Varicella-zoster virus

Varicella is an acute infectious disease caused by varicella-zoster virus (VZV). VZV belongs to the Alphaherpesvirinae subfamily of Herpesviridae, a group of enveloped double-stranded DNA (dsDNA) viruses.

Varicella-zoster virus (VZV) can establish lifelong persistent infections and cause severe diseases in humans of all ages. The virus can be spread from person to person by direct contact, inhalation of aerosols from vesicular fluid of skin lesions of acute varicella or zoster, and possibly through infected respiratory secretions that also may be aerosolized.

Primary infection leads to acute varicella or “chickenpox”, usually from exposure either through direct contact with a skin lesion or through airborne spread from respiratory droplets. After the primary infection, VZV stays in the body (in the sensory nerve ganglia) as a latent infection. Varicella is characterized by a pruritic, maculopapular, vesicular rash that evolves into noninfectious dried crusts over a 3- to 7-day period.

Reactivation of latent infection causes herpes zoster (shingles). Shingles is not caused by the same virus that causes genital herpes, a sexually transmitted disease. Shingles cannot be passed from one person to another. However, the virus that causes shingles, the varicella zoster virus, can be spread from a person with active shingles to another person who has never had chickenpox.

VZV enters the host through the respiratory tract and conjunctiva. It replicates at the site of entry in the nasopharynx and in regional lymph nodes. A primary viremia occurs 4 to 6 days after infection and disseminates the virus to other organs, such as the liver, spleen, and sensory ganglia.
Varicella-zoster virus

Hepatitis B transmission

Hepatitis B is a viral infection that attacks the liver and can cause both acute and chronic disease. It is caused by the hepatitis B virus (HBV) and can cause acute and chronic infection leading to severe complications, including cirrhosis (liver scarring) and liver cancer in 20–30% of patients.

Hepatitis B virus (HBV) is a deoxyribonucleic acid (DNA) virus belongs to family hepadnaviridae which includes two genera; orthohepadnavirus (infecting mammals) of which hepatitis B virus is the prototype, and avihepadnavirus (infecting birds) of which DHBV is the prototype.

HBV infection affects approximately two billion people worldwide at some point of their lives; among whom 350 million suffer from chronicity of this infection becoming a carrier of this virus.

HBV has been found in virtually all body secretions and excretions. HBV is transmitted primarily through:
• Birth to an infected mother. Between 80–90% of infants infected during the first year of life develop chronic infection.
• Sexual contact with an infected person
• Sharing contaminated needles, syringes, or other injection-drug equipment

• Hepatitis B can also be transmitted through medical and dental procedures, tattooing, piercing, sharing personal hygiene items, razors, and manicure and pedicure material contaminated with infected blood.

HBV is not spread through breastmilk, food or water or by casual contact such as hugging, kissing or sharing food or drinks with an infected person.

Hepatitis B infection acquired in adulthood leads to chronic hepatitis in less than 5% of cases, whereas infection in infancy and early childhood leads to chronic hepatitis in about 95% of cases.
Hepatitis B transmission

Ebola hemorrhagic fever

Ebola hemorrhagic fever is a severe, often fatal disease in humans. It is usually transmitted to humans through direct contact with blood, tissue, body fluids and secretions from an infected animal or human.

The causative agent is classified in the genus Ebolavirus of the Filoviridae family. Filoviruses are filamentous enveloped viruses containing a non-segmented, negative-strand genomic RNA of approximately 19 kilobases.

The virus in the blood or body fluids can enter another person’s body through broken skin or unprotected mucous membranes, such as eyes, nose, or mouth. The viruses that cause Ebola are often spread among family and friends because they are in close contact with blood or body fluids when caring for ill persons.

Ebola hemorrhagic fever's complex pathophysiology, characterized by immunosuppression as well as stimulation of an intense inflammatory response, results in a syndrome similar to septic shock.

Initial symptoms are sudden onset of fever and fatigue, muscle pain, headache and sore throat. Usually followed by: vomiting, diarrhea, rash, impaired kidney and liver function, spontaneous bleeding internally and externally (in some cases).

