Update: multistate outbreak of monkeypox--Illinois,Indiana, Kansas,Missouri, Ohio,and Wisconsin, 2003

CDC and state and local health departments continue to investigate cases of monkeypox among persons who had close contact with wild or exotic mammalian pets or persons with monkeypox. This report updates epidemiologic, laboratory, and animal data for U.S. cases.     

Update: multistate outbreak of monkeypox--Illinois,Indiana, Kansas,Missouri, Ohio,and Wisconsin, 2003

CDC and state and local health departments continue to investigate cases of monkeypox among persons who had contact with wild or exotic mammalian pets or persons with monkeypox. This report updates epidemiologic, laboratory, and smallpox vaccine use data for U.S. cases.     

Update: multistate outbreak of monkeypox--Illinois,Indiana, Kansas,Missouri, Ohio,and Wisconsin, 2003

CDC and state and local health departments continue to investigate cases of monkeypox among persons in the United States who had contact with wild or exotic mammalian pets or with persons with monkeypox. This report updates results of the epidemiologic investigation, provides information on the use of smallpox vaccine during the outbreak, and summarizes the animal tracing activities to identify the origin and subsequent distribution of infected animals.     

Endemic human monkeypox, Democratic Republic of Congo, 2001-2004

By analyzing vesicle fluids and crusted scabs from 136 persons with suspected monkeypox, we identified 51 cases of monkeypox by PCR, sequenced the hemagglutinin gene, and confirmed 94% of cases by virus culture. PCR demonstrated chickenpox in 61 patients. Coinfection with both viruses was found in 1 additional patient.     

Human monkeypox: secondary attack rates

Data on human monkeypox collected in Zaire during the six years 1981-86 were analysed to assess the extent of interhuman transmission of monkeypox virus. Among the 2278 persons who had close contact with 245 monkeypox patients infected from an animal source, 93 fell ill and were presumed to have been infected from the known human source: 69 of these were spread in the first generation, 19 in the second generation, and the remaining five cases in the third and fourth generation.     

Human monkeypox, 1970-79

Increasing attention has been given to human monkeypox since the achievement of global smallpox eradication. Monkeypox, which was first described in Central Africa in 1970, resembles smallpox clinically but differs from it epidemiologically. Forty-seven cases of human monkeypox have occurred since 1970 in 5 Central and West African countries; 38 of these cases have been reported from Zaire. The evolution of the illness and the sequelae of monkeypox and smallpox are the same; monkeypox has a case-fatality rate of about 17%. Children below 10 years of age comprise 83% of the cases. All cases have occurred in tropical rainforest areas and clustering of cases has been observed in certain zones within countries and within families. Person-to-person spread may have occurred in 4 cases; the secondary attack rate among susceptible, very close family members was 7.5% (3 cases/40 contacts) and among all susceptible contacts was 3.3% (4 cases/123 contacts)—much lower than the 25-40% secondary attack rate that occurs with smallpox. Although the low transmission rate and the low frequency of disease indicate that monkeypox is not a public health problem, more data are needed.     

Extended Human-to-Human Transmission during a Monkeypox Outbreak in the Democratic Republic of the Congo

A 600-fold increase in monkeypox cases occurred in the Bokungu Health Zone of the Democratic Republic of the Congo during the second half of 2013; this increase prompted an outbreak investigation. A total of 104 possible cases were reported from this health zone; among 60 suspected cases that were tested, 50 (48.1%) cases were confirmed by laboratory testing, and 10 (9.6%) tested negative for monkeypox virus (MPXV) infection. The household attack rate (i.e., rate of persons living with an infected person that develop symptoms of MPXV infection) was 50%. Nine families showed >1 transmission event, and >6 transmission events occurred within this health zone. Mean incubation period was 8 days (range 4–14 days). The high attack rate and transmission observed in this study reinforce the importance of surveillance and rapid identification of monkeypox cases. Community education and training are needed to prevent transmission of MPXV infection during outbreaks.     

Reemergence of Human Monkeypox and Declining Population Immunity in the Context of Urbanization,Nigeria, 2017–2020

A monkeypox outbreak in Nigeria during 2017–2020 provides an illustrative case study for emerging zoonoses. We built a statistical model to simulate declining immunity from monkeypox at 2 levels: At the individual level, we used a constant rate of decline in immunity of 1.29% per year as smallpox vaccination rates fell. At the population level, the cohort of vaccinated residents decreased over time because of deaths and births. By 2016, only 10.1% of the total population in Nigeria was vaccinated against smallpox; the serologic immunity level was 25.7% among vaccinated persons and 2.6% in the overall population. The substantial resurgence of monkeypox in Nigeria in 2017 appears to have been driven by a combination of population growth, accumulation of unvaccinated cohorts, and decline in smallpox vaccine immunity. The expanding unvaccinated population means that entire households, not just children, are now more susceptible to monkeypox, increasing risk of human-to-human transmission.     

