Monkeypox

Monkeypox, according to World Health Organization (WHO) Fact Sheet 161, December 1997, "is a viral disease with a clinical presentation in humans similar to that seen in the past in smallpox patients. Smallpox no longer occurs, following its worldwide eradication in 1980, whereas monkeypox is still seen as a sporadic disease in parts of Africa.

"The virus responsible for monkeypox is related to the virus that used to cause smallpox (both are orthopoxviruses). Vaccination against smallpox (no longer necessary) also gave protection against monkeypox. Before the eradication of smallpox, vaccination was widely practised and protected against both diseases. However, children born after 1980 have not been vaccinated against smallpox and are likely to be more susceptible to monkeypox than older members of the population. The death rate from monkeypox is highest in young children, reaching about 10%.

"Most cases occur in remote villages of Central and West Africa close to tropical rainforests where there is frequent contact with infected animals. Monkeypox is usually transmitted to humans from squirrels and primates through contact with the animal's blood or through a bite.

"Following reports of ongoing cases of human monkeypox in the Democratic Republic of the Congo ('DRC', formerly Zaire) representing a new pattern of the disease, the Ministry of Health in DRC and the World Health Organization (WHO) organized two investigations in February and October 1997.

"In the past, an outbreak of monkeypox in DRC would have been limited to the village and would not last long because it did not spread extensively after the first patients recovered. However, the present study indicates that monkeypox disease is changing its pattern of infection in humans. The outbreak had a much higher rate of person to person transmission than seen previously, and spread through many generations of transmission, thus maintaining the outbreak for more than a year.

"Previous studies over a twenty-year period had shown that the rate of transmission of monkeypox within households was low, suggesting that the disease had a low potential for transmission from person to person. Outbreaks were generally self-limiting after one or two sequential transmissions. However, the two recent WHO studies have to-date shown that:


 * "The outbreak in DRC presents the largest cluster of monkeypox cases - albeit with less severe clinical disease - ever reported: 511 suspect cases were identified with onset of disease between February 1996 and October 1997; some of these suspect cases are thought to be chickenpox and laboratory confirmation studies are underway;
 * "The proportion of suspect cases who were 16 years of age or older (21%) was higher than previously reported (8%). Young children had mostly been affected in previous outbreaks;
 * "The percentage of suspect cases from person to person transmission (78%) was higher than previously reported (30%). This was associated with the clustering of cases in household compounds and prolonged chains of transmission from person to person;
 * "Secondary attack rates among contacts of primary cases (those thought to be infected by animal contact) have been calculated, on a preliminary basis, at 8%, which is similar to secondary attack rates of 4-12% estimated in Zaire in the early 1980s;
 * "The proportion of deaths (2%) was lower than previously reported (10%); all were aged under eight years and died within three weeks of disease onset.

"The ending of vaccination programmes against smallpox in the late 1970's has probably led to an increase in susceptibility to monkeypox and could explain the larger size of the most recent outbreak, the higher proportion of patients aged 15 and over, and the spread through many generations of transmission.

"WHO is concerned that monkeypox could pose a public health problem in this region of DRC and therefore vigilance must be maintained by strengthening detection systems for monkeypox and completely investigating future outbreaks.

"Further WHO studies are planned in the region to determine the need for additional risk-reduction measures.

"In May 1996, the 49th World Health Assembly decided that the last remaining stock of smallpox virus held in two research centres in the Russian Federation and the United States of America should be destroyed as the last step in the complete and final global elimination of smallpox. It also decided that WHO would keep 500 000 doses of smallpox vaccine (which is also effective against monkeypox). The smallpox vaccine seed virus (vaccinia virus strain Lister Elstrea) will be maintained in the WHO Collaborating Centre on Smallpox Vaccine at the National Institute of Public Health and Environmental Protection in Bilthoven, Netherlands, so that new stocks of vaccine can be produced if needed." - The following is copied from a 2000 Stanford University web page on Monkeypox, a.k.a. Poxveridae.