Symptoms may appear anywhere from 2 to 21 days after exposure to Ebola, but the average is 8 to 10 days.
Ebola hemorrhagic fever

Ebola virus

Ebola virus is a violent pathogen, a lipid-enveloped negatively stranded RNA virus that belongs to the viral family Filoviridae. This family belongs to the order of the Mononegavirales which further contains members of Bornaviridae, Paramyxoviridae and Rhabdoviridae.

Ebola virus was first discovered in 1976 near the Ebola River in what is now the Democratic Republic of the Congo. Since then, outbreaks have occurred sporadically in Africa.

Morphologically, when studied under an electron microscope, the viral particles look like long stretched filaments with some particles tending to curve into an appearance looking like the number 6.

Five species of Ebola virus have been identified: Zaire ebolavirus (ZEBOV), Sudan ebolavirus (SUDV), Bundibugyo ebolavirus (BDBV) Taï Forest ebolavirus (TAFV) and Reston ebolavirus (RESTV). Among them, BDBV, ZEBOV, and SUDV have been associated with large outbreaks in Africa.

The Ebola virus has an incubation period ranging between 2 and 21 days. Initially, the patient manifests signs and symptoms of flu that rapidly progress to bleeding, shock and multiple organ failure.

Ebola disease is a severe, often fatal illness in humans. The virus is transmitted to people from wild animals and then spreads in the human population through human-to-human transmission.

Ebola virus infections are depicted by immune suppression and a systemic inflammatory response that leads to damage of the vascular, coagulation and immune systems, causing multi-organ failure and shock.
Ebola virus

Yellow fever

Yellow fever is a viral haemorrhagic fever which strikes an estimated 200 000 persons world-wide each year and causes an estimated 30 000 deaths.

The yellow fever (YF) virus is a Flavivirus, which currently contains over 70 viruses, of which most are arthropod-borne, including the dengue viruses. The virus is transmitted by Haemagogus, Sabethes or Aedes aegypti mosquitoes.

Yellow fever outbreaks occur in both rural and urban settings. In urban settings, outbreaks are likely to be larger and are difficult to control.

Yellow fever was an unknown disease until the discovery of the Americas. It probably originated in Africa and was possibly introduced to the American continent by ships carrying slaves and the vector Aedes aegypti. The first epidemic was reported in the American continent, where it is possible to characterize with greater certainty the infection by yellow fever, occurred in the Yucatán peninsula in 1648.

There are three different epidemiological patterns of yellow fever virus transmission: the sylvatic or forest pattern; the Aedes aegypti-borne urban cycle; and an intermediate cycle that bridges these two patterns. The different epidemiological patterns of transmission lead to the same clinical disease.

The incubation period is from three to six days after a bite from an infected mosquito. The classic form of yellow fever is a severe systemic disease with a high case-fatality rate, characterized by fever, prostration, compromised liver, kidney, and cardiac function, hemorrhagic manifestations, and shock. The progression of the disease can include three clinically distinct stages: infection, remission, and intoxication.
Yellow fever

Viral infection

Viruses are ubiquitous and cause a wide spectrum of disease in humans ranging from asymptomatic infection, severe debilitating illness, and sudden death. Viruses are broadly classified as ribonucleic acid and deoxyribonucleic acid base on the genome.

During infection, a virus must attach itself to a cell that it then commandeers and injects with its nucleic acid. The virus genetic code overrides the host cell’s genetic code, using the host cell to carry out the virus’s activities and to reproduce viral particles that leave the host cell and infection other cells.

Transmission of blood-borne viruses can result from sexual intercourse and maternal-fetal transmission on the community setting, needle stick injury and other exposure-prone procedures in the health-care setting.

Viruses have long been known to cause certain infections diseases, and many of them produce a long-lasting immunity against re-infection by the same virus.

Traditionally, the epidemiological control of most viral infections depends on the isolation of cases, quarantine of contracts, personal protection by infection control measures and mass vaccination, because specific antiviral treatment is generally not available for most viral infections.
Viral infection

Virus infection disease: Rabies

Infectious Disease - Rabies
At the end of the nineteenth century, hundreds of people died from rabies every year. Almost invariably, these people got the disease from the bite of a domestic animal, usually a dog.

