Smallpox

 

Alternative Names:Variola – major and minor; Variola

Definition:
Smallpox is an infectious disease unique to humans, caused by either of two virus variants named Variola major and Variola minor. The disease is also known by the Latin names Variola or Variola vera, which is a derivative of the Latin varius, meaning spotted, or varus, meaning “pimple”. The term “smallpox” was first used in Europe in the 15th century to distinguish variola from the great pox (syphilis).

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Smallpox localizes in small blood vessels of the skin and in the mouth and throat. In the skin, this results in a characteristic maculopapular rash, and later, raised fluid-filled blisters. V. major produces a more serious disease and has an overall mortality rate of 30–35%. V. minor causes a milder form of disease (also known as alastrim, cottonpox, milkpox, whitepox, and Cuban itch) which kills ~1% of its victims. Long-term complications of V. major infection include characteristic scars, commonly on the face, which occur in 65–85% of survivors. Blindness resulting from corneal ulceration and scarring, and limb deformities due to arthritis and osteomyelitis are less common complications, seen in about 2–5% of cases.

Smallpox is believed to have emerged in human populations about 10,000 BC. The disease killed an estimated 400,000 Europeans each year during the 18th century (including five reigning monarchs), and was responsible for a third of all blindness. Between 20 and 60% of all those infected—and over 80% of infected children—died from the disease.

During the 20th century, it is estimated that smallpox was responsible for 300–500 million deaths. In the early 1950s an estimated 50 million cases of smallpox occurred in the world each year. As recently as 1967, the World Health Organization estimated that 15 million people contracted the disease and that two million died in that year. After successful vaccination campaigns throughout the 19th and 20th centuries, the WHO certified the eradication of smallpox in December 1979. To this day, smallpox is the only human infectious disease to have been completely eradicated.

Causes & Risk Factors:
Smallpox is caused by infection with variola virus, which belongs to the genus Orthopoxvirus, the family Poxviridae, and subfamily chordopoxvirinae. Variola virus is a large brick-shaped virus measuring approximately 302 to 350 nanometers by 244 to 270 nm, with a single linear double stranded DNA genome consisting of 186 kilobase pairs (kbp) and containing a hairpin loop at each end. The two classic varieties of smallpox are variola major and variola minor. The closest viral relative is molluscum contagiosum, which like smallpox, infects only humans. However, unlike variola species, molluscum infection is benign. The lifecycle of poxviruses is complicated by having multiple infectious forms, with differing mechanisms of cell entry. Poxviruses are unique among DNA viruses in that they replicate in the cytoplasm of the cell rather than in the nucleus. In order to replicate, poxviruses produce a variety of specialized proteins not produced by other DNA viruses, the most important of which is a viral-associated DNA-dependent RNA polymerase. Both enveloped and unenveloped virions are infectious. The viral envelop is made of modified Golgi membranes containing viral-specific polypeptides, including hemagglutinin. Infection with either variola major and variola minor confers immunity against the other.

Four orthopoxviruses cause infection in humans: variola, vaccinia, cowpox, and monkeypox. Variola virus infects only humans in nature, although primates and other animals have been infected in a laboratory setting. Vaccinia, cowpox, and monkeypox viruses can infect both humans and other animals in nature.

Smallpox was once found throughout the world, causing illness and death wherever it occurred. Smallpox was primarily a disease of children and young adults, with family members often infecting each other.

There are two forms of smallpox:

*Variola major is a serious illness with a death rate of about 30% or more in unvaccinated people

*Variola minor is a milder infection with a death rate of less than 1%.

The incubation period for smallpox is approximately 12-14 days.

A massive program by the World Health Organization (WHO) eradicated all known smallpox viruses from the world in 1977, except for samples that were saved by various governments for research purposes. The vaccine was discontinued in the United States in 1972. In 1980, WHO recommended that all countries stop vaccinating for smallpox.

In 1980, WHO also recommended that the remaining virus samples be transferred to two WHO laboratories for storage. Those laboratories were the Centers for Disease Control (CDC) in Atlanta, Georgia, and a laboratory in Russia. Russia, however, started a program to produce the smallpox virus in mass quantities, specifically for bombs and other weaponry.

Some believe that other countries such as Iraq, Iran, and North Korea may also hold some stores of the smallpox virus. Researchers continue to debate whether or not to kill the last remaining samples of the virus, or to preserve it in case there may be some future reason to study it.

According to the CDC, since the vaccine has not been administered in the U.S. since 1972, those persons who had received the vaccine in the past are likely susceptible now (as are those who have never been vaccinated). It is not known how long previous vaccinations would remain effective, but it is unlikely that people would still have a high enough level of immunity to protect against the virus.

