The first Ebola case in the United States (美國的第一宗伊波拉）

It was reported in the news on 1st October when the first case of Ebola virus infection was diagnosed in the United States.

The patient, a 42-year-old male, is a Liberia citizen visiting his family members in the United States. He was sent to Texas Health Presbyterian in Dallas on ambulance on 28 September with high fever and vomiting. He was taken to isolation immediately and blood test confirmed ebola virus infection on 30 September.

Retrospectively, it was revealed that he first attended the same hospital on 26 September reporting low grade fever for two days.  He was diagnosed to be a common viral infection and was sent home with antibiotics.  According to the patient's family (a sister), the patient did inform a nurse at the hospital when the first time he attended the hospital on 26 September.

Progression of Ebola Symptoms
(Source: http://www.huffingtonpost.com/2014/08/02/ebola-symptoms-infection-virus_n_5639456.html)

Further on the contact tracing, the patient had his onset date on 24 September 2014 when he was in Dallas already.  Prior to that, he was in Liberia and left Monrovia in Liberia on 19 September travelling through Brussels and Washington DC and arriving in Dallas on 20 September.  

While in Liberia, the patient was a driver for shipping company.  It was reported that he might have contracted the virus from the daughter of his landlord when he took her to the hospital on September 15.  She was turned away and then died later at home with no exact date provided.  

In other words, the patient might have developed symptoms on day 9 with initially mild flu-like symptoms then progress to systemic symptoms, notably vomiting and high fever before admitted to an isolation facility.

He should have become infectious and spreading the virus since 24 September.  Contact tracing was focussed on his contacts between 24 to 28 September.  As for his travelling on United Airlines flight 951 from Monrovia to Washington Dulles and flight 822 to Dallas/Fort Worth, spread was unlikely as he was asymptomatic at that time.  It was also supported by information from CDC that he was not running a fever when his temperature was checked while boarding a plane in Monrovia.  

According to CDC, a person shall be put under investigation (Person Under Investigation, PUI) if he/she has both consistent symptoms and risk factors as follows: 

(a) Clinical criteria: fever and additional symptoms such as severe headache, muscle pain, vomiting, diarrhea, abdominal pain, or unexplained hemorrhage; AND

(b) Epidemiologic risk factors within the past 21 days before the onset of symptoms, such as contact with blood or other body fluids or human remains of a patient known to have or suspected to have EVD; residence in, or travel to, an area where EVD transmission is active; or direct handling of bats or non-human primates from disease-endemic areas.

Reference: 

Bulluz, Julia.  15 Things you need to know about Ebola - A Dallas hospital failed to diagnose America's first-ever Ebola case.  Vox.  2 October 2014. (http://www.vox.com/cards/ebola-facts-you-need-to-know/texas-hospital-diagnoses-the-first-case-of-ebola-in-the-us#E6660684)

CDC.  Case definition for Ebola Virus Disease.  (http://www.cdc.gov/vhf/ebola/hcp/case-definition.html)

Greg Botelho.  U.S. Ebola patient: The travels and health travails of Thomas Eric Duncan.  CNN.  3 October 2014.  http://edition.cnn.com/2014/10/01/health/us-ebola-patient/index.html?iid=article_sidebar

The Moving Castle of Ebola 伊波拉之移動城堡

Having looked at the various human ebola outbreaks in the past forty years, the next question is how do they move from one place to another, and what happens during those quiescent period?

To understand the first question, we first look at the life cycle of ebolavirus.  Though not yet fully understood, the virus primarily survives in fruit bats of the Pteropodidae family.
They cause infection to wild animals and mammals like apes only occasionally.  Infection in human occurs primarily because of human animal contact followed by human to human spread.  The following graph from CDC summarizes such transmission routes.

Ecology of Ebolavirus. CDC, US.            (http://www.cdc.gov/vhf/ebola/resources/virus-ecology.html)

This suggests that, even in the absence of reported human infection, the virus exists, probably widely in the fruit bat family.

Natural host fruit bat of Ebolavirus. UNC website. (http://news.unchealthcare.org/news/2014/june/dispatch-from-guinea-containing-ebola)

The World Health Organization has put together the geographical locations of where serological evidence, such as the detection of antibodies in serum suggesting prior infection, to ebolavirus.  As from the health map obtained from the WHO website, apart from those countries with known ebola outbreaks in central and western africa, there are evidence to show infection has occurred in other parts of Africa such as Medagasgar and in South East Asia.  This coincides the areas within which the ebola host fruit bats are found.  Of note is that the fruit bat is also found as far as the east coast of Australia.

Distribution of the natural host fruit bat of ebola virus and areas with known evidence of human or animal infections. WHO website.

The map also showed that the Reston ebolavirus, so far considered not causing human diseases, have caused infections in animals in Mainland China as well as all over the United States, the latter through importation of infected Monkeys rather than due to the presence of natural host.  Such evidence suggested that, during the period of apparent quiescent, infection still occurs in various areas where the natural hosts are found without causing devastating human outbreaks.

Photo credit:
University of North Carolina News Room on Ebola hemorrhagic fever.
http://news.unchealthcare.org/news/2014/june/dispatch-from-guinea-containing-ebola

The Four Waves of Ebola 四波伊波拉

Ebolavirus was first identified in 1976 in Africa.  Over the nearly forty years of history, it has been found to cause acute viral illness with sudden onset of fever, intense weakness, muscle pain, headache, and sorethroat. Shortly after there will be gastrointestinal symptoms (vomiting and diarrhoea), rash, organ damage and various bleeding disorders.  There will be decreased white cells and platelets as well as abnormal liver enzymes.

