By Chukwuma Muanya From allAfrica

A NEW study “On the Quarantine Period for Ebola Virus” published, last week, in the PLOS Currents: Outbreaks suggests that 21 days might not be enough to completely prevent spread of the virus.

The study by United States researchers from Drexel’s College of Engineering led by Prof. Charles Haas looks at the murky basis for human knowledge about the virus, namely previous outbreaks in Africa in 1976 (Zaire) and 2000 (Uganda) as well as the first nine months of the current outbreak.

According to the story, in both cases, data gathered by the World Health Organization (WHO) reported a two to 21 day incubation period for the virus -meaning that after 21 days if the individual hasn’t presented symptoms they are likely not to be infected or contagious.

This is likely the genesis of the United States Centers for Disease Control (CDC) and Prevention’s 21-day quarantine period, but there is little indication from the CDC as to what other considerations played into this policy.

Meanwhile, another study published yesterday in The Lancet suggests that most people from West Africa especially Nigerians and Senegalese may be immune to the deadly Ebola virus, ravaging the region.

The current outbreak, the worst on record since the virus was discovered in 1976, has claimed the lives of 4,493 people, infecting 8,997, the World Health Organisation said yesterday.

But a team of scientist in the United States believe the Ebola virus may be silently immunising a significant portion of the population, who never fall ill or infect others, protecting them from future infection.

The researchers say these people will never show the tell-take signs of the disease, the high fever, headaches and flu-like symptoms.

The scientists at the universities of Texas and Florida if this immunity can be identified it could revolutionise the way public health authorities are tackling the epidemic in West Africa.

They will never succumb to the extreme vomiting, diarrhoea, nor the deadly internal bleeding.

If this immunity can be confirmed and identified, it could, a team of researchers from the University of Florida and the University of Texas say, change the strategy for fighting the disease.

They suggest those found to be naturally immune to Ebola could help slow the spread of the disease in two important ways.

Firstly they can be recruited to work as health workers and caregivers, helping treat the most contagious patients and high-risk communities.

And secondly their natural immunity may make them prime candidates for donating blood for transfusions to help treat victims.

Dr Steve Bellan and Dr Lauren Ancel Meyers of the University of Texas, have called on public health authorities conduct studies in Sierra Leone, Liberia and Guinea – the three worst-affected nations.

That research would aim to determine how commonplace it is for people to be infected with Ebola without ever developing the symptoms, or spreading the disease.

Then, they say, it can be established whether those individuals will be protected from future infection.

Bellen, said: ‘Ultimately, knowing whether a large segment of the population in the afflicted regions are immune to Ebola could save lives.

‘If we can reliably identify who they are, they could become people who help with disease-control tasks, and that would prevent exposing others who aren’t immune.

‘We might not have to wait until we have a vaccine to use immune individuals to reduce the spread of disease.’

Led by Bellan, the team, which also included Juliet Pulliam, an assistant professor at the University of Florida, looked at studies conducted in the aftermath of past outbreaks.

One showed 71 per cent of people who had close contact with an Ebola patient and tested positive for the virus did not fall ill.

Another revealed 46 per cent of people who came into close contact with a victim and did not get sick, had evidence of infection with the virus.

Pulliam, added: “We want to know whether people who are infected without getting sick become immune.

“If these people are protected from future infections, this would open up new opportunities for controlling the disease.”

She added: “If infection without disease protects people from future Ebola infections and illness, the epidemic should decline sooner than currently predicted and affect a smaller number of people.”

But it is not yet known whether such infection provides immunity.

The scientists conclude that resolving the question of whether asymptomatic infection provides immunity could be critical.

The outcome, and subsequent identification of naturally immune individuals, could help shape public health efforts to contain the disease, as well as allowing for accurate estimates for the likely spread of the disease.

Meyers, said: “Understanding the prevalence and immunological effects of these silent Ebola infections is critical to making reliable epidemic projections and improving control efforts.

