A recurrant theme in this blog is that most of the infectious disease threats humans face today originate from animal hosts (aka are `zoonotic'), and that the incidence of these diseases jumping species has increased markedly over the past 3 decades.
Six years ago, in Emerging zoonotic viral diseases L.-F. Wang (1, 2) * & G. Crameri wrote:
The last 30 years have seen a rise in emerging infectious diseases in humans and of these over 70% are zoonotic (2, 3). Zoonotic infections are not new. They have always featured among the wide range of human diseases and most, e.g. anthrax, tuberculosis, plague, yellow fever and influenza, have come from domestic animals, poultry and livestock. However, with changes in the environment, human behaviour and habitat, increasingly these infections are emerging from wildlife species.
We explored some of the reasons behind this shift nearly a decade ago in The Third Epidemiological Transition - which focused on the work of anthropologist and researcher George Armelagos (May 22, 1936 - May 15, 2014) - of Emory University.
Emerging infectious diseases are considered such an important public health threat that the CDC maintains as special division – NCEZID (National Center for Emerging and Zoonotic Infectious Diseases) – to deal with them, and 25 years ago the CDC established the EID Journal dedicated to research on emerging infectious diseases.
And over the past 15 years we've followed dozens of EIDs, including MERS-CoV, H5N1, H7N9, EA H1N1 G4, Zika, Chikungunya, Ebola, Lyme Disease, SFTS, Nipah and Hendra, Hantavirus, The Heartland Virus, the Bourbon Virus, and many more.
While most of these emerging disease threats don't have serious pandemic potential, the sudden emergence of COVID-19 illustrates how quickly we can be blindsided by an obscure or unknown threat.
Even something with less than pandemic potential (like Zika, Ebola, or Lyme Disease) can have profound impacts on public health.
So we tend to pay attention when something new, or highly unusual, jumps species to infect a new host, particularly when that host is a human. Given limits of surveillance, if one case is reported, there are almost certainly others flying under the radar.
Three days ago, in WHO Update & Risk Assessment On Monkeypox In The DRC, we revisited the ongoing Monkeypox epidemic in Central Africa, and discussed how the waning immunity from smallpox vaccines (last given in 1980) have opened the door to other, less lethal pox viruses to flourish and spread.
Over the past decade several novel poxviruses - for which we have limited knowledge - have been discovered, including:
- Two years ago, in EID Journal: Novel Poxvirus in Proliferative Lesions of Wild Rodents in East-Central Texas, USA we looked at research into a new poxvirus discovered in east-central Texas.
- In 2017, Italian researchers isolated a new pox virus in a cat (see EID Journal Novel Orthopoxvirus and Lethal Disease in Cat, Italy).
- In 2013 two people were found infected with a novel poxvirus in Eastern Europe (and a 3rd from 2010 identified retrospectively) (see NEMJ Human Infection with a Zoonotic Orthopoxvirus in the Country of Georgia).
But most pertinent to today's blog - in 2015 a middle-aged female resident of Fairbanks, Alaska presented to an urgent care facility with what she thought was a spider bite on her shoulder, along with fever, fatigue and tender lymph nodes (see Clin. Inf. Dis Novel Orthopoxvirus Infection in an Alaska Resident).
While she had contact with a house guest from Azerbaijan, and there were signs of small mammals around her residence, no source of exposure was determined. The virus was determined to be genetically distinct from other known poxviruses, and was likely locally acquired.
Tests for shingles and chickenpox were negative, and subsequent lab tests revealed she had a never-before-seen novel pox virus. The lesion resolved after about 6 months.
Second Case of Novel Orthopoxvirus Infection in a Fairbanks-area Resident
In July 2015, a woman residing in the Fairbanks area developed a small (approximately 1 cm) ulceration with a whitish border on her right shoulder surrounded by erythema. She also experienced fever and fatigue. The treating physician suspected a viral infection. Ultimately, the lesion was found to be caused by an orthopoxvirus belonging to a previously undiscovered lineage. 1 The lesion fully resolved after about 6 months.
Orthopoxvirus is a genus of double-stranded DNA viruses that infect a variety of animals, including humans, cattle, cats, and rodents. There are likely many undiscovered species of Orthopoxvirus circulating in North American mammals. 2 The woman infected in 2015 had contact with small mammals and their droppings, but no molecular or serological evidence of orthopoxvirus infection was found in a taxonomically narrow sample of 12 small mammals trapped from her property. 1
The virus discovered in Alaska in 2015 is not closely related to other known orthopoxviruses. Virologists have proposed that the lineage represents a new species of Orthopoxvirus, which they named “Alaskapox virus”. 3
In August 2020, a different woman who also lived in the Fairbanks area presented with similar symptoms. A small grey lesion appeared on her left upper arm, followed by erythema approximately 4 days later. She reported tender axillary adenopathy, shoulder pain, fatigue, and subjective fever at night. This patient’s lesion was deroofed and submitted to the US Centers for Disease Control and Prevention (CDC) for orthopoxvirus testing. The specimen tested positive on a generic orthopoxvirus PCR assay and sequencing confirmed that it belonged to the lineage identified in 2015.
This is only the second known case of Alaskapox virus infection. Both occurred in residents of the Fairbanks area who did not have recent history of out-of-state travel. The respective symptom onset dates were more than 5 years apart and we did not identify any epidemiologic link between the cases.
Based on what is known about the epidemiology and ecology of other orthopoxviruses, and based on evidence from these two cases, we hypothesize that Alaskapox virus is most likely enzootic in one or more species of mammals in Interior Alaska and that humans are only occasionally infected. Both cases occurred during mid- to late summer in residents of forested areas near Fairbanks. While the similar time of year may be purely coincidental, it may also reflect the fact that small mammal populations are likely at or near their peak population size in late summer and that humans in Interior Alaska spend more time outdoors during the summer than other times of year.
The available evidence suggests that the public health impact of Alaskapox virus is limited. Importantly, there is no evidence of human-to-human transmission.
The animal-to-human transmission route is unclear, but accidental inoculation of pre-existing breaks in the skin with infectious fomites is one possibility. It is reassuring that both known infections caused self-limiting illness. However, much remains unknown about the epidemiology and pathology of Alaskapox virus. Increased awareness among clinicians may lead to the identification of additional cases and thereby inform a fuller understanding of the incidence, risk factors, and spectrum of illness. The Alaska Section of Epidemiology is working with the University of Alaska Museum and CDC to look for a possible animal reservoir for the virus in the Fairbanks area.
1. Follow routine precautions to prevent disease transmission between humans and wildlife. 5 These include: a) not handling wild animals, b) preventing wild animals from entering buildings, c) avoiding areas with lots of animal droppings, and d) washing hands regularly.
2. Providers should first rule out other common conditions (e.g., varicella zoster and herpes simplex viruses) before requesting poxvirus testing. If no alternative diagnosis is identified, providers should contact the Section of Epidemiology at 907-269-8000 for assistance in accessing poxvirus testing.
3. Persons with suspected orthopoxvirus lesions should be advised to keep the lesions dry and covered, to not touch them, and to not share with other people towels and other items that might come into contact with the lesion. 6
While there is little reason to suspect that this Alaskapox virus will ever pose a major public health, it is a reminder that nature's laboratory is open 24/7, and we are all participants in an enormous, never-ending, and wholly unsupervised field experiment.