12 Major Disease Caused by Virus | Microbiology

Here is a list twelve major diseases caused by virus:- 1. Viral Hepatitis 2. Rabies 3. Cold Sores 4. AIDS 5. Influenza 6. Measles 7. Mumps 8. Rubella 9. Yellow Fever 10. Dengue Fever 11. Small Pox 12. Polio.

Disease # 1. Viral Hepatitis:

Hepatitis (plural hepatides) (Greek hepaticus means liver) refers to inflammation of liver resulted through any infection. At present there are nine viruses known that cause hepatitis. Out of nine, two are herpes viruses and Epstein-Barr virus, and seven hepatotoxic viruses.

However, of the seven, only five are well characterised (Table 25.7):

Hepatitis B (serum hepatitis):

Hepatitis B is caused by the hepatitis B virus (HBV). It is classified as an Orthohepadnavirus within the family Hepadnaviridae. The HBV consists of a circular dsDNA in a capsid that is enveloped. The HBV has complex structure (Fig. 25.2).

It consists of three antigenic particles:

(i) A spherical particle (22 nm diameter),

(ii) A spherical particle (42 nm diameter) containing DNA and DNA polymerase called the Dane particle, and

(iii) Tubular or filamentous particle of variable length.

The Dane particles in this form are ineffective because they are in unassembled form. The unassembled particles contain hepatitis B surface antigen (HBsAg). If these are present in blood, they represent that the person is infected (Tiollais and Buendia).

This laid down a basis for the production of first recombinant DNA vaccine for humans developed by recombinant DNA technology. HAY (Havrix Vaccine), HBV (hepatitis B virus);*, Hepatitis F and G are the newly discovered viruses and not well characterized so far.

Normally, the HBV is transmitted through blood transfusion, contaminated equipment, drug users’ unsterile needles, or anybody secretion (i.e. saliva, sweat, semen, breast milk, urine, faeces, etc.). However, HBV can pass from blood of infected mother to the foetus through placenta.

About 200 million people are victimized each year. Hepatitis B is more dangerous than the cancer. In India, the number of hepatitis B patients is increas­ing gradually.

The symptoms of hepatitis B vary. It includes fever, loss of appetite, nausea, abdominal abnormality and fatigue. After 1-3 months of incubation, HBV infects liver, destroys hepatic cells and releases the enzyme transaminase into blood stream.

It is followed by jaundice. Con­sequently a product of haemoglobin (bilirubin) is accumulated in the skin and other tissues. This results in yellow ap­pearance of skin, eyes, and urine as well. Chronic hepatitis B infection also causes the primary liver cancer (hepatocellular carcinoma). Hepatitis B is known as a human carcinogen only to tobacco smokers.

The preventive and control measures are:

(i) Avoiding contact with HBV-infected blood and secretions and immunizing needles, sticks,

(ii) Intramuscular injection of hepatitis B immuno globulin within 7 days,

(iii) Use of recombinant vaccine such as Engerix-B, Recombivax HB, etc.,

(iii) Vaccination of other individuals such as carriers of HBV (household members, sex partners, blood recipients, homosexual males, international travellers).

Disease # 2. Rabies:

Rabies (Latin rabere means madness) is caused by a number of different strains of neurotropic vi­ruses. Most of them belong to the genus Lysavirus of the family Rhabdoviridae. Virion is bullet- shaped and enveloped that consists of (-) ssRNA.

When symptoms of rabies are fully materialized, mortality rate of humans increases. Most of the wild animals (e.g. foxes, coyotes and wolves, and street dogs, bats, cats, etc.) transmit the disease. Canine rabies is endemic. Virus multiplies in the salivary gland of these ani­mals.

When these animals bite hu­mans or other healthy animals, viral particles are spread through saliva. Virus attaches to the plasma mem­brane of skeletal muscle cells by glycoprotein envelope spike. It en­ters the cell and multiplies. When in sufficient number, they enter the nervous system through unmycelinated sensory and motor terminals.

They bind with the reported binding site (i.e. nicotinic acetylcholine receptor). Finally the virus reaches to the spinal cord and results in first specific symptoms (pain at wound site). As the virus disseminates, a progressive encephalitis develops. Consequently, virus spreads, throughout the body including saliva.

