Diseases caused by viruses in humans

There are many diseases caused by viruses in humans every year, Covid-19 is recent example of it, so here we will study about virus and diseases caused by it in detail.

What is a VIRUS ?

Virus are simplest living entities or particles composed of small number of macromolecules i.e. DNA/RNA or proteins or ultramicroscopic disease producing living nucleoprotein particle that can multiply within host cell. Sometimes glycoprotein and lipoprotein also present in viruses. 

Viruses are obligate parasites (i.e. totally depends on host cells).

They can infect and parasitize all form of life including bacteria.

VIRUSES have both Living or Non-living character :-

Living characters :-

• Posses DNA or RNA
• Have ability of reproduction
• Can cause infection
• Can undergo mutation and genetic variation

Non-living characters :-

• Subcellular or non-cellular
• Don’t respire or excrete
• They can be crystallized

DISCOVERY OF VIRUS :-

• Tobacco mosaic disease (TMV):- Stunts growth of the plants and give their leaves a mottled or mosaic condition.
• Edward Jenner said causative organism of small pox is virus.
• Adolf Mayer (1838) a german scientist discovered that he could transmit the disease from plant to plant by rubbing sap extracted from diseased leaves. He believed that it is caused by some unusual bacteria invisible under microscope.
• Ivanowsky a russian biologist concluded that these bacteria like infectious agent were able to pass through filter. These bacteria produce some toxin which make infection.
• Martinus Beijerink a dutch botanist discover that infectious agent in  the filterate can replicate. It can replicate only within the host. Unlike bacteria shows no growth on nutrient media. Hence voice the concept of virus.
•  In 1935, Stanley crystallized the TMV and find out they are simplest creature and made up of just protein and DNA.

CLASSIFICATION OF VIRUS :-

1) Animal virus :- They are parasites on animals and cause diseases in them. They contain both DNA/RNA as genetic material.

Diseases caused by it are : Polio, measeles, influenza, AIDS, hepatitis and many more.

2) Plant viruses :- They are parasites on plants and cause diseases in them. They contain both DNA/RNA as genetic material.

3) Bacteriophages :- Virus which are parasites on bacteria.

CHARACTERISTICS OF VIRUS :-

• Non cellular
• Nucleo proteinaceous
• Obligate parasites
• Host specificity
• Contain a protein coat called the capsid
• Acellular
• Have a nucleic acid core containing DNA/RNA.

List of diseases caused by viruses in humans are :-

Diseases caused in Humans	Virus responsible for it
Rabies	Rabies lyssavirus
Poliomyelitis	Poliovirus
Measles	Rubeola virus
Hepatitis	Hepatitis A,B &C virus
Smallpox	Variola virus
Mumps	Paramyxovirus
Influenza	Influenza virus (RNA virus)
Encephalitis	Herpes Simplex Virus
AIDS	HIV(human immunodeficiency virus)
Common cold	Rhinovirus

GUINEA WORM DISEASE :-

• Dracunculiasis (guinea worm disease) is caused by Dracunculus medinensis, the largest tissue parasite in humans.
• Guinea worm disease affects the inaccessible rural areas with unsafe water sources, low levels of knowledge about the disease.
• India certified free of guinea worm disease in 2000.

POLIO :-

• Polio (poliomyelitis) is a disabling and life threatening disease caused by the virus named poliovirus.
• It mainly affects children under 5 years of age.
• One in 200 infections leads to irreversible paralysis. Among those paralysed, 5–10% die when their breathing muscles become immobilized.
• Cases due to wild poliovirus have decreased by over 99% since 1988, from an estimated 350 000 cases then, to 6 reported cases in 2021.
• In 1988, the World Health Assembly adopted a resolution for the worldwide eradication of polio, marking the launch of the Global Polio Eradication Initiative (GPEI).

RHINOVIRUS :-

• Rhinovirus (rhin means “nose”) infection causes common cold.
• It may cause some sore throats, ear infections, and infections of sinuses (openings in the bone near the nose and eyes). They may also cause pneumonia and bronchiolitis, but this is less common.
• Symptoms like coughing, sneezing, headache and sore throat usually last for two weeks.

Hepatitis-B :-

• Hepatitis B is a vaccine preventable liver infection caused by the hepatitis B virus (HBV).
• It is spread when blood, semen, or other body fluids from a person infected with the virus enters the body of someone who is not infected. This can happen through sexual contact; sharing needles, syringes, or other drug-injection equipment; or from mother to baby at birth. 
• Symptoms include fatigue, poor appetite, stomach pain, nausea, and jaundice.

MUMPS :-

• Mumps is a viral infection that primarily affects salivary glands that are located near your ears. Mumps can cause swelling in one or both of these glands.
• Mumps was common in the United States until mumps vaccination became routine. Since then, the number of cases has dropped dramatically.
• The primary sign of mumps is swollen salivary glands that causes cheeks to puff out. Other signs and symptoms may include: Pain in the swollen salivary glands on one or both sides of your face, pain while chewing or swallowing, fever, headache, muscle aches, weakness and fatigue and loss of appetite.

