Atul Anand1, Anand Kumar Das2, Sona Bhardwaj3, Saraj Kumar Singh2
  1. Department of General Surgery, All India Institute of Medical Sciences, Patna, Bihar, India
  2. Department of Neurosurgery, All India Institute of Medical Sciences, Patna, Bihar, India
  3. Department of Microbiology, ESIC Hospital, Patna, Bihar, India.

Correspondence Address:
Saraj Kumar Singh, Department of Neurosurgery, All India Institute of Medical Sciences, Patna, Bihar, India.


Copyright: © 2023 Surgical Neurology International This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-Share Alike 4.0 License, which allows others to remix, transform, and build upon the work non-commercially, as long as the author is credited and the new creations are licensed under the identical terms.

How to cite this article: Atul Anand1, Anand Kumar Das2, Sona Bhardwaj3, Saraj Kumar Singh2. A brief review of the monkeypox virus and emerging concerns for neuroinvasiveness. 03-Mar-2023;14:78

How to cite this URL: Atul Anand1, Anand Kumar Das2, Sona Bhardwaj3, Saraj Kumar Singh2. A brief review of the monkeypox virus and emerging concerns for neuroinvasiveness. 03-Mar-2023;14:78. Available from:

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Background: Amidst the ongoing COVID-19 pandemic, monkeypox virus (MPXV) disease has been recognized as another disease of pandemic nature by the World Health Organization. Nearly four decades after the eradication of smallpox, as half of the world population is naïve to ortho-pox viruses (supposedly due to lack of immunity by vaccination), MPXV remains the most pathogenic species of the family of poxviruses.

Methods: The articles on MPXV were searched on PubMed/Medline and data were retrieved and analyzed.

Results: Although reported as a disease of milder exanthem and lower mortality as compared to smallpox, the MPXV disease tends to be neuroinvasive. This article highlights the neurological signs and symptoms of MPXV disease and discusses, in brief, the management strategies.

Conclusion: Neuroinvasive properties of the virus as demonstrated in in vitro studies, and further verified by neurological illnesses in patients, present a special threat to mankind. Clinicians must be prepared to recognize and treat these neurological complications and start treatment to limit long-lasting brain injury as seen in patients with COVID-19.

Keywords: Central nervous system, Monkeypox virus, Neurological, Pathogenesis


Viruses are important contributors to the World Health Organization’s (WHOs) current list of priority diseases. Crimean-Congo hemorrhagic fever, Marburg virus disease, Middle East respiratory syndrome coronavirus, severe acute respiratory syndrome, Ebola virus disease, Lassa fever, Nipah virus diseases, Zika virus disease, Rift Valley fever, and the novel coronavirus (COVID-19) are currently included in the list.[ 16 , 53 ] Many of these illnesses have some manifestations in the central nervous system (CNS) (meningitis, encephalitis, intracranial hemorrhage, seizures, etc.). This is reinforced by the ongoing COVID-19 pandemic, which has drawn attention to it in particular and serves as a reminder that the nervous system may be impacted by infections with the capacity to spread quickly and extensively despite intensive efforts.[ 15 , 41 ] The WHO has recently recognized the monkeypox virus (MPXV) illness as a “Public Health Emergency of International Concern (PHEIC).”[ 64 ] As the MPXV infection spreads across the globe, reports of its neurological symptoms are emerging. These symptoms might be linked to the virus’s neuroinvasive characteristics. While there is a paucity of literature commenting on these neurological manifestations, it is essential to have a thorough review of the neurological symptoms of the MPXV to begin treatment as soon as a diagnosis is made and prevent long-lasting brain damage like that seen in the COVID-19 pandemic.[ 41 ]


