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MERS-CoV
MERS-CoV particles as seen by negative stain electron microscopy. Virions contain characteristic club-like projections emanating from the viral membrane.
MERS-CoV particles as seen by negative stain electron microscopy. Virions contain characteristic club-like projections emanating from the viral membrane.
Virus classification
Group: Group IV ((+)ssRNA)
Order: Nidovirales
Family: Coronaviridae
Subfamily: Coronavirinae
Genus: Betacoronavirus
Species: MERS-CoV

Overview

Ten years after the outbreak of SARS-CoV, the MERS-CoV is identified as the agent of a lethal pneumonia in patients who have recently been related to the Arabian Peninsula. The Middle east respiratory syndrome coronavirus (MERS-CoV), also termed EMC/2012 (HCoV-EMC/2012), is positive-sense, single-stranded RNA novel species of the genus Betacoronavirus.[1][2]

First called novel coronavirus 2012 or simply novel coronavirus, it was first reported in 2012 after genome sequencing of a virus isolated from sputum samples from patients, in a 2012 outbreak of a "new flu".

As of 14 May 2014, several MERS-CoV cases have been reported in different countries, including Saudi Arabia, Malaysia, Jordan, Qatar, Egypt, the United Arab Emirates, Tunisia, Kuwait, Oman, Algeria, Bangladesh, the United Kingdom and the United States.[3]

Virology

The Middle East respiratory syndrome coronavirus (MERS-CoV) is an emerging type of coronavirus, specifically a betacoronavirus of the lineage C. Attending to the phylogenetic classification, the MERS-CoV is classified into two clades - clade A and clade B. Initially, the reported cases of MERS-CoV were clade A clusters, however, recently reported cases are genetically distinct, including clade B clusters.[4]

Until May 23rd 2013, MERS-CoV was being described as a SARS-like virus or colloquially as "Saudi SARS. Since then it is known to be distinct, not only from SARS-CoV, but also from other known endemic coronaviruses, such as betacoronavirus HCoV-OC43 and HCoV-HKU1, as well as from the common cold coronavirus.[5]

Origin

The first reported case of a human infected by MERS-CoV was in September 2012, in Saudi Arabia. This patient developed a lethal infection marked by a severe pneumonia and renal failure. However, some reports claim that the infection might have occurred first in a family from Jordan in April 2012. The virus was first isolated by an egyptian physician, while he was examining the lungs of a previously unknown MERS-CoV infected patient. The isolated infected cells showed cytopathic effect with syncytia formation and noted rounding.[6][7][8][9]

In September 2012, a second case was reported in a 49 year old man in Qatar. This patient presented with flu-like symptoms and the viral sequence was proved to be similar to the one from the first case. In November of the same year, identical cases kept appearing in Saudi Arabia and Qatar, with associated deaths.

Up until now it hasn't been determined if the infections were the result of a zoonotic event, with further human-to-human transmission or if they were a case of multiple zoonotic events from a common source. A study from the Riyadh University has suggested that, since the the virus first appeared, there may have been 7 different zoonotic transmissions. Although there is still limited data, it has been noted that the coronavirus has a large genetic diversity among animal reservoirs, yet the sample analysis of the infected patients suggests a common genome and therefore source. Since this early period, several clusters of infection have been created, suggesting that a human-to-human transmission has occurred.[2]

Molecular clock analysis studies have determined that the viruses from the EMC/2012 and from England/Qatar/2012 date from 2011. This suggests, not only a single zoonotic event as source of the reported cases, possibly implying that the MERS-CoV has been present asymptomatically in the human population for longer than one year without being detected, but also that it might have had an independent transmission from an unidentified source.[10][11]

Tropism

Studies have shown that in humans, unlike most viruses that tend to infect ciliated cells, MERS-CoV has a strong tropism for the nonciliated bronchial epithelium. Also, it has been noted that the virus has the capacity to evade the innate immune system and inhibit interferon production.[12][13]

It took only 6 months for the MERS-CoV receptor to be identified and published. Initially, due to the similarityies between the MERS-CoV and the SARS-CoV, it was proposed that the MERS-CoV would use the same cellular receptor for infection, as the SARS-CoV, namely the angiotensin converting enzyme 2.[2][14][15] However, the cellular receptor for MERS-CoV was later identified as being the dipeptidyl peptidase 4 (DDP4) or CD26.[13] The DPP4 receptor is an ectopeptidase, which is similar to other molecules that other coronaviruses use to infect cells, such as the human angiotensin-converting enzyme 2, for SARS-CoV, and the aminopeptidade N, for alphacoronaviruses. The amino acid sequence of this receptor is a highly conserved sequence across species, being expressed in human bronchial epithelium and kidneys, and its enzymatic activity is not required for the process of infection.[13][16] When comparing the receptor for MERS-CoV with the one for SARS-CoV, it is important to notice that both are shed of the cell surface after the respective infections. In the case of SARS-CoV, the loss of this receptor leads to the worsening of the condition, evolving to a more severe pulmonary disease. On the other hand, DDP4 is a neutrophil chemorepellent and its loss from the cell surface leads to cellular changes that may alter the composition of the immune cell infiltrate, which may consequently alter the evolution of the infectious state.[2][17][18][19]