Phylogenetic and Ecologic Perspectives of a Monkeypox Outbreak,Southern Sudan, 2005

Identification of human monkeypox cases during 2005 in southern Sudan (now South Sudan) raised several questions about the natural history of monkeypox virus (MPXV) in Africa. The outbreak area, characterized by seasonally dry riverine grasslands, is not identified as environmentally suitable for MPXV transmission. We examined possible origins of this outbreak by performing phylogenetic analysis of genome sequences of MPXV isolates from the outbreak in Sudan and from differing localities. We also compared the environmental suitability of study localities for monkeypox transmission. Phylogenetically, the viruses isolated from Sudan outbreak specimens belong to a clade identified in the Congo Basin. This finding, added to the political instability of the area during the time of the outbreak, supports the hypothesis of importation by infected animals or humans entering Sudan from the Congo Basin, and person-to-person transmission of virus, rather than transmission of indigenous virus from infected animals to humans.     

Retrospective analysis of monkeypox infection

Serologic cross-reactivity between orthopoxviruses is a substantial barrier to laboratory diagnosis of specific orthopoxvirus infections and epidemiologic characterization of disease outbreaks. Historically, time-consuming and labor-intensive strategies such as cross-adsorbed neutralization assays, immunofluorescence assays, and hemagglutination-inhibition assays have been used to identify orthopoxvirus infections. We used cross-adsorption to develop a simple and quantitative postadsorption ELISA for distinguishing between monkeypox and vaccinia infections. Despite the difficulty of diagnosing clinically inapparent monkeypox in previously vaccinated persons, this technique exhibited 100% sensitivity and 100% specificity for identifying clinically overt monkeypox infection irrespective of vaccination history. We also describe a Western blot technique in which up to 3 diagnostic bands may be used to distinguish between vaccinia and monkeypox infection. The techniques described provide independent diagnostic tests suitable for retrospective analysis of monkeypox outbreaks.     

Experimental infection of prairie dogs with monkeypox virus

Studies of experimental infection of prairie dogs (Cynomys ludovicianus) with monkeypox virus are described. After intraperitoneal infection, all of the animals died within 11 days. Virus was cultured from their blood and oropharynx several days before death; at necropsy, most of the organs tested contained monkeypox virus. Marked hepatic and splenic necrosis were observed, along with mild inflammatory changes in the lungs. After intranasal (IN) infection, the primary pathologic changes were in the lungs and pleural cavity. Some of the IN infected animals (40%) survived, and monkeypox virus could be cultured from their nasal discharge and oropharynx for <22 days. Ulcerative lesions also developed on the lips, tongue, and buccal mucosa of the surviving animals. Our findings support an earlier report, which suggested that infected prairie dogs can transmit monkeypox virus by respiratory and mucocutaneous contact with susceptible animals and persons.     

2022年猴痘流行特点及研究进展

猴痘是由猴痘病毒引起的人兽共患病。既往猴痘主要流行于中非与西非地区。2022年5月7日至12月25日,全球已有110个国家和地区发现猴痘病例,并在以MSM为主的人群中出现了广泛的人际传播,猴痘在全球多个非流行国家和地区的暴发引起全球的高度关注。研究表明本轮猴痘的流行情况、传播特点和临床表现与既往经典猴痘存在差异。现就本轮猴痘流行病学改变、临床特征和预防治疗方面的研究进展进行综述,以期为猴痘的防控提供科学参考。     

猴痘的流行病学特征及其科学防控

猴痘是由猴痘病毒(monkeypox virus, MPXV)引起的一种罕见的、散发的、天花样临床表现的急性传染病。2022年5月以来,全球报告了超过1 000例猴痘实验室确诊病例,这是全球首次猴痘非流行国家和流行国家同时报告了多个猴痘病例和聚集性病例,对全球猴痘疫情的防控提出了新挑战。本文就猴痘的病原学特征、流行现状、流行病学特征、防控措施等方面的研究进展进行综述,以期为科学防控提供参考。     

Monkeypox virus phylogenetic similarities between a human case detected in Cameroon in 2018 and the 2017-2018 outbreak in Nigeria

A monkeypox virus was detected from a human clinical case in 2018 in Cameroon; a country where no human cases were reported since 1989. The virus exhibited close genetic relatedness with another monkeypox virus isolated in Nigeria during the 2017–2018 outbreak. Although our molecular findings argue in favor of an extension of the monkeypox outbreak from Nigeria into Cameroon, the possibility that the monkeypox virus detected could be indigenous to Cameroon cannot be ruled out.     