MPXV is a double-stranded enveloped DNA virus of the family Poxviridae, subfamily Chordopoxvirinae, and genus Orthopoxvirus.[ 32 , 60 ] There are two separate strains of MPXV, one from Central Africa’s Congo Basin and the other from West Africa, of which the former is more virulent in terms of morbidity, mortality, and human-to-human transmission.[ 11 , 37 ] The exact reservoir of this zoonotic disease is unknown; it was first identified in captive monkeys at the State serum institute of Copenhagen, Denmark in 1958.[ 38 ] Other possible reservoirs are squirrels of the genera Funisciurus and Heliosciurus, elephant shrew, and Gambian giant rats (Cricetomys spp.).[ 8 , 34 ] The first case of human infection was documented in 1970 in a 9-month-old child from Zaire (now the Democratic Republic of Congo).[ 36 ] The increase in MPXV cases was steady till 2017 when outbreaks were reported in the Democratic Republic of Congo, Central African Republic, Cameroon, Liberia, and Nigeria.[ 17 , 42 ] The situation updates of the WHO published on 27 June 2022 have reported the outbreak of MPXV disease in non-endemic countries, for example, the European nations, predominantly in the United Kingdom (UK), Germany, Spain, and Portugal.[ 44 ] Monkeypox viral disease was deemed a ‘PHEIC by the WHO on July 23, 2022.[ 64 ] As per the WHO data, a total of 67,556 cases across 106 countries have been confirmed with a death toll of 27 (till September 29, 2022). A total of 12 confirmed cases have been reported in India to date.[ 1 ]


Monkeypox is a vesicopustular illness with a secondary attack rate of around 10% in those who have not received the smallpox vaccine.[ 30 ] The two modes of transmission are zoonotic transmission and human-to-human transmission [ Figure 1 ]. Zoonotic transmission occurs during the hunting and handling of these animals.[ 51 ] Human-to-human transmission, the main mechanism responsible for recent outbreaks, occurs by direct inoculation through contact with body fluids, such as blood, saliva, respiratory droplets, and exudates from lesions.[ 30 ] On entry, the virus multiplies at the site of inoculation. It then either spreads to draining lymph nodes or blood (primary viremia). A secondary viremia occurs after its spread from lymphatic organs to blood. Finally, the virus lodges in the skin and other mucosal sites such as the nose, pharynx, eyes, and anogenital areas.[ 63 ] At the cellular level, viral entry into host cells is facilitated by the interaction of viral proteins with host glycosaminoglycans and subsequent endocytosis.[ 3 ] The mechanisms of neuroinvasion of the virus into the CNS in humans are unknown at present, due to a lack of studies in humans. Animal investigations have provided us with some insights regarding the MPXV’s neuroinvasiveness. The works of Tesh et al.,[ 62 ] Kulesh et al.,[ 35 ] Xiao et al.,[ 65 ] Hutson et al.,[ 27 - 29 ] Falendysz et al.,[ 21 - 23 ] Earl et al.,[ 18 , 19 ] and Sergeev et al.[ 58 , 59 ] deserve mention. In a series of tests, they inoculated animals such as squirrels, dogs, mice, and rats through different routes (primarily intraperitoneal and intranasal). The viral load was assessed by nucleic acid amplification tests, bioluminescence, and plaque assays in the blood, liver, spleen, brain, lymph nodes, and other organs (mainly on necropsy specimens). All of these experiments consistently showed the presence of the MPXV in brain tissues. Although these experiments highlight the neurotropism of the MPXV, identifying the MPXV transmission paths to the CNS is also crucial. Although the precise MPXV transmission channels are currently unknown, recent research on animal subjects has identified two plausible routes that may be responsible for neuroinvasiveness are: the olfactory epithelium pathway and the monocyte-macrophage pathway [ Figure 2 ].[ 57 ] For example, after intranasal injection of ground squirrels with the Congo Basin strain, the virus dramatically increased in the nasal septum and brain tissue.[ 59 ] In addition, intranasal inoculation of the MPXV revealed that the virus replicated more intranasally and in the animal brain according to bioluminescence imaging.[ 18 ] Although again, there is a paucity of studies in humans, these results indicated that MPXV transmission into the brain parenchyma may occur primarily through the nasal cavity and olfactory epithelium. Another way for the MPXV to enter the CNS, which may be responsible for CNS spread in humans as well, is through infecting circulating leukocytes, such as macrophages and monocytes, which is evident from the detection of MPXV-Zaire 79 antigens in monocytes of macaques after intravenous injection.[ 61 ]

Figure 1:

Modes of transmission of the monkeypox virus.


Figures 2:

(a and b) Potential pathways of “neurotropism” of the virus.