Transmission

Since may 29th 2013, the WHO has warned that the MERS-CoV should be considered a "threat to the entire world".[2] Transmission of MERS-CoV is prone to occur in immunocompromised patients, or in patients with other comorbidities, such as diabetes or renal failure.[2] In a study of 23 patients of the largest outbreak so far, in Saudi Arabia, was determined that 74% had underlying diabetes mellitus, 52% renal disease and 43% lung disease, highlighting the impact of underlying comorbidities in the overall risk of infection with MERS-CoV. This evidence is further supported by the fact that cases of infected family members and health-care workers was only reported in 1 to 2% of contacts.[2][20]

At the present time it is not known the stage at which an infected MERS-CoV patient becomes contagious, if he is able to transmit the virus while there is still no evidence respiratory illness, or if there is transmission only after symptom onset. If the first is correct, then the the control of a larger outbreak will be more challenging, considering the prevalence of global traveling nowadays.[2]

One of the major gaps of knowledge about this virus is that its prevalence in the community is not known, therefore, and since most of the identified cases were patients with underlying comorbidities, there is a possibility of MERS-CoV to be a common infection in Saudi-Arabia, with which patients without these comorbidties only develop minor respiratory symptoms or are asymptomatic.[2]

Natural reservoir

Early research suggested the virus is related to one found in the Egyptian tomb bat. In September 2012 Ron Fouchier speculated that the virus might have originated in bats.[21] Work by epidemiologist Ian Lipkin of Columbia University in New York showed that the virus isolated from a bat looked to be a match to the virus found in humans.[22][23] [24] 2c betacoronaviruses were detected in Nycteris bats in Ghana and Pipistrellus bats in Europe that are phylogenetically related to the MERS-CoV virus.[25]

Recent work links camels to the virus. An ahead-of-print dispatch for the journal Emerging Infectious Diseases records research showing the coronavirus infection in dromedary camel calves and adults, 99.9% matching to the genomes of human clade B MERS-CoV.[26]

At least one person who has fallen sick with MERS was known to have come into contact with camels or recently drank camel milk.[27]

On 9 August 2013, a report in the journal The Lancet Infectious Diseases showed that 50 out of 50 (100%) blood serum from Omani camels and 15 of 105 (14%) from Spanish camels had protein-specific antibodies against the MERS-CoV spike protein. Blood serum from European sheep, goats, cattle, and other camelids had no such antibodies.[28] Countries like Saudi Arabia and the United Arab Emirates produce and consume large amounts of camel meat. The possibility exists that African or Australian bats harbor the virus and transmit it to camels. Imported camels from these regions might have carried the virus to the Middle East.[29]

In 2013 MERS-CoV was identified in three members of a dromedary camel herd held in a Qatar barn, which was linked to two confirmed human cases who have since recovered. The presence of MERS-CoV in the camels was confirmed by the National Institute of Public Health and Environment (RIVM) of the Ministry of Health and the Erasmus Medical Center (WHO Collaborating Center), the Netherlands. None of the camels showed any sign of disease when the samples were collected. The Qatar Supreme Council of Health advised in November 2013 that people with underlying health conditions, such as heart disease, diabetes, kidney disease, respiratory disease, the immunosuppressed, and the elderly, avoid any close animal contacts when visiting farms and markets, and to practice good hygiene, such as washing hands.[30]

A further study on dromedary camels from Saudi Arabia published in December 2013 revealed the presence of MERS-CoV in 90% of the evaluated dromedary camels (310), suggesting that dromedary camels not only could be the main reservoir of MERS-CoV, but also the animal source of MERS.[31]

According to the 27 March 2014 MERS-CoV summary update, recent studies support that camels serve as the primary source of the MERS-CoV infecting humans, while bats may be the ultimate reservoir of the virus. Evidence includes the frequency with which the virus has been found in camels to which human cases have been exposed, seriological data which shows widespread transmission in camels, and the similarity of the camel CoV to the human CoV.[32]

On 6 June 2014, the Arab News newspaper highlighted the latest research findings in the New England Journal of Medicine in which a 44-year-old Saudi man who kept a herd of nine camels died of MERS in November 2013. His friends said they witnessed him applying a topical medicine to the nose of one of his ill camels--four of them reportedly sick with nasal discharge--seven days before he himself became stricken with MERS. Researchers sequenced the virus found in one of the sick camels and the virus that killed the man, and found that their genomes were identical. In that same article, the Arab News reported that as of 6 June 2014, there have been 689 cases of MERS reported within the Kingdom of Saudi Arabia with 283 deaths.[33]

Taxonomy

MERS-CoV is more closely related to the bat coronaviruses HKU4 and HKU5 (lineage 2C) than it is to SARS-CoV (lineage 2B) (2, 9), sharing more than 90% sequence identity with their closest relationships, bat coronaviruses HKU4 and HKU5 and therefore considered to belong to the same species by the International Committee on Taxonomy of Viruses (ICTV).