Because of the efforts of Louis Pasteur and many others, it is rare today for some one to die from rabies. And the few cases of rabies that arise each year almost invariably come about as a result of a bite from a wild animal, like a skunk or a bat. The rarity of the disease and the elimination of rabies from domestic animals are due largely to Pasteur’s discoveries and intense vaccination programs.

But rabies remains as a glaring example of the pain and suffering that can follow infection. And rabies is only one example of thousands of infectious diseases – diseases caused by prions, viruses, bacteria, fungi, and parasites – that make us sick and kill us. Some infectious may be essential. Others are terrifying.

A rhabdovirus virus causes rabies. There are many different types of rhabdoviruses and they cause a whole range of disease – rabies is one of the worst. The rabies is bullet shaped, covered with a large sheet of host-cell membrane and fortunately for all of us, is easily destroyed by soaps or drying. Rabies viruses are about 75 nm (nanometers) in diameter and about 150 to 300 nm long. A nanometer is one billionth of a meter, far beyond the realm human vision. These are tiny packets of trouble.

Rabid animals transmit rabies in their saliva. From the bite wound, the virus makes its way into neurons. Then it travels along the neurons to the central nervous system (brain and spinal cord) where it sets up shop. In the central nervous system, the rabies virus begins to destroy neurons as it produces more virus. Some of the new virus particles travel to the salivary gland, where they help spread the disease to others through bites.

In the process of its self-replication, the rabies virus decimates many of the neurons in the central nervous system. The result is a mental meltdown. But the virus doesn’t destroy all of the brain – just enough to drive the dog mad, just enough to make dog want to bite every other living thing it sees and pass on the infection.
Virus infection disease: Rabies

Virus mode of transmission

Although human respiratory diseases of viral origin can be virtually indistinguishable clinically, the causative viruses are quite heterogeneous, not only in their virion structure and genome composition but also in the routes by which they transmitted among humans.

Zoonotic viruses replicate in the reservoir animal host and are usually transmitted to human by direct contact or the bite of a hematophagus arthropod.

For example, rabies virus is transmitted by the saliva from a bite of a rabid animal and simian foamy virus can be transmitted by bites from an infected monkey.

Viruses are transmitted either through the mucosal surfaces of the airways, the intestinal or genital tract, or the eye, abrasion of the skin or by directly gaining access to the bloodstream.

Mucosal entry is most common. Viruses, such as influenza viruses, parainfluenza viruses, certain types of adenoviruses or rhinoviruses spread through the airways and are transmitted by droplets at are formed during coughing or sneezing of an infected individual.

Other viruses such a human Papilloma virus (HPV) is spread through sexual contact. HPV may be transmitted through direct contact (oral to genital, oral to oral, skin to skin) although it is typically transmitted through the skin-to-skin route.

Although humans may become ill as a result of the virus, they are generally considered dead-end hosts for many of the viruses because they do not develop sufficient viremia to infect feeding vectors and thus do not contribute to the transmission cycle.
Virus mode of transmission

Basic information about Zika fever

Zika is spread mostly by the bite of an infected Aedes species mosquito (Aedes aegypti and Aedes albopictus). The Zika virus, first identified in Uganda 1947, is transmitted by the same type of mosquito that carries dengue fever, yellow fever and chikungunya virus.

The viral disease has spread by outbreaks to many different countries, with an ongoing outbreak in Brazil and Puerto Rico; the first diagnosis of Zika virus in the U.S. occurred in Harris County (Houston), Texas, in January 2016.

A mosquito bites an infected person and then passes those virus to other people it bites. These mosquitoes are aggressive daytime biters. They can also bite at night. Zika can be passed from a pregnant woman to her fetus. Infection during pregnancy can cause certain birth defects.

Aedes aegypti

For most people it is a very mild infection and isn't harmful. However, it may be more serious for pregnant women, as there's evidence it causes birth defects – in particular, abnormally small heads (microcephaly). There is no vaccine or medicine for Zika.

Many people infected with Zika virus won’t have symptoms or will only have mild symptoms. The most common symptoms of Zika are: fever, rash, joint pain (with possible swelling, mainly in the smaller joints of the hands and feet), conjunctivitis (red eyes), itching all over the body. Other symptoms include: muscle pain, headache.