As regards its transmission, it is through contact of body fluids containing the virus.  There is an incubation period of 2 to 21 days.  People are infectious as long as their blood and secretions contain the virus - can last much longer after their own recovery.

Ebolavirus belongs to the family of Filoviridae (the filovirus).  There are two other genus in this family, the Marburgvirus, and Cuevavirus.

Genus Ebolavirus comprises 5 distinct species. Zaire ebolavirus (EBOV) seems to be causing the worst and deadliest outbreaks and Sudan ebolavirus (SUDV) and Bundibugyo ebolaviruses (BDBV) can also cause highly fatal diseases. The Reston ebolavirus (RESTV) is found in the Phillipines and Mainland China.   can infect humans but no known human illness or deaths have been reported.  The Taï Forest ebolavirus (TAFV) has been reported causing a non-fatal case in Cote d'Ivoire in 1994.

A summary of major Ebola outbreaks from Bloomberg (http://www.bloomberg.com/news/2014-08-18/ebola-spurs-nigeria-surveillance-regional-border-limits.html)

The above graph, published at Bloomberg in an article on the subject by Zoker and Chen, has nicely shown the geographical relationships of the major outbreaks across the African continents over the past years.  When we look further into the species of the ebola virus causing these outbreaks, we can actually identify three different patterns caused by three out of the five species of Ebola virus.

The Four Waves of Spreading Zaire ebolavirus (EBOV)

This Zaire ebolavirus seems to be the most deadly species of the genus.  It was first detected (1976) in an outbreak in 1976 in the then Zaire, which subsequently changed to the present Democratic Republic of Congo, in Central Africa.  The species causing this outbreak was identified as the Zaire Ebola virus.  It caused 391 reported cases with 281 deaths, with a case-mortality rate of 88%.  It was placed under the Genus Ebola virus because cases were initially found in northern Zaire near the River Ebola.

The second wave (1994 to 1996) of Zaire Ebolavirus was detected in 1994 in Gabon - after an apparent 18-year quiescent period after the 1976 outbreak.  In 1995, an outbreak of the same virus also occurred in Zaire resulting in 315 cases with 254 deaths, with mortality again high at 81%.  The outbreak in Gabon continued till 1996 with 143 cases and 97 deaths and mortality at 68%.  One fatal case, presumably an imported case from Gabon, was detected in South Africa in 1996.

The third wave (2001 to 2008) of Zaire Ebolavirus outbreak occurred fiver years later in 2001 in Gabon again, and also newly found in Congo, the country located between Gabon and Zaire.  Zaire has undergo political change and had been renamed as the Democratic Republic of Congo since 1997, had its third Zaire Ebolavirus outbreak in 2007 to 2008.  The case numbers in Gabon, Congo and the Democratic Republic of Congo were 65, 249, and 296 with case-mortality rate of 82%, 85% and 68% respectively.

Ebolavirus Outbreak Dec 2013 to Aug 2014 in West Africa (WHO) http://who.int/csr/disease/ebola/geographic-map-29-aug-2014.png?ua=1)

As we can see now, the current outbreak occurring in West Africa since December 2013 is basically the fourth wave (2013 to current) of the Zaire Ebolavirus outbreak.  Over the past five years of silent period, the virus has travelled through more than 3,000 km west to Guinea, with subsequent detection in Sierra Leone, Liberia, as well as Nigeria.  Based on the WHO statistics, as of 11 August 2014, the number of cases in these countries are:

• Guinea - 510 cases, 377 deaths
• Liberia - 670 cases, 355 deaths,
• Sierra Leone - 783 cases, 334 deaths, and
• Nigeria - 12 cases, 3 deaths.

Sudan ebolavirus (SUDV) primarily in Sudan and Uganda

Around the time of the first Zaire ebolavirus outbreak, a similar outbreak was also detected in a neighbouring country, Sudan (north to Zaire), due another species, named Sudan Ebolavirus.  The worst first outbreak in 1976 resulted in 284 cases with 151 deaths, with a case-fatality rate of 53%; followed by two smaller outbreaks in 1979 (34 cases and 65% deaths) and in 2004 (17 cases and 41% deaths).

Sudan ebolavirus was detected outside Sudan in Uganda, a country south to Sudan in Central Africa, in 2000 and again in 2011 to 2012.  In the first outbreak, there were 425 cases with 224 deaths (case fatality rate 53%).  The second one was smaller causing 32 cases and 22 deaths (69% deaths).  

Budibugyo eboavirus (BDBV) detected in 2007 and 2012

There is a third species, the Budibugyo ebolavirus, found to be able to cause human outbreaks and deaths.  It was first detected in Uganda in 2007 with 149 cases and 27 deaths, with a case fatality rate of 25%.  It was detected in Democratic Republic of Congo (the previous Zaire) in 2012 resulting in 57 cases including 29 deaths.

Reference: 

Ebolavirus outbreaks updates at World Health Organization

Elise Zoker and Caroline Chen.  Ebola Spurs Nigeria Surveillance, Regional Border Limits at Bloomberg access http://www.bloomberg.com/news/2014-08-18/ebola-spurs-nigeria-surveillance-regional-border-limits.html.