Symptoms begin after 2 to 16 weeks of exposure of virus. There are anxiety, irritability, depression, fatigue, loss of appetite, fever and sensitivity to light and sound. Consequently, it results in paralysis.

In about 50% patients painful spasm of throat and chest muscles occur when the patients swallow liquid. Therefore, patients do not take liquid. This stage has been called hydrophobia (fear of water). When the region that regulates breathing is destroyed, it results into death of patients.

Rabies can be diagnosed by observing the Negri bodies (mass of viruses or subunits of unassembled viruses) under light microscope. However, today diagnosis is done by direct immuno-fluorescent-antibody (DIFA) of brain tissue, isolation of viral particles, testing the Negri bodies, and rapid enzyme-mediated immuno-diagnosis test.

Prevention and control of rabies involve pre-exposure vaccination of dogs and cats and post exposure vaccination of humans. The effective vaccines are available in market.

Disease # 3. Cold Sores:

Cold sores or fever blisters (herpes labialis) are caused by herpes simplex virus type 1 (HSV- I). Similar to other herpes, it also contains dsDNA present in enveloped icosahedral capsid (25.3) Cold Sore on lips is shown in Fig. 25.3.

HSV-1 (also called human herpesvirus-1 or HHV-1) is primarily associated with oral (cold sores) and ocular lesions (Fig. 25.3). The virus enters the peripheral sensory nerves during primary infection and migrates along the axons to sensory nerve ganglia in the central nervous system.

This results in the virus to escape the immune response. During latent infection of nerve cells, viral DNA is maintained as an episome with limited expression of specific virus genes required for the maintenance of latency.

Various disturbances such as physical (injury, U.V, hor­mones) or psychological (stress, emotional upset perhaps affecting immune system/hormonal balance) upset the deli­cate balance of latency. When the latent virus reactivates, it leads to recurrent disease i.e. virus travels from sensory nerves to surface of body and multiplies to cause the damage of the tissue.

Transmission occurs through direct contact of epithelial tissue with virus. At inoculation sites, blisters develop due to destruction of virus mediated host tissue. In severe cases, blisters occur on the surface epidermis of lips, mouth and gums. Blisters may heal within a week. After primary infection the virus travels to nerve ganglion, where it remains in latent stage for the life time of infected person.

Certain stresses such as sunlight, fever, emotions may reactivate the virus. After being reactivated it moves from nerve ganglion to down a peripheral nerve to the border of lips or other part of the face, and produce the second fever blisters. Recurring infection may occur in eye causing eye inflammation. This causes a major blindness to patients.

The antigen of Virus can be detected by several enzyme immunoassay kits such as VIDAS, HERPCHECK, etc.

Disease # 4. AIDS (Acquired Immuno-Deficiency Syndrome):

It is the first great pandemic of second half of 20th century. AIDS is caused by the human immunodeficiency Virus (HIV) which is a lenti-virus within the family Retroviridae. For detailed description of virus and working of immune system.

According to WHO, 19 million people are infected worldwide and over 40 million people will have to be infected by the year 2000. Upto June 1995, about 476, 899 cases and deaths have been reported in the USA.

(i) Transmission:

It is a transmissible disease. The groups, most at risk acquiring AIDS are (in descending order of risk) homosexual/bisexual men, intravenous drug users, prostitutes, heterosexual (who have intercourse with drug users, prostitutes and bisexuals), transfusion patients or haemophilics (who receive donated blood), users of contaminated needles and syringe, and children born of infected mothers.

About 90% of children from HIV positive mothers were infected during pregnancy, at birth or during breast-feeding. The mortality rate is about 92% of the diagnosed persons. Worldwide about 5.3 million people were infected in 1996 and some 5.8 million were infected in 1997. How­ever, 2.3 million people died of AIDS in 1997 i.e. a 50% increase over 1996.

(ii) AIDS in India:

According to a report of United Nations, India has the largest number of HIV-infected persons. However, the first case of AIDS in India was registered in 1986. Since then, HIV prevalence has been re­ported in all states and Union territo­ries.