 The virus causes born defects in babies born to some infected pregnant women. The CDC has confirmed Zika can spread through sex, usually after a person traveled to an area where Zika has broken out, got the virus, and gave the virus to a sex partner who did not travel. Infected women and men can both pass the virus to sex partners -- even if they haven’t shown symptoms of infection
Basic information about Zika fever

Reference
https://www.cdc.gov/zika/about/index.html 
http://www.webmd.com/a-to-z-guides/zika-virus-symptoms-prevention#1 
http://www.nhs.uk/Conditions/zika-virus/Pages/Introduction.aspx 
http://www.medicinenet.com/zika_virus/article.htm

Swine Influenza Virus H1N1

Viruses of the classical H1N1 lineage were the dominant cause of influenza among pigs in North America from their first isolation.

Classical H1N1 viruses have also been isolated from pigs in South America, Europe and Asia.

There is only limited evidence of maintenance of human H1N1 influenza viruses after natural introduction into swine populations but human H3N2 viruses have been recovered frequently from pigs in Asia and Europe.

Experimental infection studies have shown that pigs can be infected with a wide range of avian influenza virus (AIVs) and naturally acquired infections of pigs with AIVs have also been documented from multiple areas of the world.

In particular, an avian H1N1 virus introduction into pigs Europe in late 1970s spread throughout much of the European continent and United Kingdom and ultimately became a dominant cause of swine flu in these areas.

These avian-like H1N1 viruses have also undergone genetic/antigenic drift and have spread from pigs to domestic turkeys.

The occurrence of influenza virus infections in pigs poses two important public health issues: zoonotic infections of people with swine influenza viruses and the potential for pigs to serve as hosts for the creation of novel viruses of pandemic potential for the human population.

Infections with swine influenza viruses is generally limited to the respiratory tract, with virus replication demonstrated in epithelial cells of the nasal mucosa, tonsils, trachea, lungs and tracheobronchial lymph nodes.

Swine flu is an acute infections and virus clearance is extremely rapid. In most experimental studies, nasal virus shedding begins on day 1 postinoculation (P1) and ceases within 7 days.

Likewise, swine influenza virus could not be isolated from lungs or other respiratory tract tissues after day 7.

Infections with H1N1, H1N2 and H3N2 subtype viruses are clinically similar, and viruses of all subtypes have been associated with acute respiratory episodes in most European countries.

Disease onset is sudden, after an incubation period of 1 – 3 days. Disease signs typically appear in a large percentage of animals of all ages within a herd or epidemiological unit.
Swine Influenza Virus H1N1

How is measles transmitted?

Measles virus causes a potentially serious generalized infection characterized by a maculopapular rash (rubeola). It is one of the most highly contagious infections agents and outbreaks can occur in populations in which less than 10% of persons are susceptible.

Like influenza virus and rhinovirus, measles virus is transmitted by the cough or sneeze of an infected individual.

Chains of transmission commonly occur among household contacts, school children and health care workers. An uninfected person can get measles just by breathing the air in a room that was previously occupied by an infected person. There will be aerosolization of particles from evaporated respiratory secretions called droplet nuclei.

These are small less 5 um particles that may remain suspended in the air for long periods and me be widely disperse by air currents.

The measles can live in the air for two hours after an infected person leaves the room. People can also get measles if they have direct contact with fluid from the nose or mouth of an infected person.

Measles virus usually causes no disease symptoms until about ten days after infection. This period of ‘silence’ results because the innate immune system deals so effectively with the initial measles attack that few airway cells are infected and little new virus is produced.
How is measles transmitted? 

Etiology of bird flu

This acute, highly contagious respiratory infection usually occurs in colder months and in infrequent epidemics. It is an acute highly infectious of the upper and lower respiratory tracts that occurs in isolated cases or in epidemics.

The disease is directly transmitted by droplets inhaled from an infected personals sneezing or coughing or by indirect contact with contaminated objects, such as drinking glass.

The virus resists host antiviral cytokines, inducing excessive host pro-inflammatory responses. It may cause death by ‘cytokine storm’ rather than by inherent pathogenicity.

One type of bird flu is caused by the avian influenza A virus which can cause infection in birds and humans. Type A is the most virulent and usually affects young adults first and then spreads to the very young and very old in community.