On inoculation, a febrile prodromal phase follows with an incubation period of 7–17 days. This phase manifests as fever, headache, malaise, myalgia, and lymphadenopathy, and lasts for about 1–4 days. The febrile phase is followed by a rash period lasting about 14–28 days, characterized by centrifugally distributed painful and pruritic rashes, which evolve from maculopapular to vesicopustular.[ 20 , 40 ] Notably, these rashes are all of similar sizes, at the same stage of evolution, and are often umbilicated.[ 40 ] Adenopathy is more marked as compared to smallpox.[ 14 , 20 ] In addition to mostly cutaneous involvement of facial, truncal, and skin of extremities in the previous outbreaks, the recent outbreaks are characterized by involvement of mucosal sites of the oral cavity, genitourinary tract, and anal canal–manifesting as severe proctitis, urethritis, balanitis, and pharyngitis, highlighting the importance of the sexual route of transmission as seen in bisexual, and men having sex with men (MSM) groups.[ 50 ] As the lesions become pustular and secondary bacterial infections occur, a second febrile phase follows.[ 20 ]

Mortality is uncommon-the case fatality rate varies from 1% to 11%.[ 7 , 14 ] Infants, young children <10 years of age, pregnant women, patients with HIV, and other immunodeficiency states constitute the vulnerable groups. Smallpox vaccination offers some protection, as severe complications are more common in the unvaccinated group (74%) than in vaccinated ones (40%).[ 40 ] Typical complications include bronchopneumonia, encephalitis, blindness due to corneal scarring, and septicemia.[ 20 , 40 ]

Neurological manifestations range from non-specific symptoms such as headache, myalgia, fatigue, and photophobia to severe complications such as seizures and encephalitis. The WHO data report headache as one of the symptoms in about 30% of patients [ Table 1 and Figure 3 ].[ 1 ] In keeping with this, other studies have also reported headache as the most prevalent neurologic symptom among MPXV disease cases that have been documented in the literature (50%), with seizures, disorientation, or encephalitis being less common (2%).[ 5 ] Existing human MPXV illness case series occasionally mentioned patients with neurologic issues, although there were rarely many specifics given. On a careful review of studies of cases in the African continent [ Table 2a ][ 24 , 25 , 31 , 33 , 46 , 47 , 52 , 67 , 68 ] and the non-African nations [ Table 2b ][ 2 , 4 , 10 , 13 , 26 , 45 , 48 , 54 , 55 , 56 , 66 ], there was a dearth of information on radiological findings of CNS infestations, and cerebrospinal fluid (CSF) analysis in patients infected with the monkey-pox virus. None of the studies from African nations[ 24 , 25 , 31 , 33 , 46 , 47 , 52 , 67 , 68 ] reported on radiological findings and CSF changes, while only few cases[ 48 , 56 ] in non-African nations had these findings reported [ Tables 2a and b ]. In an analysis of 282 instances in the Congo Basin during the 1980s, a case of a 3-year-old girl who developed encephalitis and succumbed after being in a coma, the 2nd day after hospitalization has been mentioned.[ 31 ] In an examination of 40 hospitalized cases of monkeypox sickness from Nigeria, a 28-day-old neonate and, a 43-year-old man with HIV had probable encephalitis and seizures.[ 46 ] Acute disseminated encephalomyelitis and Guillain-Barre syndrome are caused by secondary immune-mediated neurological insults and the neurotropism of the MPXV.[ 12 ] CSF, electroencephalogram (EEG), and magnetic resonance findings of the brain have been described as a case report in a 6-year-old girl from the Mid-West United States outbreak of 2003.[ 56 ] The CSF analysis picture initially showed increased pleocytosis with polymorphonuclear predominance with was later replaced by lymphocytic predominance as pleocytosis decreased by day 5–7 of the illness.[ 56 ] IgM antibodies to the virus have been identified by enzyme-linked immunosorbent assay (ELISA) in the CSF.[ 56 ] EEG shows diffuse slowing. Magnetic resonance imaging demonstrates diffuse brain edema, meningeal enhancement, and signal abnormalities in the parietal cortex and thalamus.[ 56 ] Neurological symptoms, though reported as case reports, can be further limited by starting treatment as early as the diagnosis of monkeypox illness is made.

Figure 3:

Bar diagram showing proportion of symptoms in monkeypox illness (see Table 1 for details). Adapted from: 2022 Monkeypox Outbreak: Global Trends [Internet]. [Cited 2022 Dec 19]; Available from: (S.R: Systemic rashes, G.R: Genital rashes, O.R: Oral rashes, G.L: General lymphadenopathy, L.L: Local lymphadenopathy, H: Headache, Fa: Fatigue, M: Myalgia, Fe: Fever, S.T: Sore throat, C: Chills, V: Vomiting, A: Asymptomatic).