Viruses
› ssRNA viruses
› Group: IV; positive-sense, single-stranded RNA viruses
› Order: Nidovirales
› Family: Coronaviridae
› Subfamily: Coronavirinae
› Genus: Betacoronavirus[35]
› Species: Betacoronavirus 1 (commonly called Human coronavirus OC43), Human coronavirus HKU1, Murine coronavirus, Pipistrellus bat coronavirus HKU5, Rousettus bat coronavirus HKU9, Severe acute respiratory syndrome-related coronavirus, Tylonycteris bat coronavirus HKU4, MERS-CoV

Strains:

  • Isolate:
  • Isolate:
  • NCBI

Microbiology

The virus grows readily on Vero cells and LLC-MK2 cells.[37]

Research and patent

Saudi officials had not given permission to Dr. Zaki to send a sample of the virus to Fouchier and they were angered when Fouchier claimed the patent on the full genetic sequence[38] of the Middle East respiratory syndrome coronavirus.[38]

The editor of The Economist observed, "Concern over security must not slow urgent work. Studying a deadly virus is risky. Not studying it is riskier."[38] Dr. Zaki was fired from his job at the hospital as a result of sharing his sample and findings.[39][40][41][42]

At their annual meeting of the World Health Assembly in May 2013, WHO chief Margaret Chan declared that intellectual property, or patents on strains of new virus, should not impede nations from protecting their citizens by limiting scientific investigations. Deputy Health Minister Ziad Memish raised concerns that scientists who held the patent for the MERS-CoV virus would not allow other scientists to use patented material and were therefore delaying the development of diagnostic tests.[43] Erasmus MC responded that the patent application did not restrict public health research into MERS coronavirus,[44] and that the virus and diagnostic tests were shipped—free of charge—to all that requested such reagents.

Corona Map

There are a number of mapping efforts focused on tracking MERS coronavirus. On 2 May 2014, the Corona Map was launched to track the MERS coronavirus in realtime on the world map. The data is officially reported by WHO or the Ministry of Health of the respective country.[45] HealthMap also tracks case reports with inclusion of news and social media as data sources as part of HealthMap MERS.

See also

References

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  15. Muller, M. A.; Raj, V. S.; Muth, D.; Meyer, B.; Kallies, S.; Smits, S. L.; Wollny, R.; Bestebroer, T. M.; Specht, S.; Suliman, T.; Zimmermann, K.; Binger, T.; Eckerle, I.; Tschapka, M.; Zaki, A. M.; Osterhaus, A. D. M. E.; Fouchier, R. A. M.; Haagmans, B. L.; Drosten, C. (2012). "Human Coronavirus EMC Does Not Require the SARS-Coronavirus Receptor and Maintains Broad Replicative Capability in Mammalian Cell Lines". mBio. 3 (6): e00515–12–e00515–12. doi:10.1128/mBio.00515-12. ISSN 2150-7511.
  16. "Receptor for new coronavirus found". nature.com. 2013-03-13. Retrieved 2013-03-18.
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  18. Lambeir AM, Durinx C, Scharpé S, De Meester I (2003). "Dipeptidyl-peptidase IV from bench to bedside: an update on structural properties, functions, and clinical aspects of the enzyme DPP IV". Crit Rev Clin Lab Sci. 40 (3): 209–94. doi:10.1080/713609354. PMID 12892317.
  19. Herlihy SE, Pilling D, Maharjan AS, Gomer RH (2013). "Dipeptidyl peptidase IV is a human and murine neutrophil chemorepellent". J Immunol. 190 (12): 6468–77. doi:10.4049/jimmunol.1202583. PMC 3756559. PMID 23677473.
  20. Assiri, Abdullah; McGeer, Allison; Perl, Trish M.; Price, Connie S.; Al Rabeeah, Abdullah A.; Cummings, Derek A.T.; Alabdullatif, Zaki N.; Assad, Maher; Almulhim, Abdulmohsen; Makhdoom, Hatem; Madani, Hossam; Alhakeem, Rafat; Al-Tawfiq, Jaffar A.; Cotten, Matthew; Watson, Simon J.; Kellam, Paul; Zumla, Alimuddin I.; Memish, Ziad A. (2013). "Hospital Outbreak of Middle East Respiratory Syndrome Coronavirus". New England Journal of Medicine. 369 (5): 407–416. doi:10.1056/NEJMoa1306742. ISSN 0028-4793.
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  28. Template:Cite doi
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  44. "Corona Map" (Press release). 2 May 2014.

External links

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