Smallpox Disease
Smallpox is a highly contagious disease caused by the smallpox virus, an orthopoxvirus. It causes death in up to 30% of cases. Natural infection was eradicated. The main concern about the outbreak of epidemics is linked to bioterrorism.
It presents with severe systemic symptoms and a characteristic pustular rash. Treatment is usually supportive and potentially with antiviral drugs. Prevention involves vaccination which, due to related risks, is limited to selected patients.
No cases of smallpox have occurred in the world since 1977, due to vaccination on a worldwide scale. In 1980, the World Health Organization (WHO) recommended the suspension of the routine practice of smallpox vaccination. In the United States, this practice ceased in 1972.
Since humans are the only natural host of the smallpox virus and because the virus cannot survive > 2 days in the environment, WHO has declared the natural infection eradicated.
Concerns regarding bioterrorism are related to smallpox virus samples stored in research centers or even artificially created viruses that could cause them to reappear (see Biological agents such as weapons and Centers for Disease Control and Prevention [CDC]: Smallpox / Bioterrorism ).
Pathophysiology of smallpox
There are at least 2 strains of the human smallpox virus:
Variola major (classic smallpox), the most virulent strain
Variola minor (alastrim), the least virulent strain
Smallpox presents human-to-human transmission by inhalation of respiratory droplets or, to a lesser extent, by direct contact. Contaminated clothing or bedding can also transmit the infection. Contagiousness is maximum for the first 7-10 days from the onset of the rash. Once the scabs have formed on the skin lesions, the infectivity decreases.
The attack rate reaches 85% in unvaccinated individuals, and infection can lead to up to 4-10 secondary cases for each index case. However, the infection tends to spread slowly and, more importantly, between people in close contact with each other.
The virus invades the oropharyngeal or respiratory mucosa and multiplies in the regional lymph nodes, then leading to viraemia. Finally, it is localized in the small blood vessels of the dermis and oropharyngeal mucosa. The other organs are rarely involved clinically, except for occasional involvement of the central nervous system, in which encephalitis can develop. Secondary bacterial infections of the skin, lungs, and skeletons can develop.
Smallpox Symptomatology
Variola major
The major variant has an incubation period of 10-12 days (ranging from 7 to 17 days), followed by a prodromal period of 2-3 days characterized by fever, headache, low back pain, and extreme malaise. Sometimes severe abdominal pain and vomiting may occur. After the prodromal phase, maculo-papular lesions appear on the oropharyngeal mucosa, face and arms, rapidly spreading to the trunk and legs. Oropharyngeal lesions ulcerate rapidly. After 1-2 days, the skin lesions become vesicular and then pustular. Papules are more numerous on the face and limbs than on the trunk and can affect the palms of the hands. The pustules are rounded and tense and appear deeply located. The skin lesions of smallpox, unlike those of chickenpox, are all at the same stage of evolution in a certain part of the body. After 8 or 9 days the pustules become scabs. Major residual scars are typical.
The mortality rate is around 30%. Mortality is due to the massive inflammatory response that causes shock and multi-organ failure and usually occurs during the 2nd week of illness.
About 5-10% of people with variola major develop a hemorrhagic or malignant variant (flatpox).
The haemorrhagic form is rarer and has a shorter and more intense prodromal period, followed by generalized erythema and cutaneous and mucous haemorrhages. It is invariably fatal within 5 to 6 days.
The malignant form has a similar severe prodromal period, followed by the development of confluent, flat, non-pustular skin lesions. In survivors, the epidermis frequently peels.
Variola minor
Variola minor causes similar but much less severe symptoms, with a less extensive rash.
The mortality rate is < 1%.
Smallpox Diagnosis
PCR (Polymerase Chain Reaction)
Electron microscopy
Unless laboratory exposure is reported or an outbreak (bioterrorism) is suspected, only patients who meet the clinical definition of smallpox should be tested for possible false-positive results. An algorithm for assessing the risk of smallpox in patients with fever and rash is available on the CDC website ( CDC Algorithm Poster for Evaluation of Suspected Smallpox ).
The diagnosis of smallpox is confirmed by documenting the presence of smallpox DNA by Polymerase Chain Reaction (PCR) in samples from vesicles or pustules. Or the presence of the virus can be identified by electron microscopy or viral culture of the material scraped from skin lesions and subsequently confirmed by PCR (Polymerase Chain Reaction). Any suspected case of smallpox must be immediately reported to the public health authorities or the Centers for Disease Control and Prevention (CDC) at 770-488-7100. ASL of reference.) These agencies, therefore, work to carry out the analyzes in a laboratory with a high level of safety (level 4 biosecurity).
Point-of-care (bedside) antigen detection tests are under development.