Risk factors for smallpox include being a laboratory worker who handles the virus (rare), or being in the environment where the virus was released as a biological weapon.

THE RISK OF TERRORISM
It is conceivable that smallpox could be deliberately reintroduced into the population. Smallpox could be released by aerosol, and it would spread easily because the virus remains very stable in aerosol form.

It would take no more than 50-100 cases to cause legitimate concern on an international level. Emergency measures would need to be taken immediately.

Smallpox is highly contagious from one person to another. It is most contagious during the first week, and is spread from saliva droplets. It may continue to be contagious until the scabs from the rash fall off. It may also be spread from bed sheets and clothing.

Researchers believe that the smallpox infection (if released in aerosol form, under favorable conditions, without sunlight) could remain viable for as long as 24 hours. In unfavorable conditions, the virus may only remain viable for 6 hours. There is clear evidence that shows that the virus can remain viable on bed linens and clothes for significant periods of time.

Symptoms :
There are two clinical forms of smallpox. Variola major is the severe and most common form of smallpox, with a more extensive rash and higher fever. There are four types of variola major smallpox based on the Rao classification: ordinary, modified, flat, and hemorrhagic.

Ordinary
Ninety percent or more of smallpox cases among unvaccinated persons are of the ordinary type. In this form of the disease, by the second day of the rash, the macules become raised papules. By the third or fourth day the papules fill with an opalescent fluid to become vesicles. This fluid becomes opaque and turbid within 24–48 hours, giving them the appearance of pustules; however, the so-called pustules are filled with tissue debris, not pus.

By the sixth or seventh day, all the skin lesions have become pustules. Between 7 and 10 days the pustules mature and reach their maximum size. The pustules are sharply raised, typically round, tense, and firm to the touch. The pustules are deeply embedded in the dermis, giving them the feel of a small bead in the skin. Fluid slowly leaks from the pustules, and by the end of the second week the pustules deflate, and start to dry up, forming crusts (or scabs). By day 16-20 scabs have formed over all the lesions, which have started to flake off, leaving de-pigmented scars.

Ordinary smallpox generally produces a discrete rash, in which the pustules stand out on the skin separately. The distribution of the rash is densest on the face; more dense on the extremities than on the trunk; and on the extremities, more dense on the distal parts than on the proximal. The palms of the hands and soles of the feet are involved in the majority of cases. In some cases, the blisters merge together into sheets, forming a confluent rash, which begin to detach the outer layers of skin from the underlying flesh. Patients with confluent smallpox often remain ill even after scabs have formed over all the lesions. In one case series, the case-fatality rate in confluent smallpox was 62%

Modified
Referring to the character of the eruption and the rapidity of its development, modified smallpox occurs mostly in previously vaccinated people. In this form the prodromal illness still occurs but may be less severe than in the ordinary type. There is usually no fever during evolution of the rash. The skin lesions tend to be fewer and evolve more quickly, are more superficial, and may not show the uniform characteristic of more typical smallpox. Modified smallpox is rarely, if ever, fatal. This form of variola major is more easily confused with chickenpox.

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Flat
In Flat-type smallpox (also called malignant smallpox) the lesions remain almost flush with the skin at the time when raised vesicles form in ordinary-type smallpox. It is unknown why some people develop this type of disease. Historically, flat-type smallpox accounted for 5%–10% of cases, and the majority (72%) were in children. Flat smallpox is accompanied by a severe prodromal phase that lasts 3–4 days, prolonged high fever, and severe symptoms of toxemia. The rash on the tongue and palate is usually extensive. The skin lesions mature very slowly and by the seventh or eighth day the lesions are flat and appear to be buried in the skin. Unlike ordinary-type smallpox, the vesicles contain very little fluid, are soft and velvety to the touch, and may contain hemorrhages. Flat-type smallpox is nearly always fatal.

Hemorrhagic
Hemorrhagic smallpox is a severe form of smallpox that is accompanied by extensive bleeding into the skin, mucous membranes, and gastrointestinal tract. This form developed in perhaps 2% of infections and occurred mostly in adults. In hemorrhagic smallpox the skin does not blister, but remains smooth. Instead, bleeding occurs under the skin, making the skin look charred and black (this is known as black pox).

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In the early, or fulminating, form, hemorrhaging appears on the second or third day as sub-conjunctival bleeding turns the whites of the eyes deep red. Hemorrhagic smallpox also produces a dusky erythema, petechiae, and hemorrhages in the spleen, kidney, serosa, muscle, and, rarely, the epicardium, liver, testes, ovaries and bladder. Death often occurs suddenly between the fifth and seventh days of illness, when only a few insignificant skin lesions are present. A later form of the disease occurs in patients who survive for 8–10 days. The hemorrhages appear in the early eruptive period, and the rash is flat and does not progress beyond the vesicular stage. Patients in the early stage of disease show a decrease in platelets, prothrombin, and globulin, and an increase in circulating antithrombin. Patients in the late stage have significant thrombocytopenia; however, deficiency of coagulation factors is less severe. Some in the late stage also show increased antithrombin. This form of smallpox occurs in anywhere from 3–25% of fatal cases (depending on the virulence of the smallpox strain).