By a report of India Govern­ment, upto October 31, 1997, out of 3.20 million individuals practising risk behaviours and suspected AIDS cases (who were screened for HIV infec­tion), 67,311 were found seropositive and 5002 cases of AIDS have been reported.

Highest number of HIV infec­tions has been reported in Maharashtra and Tamil Nadu, and among inject­able drug users (IDU) of Manipur. The predominant mode of transmission infection of the AIDS patients is through heterosexual contact (74.2%), followed by blood transfusion and blood produced infusion (7.0%) and IDU (7.2%). Males account for 78.7% of AIDS cases and females 21.3%. However, the majority of cases (89%) are in the age group of 15-44 years.

HIV slowly breaks down the body’s immune system and makes it easier for the HIV infected persons to get a variety of illness known as “opportunistic infections” (Table 25.8).

Soon after the record of first case of AIDS in 1986, a National AIDS committee was constituted. Thereafter, the Government launched the National AIDS control programme which focused attention on increasing awareness of HIV/AIDS, screening of blood for HIV and testing of individual’s practising risk behaviours.

In 1992, the National AIDS Control Organisation (NACO) which works under the Ministry of Health was established to prepare the programme for making aware the youths.

NACO is functioning in the following ways:

(a) It makes multimedia strategy for intersectoral collaboration with the Ministry of Information and Broadcasting, mass media, advocacy, involving NGOs, and implementing training and research.

(b) It has implemented a school education programme in 18 states, and developed the curriculum and training. To create awareness each year December 1 is celebrated as World AIDS Day.

(c) Counselling, training and provision of counselling services.

(d) Social marketing to increase the use of affordable quality condoms.

All over the country sero surveillance centres and sentinel sites have been established for monitoring HIV trends overtime in certain sections of the general population. In Manipur a pilot continuum of care programme has been implemented.

The Bombay High Court has given the judgement for financial compensation by a company to an employee who was fired on being diagnosed HIV-positive. The Govt, of India has made active effort to involve NGOs (Non Government Organisations) participation. The process of funding NGOs has been decentralised.

(iii) Prevention and Control of AIDS:

Prevention and control of AIDS involve:

(a) The screening of blood and heat treatment of blood product to destroy the virus,

(b) Education to people about AIDS,

(c) Education about protected sexual behavior and practices including the use of condoms,

(d) Education of intravenous drug users to avoid sharing needles and syringe,

(e) Regular testing for HIV, and

(f) Taking helps from NGOs.

Attempts are being made to develop a vaccine that can (a) stimulate the production of neutralizing antibodies which can bind to the virus envelope and prevent from entering the cell, and (b) promote the destruction of those cells which are already infected by the virus. So far no vaccine has been produced possibly due to continuous changing in antigenic properties of the virus.

Disease # 5. Influenza (Flu):

Influenza (Italian, to influence) or flu is a viral diseased caused by orthomyxo-virus in respiratory system. Based on antigenic properties of N and H spikes influenza virus is classified into A, B and C groups. However, it frequently changes its antigenicity. These changes are referred to as antigenic variations.

The small variations are called antigenic drift, and large changes are known as antigenic shift. Antigenic variations occur yearly in group A, less frequently in group B and unknown in group C. Changes in antigenic properties lead to infection in humans.

This is why it causes worldwide pandemic; for example, pandemics of 1918 and 1957 were severe, whereas that of 1977 was mild. Pandemic of 1918-1919 was most destructive where 550,000 deaths were recorded in the U.S.A. alone.

Virus enters the respiratory system through inhalation or ingestion of contaminated respiratory secretion. After hydrolyzing the mucus by using neuramidase present in spikes, the virus adheres to epithelial cell with the help of haemagglutinin spike protein.

Consequently, some parts of plasma membrane of the cell bulge inwardly and form a vesicle. The vesicle encloses the virus. When pH decreases, haemagglutinin molecules undergo conformational changes. The hydrophobic ends of haemagglutinin spring outward and extend outward the vesicle. Conse­quently, nucleocapsid is released into the cytoplasm.