The natural reservoirs of influenza A viruses – the etiologic agents of avian flu - are the aquatic birds of the world, particularly ducks, in which the viruses appear to be in evolutionary stasis or equilibrium with their natural host causing no disease.
Etiology of bird flu

Coronavirus

Coronaviruses comprise a large family of viruses infecting a broad range of vertebras, from a mammalian to avian species.

The viruses were initially named based on the disease syndrome they were isolated from and subsequently shown to cause following experimental inoculation. The word ‘coronavirus’ derives from the crown-like appearance of this type of virus in images generated by electron microscopes.

Coronaviruses are currently placed in the family Coronaviridae and together with the family Arteriviridae, comprise a new order: Nidovirales.

Coronaviruses are enveloped, positive-stranded RNA viruses that can infect a variety of vertebrates and are mainly associated with respiratory and enteric disease.

Coronaviruses are associated mainly with respiratory, enteric, hepatic and central nervous system disease

In humans, coronaviruses infections manifest usually as mild respiratory tract disease and only occasionally more severe symptoms, particularly on elderly or immune compromised individuals, are observed.

One type coronavirus is Middle East Respiratory Syndrome. It is a viral respiratory illness and it was first reported in Saudi Arabia in June 2012.

The virus which caused Middle East Respiratory Syndrome is caused by a beta coronaviruses. Most people who suffer from the MERS-CoV (Middle East Respiratory Syndrome Coronavirus) infection will develop severe acute respiratory illnesses, the symptoms of which include fever, coughing and shortness of breath.

MERS-CoV is closely related to SARS coronavirus, which was originated In China. It claimed 800 lives worldwide from 2002 to 2003.
Coronavirus

Orthopoxvirus: Variola virus

Poxviruses that cause disease in humans belong to four different genera of the vertebra poxvirus subfamily. The majority these viruses belong to the genus Orthopoxvirus.

Poxviruses were first visualized by electron microscopy in 1938. The genus Orthopoxviruses comprises many related viruses and includes, in addition to variola major, vaccinia, virus, cowpox, monkeypox, ectromelia, camelpox, taterapox, Uasin Gishu disease and racoonpox.

The orthopoxvirus Variola virus is the only member species of the Orthopoxvirus genus which is a solely human pathogen.

Variola virus, like all orthopoxviruses, replicates solely in the cytoplasm of infected cells. At least two types of Variola virus have been clearly described that have distinct biological and genetic properties and different human clinical and epidemiological manifestation.

These have been described as variola major and Variola minor. Another variant has been suggested, intermedius.

The virion of Variola virus has the same size and shape as that of all other orthopoxviruses.

The most important property of variola virus, in relations its effects on the human host, is its virulence. Some epidemics of smallpox were associated with high mortality and other with a low mortality.

The genetic difference between the variola strains most likely reflects differences in their replication and host-cell assembly leading to a greater or lesser virulence.
Orthopoxvirus: Variola virus

Smallpox

Smallpox scars were bigger and deeper than chickenpox scars they covered the whole face. It is an infection that is highly contagious or easily spread from person to person.

Smallpox was spread by people breathing it in. It entered the body and found a home in the back of the throat where it mixed with saliva. 

Smallpox is caused by variola virus, a member of the orthopox virus. Orthopox viruses include cowpox and chicken pox. A virus is a microscopic agent that infects and replicates in living cells.

People who got smallpox had tiny little bumps all over their body. Pox is from Latin word for ‘spotted’. 

When variola invades human cells, the cell is forced to reproduce the virus until there are hundreds of thousands of viruses inside.

Smallpox deaths attributable to complications other than hemorrhage usually occurred eighteen days or more after symptoms began.

These other potentially life-threatening complications most often resulted from secondary bacterial infection of wounds in the skin originally case by the virus.
Smallpox

West Nile virus

West Nile virus was first isolated from a febrile adult woman in the West Nile District of Uganda in 1937. 

The virus is a member of the Japanese encephalitis antigenic complex in the family Flaviviridae, genus Flavivirus. The Flavivirus are a genus of arboviruses that included viruses that cause yellow fever, St. Louis encephalitis and dengue fever.

The West Nile virus is a mosquito-borne disease that can cause inflammation of the brain in humans. In 1999, the virus appeared in North America for the first time, and the following year the virus was reported in 12 states along the East coast. The outbreak in New York was the first sign of these infection in the Western world.