Common Symptoms are:

*High fever
*Fatigue
*Severe headache
*Backache
*Malaise
*Raised pink rash — turns into pus-filled lesions that become crusty on day 8 or 9
*Delirium
*Vomiting
*Diarrhea
*Excessive bleeding

Diagnosis:
The clinical definition of smallpox is an illness with acute onset of fever greater than 101°F (38.3°C) followed by a rash characterized by firm, deep seated vesicles or pustules in the same stage of development without other apparent cause.

Microscopically, one sees Guarnieri bodies, which are aggregates of the virus. Guarnieri bodies appear as pink blobs. The absence of Guarnieri bodies cannot be used to rule out smallpox, however.

If a clinical case is observed, smallpox is confirmed using laboratory tests. The diagnosis of an orthopoxvirus infection can be made rapidly by electron microscopic examination of pustular fluid or scabs. However, all orthopoxviruses exhibit identical brick-shaped virions by electron microscopy. Definitive laboratory identification of variola virus involves growing the virus on chorioallantoic membrane (part of a chicken embryo) and examining the resulting pock lesions under defined temperature conditions. Strains may be characterized by polymerase chain reaction (PCR) or restriction fragment length polymorphism (RFLP) analysis. Serologic tests and enzyme linked immunosorbent assays (ELISA), which measure variola virus-specific immunoglobulin and antigen have also been developed to assist in the diagnosis of infection.

Chickenpox was commonly confused with smallpox in the immediate post-eradication era. Chickenpox and smallpox can be distinguished by several methods. Unlike smallpox, chickenpox does not usually affect the palms and soles. Additionally, chickenpox pustules are of varying size due to variations in the timing of pustule eruption: smallpox pustules are all very nearly the same size since the viral effect progresses more uniformly. A variety of laboratory methods are available for detecting chickenpox in evaluation of suspected smallpox cases.

Risk Factors:
Complications of smallpox arise most commonly in the respiratory system and range from simple bronchitis to fatal pneumonia. Respiratory complications tend to develop on about the eighth day of the illness and can be either viral or bacterial in origin. Secondary bacterial infection of the skin is a relatively uncommon complication of smallpox. When this occurs, the fever usually remains elevated.

Other complications include encephalitis (1 in 500 patients), which is more common in adults and may cause temporary disability; permanent pitted scars, most notably on the face; and complications involving the eyes (2% of all cases). Pustules can form on the eyelid, conjunctiva, and cornea, leading to complications such as conjunctivitis, keratitis, corneal ulcer, iritis, iridocyclitis, and optic atrophy. Blindness results in approximately 35% to 40% of eyes affected with keratitis and corneal ulcer. Hemorrhagic smallpox can cause subconjunctival and retinal hemorrhages. In 2% to 5% of young children with smallpox, virions reach the joints and bone, causing osteomyelitis variolosa. Lesions are symmetrical, most common in the elbows, tibia, and fibula, and characteristically cause separation of an epiphysis and marked periosteal reactions. Swollen joints limit movement, and arthritis may lead to limb deformities, ankylosis, malformed bones, flail joints, and stubby fingers.

Treatment
Smallpox vaccination within three days of exposure will prevent or significantly lessen the severity of smallpox symptoms in the vast majority of people. Vaccination four to seven days after exposure likely offers some protection from disease or may modify the severity of disease. Other than vaccination, treatment of smallpox is primarily supportive, such as wound care and infection control, fluid therapy, and possible ventilator assistance. Flat and hemorrhagic types of smallpox are treated with the same therapies used to treat shock, such as fluid resuscitation. Patients with semi-confluent and confluent types of smallpox may have therapeutic issues similar to patients with extensive skin burns.

No drug is currently approved for the treatment of smallpox. However, antiviral treatments have improved since the last large smallpox epidemics, and studies suggest that the antiviral drug cidofovir might be useful as a therapeutic agent. The drug must be administered intravenously, however, and may cause serious renal toxicity.

If the smallpox vaccination is given within 1-4 days of exposure to the disease, it may prevent illness, or at least lessen the degree of illness associated with the disease. Treatment, once the disease symptoms have started, is limited.

