Ebola viruses are highly virulent zoonoses affecting both humans and nonhuman primates. The virus contains a single-strand linear RNA of 18-19 kb encoding seven genes (NP, VP35, VP40, VP30, VO24 and GP).
Furthermore, five genetically distinct species are known for it, including: Zaire Ebola virus (ZEBOV), Sudan Ebola virus (SEBOV), Cote d'Ivoire Ebola virus, Bundibugyo Ebola virus (BEBOV) and Reston Ebola virus (REBOV) with different genomic sequence, genomic overlap number and location, and virulence. REBOV can only affect nonhuman primates, while the other four versions are responsible for Ebola hemorrhagic fever (EHF) breakouts.
Ebola outbreaks have occurred every 1.5 years for a total of seven prior events with more than 100 reported cases. The most recent outbreak before 2014 occurred in 2012 with a fatality rate of 46.8 percent. The latest outbreak began in Guinea in December 2013 and spread to Sierra Leone, Liberia and Nigeria with a fatality rate of 54 percent.
Fruit bats have been reported to be the normal carrier in nature. The virus is generally transmitted from wildlife to people through contact with bats or intermediate hosts, including monkeys, apes and pigs. However, it is only transmitted through direct contact with blood or body fluids (saliva, breast milk, urine, semen, sweat, stool, tears).
Through careful monitoring of fever among persons who have visited or come into contact with confirmed Ebola patients, the outbreak transmission can be contained. As a result, patients suspected of presenting Ebola-type symptoms should be quarantined.
The basic reproductive number (the average number of secondary infections generated by one primary case in an entirely susceptible population) is reported to be 2.7 for Ebola. The number appears to be high, but the effective reproduction number can be lowered to 0.3-0.4 if necessary interventions are performed on a timely manner. In disease epidemiology, the reproductive numbers less than 1 are referred to as an impossible transmission of the disease from the patient to another individual during the infection period.
On the other hand, even after recovery, the virus may still be found in the body fluids of the patient for an extended period of time (many months). Therefore, it is important that the patient can be released out of quarantine only after confirming that the virus is no longer present.
There are no approved antiviral drugs or vaccines against these viruses, partly due to a lack of knowledge about the virus's biological action as well as its high virulence. Any Ebola virus handling should be performed in biosafety level 4 (BSL-4) laboratories, of which there are only 21 available worldwide. This is a standalone building that contains designated shower rooms with entry only allowed upon wearing a positive-pressure personal protection suit equipped with a segregated air supply.
However, prevention along with a strong focus on clinical management of additive care for complications — such as hypovolemia, electrolyte abnormalities, hematologic abnormalities, refractory shock, hypoxia, hemorrhage, septic shock, multiorgan failure and disseminated intravenous coagulation — can go a long way. Furthermore, proper diagnosis, adequate training in specialty care units, adequate properly trained medical staff, along with adequate personal protective equipment and proper use of it, can make a big difference.
The diagnostic tests available for this virus include enzyme-linked immunosorbent assay (ELISA), IgM ELISA, polymerase chain reaction (PCR) and virus isolation that could be helpful within a few days after the start of the symptoms. IgM and IgG antibodies can help later in the disease course or after the recovery, and immunohistochemistry testing, PCR and virus isolation are retrospectively used in deceased patients.
The prevention of an Ebola outbreak requires us to invest in understanding the disease epidemiology in more detail. There are certain questions that remain unaddressed at this time. However, there is a pressing need to address them as soon as possible, because we will have other outbreaks to come.
Some of these questions include: the role of aerosol transmission (large droplets, small particles adjacent to the source patients), the role of environmental contamination, the degree of transmission by minimally or moderately ill patients, and length of persistence for the clinically relevant infection. Furthermore, many experts and research institutes consider the Ebola virus as a potential biological weapon.