Symptoms of influenza are chills, fever, headache, malaise and muscular pain. These symptoms appear when epithelial cells die due to attack of activated T cells. The flu is recovered in 3 to 7 days. Influenza alone is not fatal. Death is caused probably due to secondary bacterial invasion by Sta­phylococcus aureus.

Streptococcus pneumoniae and Haemophilus influenzae. The recommended antivi­ral drugs are amantadine and rimantidine. Salicylic acid must be avoided in youngs of below 14 years age. One should avoid the contact and droplets of the patients.

Disease # 6. Measles (Rubeola):

Measles (Latin rubeus means red) is highly contagious disease caused by Morbilliviras of the family Paramyxoviridae. It is endemic throughout the world. Virus is a helical RNA virion and closely related to mumps or Rs virus. Its size is 125-250 nm with 18 nm diameter of nucleocapsid. The genetic material is single stranded RNA of molecular weight of 5-6 × 10⁶ Daltons. Capsid contains spikes consisting of haemagglutinin property.

The virus enters through the respi­ratory tract or conjunctiva of the eyes. The membrane co-factor protein (i.e. the comple­ment regulator CD46) acts as the receptor for measles virus. The incubation period is 10 to 21 days. The first symptom is a nasal discharge on about 10th day followed by cough, fever, headache and conjunctivitis.

Faintly pink coloured muscles like skin eruptions occur within 3 to 5 days that last about 5 to 10 days. Lesions of oral cavity contain diagnostically important bright-red koplik’s spots with a bluish-white region in the centre of each one. Thereafter, infrequent progressive degeneration of the central nervous system occurs. This is called sub-acute sclerosing pan-encephalitis.

There is no specific treatment of measles. The use of attenuated measle vaccine (Attenuvax) alone or in combination (MMR vaccine i.e. measles, mumps, rubella) is recommended for children. However, it has been found that measles infects 44 million people and kills 1.5 million per annum throughout the world. Since the beginning of public health immunization programme, about 98% cases have decreased.

Disease # 7. Mumps:

Mumps is an acute disease that occurs mainly in school age children. It is caused by paramyxovirus (Fig. 15.8A). The virus is transmitted in saliva and respiratory droplets. It enters the respi­ratory tract of non-immune individuals through con­tact. The symptoms are swelling and tenderness of the salivary (parotid) glands after 16 to 18 days of infection. Therefore, this disease is also known as epidemic parotitis.

Swelling persists for about 1-2 week with low fever. In the post-pubescent males certain complications e.g. meningitis and inflamma­tion of epididymis and testes associated with the disease occur. In adults mumps is dangerous for reproductive system.

Some males may develop orchi­tis i.e. swelling of testicles to 3 or 4 times of normal size. This results in decline in sperm counts. In contrast, in females, there may develop oophoritis i.e. lower back pain and enlargement of ovaries.

Prevention of mumps is keeping the children with mumps free from school or other activities for 2 weeks. Therapy of mumps is the use of a live attenuated mumps virus vaccine. It is given as part of the tripple MMR vaccine.

Disease # 8. Rubella (German Measles):

In the 1800s, Rubella (Latin rubellus means reddish) was first described in Germany; hence it is called German measles. It is caused by rubella virus which is a member of the family Togaviridae and contains ssRNA. It causes skin disease on children of 5 to 9 years of age. Rubella is distributed throughout the world, and occurs during winters and spring seasons.

Virus spreads through droplets and sheds through respiratory secretions of the patients. After entering into body, it takes about 12 to 23 days to get established. Small red spots develop on body that last in about three days. Rash of small red-spots is followed by a light fever. The rash is immunologically mediated, and not caused by the Virus. This results in appearance of rash and di-appearance of virus from the blood.

Rubella is a mild disease; however, it can be disastrous in the first three months of pregnancy. This leads to fatal death, premature delivery or several congenial defects in heart, eyes, and ears of the growing baby. This disease is called congenital rubella syndrome. All children and women of child bearing age can be infected by rubella. Therefore, the live attenuated rubella vaccine is recommended to them.