"The epidemiology of monkeypox is completely different from that of smallpox. Firstly, this virus is a rare zoonosis found only in the small villages of the tropical rain forests of western and central Africa, with cases mostly reported in Zaire. As a result of intensive surveillance efforts conducted by the World Health Organization, only 400 cases were reported worldwide from the time infection by monkeypox virus was first observed in 1970 to the time when surveillance ceased in 1986.

"Monkeypox virus is believed to be transmitted through direct contact with wild animals killed for food, such as squirrels and monkeys. A very important feature of monkeypox is that person-to-person transmission is rare, accounting for less than 1/3 of observed cases.

Incubation period: "Incubation period is between 10-14 days, usually 12 days.

Clinical Features and Outcomes: "The clinical features are almost indistinguishable from those of ordinary-type smallpox, with the exception of the enlargement of cervical and inguinal lymph nodes. Like ordinary-type small pox, monkeypox virus produces a generalized pustular rash with smaller lesions, a fever, and minor toxemia. It also has a healing period that progresses more rapidly.

Pathogenesis and Pathology: "The pathogenesis of human monkeypox is very similar to that of smallpox, with the exception that viral entry from a wildlife source probably occurs via small lesions on the skin or oral mucous membranes. Viral entry may also occur via the respiratory tract in the rare cases of person-to-person transmission.

"Like smallpox, monkeypox virus replicates in lymphoid tissue, although it has a greater degree of lymphadenopathy. The virus first localizes in mononuclear phagocytic cells, is released into the bloodstream, and then localizes again in skin cells. For more detailed information, please refer to the pathogenesis section of smallpox virus.

Prevention and Management: "Vaccination with smallpox vaccine immunizes against monkeypox, but it is not justified since the disease is so rare. In the United States, vaccinia vaccination is recommended for laboratory workers who directly handle cultures or animals infected with monkeypox virus.

"Management for monkeypox involves effective surveillance efforts such as those undertaken by the World Health Organization prior to 1980. An important thing to remember is that unlike smallpox, human monkeypox has a lower capacity for human spread. This makes identification and containment much more accessible." - Viability and Vaccine

"Smallpox has been eradicated, but at least 2 sites, the Centers for Disease Control and Prevention (CDC) in Atlanta, Ga, and the Russian State Research Center of Virology and Biotechnology in Koltsovo still maintain viable variola. The extent of clandestine stockpiles remains a matter of debate and concern. The World Health Organization has recommended the destruction of remaining stocks by June 30, 1999. If variola were released by an enemy or by terrorists, morbidity and mortality could be devastating. Its person-to-person communicability, high mortality, and stability make variola a significant potential BW (Bioweapon) threat. In addition, animal poxviruses that are virulent to humans (eg, monkeypox) or recombinant poxviruses could be developed as BW weapons. While approximately 20 million doses of smallpox vaccine are stored worldwide, the vaccine is gradually losing potency, and the number of smallpox-naïve individuals continues to increase as vaccination has virtually ceased."

Monkeypox could be used as bioweapon (Cache file).

"The Russians worked with monkeypox virus, a close cousin to smallpox, in their bioweapons program and it is possible terrorists could use it in a biological attack against the United States, scientists and former United Nations weapons inspectors told United Press International. Although some biological weapons experts are concerned with the possibility of terrorists using another smallpox-related virus called camelpox, which Iraq has admitted to researching, Mark Buller, a biologist at Saint Louis University who conducts research on smallpox vaccines, said he is more concerned about monkeypox. Buller's concern stems from the fact that monkeypox, unlike camelpox, causes mortality in humans and the incidence of human infection is on the rise in central and western Africa. In addition, the Russian biowarfare experts are known to have worked with the virus in the Soviet Union's biological weapons program. - United Press International (June 9, 2002)"Also see file. --

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