Disease Producing DNA Viruses
Disease Producing DNA Viruses
A. Variola and Vaccinia Viruses
1. Variola Viruses (small pox virus)
- Variola major
- Variola minor
2. Vaccinia virus (cow pox virus)
B. Herpes Simplex Virus (HSV)
C. Varicella Zoster Virus (VZV) (chicken pox virus)
E. Adeno Viruses
F. Human Parvo Viruses
G. Papova, polyoma and Papilloma Viruses
H. Cytomegalo Viruses (CMV)
I. Epstein Barr Virus (EB)
J. Hepatitis B Virus (HBV)
Variola and Vaccinia Viruses
Variola Virus (small pox virus) is the causative agent of small pox, one of the most highly communicable diseases. It is brick shaped and multiplies in the cytoplasm. There are two variants of this virus pathogenic to humans viz. Variola major and Varioa minor.
Variola major causes severe illness and claimed many human lives. Variola minor causes a very mild variety of small pox. Variola virus consists of central biconcave DNA core covered by two coats (inner and outer). It also contains a lateral body on either side of DNA core. The small pox disease is characterised by vesicles deeply embedded in the skin. The vesicles breakdown, scabs fall off and pitted permanent scars are left. Variola virus can even cause conjunctivitis or blindness. It may be remarked here that small pox has been almost completely eradicated from the world and there is no longer any need for smallpox vaccination.
Vaccinia Virus is almost similar to Variola virus in its biological properties. It is an artificial virus and does not occur in nature. Jenner originally used this cow pox virus for vaccination against small pox. Commercial vaccines were prepared by inoculating vaccinia virus in the skin of calves, sheep and buffalo.
Herpes Simplex Virus (HSV)-
Humans are HSV’s only natural host. HSV is spherical and multiplies in the nucleus. Two serotypes are reconized; HSV type 1 and HSV type 2. HSV is responsible for many types of infections such as Occular Herpes a type of eye disease; genital herpes a veneral disease transmitted by sexual intercourse; neonatal herpes (mother to baby); Herpes labialis (border of lip is involved); Herpes Simplex Dermatitis, Herpes Simplex Hepatitis, Herpes Simplex Encepalitis, Herpes Simplex Meningitis etc. The usual vehicles for transmission are contaminated saliva; secretions from eyes, pharynx or genitalia. Skin to skin contact can spread the virus. It may be mentioned here that HSV type 1 and 2 can often cause cancer in certix.
Varicella Zoster Virus (VZV)-
It is almost similar to HSV in its morphology. It causes Chicken Pox.-Chicken Pox- Chicken pox is one of the commonest childhood infections and it may occur at any age. The incubation period varies 2 to 3 weeks. It is transmitted by coughing or sneezing or by direct contact with the patient. The vesicles are surrounded by red rim. There are rarely depressed scars as seen in small pox. If the infection is severe it may lead to complications such as haemorrhagic eruption, leukaemia, viral pneumonia, encephalitis etc.
The name is derived from the fact that they were first found in adenoid tissue removed by surgical operations. They multiply in nucleus and have no envelope. They enter through the respiratory tract and exit through the respiratory secretions. The adenoviruses have more than thirty three serotypes and type 12, 18, 31 can cause tumours in humans. The diseases produced by adeno viruses are pharyngitis, pneumonia, acute respiratory disease and pharyngo-conjunctival fever. Sometimes they infect the eye to cause mild conjunctivitis. Transmission is through nasopharyngeal secretion or sputum of saliva or through physical contact or droplets.
Human Parvo Viruses-
They are small and simplest DNA viruses without envelope. They often cause disease in animals. Parvo-virus B-19 is the only one which infects humans. The first human parvo-virus was discovered by Paver in 1973 in stool specimens. The second was found in the serum of blood donors and a third type was recovered from human tissue.
Papova, Polyoma and Papilloma Viruses-
They are small DNA tumour producing viruses which cause a variety of tumours in different parts of the human body.
Cytomegalo Virus (CMV)-
It was first reported in the early years of 20th century. The virus is present in saliva, urine, semen, uterine cervix, blood and human milk. It can spread through saliva or by inhalation or sexual intercourse. It is a source of cytomegalo inclusions disease but it can also cause tumours.
Epstein Barr Virus (EB)-
It was first reported in 1964 in African children. It causes tumour in jaw. Infection occurs through respiratory tract by close contact with patients. The common mode of infection is believed to be by kissing; hence the disease is also known as kissing disease. It is characterised by sore throat and presence of abnormal lymphocytes in the peripheral blood.
Hepatitis B Virus (HBV)-
It is a DNA virus and can cause carcinoma in humans