T4 cell population creates an immune deficiency. This paves way for many opportunistic pathogens to attack. AIDS by itself is not a killer disease. It is only the other opportunistic pathogens which kill the infected persons.
HIV infection causes fever, loss of body weight, persistent generalized lymph node enlargement and opportunistic infections like T.B . etc. The AIDS patients may also have headache, fatigue, persistent diarrhoea, dry cough, lymphomas and damage of the central nervous system. Often there is appearance of thrush in the mouth and throat and night sweats. Changes in behaviour and mental illness may also occur.
Primarily HIV is sexually transmitted. It is predominant among homosexuals. Persons with veneral diseases, persons who have many sexual partners and prostitutes will have more chances of HIV infection. The commonest method of transmission is through sexual intercourse with many persons.
The other methods of transmission are during blood transfusion, tissue or organ donation of HIV infected persons to healthy persons, injections with unsterilized syringes and needles and shared needles by drug addicts. AIDS can spread from infected mother to the child during pregnancy or through breast feeding.
Since there is no cure for AIDS the best approach to control AIDS is prevention. Reduction of sexual promiscuity and adoptions of prophylactic measures (such as the use of condoms) can reduce transmission through sexual intercourse. Transmission through the shared needles by drug addicts may be reduced by proper education. The transmission through blood transfusion may be eliminated by proper serological screening of donated blood for the presence of HIV antibodies. Transmission from infected mother to child can be reduced by preventing or terminating pregnancy. Drugs like AZT (azidothymidine) only help to increase the life span of the victim by few a months and do not offer complete cure for the disease.
Cancer is an uncontrollable and unorganized growth of cells causing malignant tumour. The cells of this tumours have the capacity to spread indiscriminately anywhere in the body. In recent years, there has been increasing evidence to prove that the cancer is caused by the DNA virus called Simian virus (SV-40) and a group of RNA viruses called retroviruses. The cancer causing viruses are also called oncogenic viruses. It is now believed that some viruses are involved in leukemia, sarcoma and some kind of breast cancer also. "Corona"
Severe Acute respiratory Syndrome (SARS) is a respiratory illness that has recently been reported in South East Asia, North America and Europe.
It has created panic among the people all over the world and has resulted in great economic loss for many countries like China, Singapore etc.
It begins with high fever. Other symptoms include headache, discomfort and body aches. Patient may develop dry cough and have trouble in breathing.
It appears to spread by person to person contact especially with infectious material (for example respiratory secretions.)
The viruses that cause SARS are constantly changing their form which will make developing a vaccine difficult. SARS is caused by a group of viruses called corona viruses which are enveloped viruses. Their genome is single stranded RNA. The nucleocapsid is helical. These viruses have petal shaped surface projections arranged in a fringe like a solar corona.