Smallpox Treatment
Supportive therapy
Isolation
Possibly tecovirimat, consider cidofovir or brincidofovir (CMX001)
Treatment of smallpox is usually supportive, with antibiotics for any bacterial superinfections. However, the antiviral drug tecovirimat was approved by the US Food and Drug Administration (FDA) in 2018 based on experimental studies and is the first drug to be licensed for the treatment of smallpox ( 1 ). Although its efficacy against smallpox in humans is unknown, tecorvirimat is likely the drug of choice for the treatment attempt and is available from the US Department of Health and Human Services National Strategic Reserve. Cidofovir and investigational drug brincidofovir (CMX001) can be considered ( 2 ).
Isolation of individuals with smallpox is essential. In limited outbreaks, patients can be isolated in the hospital using airborne transmission precautions in an airborne infection isolation room. In mass outbreaks, home isolation may be necessary. The contacts must be placed under surveillance, usually by measuring their body temperature daily; if they develop a temperature > 38 ° C or other signs of illness, they should be isolated in their home.
Smallpox prevention
Smallpox vaccines licensed in the United States consist of replication-competent live vaccine virus (ACAM2000) and JYNNEOS, a modified live attenuated (replication-limited) vaccinia-virus Ankara (MVA) vaccine ( 1). Vaccinia is related to smallpox and provides cross-immunity.
The ACAM2000 vaccine is administered with a bifurcated needle dipped in the reconstituted vaccine. The needle is driven rapidly 15 times into an area approximately 5 mm in diameter with enough force to produce a slight dripping of blood. The vaccination site is covered with a bandage to prevent the vaccine virus from spreading to other areas of the body or to close contacts. Fever, malaise, and myalgia are common the week following vaccination.
The effectiveness of vaccination is indicated by the development of a pustule around the 7th day. Revaccination can only produce a papule surrounded by erythema, of maximum intensity between the 3rd and 7th day. Individuals who do not exhibit these signs of efficacy should receive a
JYNNEOS is administered as 2 subcutaneous injections 4 weeks apart. It is licensed by the Food and Drug Administration (FDA) for people aged 18 and over and may have a particular role in vaccinating people for whom ACAM2000 may be contraindicated, such as those with immunocompromised states or atopic dermatitis.
Another experimental live vaccine, the Aventis Pasteur Smallpox Vaccine (APSV), is also available at the Strategic National Stockpile in an emergency.
After a single vaccination, the immune response begins to weaken after 5 years and is probably negligible after 20 years. In individuals successfully revaccinated one or more times, some residual immunity may persist for ≥ 30 years.
Until an outbreak in the population occurs, pre-exposure vaccination remains recommended only for those at high risk of exposure to the virus Live vaccine virus complications
Risk factors for complications include extensive skin manifestations (particularly eczema), immunosuppressive disease or therapy, eye inflammation, and pregnancy. Widespread vaccination is not recommended due to the related risks.
Serious complications occur in approximately 1 in 10 000 patients after primary vaccination and include
Post-vaccine encephalitis
Progressive vaccinia
Eczema vaccinico
Generalized vaccinia
Myocarditis and/or pericarditis
Keratinitis vaccine
Non-infectious skin rashes
Post-vaccination encephalitis occurs in approximately 1 in every 300,000 primary vaccination recipients, typically 8-15 days after inoculation.
Progressive vaccinia (vaccinia necrosum ) results in persistent vaccinia (vesicular) lesions, which spread to adjacent skin and later to other skin areas, bones, and viscera. Progressive vaccinia can occur after primary vaccination or after revaccination, but occurs almost exclusively in patients with an underlying defect in cell-mediated immunity; sometimes it is fatal.
Vaccine eczema occurs with skin lesions localized to areas of active eczema or even in remission.
Generalized vaccinia is due to hematogenous dissemination of the vaccinia virus and causes vaccine lesions in multiple parts of the body; it is usually benign.
Vaccine keratitis is a rare complication that occurs when the vaccine virus is inadvertently inoculated into the eye.
Some serious vaccination complications are treated with vaccine immunoglobulins; One case of vaccine eczema apparently successfully treated with vaccine immunoglobulins, cidofovir, and tecovirimat has been reported. In the past, high-risk patients receiving post-exposure vaccination were simultaneously given vaccine immunoglobulins in an attempt to prevent complications. The effectiveness of this procedure is unknown and is not recommended by the CDC. In the United States, vaccine immunoglobulins are only available from the CDC.
Post-exposure prophylaxis
Post-exposure vaccination with a replication-competent vaccine can significantly prevent or limit disease severity and is indicated in family members and in people in close contact with smallpox patients. Early administration is most effective, but some benefits can be seen for up to 7 days after exposure.