Prior to its appearance in North America, West Nile virus occurred in parts of Africa, Asia, and Europe and a number of different mosquito species were identified as its vectors in natural cycles involving birds as amplifying hosts.

Illness from this virus is essentially a disease of the elderly. Although it may occur in people of all ages from five to 90. Being over 50 years old is the major risk factor for development of encephalitis. Persons 50-60 years old are 10 times more likely to experience central nervous system disease than younger person.

The illness presents as fever with hot flashes, night sweats, weakness, nausea, eye pain, upper respiratory symptoms and vomiting. Lynphadenopathy and a diffuse macular papular, or morbiliform rash may occur.
West Nile virus

Ebola infection

The causative agent is Ebola virus. Ebola virus has its origin in Africa. It causes hemorrhagic fever in humans with an extremely high lethality. The most striking symptom is uncontrolled bleeding from any orifice.

Ebola virus is transmitted through contact with patient body fluids. Infectious virions may persist for weeks in the same of recovered patients.

Contaminated needles can also cause the infection. Nosocomial and community-acquired transmission can occur. Transmission through semen may occur up to 7 weeks after clinical recovery.

During infection, the Ebola virus accumulates in high numbers in the liver, spleen, lymph nodes, and lungs, severely damaging these organs during the course of the disease.

The initial symptoms of infection may include flu-like symptoms such as fever, chills, muscle and headaches, nausea, vomiting, loss of appetite, and malaise.

Zaire and Sudan strains produce a disease characterized by multifocal organ necrosis, coagulopathy, extensive visceral effusions, hemorrhagic shock, and death.

As viremia overtakes the immune system, disseminated intravascular coagulopathy occurs and the patient may go into shock or coma.

Ebola infection

Flu Viral Infection

Influenza viruses have special features that can over power a body’s immune system. It affects respiratory tract – nose, throat, bronchial tubes and lungs.

First, influenza virus are efficient travelers.

Second, they have an amazing ability to copy themselves.

And third, flu viruses are unique in that once a strain has spread in a population, its structure changes and it then is capable of causing a new form of flu because the antibodies produces to combat the original virus are not effective against the new form.

An entirely new strain appears about every 10 years.

Not only do influenza viruses travel easily from person to person, they do so secretly for part of the time.

A person with the flu may be contagious for several days before he or she know it.

When an infected person coughs or sneezes, he or she releases tiny droplets of water from the mouth and nose.

The most common way to catch the flu is by inhaling that tiny droplets. Less often it is spread when the person touch a surface such as a faucet handle or phone that has the virus on it and then touch his own mouth, nose, or eyes.

The virus’s ability to turn normal human or animal host cells into flu-copying machines is another reason influenza can take over immune systems.

After an incubation period of 1 to 4 days, people infected with influenza virus develop an abrupt fever, headache, sore throat and dry cough that can in some cases progress to viral pneumonia, respiratory failure and death.
Flu Viral Infection

The word of Influenza

The word of Influenza
The word influenza is Italian for influence, as in the astral or occult influence of a visitation or outbreak that affects many people at the same time. First used in 1504, the word signified any disease epidemics.

In a severe flu outbreak of 1743 the word influenza was applied to the epidemic that began in Italy and spread throughout Europe.

Since then, the influenza, shortened to flu, means a serious infectious disease characterized by muscle and joint aching, prostration, and respiratory congestion with fever and headache.

It was not until 1931 that an influenza virus was identified in pigs, and finally in 1933 a human influenza virus was discovered by three researchers: Smith, Andrewes, and Laidlaw.

Both of these viruses were closely related to the Spanish flu virus of 1918. During the time of the 1918 flu pandemic, however, the suspected culprit was a bacterium named Hemophilus influenza. Viruses had not yet been discovered.

Although most people consider the flu simply and annoyance, and possibly a danger to seniors in poor health, influenza has been responsible for repeated, devastating worldwide pandemics capable of bringing entire nations to their knees.

It is hard to imagine today, but in 1918 the entire world was in the clutches of a deadly flu virus. The 1918 flu still remains the greatest plague the world has ever seen.
The word of Influenza