Disease # 9. Yellow Fever:

Yellow fever is the first human viral disease caused by yellow fever virus which was discovered by Walter Read in 1901. Carlos Huan Finley demonstrated experimentally that it is transmitted by a mosquito, Aedes aegypti from one human to other human in urban areas. However, in sylvatic (sylvatic means in the woods or affecting wild animals) it is transmitted by mosquitoes to monkeys and from monkeys to humans.

Yellow fever is caused by a flavivirus that is endemic in many tropical areas, such as Mexico, South America and Africa. After entering in humans, it spreads to local lymph node and multiplies therein. Later on it moves to liver, spleen, kidneys and heart. The symptoms are fever, chills, headache and backache along with vomiting. In severe cases, the affected organs show lesions with haemorrhage.

No treatment of yellow fever is available so far. It is diagnosed serologically. Vaccine contains attenuated yellow fever 17 D strain or the Dakar strain virus. Therefore, adopting vaccination and control of insect vectors are the steps for control of this disease.

Disease # 10. Dengue Fever:

Dengue fever is caused by an RNA containing virus of icosahedral symmetry. The virus capsid is enveloped. This disease has been found severe in areas of southeast pacific and in Southeast Asia.

However, a pandemic effect spread in Delhi and adjoining areas in India in 1996. Symptoms involve severe fever and prostra­tion followed by acute pain in limbs and muscles. Patients experience bone-breaking pain; therefore, it is also called break-bone fever.

Dengue fever is transmitted by a mosquito, Aedes that lays eggs in stagnant fresh water such as in ditches, coolers, etc. The virus is transmitted when the mosquitoes inject their saliva in human body. It is interesting to note that only female bites frequently for getting human blood for egg produc­tion.

After 9 to 10 days of consuming blood the mosquitoes become infectious, thereafter, dies whether transmit dengue or not. After infection, human develops dengue haemorrhagic fever. Thus, there are four types of virus of dengue. It was found in Delhi that all the virus were not equally effective. Only one out of four was dangerous.

Disease # 11. Small Pox:

Diseases caused by box Viruses e.g, smallpox have been known for centuries. One of the earliest documented evidence is the Egyptian pharaoh V. Ramses who died of smallpox about 2,000 years B.C. It was thought that smallpox have been transferred to Europe around the early 700s and then to the Americas in the early 1,500s.

It is well accepted fact that the main defeat of the Aztecs was due to a smallpox epidemic. Within two years more than 3.2 million Aztecs died of small pox.

Small pox (variola) was very dangerous and fatal of all viral diseases. Smallpox has played a major role in reducing Indian resistance to the European colonization of North America. In Mexico Indian population declined by 90% within 100 years of contact with Spanish. This has been due to small pox and other diseases.

Before contact with Europeans, 10-12 million Indians lived in north of Rio Grade. In addition, in 1600 A.D. about 72,000 lived in New England, but by 1674 A.D. around 8,600 remained in New England. Such catastrophe is considered with the fact of European contact with Native Americans.

Europeans have already suffered from small pox during 16th country. They only carried over the inoculum. Moreover, many American cities e.g. Boston, Philadelphia and Plymouth, grew upon cities of previous Indian villages.

Virus is brick-shaped and consists of dsDNA of largest size, 270 nm which is packed in nucleocapsid. This is surrounded by a swirling series of fibres. The early symptoms are chills, fever and general prostration.

When temperature falls, pinkish red spots (macules) develop first on scalp and forehead and later on neck and extremities. In the last macules develop on trunk. Thereafter, these spots are converted into pink pumples or papules. These turn into fluid filled vesicles.

The term variola is derived from Latin varus which means pimples. In the advanced stage the vesicles got coalesced to form pustules that cover the whole surface of body; when the pustules burst, pus comes out.

The pustules are deep in skin as compared to chicken pox that appears on surface. Sometime the pustules form soft crust. After falling the crusts, pitted scars or pocks are formed. Thus the name small pox differs from the pock developed from the larger lesions of syphilis or chicken pox.

Small pox is transmitted by contact with skin or body fluid such as urine, blood or droplets. In 1798, Edward Jenner (an English physician) found that milk maids and other, who were working with dairy cattle, contracted the closely related mild form of pox called cowpox or vaccinia (Latin vacca means cow). But those, who had contracted cowpox and had recovered from it, did not contract small pox.

