Ebola (Ebola Virus Disease)
Ebola Virus Disease (EVD) is a rare and deadly disease in people and nonhuman primates. The viruses that cause EVD are located mainly in sub-Saharan Africa. People can get EVD through direct contact with an infected animal (bat or nonhuman primate) or a sick or dead person infected with Ebola virus. Ebola virus disease (EVD), one of the deadliest viral diseases, was discovered in when two consecutive outbreaks of fatal hemorrhagic fever occurred in different parts of Central Africa. The first outbreak occurred in the Democratic Republic of Congo (formerly Zaire) in a village near the Ebola River, which gave the virus its name.
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Nov 01, · Five Ebola virus species within the genus Ebola virus are known, including four that cause EVD in humans (a fifth species has only caused disease in nonhuman primates [NHPs]). 3 The outbreak of EVD in West Africa, caused by Ebola virus (Zaire ebolavirus species), is the largest outbreak of EVD in history. 4. Ebola virus disease – Democratic Republic of the Congo 11 June Ebola virus disease – Operational readiness and preparedness in nine countries . Mar 05, · The last Ebola outbreak in Guinea, which started in , quickly spread to neighbouring Liberia and Sierra Leone. By the time it was finally brought under control, it had become the deadliest Ebola outbreak since the virus was first detected in , with some 28, cases and 11, deaths. Borderline readiness.
Cite This Article. Using histories of household members of Ebola virus disease EVD survivors in Sierra Leone, we calculated risk of EVD by age and exposure level, adjusting for confounding and clustering, and estimated relative risks. Compared with risk for persons 20—29 years of age, exposure-adjusted relative risks were lower for those 5—9 0. Lower risk for 5—year-olds, after adjustment for exposure, suggests decreased susceptibility in this group.
In Ebola epidemics in West Africa and elsewhere, children appear to have been relatively spared 1 — 5. Among children, the World Health Organization has reported a slightly increasing incidence with increasing age in Liberia and Sierra Leone but no clear pattern in Guinea 4.
In contrast, published case-fatality rates for EVD are lowest for persons 10—15 years of age and highest for young children and older adults 4 , 7. These age patterns could result from bias in recognizing, diagnosing, or reporting cases; differences in exposure; or differences in susceptibility to disease.
Official data from the West Africa outbreak are known to be inaccurate 8 , 9. In previous, smaller outbreaks, case ascertainment could have been more complete because of the smaller scale, but EVD cases might have been missed, especially mild cases; deaths may also have been missed because the elderly and very young are more likely to sicken and die from other causes.
Children with fever are less likely than adults to visit health facilities for care, and children may be underreported as contacts Exposure patterns are likely to differ by age and sex.
Women may be more at risk from caring for the sick and men from carrying sick persons to the hospital. Children may be deliberately kept away from sick persons and funeral rites, and lower incidence among children has been attributed to these factors 1 , However, preventing exposure of young children in Ebola-affected households is difficult. Children need to be held, fed, and cared for and often share beds with adults or other children; they may also be exposed through breastfeeding Assessing whether risk by age depends on exposure or susceptibility requires a comparison of exposures in persons with and without EVD.
A recent systematic review of risk factors for transmission of Ebola virus found few studies reporting data on risks 14 and no previous study large enough to stratify in detail by age 3 , 13 , 15 — We interviewed a large cohort of EVD survivors and their household members to determine exposure levels of all members, living and dead, and to calculate attack rates and relative risks by age, sex, and type of exposure.
During July—August , members of the study team, which had assisted in survivor reintegration into the community, contacted survivors or their parents or guardians and asked them to bring all household members who were present at the time Ebola was affecting their household to an interview to be conducted at 1 of various locations.
To make contact, the field team went to addresses of survivors when addresses were available and complete enough to locate or used telephone numbers when available. Team members were university graduates, nurses, and paramedics and included Ebola survivors; they received extensive training in interview techniques and were supervised by the first 2 authors H. Households were defined as persons eating from the same pot at the time EVD was in the household, regardless of how much time had been spent in the household, and included persons who joined the household to assist someone who was ill.
We asked household members to describe in their own words what had occurred in the household. For each person reported as having had EVD, we asked what symptoms occurred at home and which persons had helped that person during his or her EVD illness, shared a bed or had contact with the person, or had contact with the body if the person died.
Adults spoke for young children and corroborated information from older children. Using probing questions and predefined exposure levels, we assigned a maximum exposure for persons who had been present in the household. The levels, which we developed on the basis of the literature and discussion with ETC staff, included touching the corpse of someone who died from EVD; direct contact with body fluids of a wet patient i.
We also asked about exposures outside the home and classified these exposures by using the same scale. For those reported as not having had EVD, we asked about any symptoms at the same time that others in the household had EVD. Deaths for which the family was unsure of the cause and symptomatic persons who were not tested or did not receive a diagnosis of EVD were classified as probable EVD case-patients if they fit the Sierra Leone case definition for probable cases For each household, the first person who became ill was identified as the likely primary case-patient.
Some households reported 2 people who became ill at the same time, and they are counted as co-primary case-patients. To avoid overburdening participants, we did not collect time sequences or dates and defined all nonprimary case-patients in a household as subsequent case-patients.
Our initial descriptive analysis of outcomes by age and sex included all household members. We subsequently analyzed primary case-patients separately because their exposure occurred outside the household, and we compared their characteristics with those of all other household members.
In the analysis of risks for disease by age, sex, and exposure level, we excluded primary case-patients and household members who were alive but not present for the interview and unable to consent to individual data collection. We explored the following variables for their effects on disease risk and as confounders of the associations of other variables and disease risk: having a spouse who contracted EVD first; occupation; being household head versus household member; and household-level variables i.
