2 . PATHOGENESIS

  PATHOGENESIS

Ebola viruses have all been associated with hemorrhagic fever in humans and/or non-human primates with differences in pathogenicity. Based on available evidence, the REBOV strain is fatal in macaques although it has a lower-case fatality rate than ZEBOV. It is unclear whether REBOV infection in domestic pigs in the Philippines resulted in clinical symptoms in this species. Several animal handlers manipulating monkeys in Reston (USA) or pigs in Manilla (Philippines) have developed antibodies to REBOV while remaining asymptomatic. It is thus presumed that REBOV has a low pathogenicity or is non-pathogenic in humans whilst the ZEBOV and SEBOV strains are known for their virulence and high case fatality rate (53 -90%) in humans.

 OCCURRENCE

Up to 2013, EVD occurred mainly in the rainforest areas of Central Africa (DRC, Sudan, Gabon, and Uganda). West Africa has only known to be affected by a limited episode in Tai Forest ebolavirus (TEBOV) in Ivory Coast in 1994. The severe epidemics, starting in 2013-14, affect a large West African region (Guinea, Sierra Leone, and Liberia) with imported cases in Nigeria and Senegal. Another alarming event is that the epidemics penetrate densely populated areas including capital cities.

Evidence for REBOV infection has been found in Asia (China, the Philippines).

 Field studies and epidemiological surveys in Africa have demonstrated widespread antibody prevalence to Ebolaviruses in fruit bats suggesting that fruit bats may be natural hosts for EBOV. A recent survey also mentioned the hypothesis of insectivorous bats role (this need to be confirmed). However, when bats and other vertebrate species were experimentally inoculated, only fruit bats became infected and shed virus in faeces without showing any clinical signs.

Monkeys are not considered as natural hosts because of their high sensitivity to the virus and their high mortality rate when infected.

The related Marburg virus has been isolated from fruit bats (Rousettus aegyptiacus) in Uganda.

The role of pigs in EVD epidemiology is unclear. There is no evidence that domestic animals play an active epidemiological role in the transmission of the disease to humans.