Therefore, Jenner procured some material from cow-pox for small pox, and established the process of vaccina­tion. This method of vaccination became very famous in 1806. Napoleon ordered his army to be vaccinated by the above method.

This process of vaccination is based on the principle that cowpox virus after entering the blood in­creases the production of antibodies. Since both cowpox and small pox viruses are similar, the antibodies are equally effective on both of them.

A worldwide effort to vaccinate everyone against smallpox began with the ultimate goal to rid the world of the plague-like epidemic. The World Health Organization (WHO) declared the virus officially eradicated in 1977, with samples retained at laboratories within the two then global superpowers, the United States and the Soviet Union.

In 1967, the World Health Organisation (WHO) received funds and launched a Global eradication programme. Through proper surveillance small pox cases were identified and vaccinated.

The last case of small pox had been in 1974 in Bangladesh, in 1976 in Ethiopia and in 1977 in Somalia. In 1979, WHO has announced that small pox has been eradicated from the earth, except that which has been kept in four research laboratories of the U.S.A., Russia, U.K. and Japan with the permission of WHO.

The WHO is now trying to decide whether or not to destroy the remaining stock of small pox virus. After September 2001, the American and UK governments have had increased concern over the use of smallpox or a small pox like disease in ‘bio-terrorism’.

Disease # 12. Polio:

Poliomyelitis (Greek polios means gray and myelos means marrow or spinal cord), polio or infantile paralysis is caused by the poliovirus which is a member of family Picornaviridae. Polio is of very ancient origin. Various Egyptian hieroglyphics of about 2000 B.C. show persons with withered legs and arms.

In 1840, Jacob von Heine, a German orthopaedic described the clinical features of poliomyelitis and found that spinal cord was the area where individuals suffered. In 1890, Oscar Median (a Swedish pediastrician) recognised that a system phase (of fever development) occurred early, and complicated by paralysis.

In 1908, Karl Landsteiner and William Popper successfully transmitted the disease to monkeys. In 1949, J. Enders, T. Weller and F. Robbins discovered that the poliovirus could be propagated in vitro in cultures of human embryonic tissues of non-neural origin. This led to a milestone for the development of vaccine.

In 1952, D. Bordian recognised three serotypes of poliovirus. In 1953, J. Salk successfully immunized humans with formalin-inactivated poliovirus and in 1955, this vaccine (IPV) was licensed.

Salk vaccine is administered in a series of three intramuscular injections. In 1962, the live attenuated polio viral vaccine (oral polio vaccines, OPV) was developed by Albert Sabin. The vaccines prepared by Salk (1954) and Sabin (1962) are known as Salk vaccine and Sabin vaccine, respectively.

Poliovirus is a (+) ssRNA virus of molecular weight 2.5 × 10⁶ Daltons (7.7 kb) with an icosahedral capsid. It has a diameter of about 27-30 nm. There are three types of polio: Type I (Brunhidle strain) causing moderate cases of paralysis. Type II (Lansing strain) causing greatest number of paralysis and Type III (Leon strain) rarely causing paralysis.

It enters the body through contaminated water/food, reaches to intestine and survives therein. It multiplies in mucosa of tonsils and or gastrointestinal tract. The initial symptoms are fever, headache, nausea, vomiting and intestinal cramps resulting in loss of appetite. Sometimes the virus enters blood stream and causes viremia.

In 99% cases, viremia is transient, and in 1% cases, the viremia persists, and the virus enters the central nervous system and causes polio. Poliovirus has high affinity for anterior horn motor nerve cells of the spinal cord. After infecting these cells, it multiplies and destroys them resulting in motor and muscle paralysis.

In developing countries 4 of every 1,000 children born annually have polio. It can be controlled only through vaccination. Government of India launched two major vaccination programmes in 1996 and in subsequent years with the name Pulse Polio Immunization.

It is hoped that polio control by vaccination on global basis would be possible by the year 2010. The vaccines which are available at present are effective for all the three types of strains of polio virus. A child below 5 years age must be vaccinated at two years intervals.