Our analysis used logistic regression and adjusted for household clustering by using random effects. We also performed a sensitivity analysis that excluded case-patients and deaths classified as probable EVD cases. Figure 1. EVD, Ebola virus disease. We collected detailed information for persons, including exposure histories for Figure 1. Figure 2. Because most probable case-patients were children, the lower risk for children was more extreme when probable case-patients were excluded Table 2.
EVD risk was similar for male and female study participants, even when results were stratified by age Figure 2 , panel B. Primary case-patients were identified for 91 households and co-primary case-patients in 3 households.
Children or students were least likely to be primary case-patients. In 5 households, primary case-patients joined the household when they were already ill. Thirty primary case-patients visited a household with an EVD patient; 16 of those 30 went to help the ill patient. Eight prepared bodies for burial or touched the corpse; 6 attended funerals; 4 carried a person with EVD symptoms; 8 attended healthcare facilities; and 12 worked as healthcare or front-line workers, 5 of whom were known to have treated an EVD patient.
Only 10 1. Figure 3. Levels of exposure to Ebola virus disease among households of Kerry Town survivors, excluding primary case-patients, by age and sex, Sierra Leone, — A Male participants; B female participants. Levels of Attack rates increased steeply and linearly with the predefined exposure levels. After adjustment for age and sex, attack rates varied by occupation and were higher in larger and more crowded households.
We found no clear associations with household-level measures of sanitation nor with having a spouse who developed EVD first Table 4.
Sex was kept in the model a priori but was not associated with EVD risk. In the full model, the association with age was still J-shaped. The lowest risk was for persons 5—19 years of age, and risks were higher for older than younger adults.
Additional adjustment for other available variables had little effect on associations. In the sensitivity analysis that excluded probable EVD cases, associations with exposure levels were stronger, and the J-shaped association with age was more marked Table 5. This pattern was similar whether probable case-patients were included or not. Children were less likely than adults to be primary case-patients, and among child primary case-patients, no particular trend by age was observed Table 3.
Our study included only survivor households because it was conducted by building on survivor-support links; consequently, it missed households with only fatal cases and those in which no one sought care. These characteristics would tend to increase attack rates and may explain the high attack rate overall and the association of attack rate with household size.
After excluding primary case-patients, we examined the extent to which age patterns could be explained by exposure levels. After we adjusted age-specific incidence data by exposure, children 5—19 years of age still had a lower risk for EVD, although the lower risk was less marked, and the increased risk with age for adults no longer plateaued but continued upward.
If we measured exposure accurately, these findings suggest that some of the variation in risk by age within households results from differences in susceptibility. Instead, we encouraged families to tell their stories, ensuring that we learned which household members had contact with each EVD patient and what type of contact.
Consequently, the conversation flowed naturally, with different household members contributing and providing details, helping to minimize recall bias. This approach also enabled us to acquire details for children and for persons who had died, although use of proxy respondents may have limited accuracy of exposure measurement. We conducted the interviews 4—9 months after the illness, but participants provided considerable detail in their responses.
Inaccuracies in recall would lead to a failure to adjust completely for exposure level, whereas any tendency to recall greater exposures for household members with EVD would increase the association with exposure and result in the association between age and EVD being overadjusted for exposure level. We predefined exposure levels so that we could record only the highest level and not probe for details for possible lower levels. This approach differed from that of other studies 13 , 14 , 16 , which recorded several exposures and adjusted during analysis.
Our hierarchy of exposure appears to be accurate; we found strong correlations between EVD risk and each increase in exposure level. As others have reported 13 , 14 , 16 , the highest risk for EVD exposure was from contact with dead bodies. Risk was also high from direct contact with fluids and with wet patients and was lower but still considerable 5-fold [fold in the sensitivity analysis], compared with minimal risk from direct contact with dry patients and indirect contact with wet patients Tables 4 , 5.
We found no discernible increase in risk from indirect contact with dry patients compared with exposures classified as minimal risk Table 1. Overall, after exclusion of primary and co-primary case-patients, we found a high household attack rate, higher than found in previous studies 23 , perhaps reflecting the urban setting and the bias toward households with multiple cases.
A lower susceptibility to EVD among children is possible. Lower attack rates or case-fatality rates in children have been found for other viral diseases, including varicella 24 , smallpox 25 , and West Nile virus disease For EVD, different cytokine and chemokine responses related to survival have been noted for adults and children We found little difference in risk by sex, even when stratified by age.
Household-level measures of sanitation had surprisingly little effect on the outcome Having a spouse who contracted EVD first was not a risk factor after we adjusted for age; consequently, sexual transmission did not appear to be an important factor in the acute phase.
Although some were linked to high-risk activities, more were related to visits to friends and relatives, including some visits to nurse sick relatives. Other households were infected by taking in sick relatives. These activities show remarkable altruism at a stage of the epidemic when Ebola was well known. More support to families to protect themselves in the home when they helped those not known to have EVD might have prevented these transmissions. Much of what we know about risks for Ebola virus transmission comes from anecdotal reports or case series Few studies have measured risk associated with particular exposures directly 13 , 15 , 16 , 18 , 23 , and none have been large enough to examine risk by age in detail.
After we adjusted for exposure, age patterns for Ebola attack rates were similar to those for case-fatality rates. Inherent differences in susceptibility, which warrant further investigation, likely underlie both distributions. Her research interests include emerging infectious diseases and humanitarian emergencies. Table of Contents — Volume 22, Number 8—August