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DRC Ebola Outbreak 2019 Blog 5 Screening and Undetected Ebola virus Carriers
The World Health Organization Disease Outbreak Network (WHO DON) internet site is an archive where readers can access the latest information on EID outbreaks. Commenting on the North Kivu and Ituri Ebola outbreak, the WHO DON publication Risk Assessment Section previously classified the areas geographically near an Ebola outbreak as “high-risk zones” and the areas distant from an outbreak as “low-risk zones” (30). There is a logical claim that further distance from an epidemic zone decreases the immediate probability of Ebola transmission to that location, but the implication that low-risk zones are free from the threat of pandemic extension from high-risk zones is false.
EID-infected travelers coming from high-risk zones can easily reach their home countries by airplane, previously classified as low-risk zones. As a pandemic spreads across many nations, the suggestion that low-risk zones need not worry about high-risk zones is dangerously misleading. The WHO DON no longer classifies regions as low-risk zones or high-risk zones. As discussed below some experts in the field believe that there are undefined barriers which will safely separate pandemic zones and nations from those that are not yet engulfed in the expanding epidemic. How might an EID-infected person return to their home country and pass through reinforced surveillance meant to identify EID carriers during a pandemic? Unfortunately, the issue of detecting Ebola virus disease or EID infected carriers is not as simple as originally believed.
Zoonotic EID virus diseases such as Ebola virus (and its lethal filovirus family relatives), along with Lassa virus, Nipah virus and Bolivian hemorrhagic fever virus are spread through person-to-person contact, not through aerosols. Once infected by an EID it may take a few or many days until the carrier exhibits the first symptoms of fever, headache and nausea appear. Only days later, late in the Ebola virus infection cycle are Ebola viral particles shed into the local environment from the infected carrier’s sweat, saliva, teardrops, breast milk, blood, semen, vaginal fluid, urine, feces, and objects contaminated by infectious patients, called fomites.
Fomites are solid objects that have the infectious virus on their surface. Fomites can include contaminated bed sheets, cups or funeral gowns and hair or skin of the deceased. These fomites look harmless but will be infectious for hours to many days after limited physical contact with an infected person. Either touching fomite contaminated objects or direct person-to-person physical contact is how EIDs like Ebola virus infect their host. Their virus particles enter through microscopic skin abrasions on the hand or through the eyes, nose, lips, mouth, penis, vagina or anus. Ingestion of EID-contaminated food or water is another common transmission route (31).
Diseases and infectious diseases rarely have a strictly defined list of symptoms (and signs) for diagnosis. Most often, there is a unique spectrum of symptoms for each patient, and the range for each symptom may vary from undetectable to obvious. Correctly diagnosing a disease that does not present with the classical symptoms is a skill that distinguishes a medical professional from non-professionals.
EIDs and infectious diseases present the same diagnostic challenges. Identification of clinically inapparent carriers is a major problem in controlling EID outbreaks. Clinically inapparent carriers, missing one or more symptoms, can probably still shed the infectious virus which kills and cripples others and importantly can reactivate epidemics in communities.
The presence of fever is a major symptom for detecting EIDs like Ebola virus and is used extensively, but not exclusively, to determine and test suspect Ebola virus cases (32). However, there are 3 types of acutely infected Ebola virus carriers who do not present with the ‘symptom’ of fever and they will be discussed here. The preclinical Ebola carrier is the one who is very recently infected and therefore initially does not show symptoms. Subclinical carriers have no to mild symptoms (in this case no fever) at a later stage of the infection when most people would have pronounced symptoms. The third and final type of feverless or afebrile patient is afebrile because they have taken medication. More detail of these 3 types of afebrile Ebola virus and EID carriers follows.
Preclinical (newly infected) Ebola carriers will not have a fever or any other symptoms until Ebola virus has reached a certain concentration in their blood. Preclinical Ebola virus carriers require 2 to 21 days to achieve a high virus concentration in their bloodstreams to present with an initial Ebola virus infection symptom of fever. Therefore, 100% of the preclinical Ebola cases can move freely within and among communities from 2 to 21 days before initial symptoms appear. Even with active screening for fever during an Ebola virus epidemic an afebrile person can travel a long distance in 2 to 21 days before the first symptoms appear (31).
The second type of acutely infected afebrile Ebola virus patient has subclinical symptoms. As the disease progresses in the infected carrier, when fever and other indicators of infection should be present, 10% of Ebola virus carriers have a low or no fever (32). As with most Ebola virus infections these patients are probably infectious during the late symptomatic phase of the Ebola virus infection. While the subclinical Ebola virus patient may feel somewhat ill, this unsuspecting Ebola virus carrier believes there is no need to see a health care professional.
The third type of acutely infected afebrile Ebola virus carriers is the person who self-medicates herself with aspirin, ibuprofen or acetaminophen. These analgesics, pain medications that blunt fever, relieve headache, bone and muscle aches and can incidentally hide early stage EID patients (33). Ebola virus disease patients may believe they have a simple illness and self-medicate. It is also possible that certain traditional (folk) medicines may mimic analgesic activity blunting fever and other symptoms. While some people may self-medicate to avoid detection, most people with a fever would rather determine if they have an Ebola or EID infection or not as soon as possible. Most people in the outbreak zone will realize that early knowledge and medical management of Ebola infection significantly increases their chances for survival. Medication-induced fever suppression is a consideration when unexpected EID cases appear, if the new cases can be directly linked to seemingly healthy travelers.
Listed above are some medical reasons that EIDs continue to smolder locally for 6 months or escape from one location and migrate elsewhere. These afebrile Ebola virus carriers may pass through regional or global ports of entry without detection. Importantly, clinicians within the outbreak zone have a protocol to identify most afebrile Ebola virus patients. Clinicians outside of this zone may initially miss detecting afebrile Ebola virus disease patients, because of an incomplete history and they normally don’t expect to see Ebola virus or EID patients.
In this essay there is a case of a foreign-born non-citizen bringing Ebola virus into a new country. Yet, it is more common that travelers returning to their home country bring infectious diseases with them. During the 2014 Ebola virus epidemic thousands of travelers with similar ethnic origins near the outbreak region flew to other areas of the world. Most of these travelers from the Ebola virus outbreak region had no exposure to Ebola virus, with or without a fever. Therefore, these non-exposed travelers coming from the outbreak region did not carry Ebola virus to other continents.
A large study was recently published to determine how the Zika virus entered the United States (US) from 2015 to 2018. The US Centers for Disease Control and Prevention (CDC) studied over 5,000 cases of patients who became infected by Zika virus, some of whom were infected while residing in the US. They found that none of the Zika virus cases originated from Central or South American immigrants carrying Zika virus into the US (34-35). As shall be discussed in the next section monitoring incoming travelers or healthcare workers coming from an outbreak zone over the ‘incubation period’ for EID symptoms is an important standard practice that should not be abandoned. While caution and screening are the correct and required policies for public safety for certain incoming travelers - fear and a general distrust of people coming from or passing through epidemic zones who have been properly screened has been proven to be unjustified.
Copyright © 2019 Na’eem A. Abdullah All Rights Reserved
Morning fog on the African river Sangha. Congo. Sergey Uryadnikov Photographer/ Shutterstock Photos.
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