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Mokola virus (MOKV) is a RNA virus related to the Rabies virus that has been sporadically isolated from mammals across sub-Saharan Africa. The majority of isolates have come from domestic cats exhibiting symptoms characteristically associated to Rabies virus infection.

There have been two reported cases of humans being infected with Mokola virus.

Classification

Mokola virus (MOKV) is a member of the Lyssavirus genus, which belongs to the family Rhabdoviridae. MOKV is one of four Lyssavirus species found in Africa. The other three species are the classic Rabies virus, the Duvenhage virus and the Lagos bat virus.

Emergence

MOKV was first isolated in Nigeria, in 1968, from three shrews (Crocidura species) found in the Mokola forest. The virus was shown to be morphologically and serologically related to Rabies virus. Since the initial isolation of MOKV, the virus has been mainly isolated in domestic cats and small mammals in sub-Saharan Africa.

There have been two recorded cases of human infection with MOKV, with both instances occurring in Nigeria. Both cases involved young Nigerian females. The first patient, who had been suffering from a fever and convulsions, recovered fully from infection. The second case, which occurred in 1972, involved a 6-year-old girl who had been suffering from drowsiness. The second patient ultimately suffered from paralysis and a terminal coma as a result of the MOKV infection.

The origin of the MOKV in both human cases of MOKV infection remains unidentified.

Genome and structure

The MOKV genome comprises a non-segmented, single-stranded, negative-sense RNA molecule of 11,939 nucleotides in length. It is estimated that 90.3% of the MOKV genome consists of protein-encoding or signal-encoding sequences.

The genome encodes five proteins: matrix protein M; transmembrane glycoprotein G; nucleoprotein N; phosphoprotein P; and the RNA-dependent RNA polymerase L.

MOKV is an enveloped virus, with the envelope lined with spikes consisting of the viral protein G. MOKV exhibits the 'bullet-shaped' morphology that is characteristic of members of the Rhabdoviridae family.

Evolution

This virus appears to have evolved between between 279 and 2034 before the present.

Transmission

The human cases of human MOKV infection have demonstrated the zoonotic potential of MOKV but as a natural reservoir has yet to be identified, transmission of the virus is poorly understood. Considering the MOKV isolates from small mammals and domestic cats; it has been suggested that small mammals, which are preyed upon by domestic cats, may be the natural MOKV reservoir.

Unlike other Lyssavirus species, MOKV is able to replicate inside mosquito cells in vitro, suggesting that insects may be implicated in MOKV transmission.

Pathology

Symptoms provoked by MOKV infection are very similar to the symptoms associated with Rabies virus infection, such as fever and headaches for example. Ultimately both MOKV and Rabies virus infection can lead to death by encephalitis. The similarity between the symptoms associated with MOKV and Rabies virus may be the reason why there have been so few cases of recorded MOKV infections. MOKV infections may be being falsely diagnosed as Rabies virus infections.

There is one significant difference between the symptoms observed in domestic cats infected with MOKV and Rabies virus. MOKV-infected domestic cats do not demonstrate the aggressive, unprovoked behaviour traits typically associated with Rabies virus-infected mammals.

Control

At present there is no medical or veterinary vaccine that protects against MOKV infection. It has long been established that in spite of the relatedness between MOKV and Rabies virus, immunisation with the rabies vaccine does not confer protection to MOKV infection. Isolation of MOKV from a number of domestic cats vaccinated with the rabies vaccine have demonstrated this fact.

In order to neutralize Rabies virus, the rabies vaccine targets the transmembrane glycoprotein G on the viral envelope. Variation in the amino acid sequences of the antigenic domain III within protein G between Rabies virus and MOKV has rendered the rabies vaccine ineffective against MOKV infection.