“We believe that we can and should investigate this phenomenon as soon as possible.”

Pulliam, added: “If we can take advantage of natural immunity within the affected communities, we may be able to impact the course of the epidemic even before a vaccine becomes available.

“Even if current projections overestimate how big this epidemic will become, its effects are devastating, and a global effort to control the spread of Ebola within West Africa remains imperative.”

Meanwhile, Haas, who is the head of the Department of Civil, Architectural and Environmental Engineering at Drexel said: “Twenty-one days has been regarded as the appropriate quarantine period for holding individuals potentially exposed to Ebola Virus to reduce risk of contagion, but there does not appear to be a systemic discussion of the basis for this period.”

Haas suggests that a broader look at risk factors and costs and benefits should be considered when setting this standard. With any scientific data of this nature there is a standard deviation in results -a percentage by which they may vary. In the case of Ebola’s incubation period the range of results generated from the Zaire and Uganda data varied little. This might have contributed to the health organizations’ certainty that a 21-day quarantine period was a safe course of action.

But looking more broadly at data from other Ebola outbreaks, in Congo in 1995 and recent reports from the outbreak in West Africa, the range of deviation is between 0.1 and 12 percent, according to Haas. This means that there could be up to a 12 percent chance that someone could be infected even after the 21-day quarantine.

“While the 21-day quarantine value, currently used, may have arisen from reasonable interpretation of early outbreak data, this work suggests reconsideration is in order and that 21 days might not be sufficiently protective of public health,” Haas said.

Haas, who has extensive background in analyzing risk of transmitting biological pathogens, explains that these quarantine periods must be determined by looking at the cost of enforcing the quarantine versus the cost of releasing exposed individuals. Looking at the potential tradeoff between costs and benefits as the quarantine time is extended should guide public health officials in determining the appropriate time. Obviously, with more contagious and potentially deadly diseases the cost of making a mistake on the short side when determining a quarantine is extremely high.

“Clearly for pathogens that have a high degree of transmissibility and/or a high degree of severity, the quarantine time should be greater than for agents with lower transmissibility and/or severity. The purpose of this paper is not to estimate where the balancing point should be, but to suggest a method for determining the balancing point.”

Meanwhile, a Canadian researcher is one of four scientists raising the issue that Ebola may be silently immunizing large numbers of people, who never fall ill or infect others yet become protected from future infection.

Their letter was published in the medical journal The Lancet.

The authors say if true, this finding could have significant ramifications for both projections of how widespread the disease will be, and strategies policy makers and health workers should use to contain the disease.

McMaster University’s Jonathan Dushoff, an associate professor of biology and an investigator with the Michael G. DeGroote Institute for Infectious Disease Research, is one of the authors with principal author Steve Bellan of The University of Texas (UT) at Austin and others from UT Austin and the University of Florida. They call on public health authorities to determine how commonplace it is for people to be infected by Ebola without ever developing symptoms or spreading the disease and whether these individuals are then protected from future infection.

“Although resources on the ground are scarce, now is the best time to learn more about immunity to Ebola, and the sooner we know the sooner the knowledge can be used to stop the epidemic,” said Dushoff.

Bellan said: “Ultimately, knowing whether a large segment of the population in the afflicted regions is immune to Ebola could save lives. If we can reliably identify who they are, they could become people who help with disease-control tasks, and that would prevent exposing others who aren’t immune. We might not have to wait until we have a vaccine to use immune individuals to reduce the spread of disease.”

The letter notes that researchers have found evidence of asymptomatic Ebola infection in the aftermath of earlier Ebola outbreaks; but it is yet unknown whether such infection provides immunity.

The authors conclude that resolving this question and identifying naturally immunized individuals could prove critical in public health efforts to contain the disease, as well as in accurately estimating the likely spread of the disease.

IMAGE: One of the ambulances in Monrovia picking up patients to be tested for Ebola. Photo: Boakai Fofana/allAfrica

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