Camelpox virus

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Transmission electron micrograph of camelpox virus particles. Image credit: By Oran Erster, Sharon Melamed, Nir Paran, Shay Weiss, Yevgeny Khinich, Boris Gelman, Aharon Solomony, and Orly Laskar-Levy - Erster, O.; Melamed, S.; Paran, N.; Weiss, S.; Khinich, Y.; Gelman, B.; Solomony, A.; Laskar-Levy, O. First Diagnosed Case of Camelpox Virus in Israel. Viruses 2018, 10, 78. https://doi.org/10.3390/v10020078, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=120787264

Classification

Viruses; Varidnaviria; Bamfordvirae; Nucleocytoviricota; Pokkesviricetes; Chitovirales; Poxviridae; Chordopoxvirinae; Orthopoxvirus

Species

NCBI: [1]

Orthopoxvirus Camelpox virus

Description and Significance

The camelpox virus is the causative agent of camelpox, a disease that targets (you guessed it!) camels. It is very host-specific, but it is possible to infect both primates and humans in some instances. The virus belongs to the genus Orthopoxvirus, which houses other, similar viruses such as Monkeypox, Buffalopox, Cowpox, Rabbitpox, and just about all the other Animalpoxs. Functionally, it has been described as very similar in nature to smallpox — it will bring on fever, lesions on the skin or in the mucous membranes of the mouth or respiratory tract, and generalized infection in targeted hosts. The virus is often lethal, as it will kill roughly only one in four young camels it infects. Older camels tend to be more tolerant and thus are more apt to survive after infection. Though the camelpox virus has likely existed for millenia, discovery was first noted in Punjab, India in 1909, while it was only successfully isolated in 1970. Depending on the region it is cultured in, various strains have arisen that are distinct from the original. Noteworthy strains have been identified in Russia, Kenya, Somalia, Iraq, and Yemen. Evidently, the virus is most present in regions of the world with significant indigenous camel populations — for the same reason, it is absent in northwestern Europe and the Americas. Following its discovery, Camelpox brought on major alarm due to its descriptive similarities to smallpox. The aptly named smallpox eradication programme was launched by the World Health Organization in 1959. It brought on mass vaccinations, extensive education services, and intense surveillance. Though smallpox was the more major threat, the camelpox virus was indirectly targeted and as such has seen a staggering decline in spread in prevalence. The virus is spread through both direct and indirect contact via contaminated environments. There are also the suspected capabilities of insect vectors, as infection is observed to be most prominent after rainfall.

Genome Structure

Camelpox virus (CMLV) is comprised of a single, linear double-stranded DNA molecule that is 205,719 base pairs long. In total, 211 genes are encoded in the CMLV genome, which is highly compacted, with no large non-coding sequences. The CMLV genome, like other poxviruses, has a central coding region flanked by identical inverted terminal repeats that are 7,716 BP long. The coding region contains genes that are important for nucleic acid biogenesis, virion structure and assembly, immune system evasion, and virulence (see Afonso et al. for specific genes). Many of these genes (approximately 96% of them) are highly conserved and found in other orthopoxviruses. Differences are most common in the terminal regions of the CMLV genome, where various insertions, deletions, and translocations are present. These differences likely have an effect on the host range and virulence of CMLV (Afonso et al.). Phylogenetic analysis of CMLV shows that it is well differentiated from other poxviruses, but closely related to variola virus, the causative agent of smallpox.

Cell Structure, Metabolism and Life Cycle

Camelpox virions are brick-shaped and typically 265-295 nm in size. They have an outer membrane covered in tubular proteins. (World Organization for Animal Health, 2021). Internally, the virions contain two lateral bodies that are filled with enzymes essential for virus replication. (Wong, 2018).

The camelpox virus does not maintain its own metabolic system and instead must rely on host cells for energy.