Outbreaks of monkeypox and serological surveys in nonhuman primates

In connexion with the recent detection of cases of monkeypox in man in West and Central Africa, the frequency of monkeypox outbreaks in monkeys since 1958, when the disease was first recognized in captive animals, has been investigated. Special incidence surveys were made for this purpose. During the last 3 years, a serological survey has been conducted to find natural foci of monkeypox virus, and a total of 2 242 sera from monkeys of different species from various parts of Africa and Asia have been examined for poxvirus antibodies. The survey failed to detect any significant indication of poxvirus infections. The observations suggest that although a few human cases of monkeypox have been identified, monkeypox in the natural environment is not widespread and is perhaps localized in small areas.     

Qualitative assessment of risk for monkeypox associated with domestic trade in certain animal species, United States

In 2003, US officials identified several human monkeypox cases and traced the virus exposure to infected captive prairie dogs. The virus was likely introduced through a shipment of imported African rodents, which were kept with other mammals, including prairie dogs, in a pet distribution facility in the Midwest. To prevent the further introduction and spread of the virus, federal agencies restricted the importation of African rodents and restricted the domestic trade or movement of prairie dogs and certain other rodents. In this qualitative assessment of the risk for monkeypox associated with the 2003 outbreak, we conclude that the probability of further human infection is low; the risk is further mitigated by rodent import restrictions. Were this zoonotic disease to become established domestically, the public health effects could be substantial.     

Outbreak of human monkeypox, Democratic Republic of Congo, 1996 to 1997

Human monkeypox is a zoonotic smallpox-like disease caused by an orthopoxvirus of interhuman transmissibility too low to sustain spread in susceptible populations. In February 1997, 88 cases of febrile pustular rash were identified for the previous 12 months in 12 villages of the Katako-Kombe Health Zone, Democratic Republic of Congo (attack rate = 22 per 1,000; case-fatality rate = 3.7%). Seven were active cases confirmed by virus isolation. Orthopoxvirus- neutralizing antibodies were detected in 54% of 72 patients who provided serum and 25% of 59 wild-caught animals, mainly squirrels. Hemagglutination-inhibition assays and Western blotting detected antibodies in 68% and 73% of patients, respectively. Vaccinia vaccination, which protects against monkeypox, ceased by 1983 after global smallpox eradication, leading to an increase in the proportion of susceptible people.     

Monkeypoxvirus infections

During and after the smallpox eradication campaign, human cases of monkeypox appeared in West and Central Africa, as isolated cases or as small epidemics. Since inter-human transmission has never or only very exceptionally been documented, monkeypox does not represent a serious threat to humans. The virus reservoir is among tree squirrels living in the tropical rain forests of Africa and humans are infected by hunting, killing and skinning these animals. However, the modernization of society lessens human contact with the virus reservoir. Since the eradication of smallpox, stocks of variola virus have been maintained; whether these stocks should now be destroyed is a political question, which is seriously compromised by mistrust between countries.     

Human Monkeypox Outbreak Caused by Novel Virus Belonging to Congo Basin Clade, Sudan, 2005

To determine the outbreak source of monkeypox virus (MPXV) infections in Unity State, Sudan, in November 2005, we conducted a retrospective investigation. MPXV was identified in a sub-Sahelian savannah environment. Three case notification categories were used: suspected, probable, and confirmed. Molecular, virologic, and serologic assays were used to test blood specimens, vesicular swabs, and crust specimens obtained from symptomatic and recovering persons. Ten laboratory-confirmed cases and 9 probable cases of MPXV were reported during September–December 2005; no deaths occurred. Human-to-human transmission up to 5 generations was described. Our investigation could not fully determine the source of the outbreak. Preliminary data indicate that the MPXV strain isolated during this outbreak was a novel virus belonging to the Congo Basin clade. Our results indicate that MPXV should be considered endemic to the wetland areas of Unity State. This finding will enhance understanding of the ecologic niche for this virus.     

Can variola-like viruses be derived from monkeypox virus? An investigation based on DNA mapping

The results are presented of a special study to determine whether variola-like “whitepox” viruses could arise as white pock variants of monkeypox virus after one or a few mutations. DNA mapping by cross-hybridization of restriction endonuclease DNA fragments was carried out on 18 orthopoxviruses relevant to this study, including variola and monkeypox viruses and white (non-haemorrhagic) pock producers recovered from chorioallantoic membranes infected with red (haemorrhagic) pock-producing monkeypox viruses. The distinctiveness of the DNA maps of true variola and monkeypox viruses indicated that spontaneous production of “whitepox” from monkeypox virus was genetically impossible. These and other observations led to the conclusion that the “whitepox” viruses recovered from monkeypox virus stocks had an exogenous origin.