Ebola Virus Disease (EVD)

Bats are reservoirs for a wide range of human pathogens including Nipah, Hendra, rabies, Ebola, Marburg and severe acute respiratory syndrome coronavirus (CoV). The recent implication of a novel beta (β)-CoV as the cause of fatal respiratory disease in the Middle East emphasizes the importance of surveillance for CoVs that have potential to move from bats into the human population. In a screen of 606 bats from 42 different species in Campeche, Chiapas and Mexico City we identified 13 distinct CoVs. Nine were alpha (α)-CoVs; four were β-CoVs. Twelve were novel. Analyses of these viruses in the context of their hosts and ecological habitat indicated that host species is a strong selective driver in CoV evolution, even in allopatric populations separated by significant geographical distance; and that a single species/genus of bat can contain multiple CoVs. A β-CoV with 96.5 % amino acid identity to the β-CoV associated with human disease in the Middle East was found in a Nyctinomops laticaudatus bat, suggesting that efforts to identify the viral reservoir should include surveillance of the bat families Molossidae/Vespertilionidae, or the closely related Nycteridae/Emballonuridae. While it is important to investigate unknown viral diversity in bats, it is also important to remember that the majority of viruses they carry will not pose any clinical risk, and bats should not be stigmatized ubiquitously as significant threats to public health.

The nucleotide sequences of the L gene and 5′ trailer region of Ebola virus strain Mayinga (subtype Zaire) have been determined, thus completing the sequence of the Ebola virus genome. The putative transcription start signal of the L gene was identical to the determined 5′ terminus of the L mRNA (5′ GAGGAAGAUUAA) and showed a high degree of similarity to the corresponding regions of other Ebola virus genes. The 3′ end of the L mRNA terminated with 5′ AUUAUAAAAAA, a sequence which is distinct from the proposed transcription termination signals of other genes. The 5′ trailer sequence of the Ebola virus genomic RNA consisted of 676 nt and revealed a self-complementary sequence at the extreme end which may play an important role in virus replication. The L gene contained a single ORF encoding a polypeptide of 2212 aa. The deduced amino acid sequence showed identities of about 73 and 44% to the L proteins of Ebola virus strain Maleo (subtype Sudan) and Marburg virus, respectively. Sequence comparison studies of the Ebola virus L proteins with several corresponding proteins of other non-segmented, negative-strand RNA viruses, including Marburg viruses, confirmed a close relationship between filoviruses and members of the Paramyxovirinae. The presence of several conserved linear domains commonly found within L proteins of other members of the order Mononegavirales identified this protein as the RNA-dependent RNA polymerase of Ebola virus.