The virus enters a host cell either through endocytosis or by fusing with the plasma membrane. In the cytoplasm, viral genes are uncoated and transcribed by the virus’ RNA polymerase before DNA replication proceeds. Eventually, new virions are assembled in cytoplasmic viral factories before being released through cell lysis. (ViralZone)

Map of Camelpox virus outbreaks. Image credit: Indian J Virol. 2013 Jul 16;24(3):295–305. doi: 10.1007/s13337-013-0145-0

Ecology and Pathogenesis

Skin lesions on infected camels. Image credit: By Oran Erster, Sharon Melamed, Nir Paran, Shay Weiss, Yevgeny Khinich, Boris Gelman, Aharon Solomony, and Orly Laskar-Levy - Erster, O.; Melamed, S.; Paran, N.; Weiss, S.; Khinich, Y.; Gelman, B.; Solomony, A.; Laskar-Levy, O. First Diagnosed Case of Camelpox Virus in Israel. Viruses 2018, 10, 78. https://doi.org/10.3390/v10020078, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=120787265

Camelpox virus is found in many countries with traditions of camel breeding. The virus typically affects only dromedary camels, and not bactrian camels or tylopoda. It has become endemic in many countries, with reports of outbreaks occurring in the Middle East, Africa, and Asia. A seasonal rise in cases during the rainy seasons may be linked to insect vectors (Camelpox).

The camelpox virus causes significant economic impact in the countries in which it is found. It causes high rates of sickness resulting in weight and milk reduction of affected camels and relatively high rates of death in infected camels. In adult camels, the mortality rate is 10-28%, but in young camels, it is 25-100% (Balamurugan, 2013). Death is usually caused by the occurrence of secondary infections or the development of sepsis (Camelpox). If a camel survives infection, it acquires life-long immunity as demonstrated by high levels of antibodies in recovered camels (Balamurugan, 2013).

The typical incubation period is 3-15 days. Initial symptoms include fever, enlarged lymph nodes, and skin lesions. The lesions typically appear on the head, eyelids, nostrils, and ears, but may extend to the neck, limbs, genitalia, and mammary glands. Lesions may also appear in mucous membranes. Post-mortem examinations of infected camels have shown the appearance of internal lesions in the mouth and respiratory tract (Camelpox).

References

Afonso CL, Tulman ER, Lu Z, et al. The genome of camelpox virus. Virology. 2002;295(1):1-9. doi:10.1006/viro.2001.1343

Balamurugan, V. et al. (2013) Camelpox, an emerging orthopox viral disease, Indian journal of virology : an official organ of Indian Virological Society. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC3832703/ (Accessed: 25 November 2024).

Camelpox (2024) Wikipedia. Available at: https://en.wikipedia.org/wiki/Camelpox (Accessed: 25 November 2024).

Camelpox virus, Antiviral research. Available at: https://pubmed.ncbi.nlm.nih.gov/21945248/ (Accessed: 25 November 2024).

Camelpox - an overview | ScienceDirect Topics. Available at: https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/camelpox (Accessed: 25 November 2024).

Camelpox. Available at: https://www.woah.org/fileadmin/Home/fr/Health_standards/tahm/3.05.01_CAMELPOX.pdf (Accessed: 25 November 2024).

Derrick Baxby et al. (2003) Smallpox-like viruses from camels in Iran, The Lancet. Available at: https://www.sciencedirect.com/science/article/pii/S0140673672923434 (Accessed: 25 November 2024).

Smallpox (no date) World Health Organization. Available at: https://www.who.int/health-topics/smallpox (Accessed: 25 November 2024).

World Organization for Animal Health (2021) Chapter 3.5.1., Camelpox. Terrestrial Manual. (pp. 2) Wong, D. Poxviruses. Virology Online. Available at: https://web.archive.org/web/20181015091347/http://virology-online.com/viruses/Poxviruses.htm. (Accessed: 25 November 2024).

Orthopoxvirus. ViralZone. Available at: https://viralzone.expasy.org/149.html?outline=all_by_species. (Accessed: 25 November 2024).

Author

Page authored by Keegan Summitt, Annalise Litterio, Meg Hall, & Zach Creamer, students of Prof. Bradley Tolar at UNC Wilmington.