RABIES :-

• Rabies is a fatal but preventable viral disease. It can spread to people and pets if they are bitten or scratched by a rabid animal. In the United States, rabies is mostly found in wild animals like bats, raccoons, skunks, and foxes. In many other countries dogs still carry rabies, and most rabies deaths in people around the world are caused by dog bites.
• The rabies virus infects the central nervous system. If a person does not receive the appropriate medical care after a potential rabies exposure, the virus can cause disease in the brain, ultimately resulting in death.
• Rabies can be prevented by vaccinating pets, staying away from wildlife, and seeking medical care after potential exposures before symptoms start.

HERPES DISEASE :-

• The herpes simplex virus, also known as HSV, is a viral infection that causes genital and oral herpes.
• According to WHO about 67 percent of the world’s population under age 50 had oral or genital HSV-1 in 2016.

MENINGITIS :-

• Meningitis is an inflammation of the fluid and membranes (meninges) surrounding your brain and spinal cord.
• The swelling from meningitis typically triggers signs and symptoms such as headache, fever and a stiff neck.
• Most cases of meningitis in the United States are caused by a viral infection, but bacterial, parasitic and fungal infections are other causes. 
• Neisseria meningitidis, which is spread through saliva and other respiratory fluids and causes what’s called “meningococcal meningitis”

DENGUE FEVER :-

• Dengue viruses are spread to people through the bite of an infected Aedes species (Aedes aegypti or Aedes albopictus) mosquito.
• Almost half of the world’s population, about 4 billion people, live in areas with a risk of dengue.
• Severe dengue happens when your blood vessels become damaged and leaky. And the number of clot-forming cells (platelets) in your bloodstream drops. This can lead to shock, internal bleeding, organ failure and even death.

CHIKUNGUNYA :-

• Chikungunya virus is spread to people by the bite of an infected mosquito.
• The most common symptoms of infection are fever and joint pain. Other symptoms may include headache, muscle pain, joint swelling or rash.
• Outbreaks have occurred in countries in Africa, Americas, Asia, Europe, and the Caribbean, Indian and Pacific Oceans.

ZIKA VIRUS :-

• Zika virus is similar to dengue fever, yellow fever and West Nile virus.
• It is carried by infected Aedes aegypti mosquitos, Zika is largely transmitted through bites, but can also occur through intrauterine infection.
• Symptoms of this virus are mild, with fever, rash and joint pain present.

YELLOW FEVER :-

• Yellow fever is caused by a virus that is spread by the Aedes aegypti mosquito.
• It is a viral infection spread by a particular type of mosquito. The infection is most common in areas of Africa and South America.
• In mild cases, yellow fever causes fever, headache, nausea and vomiting. But yellow fever can become more serious, causing heart, liver and kidney problems along with bleeding. Up to 50% of people with the more severe form of yellow fever die of the disease.

JAPANESE ENCEPHALITIS :-

• Japanese encephalitis virus (JEV) is a flavivirus related to dengue, yellow fever and West Nile viruses, and is spread by mosquitoes.
• JEV is the main cause of viral encephalitis in many countries of Asia with an estimated 68,000 clinical cases every year.
• Severe disease is characterized by rapid onset of high fever, headache, neck stiffness, disorientation, coma, seizures, spastic paralysis and ultimately death.
• To reduce the risk for JE, all Japanese encephalitis-endemic areas should take precautions to avoid mosquito bites. Personal preventive measures include the use of mosquito repellents, long-sleeved clothes, coils and vaporizers. 

AIDS :-

• HIV (human immunodeficiency virus) is a virus that attacks cells that help the body fight infection, making a person more vulnerable to other infections and diseases. It is spread by contact with certain bodily fluids of a person with HIV, most commonly during unprotected sex (sex without a condom or HIV medicine to prevent or treat HIV), or through sharing injection drug equipment.
• If left untreated, HIV can lead to the disease AIDS (acquired immunodeficiency syndrome).
• AIDS is the late stage of HIV infection that occurs when the body’s immune system is badly damaged because of the virus.
• Every year, on 1 December, the world commemorates World AIDS Day. People around the world unite to show support for people living with and affected by HIV and to remember those who lost their lives to AIDS.
• The most common HIV tests use blood to detect HIV infection. The enzyme-linked immunosorbent assay (ELISA) tests a patient’s blood sample for antibodies.

EBOLA VIRUS DISEASE :-

• Ebola virus disease (EVD), formerly known as Ebola haemorrhagic fever, is a rare but severe, often fatal illness in humans.
• The virus is transmitted to people from wild animals and spreads in the human population through human-to-human transmission.
• A range of potential treatments including blood products, immune therapies and drug therapies are currently being evaluated.