References

1. Von Teichman, B. F.; de Koker, W. C.; Bosch, S. J. E.; Bishop, G. C.; Meredith, C. D.; Bingham, J. (2012). "Mokola virus infection: description of recent South African cases and a review of the virus epidemiology: case report". Journal of the South African Veterinary Association. 69 (4): 169–171. {{cite journal}}: Cite has empty unknown parameter: |month= (help)CS1 maint: multiple names: authors list (link)
2. Familusi, J. B.; Moore, D. L. (1972). "Isolation of a Rabies Related Virus from the Cerebrospinal Fluid of a Child with 'Aseptic Meningitis'". African Journal of Medical Science. 3 (1): 93–96. PMID 5061272. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
3. Familusi, J. B.; Osunkoya, B. O.; Moore, D. L.; Kemp, G. E.; Fabiyi, A. (1972). "A Fatal Human Infection with Mokola Virus". American Journal of Tropical Medicine and Hygiene. 21 (6): 959–963. PMID 4635777. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
4. Von Teichman, B. F.; de Koker, W. C.; Bosch, S. J. E.; Bishop, G. C.; Meredith, C. D.; Bingham, J. (2012). "Mokola virus infection: description of recent South African cases and a review of the virus epidemiology: case report". Journal of the South African Veterinary Association. 69 (4): 169–171. {{cite journal}}: Cite has empty unknown parameter: |month= (help)CS1 maint: multiple names: authors list (link)
5. Nel, L. H. "MOKOLA VIRUS: A BRIEF REVIEW OF THE STATUS QUO" (PDF). Retrieved 22 March 2013.
6. Familusi, J. B.; Moore, D. L. (1972). "Isolation of a Rabies Related Virus from the Cerebrospinal Fluid of a Child with 'Aseptic Meningitis'". African Journal of Medical Science. 3 (1): 93–96. PMID 5061272. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
7. Familusi, J. B.; Osunkoya, B. O.; Moore, D. L.; Kemp, G. E.; Fabiyi, A. (1972). "A Fatal Human Infection with Mokola Virus". American Journal of Tropical Medicine and Hygiene. 21 (6): 959–963. PMID 4635777. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
8. Von Teichman, B. F.; de Koker, W. C.; Bosch, S. J. E.; Bishop, G. C.; Meredith, C. D.; Bingham, J. (2012). "Mokola virus infection: description of recent South African cases and a review of the virus epidemiology: case report". Journal of the South African Veterinary Association. 69 (4): 169–171. {{cite journal}}: Cite has empty unknown parameter: |month= (help)CS1 maint: multiple names: authors list (link)
9. Le Mercier, P.; Jacob, Y.; Tordo, N. (1997). "The complete Mokola virus genome sequence: structure of the RNA-dependent RNA polymerase". Journal of general virology. 78 (7): 1571–1576. {{cite journal}}: Cite has empty unknown parameter: |month= (help)CS1 maint: multiple names: authors list (link)
10. Le Mercier, P.; Jacob, Y.; Tordo, N. (1997). "The complete Mokola virus genome sequence: structure of the RNA-dependent RNA polymerase". Journal of general virology. 78 (7): 1571–1576. {{cite journal}}: Cite has empty unknown parameter: |month= (help)CS1 maint: multiple names: authors list (link)
11. Nel, L. H. "MOKOLA VIRUS: A BRIEF REVIEW OF THE STATUS QUO" (PDF). Retrieved 22 March 2013.
12. Nel, L. H. "MOKOLA VIRUS: A BRIEF REVIEW OF THE STATUS QUO" (PDF). Retrieved 22 March 2013.
13. Kgaladi J, Wright N, Coertse J, Markotter W, Marston D, Fooks AR, Freuling CM, Müller TF, Sabeta CT, Nel LH (2013) Diversity and epidemiology of mokola virus. PLoS Negl Trop Dis 7(10):e2511. doi: 10.1371/journal.pntd.0002511
14. Familusi, J. B.; Moore, D. L. (1972). "Isolation of a Rabies Related Virus from the Cerebrospinal Fluid of a Child with 'Aseptic Meningitis'". African Journal of Medical Science. 3 (1): 93–96. PMID 5061272. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
15. Familusi, J. B.; Osunkoya, B. O.; Moore, D. L.; Kemp, G. E.; Fabiyi, A. (1972). "A Fatal Human Infection with Mokola Virus". American Journal of Tropical Medicine and Hygiene. 21 (6): 959–963. PMID 4635777. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
16. Sabeta, C.T.; Markotter, W.; Mohale, D.K.; Shumba, W.; Wandeler, A.I.; Nel, L.H. (2007). "Mokola virus in domestic mammals, South Africa". Emerging Infectious Diseases. 13 (9): 1371–1373. doi:10.3201/eid1309.070466. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
17. Aitken, T. H.; Kowalski, R. W.; Beaty, B. J.; Buckley, S. M.; Wright, J. D.; Shope, R. E.; Miller, B. R. (1984). "Arthropod Studies with Rabies-Related Mokola Virus". American Journal of Tropical Medicine and Hygiene. 33 (5): 945–952. PMID 6385743. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
18. Von Teichman, B. F.; de Koker, W. C.; Bosch, S. J. E.; Bishop, G. C.; Meredith, C. D.; Bingham, J. (2012). "Mokola virus infection: description of recent South African cases and a review of the virus epidemiology: case report". Journal of the South African Veterinary Association. 69 (4): 169–171. {{cite journal}}: Cite has empty unknown parameter: |month= (help)CS1 maint: multiple names: authors list (link)
19. Nel, L. H. "MOKOLA VIRUS: A BRIEF REVIEW OF THE STATUS QUO" (PDF). Retrieved 22 March 2013.
20. Nel, L. H. "MOKOLA VIRUS: A BRIEF REVIEW OF THE STATUS QUO" (PDF). Retrieved 22 March 2013.

• Lyssaviruses