Table 1:

Symptoms of monkeypox illness.


Table 2a:

Neurological symptoms of monkeypox illness in studies from African countries.


Table 2b:

Neurological symptoms of monkeypox illness in studies from countries outside Africa.



As evident in the UK Health Security Agency case definition of probable monkeypox infection,[ 43 ] the diagnosis of monkeypox is clinical, which includes a proper history (focusing on occupation, contact with possible reservoirs, and history of travel to endemic regions, especially Africa), and typical distribution of rashes. Specific viral DNA detection may be carried out by polymerase chain reaction tests in a specimen from skin or mucosal lesions, CSF, and serum.[ 40 ] Electron microscopy may identify the virions in tissue specimens.[ 6 , 40 ] ELISA for detection of IgM antibodies in CSF and serum may show cross-reactivity with other ortho-pox viruses, is not able to distinguish a recent infection from vaccination, and may be negative in immunodeficient individuals who are not able to mount an immune response against the virus.[ 40 ] All laboratory tests must be carried out in a biosafety level three cabinet.[ 32 ]


In the absence of a clinically approved anti-viral agent, prevention remains the key. Behavioral risk-reduction strategies include avoidance of close contact with anyone suspected to have Monkeypox infection. This may be accomplished by home-based or hospital-based isolation. Airborne and contact precautions, including hand-hygiene practices as learned from the COVID-19 pandemic, are encouraged among healthcare workers. Considering the recent outbreaks, MSM should be cautious.

Symptomatic cases usually have a mild self-limiting illness, and the treatment is supportive focusing on analgesia, hydration, and nutrition. Acetaminophen, non-steroidal anti-inflammatory agents, and topical antihistamines are used when required.[ 49 ] Antibiotics are used only when rashes become pustular and secondary bacterial superinfections are suspected.

Chemotherapeutic agents at various stages of trial against the MPXV include NIOCH-14, Cidofovir, and CMX-001.[ 39 , 40 ] Centers for Disease Control and Prevention in association with the US Food and Drug Administration (US-FDA) has given Tecovirimat (TPOXX) the expanded access investigational new drug (EA-IND) status for use against monkeypox.[ 9 ] It acts by inhibiting the VP37 envelope-wrapping protein of ortho-poxviruses, thus preventing the release of virions from the intracellular compartment.[ 40 ] As part of the US Strategic National Stockpile, the medication is currently kept on hand for use against smallpox in the event of a bioterrorist attack.[ 9 , 40 ] Vaccinia virus immunoglobulin can also be used against monkeypox infection, due to serological cross-reaction amongst ortho-poxviruses. JYNNEOS vaccine is US-FDA approved for protection against both smallpox and MPXVs. It is administered with two subcutaneous injections spaced 28 days apart.[ 9 ] The FDA-approved ACAM2000 vaccine for monkeypox protection falls under the EA-IND classification. It is given as a single dose.[ 9 , 40 ]


The recent outbreaks of the MPXV may be attributed to the encroachment of human civilization into areas with zoonotic reservoirs in the setting of waning immunity against the smallpox virus. MPXV disease is a systemic illness with its effect on most organ systems unknown. Neuroinvasive properties of the virus as demonstrated in in vitro studies, and further verified by neurological illnesses in patients, present a special threat to mankind. Clinicians must be prepared to recognize and treat these neurological complications and start treatment to limit long-lasting brain injury as seen in patients with COVID-19. Lessons learned from the COVID-19 pandemic, especially the isolation and hand-hygiene practices hold true for protection against the MPXV and other potential pandemics given the emerging list of pathogens that cause human disease.

Author contributions

Saraj Kumar Singh contributed to the study conception. Material preparation and data collection were performed by Atul Anand, Anand Kumar Das and Sona Bhardwaj. The first draft of the manuscript was written by Atul Anand and Anand Kumar Das and all authors commented on previous versions of the manuscript. The first two authors have contributed equally in the preparation of the manuscript. All authors read and approved the final manuscript.

Declaration of patient consent

Patient’s consent not required as there are no patients in this study.

Financial support and sponsorship

Publication of this article was made possible by the James I. and Carolyn R. Ausman Educational Foundation.

Conflicts of interest

There are no conflicts of interest.


The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Journal or its management. The information contained in this article should not be considered to be medical advice; patients should consult their own physicians for advice as to their specific medical needs.


We acknowledge our digital artist Chandan Kumar for preparing the schematic representation.


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