There is no agent that has been specifically made for treating smallpox. Sometimes antibiotics are given for secondary infections that may occur. Vaccinia immune globulin (antibodies against a disease similar to smallpox) may help shorten the disease.

If a diagnosis of smallpox were made, exposed persons would need to be isolated immediately. The isolation would include not just the person who contracted the disease, but all other face-to-face contacts with that person.

These individuals would need the vaccine and need to be monitored. Emergency measures to protect a broader segment of the population would have to be implemented immediately, within the recommended guidelines from the CDC and other federal and local health agencies.

Possible Complications
*Bacterial infections at the skin at the sites of the lesions
*Pitted scars from pustules
*Arthritis and bone infections
*Pneumonia
*Severe bleeding
*Eye infections
*Brain inflammation (encephalitis)
*Death

Prevention
Many people were vaccinated for smallpox in the past — but the vaccination is no longer given because the virus has been eradicated. According to the CDC, the United States has supply of the smallpox vaccine sufficient for the entire population at this time.

There are some complications associated with the vaccine, should the vaccine need to be given in the future to control an outbreak. Some of these are easily treated rashes, while other potential complications are more serious. The risk of complications is relatively low. (For example, the chance of encephalitis, which could be a fatal complication, is 1 out of 300,000).

When smallpox was eradicated, the general population was no longer vaccinated because the potential complications and costs began to outweigh the benefits of taking it. The experience of vaccination of both military personnel and civilian health care workers in 2002-2003 suggested that the risk was very low but nonetheless present, and very small numbers of people had unforeseen reactions.

Smallpox vaccination is not currently being done for members of the general public. As of mid-2003, any further vaccination outside of military personnel is likely to be done, in a closely supervised fashion, in health care workers and emergency responders. There is ongoing review of smallpox vaccination, including the current and newer vaccines.

Eradication
Since Jenner demonstrated the effectiveness of cowpox to protect humans from smallpox in 1796, various attempts were made to eliminate smallpox on a regional scale. As early as 1803, the Spanish Crown organized a mission (the Balmis expedition) to transport the vaccine to the Spanish colonies in the Americas and the Philippines, and establish mass vaccination programs there. In 1842, England banned inoculation, later progressing to mandatory vaccination. The British government introduced compulsory smallpox vaccination by an Act of Parliament in 1853. In the United States, from 1843 to 1855 first Massachusetts, and then other states required smallpox vaccination. Although some disliked these measures, coordinated efforts against smallpox went on, and the disease continued to diminish in the wealthy countries. By 1897, smallpox had largely been eliminated from the United States. In Northern Europe a number of countries had eliminated smallpox by 1900, and by 1914, the incidence in most industrialized countries had decreased to comparatively low levels. Vaccination continued in industrialized countries, until the mid to late 1970s as protection against reintroduction. Australia and New Zealand are two notable exceptions; neither experienced endemic smallpox and never vaccinated widely, relying instead on protection by distance and strict quarantines.

Post-eradication
The last cases of smallpox in the world occurred in an outbreak of two cases (one of which was fatal) in Birmingham, England in 1978. A medical photographer, Janet Parker, contracted the disease at the University of Birmingham Medical School and died on 11 September 1978, after which the scientist responsible for smallpox research at the university, Professor Henry Bedson, committed suicide. In light of this accident, all known stocks of smallpox were destroyed or transferred to one of two WHO reference laboratories; the Centers for Disease Control and Prevention (CDC) in the United States and the State Research Center of Virology and Biotechnology VECTOR in Koltsovo, Russia where a regiment of troops guard it. In 1986, the World Health Organization recommended destruction of the virus, and later set the date of destruction to be 30 December 1993. This was postponed to 30 June 1995. In 2002 the policy of the WHO changed to be against its final destruction.[45] Destroying existing stocks would reduce the risk involved with ongoing smallpox research; the stocks are not needed to respond to a smallpox outbreak. However, the stocks may be useful in developing new vaccines, antiviral drugs, and diagnostic tests.

In March 2004 smallpox scabs were found tucked inside an envelope in a book on Civil War medicine in Santa Fe, New Mexico.[48] The envelope was labeled as containing the scabs and listed the names of the patients they came from. Assuming the contents could be dangerous, the librarian who found them did not open the envelope. The scabs ended up with employees from the CDC who responded quickly once informed of the discovery. The discovery raised concerns that smallpox DNA could be extracted from these and other scabs and used for a biological attack.

Disclaimer: This information is not meant to be a substitute for professional medical advise or help. It is always best to consult with a Physician about serious health concerns. This information is in no way intended to diagnose or prescribe remedies.This is purely for educational purpose

Resources:
http://www.nlm.nih.gov/medlineplus/ency/article/001356.htm
http://en.wikipedia.org/wiki/Smallpox

 

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