The New Kid on the BlockCarlos Torres-Viera
The viruses known as coronavirus (Cov) belong to the Coronaviridae family. These are viruses which nucleic acid is composed of a single positive sense RNA molecule. They were discovered in the 1960’s and their name is due to the crown- type projections on the virus surface. They are found in a wide range of animals species including chicken and other poultry, dog, cats, rat, pig, cattle, whale. In fact, they constitute a significant group of viruses of veterinary importance producing respiratory, renal, liver, gastrointestinal, and CNS diseases in animals.
In humans, a small number of coronavirus (229E, OC43) have been recognized and involved primarily as the cause of upper respiratory tract infections (common flu), occasional disease of the lower respiratory system (pneumonia), and probably of gastrointestinal disease.
Ten years ago, however, this perception of a benign virus changed when a new coronavirus was unveiled. It emerged unexpectedly in November 2002 in the Guangdong Province of China and it came to be known as SARS virus (Severe Acute Respiratory Syndrome) by the end of the epidemic in July 2003, 8098 probable cases in 29 countries had been reported, leaving 774 deaths (9.6 %) Although the virus resurfaced briefly in late 2003 and early 2004, no human case has been reported since. Despite the brief course of the epidemic, it had a significant economic impact estimated at $30 billion. The adverse economic effects were felt more severely in Canada, China, Hong Kong and Singapore. In Canada for example, the economic growth fell 1 percent and the gross domestic product fell in 3200 millions of dollars.
As for that we do not forget the importance of emerging infectious diseases a new coronavirus comes to surprises us. It was first identified in March 2012 but the number of cases have increased recently. The epicenter of the disease has been the Middle East and particularly Saudi Arabia. Until the date of this writing 80 laboratory-confirmed cases have been reported with 44 deaths in 8 countries: Saudi Arabia (65 cases and 38 deaths), Qatar, Jordan, United Arab Emirates (UAE), Tunisia, United Kingdom (UK), France and Italy. This new coronavirus has been baptized as MERS-CoV (Middle East Respiratory Syndrome Coronavirus), and as suggested by the name it presents mainly with respiratory symptoms including severe pneumonia. Little is known about this virus however; we do know that it has the ability to be transmitted from person to person in close contact. In fact have been reported several cases of infections in close relatives of infected patients and in the health personnel who attended to those sick patients. This is not surprising, since previously SARS virus was frequently characterized by infection in health care personnel to the point that in Toronto, Canada where 251 cases and 43 deaths were reported with SARS, 43 % of the cases were of healthcare workers (20 % when including all affected cases and countries). MERS-CoV, however, appears to be a less transmissible virus that SARS. Among the important element that until now has differentiated both viruses is the absence, in the case of the MERS-CoV, of highly infectious individuals (the so-called ” Super-Spreaders “), who were able to infect many other people and that was very typical of the epidemic of SARS-CoV.
One way to measure the transmissibility (and the epidemic potential of a microorganism) is by calculating the reproductive number, R which is defined as the number of effective transmission (infections) caused by an infected individual. This number would be highest when the introduction of the infectious agent occurs in populations without immunity against this infectious agent (that is to say the whole population is susceptible) and this number is known as R0 or basic reproductive number. That is to say R0 is the average number of new cases of infections caused by introducing an infectious agent in a susceptible population. For an epidemic to establish, each infected individual must be able to infect on average at least one person or more (R0 ≥ 1). If R is greater than 1 the number of cases can grow exponentially and develop pandemic potential. If on the contrary the infected individual is able to infect less than one person (R0 < 1), the epidemic become extinct (unless there are multiple introductions of the infected agent).
Mathematically, R0 can be express: R0 = k .β. D
Where k is the rate of effective contact, β represents the transmission efficiency and D is the duration of the disease. The higher k, β or D the greater will be the number of new infections (R0). In a recently published study, the R calculated for MERS-CoV was 0.69, compared to the R of SARS-CoV in its pre-pandemic period that was calculated at 0.80. When SARS-CoV extended to various countries during 2003 it was estimated that its R value was between 2.2 and 3.7. In conclusion, it seems that the capacity of the MERS-CoV to be transmitted from person to person, at least for now, is very limited and consequently it does not have potential for pandemic spread at present.
Always it is good to remember that all reported cases indicate laboratory-confirmed cases, but we do not know if there are, and how many could they be, asymptomatic cases or mildly symptomatic individuals that have not been evaluated (never went to the hospital or sought medical assistance, or if they did look for medical care were diagnosed with a different disease, e.g. “viral syndrome” ) which could cause bias in the estimates previously reported (R could be higher, the mortality rate lower).
As usual with emergent infections, the problem is what we do not know, and that includes:
a. Don’t know where it comes from (what is the reservoir). The majority of the coronaviruses have its reservoirs in animals; In the case of the SARS virus was considered that civets were the reservoir but genetic studies concluded that SARS-CoV had not been in circulation for a long period of time time animal in the Chinese markets (where civets are sold for human consumption) so there should be another reservoir. It is currently considered that bats may actually be the natural reservoir of an ancestor of SARS-CoV before jump species (to civets). In the case of the MERS-CoV it has been even stranger, because some cases have been reported in patients without apparent animal exposure.
b. Don’t know which is the mode of preferential transmission of the virus (droplets, aerosols, contact, or combination of them). In the case of SARS-CoV it was found that while the preferential mode of transmission was by respiratory droplets, the transmission could also be made through contact and aerosols.
Not knowing the above information, it is difficult to define epidemiological control measures for the disease. However, in the current circumstances it makes sense to maintain similar measures of infection control as were recommended to deal with SARS-CoV.
We can only be vigilant. In this time of rapid travel any healthcare personal in an emergency room could be facing a case of MERS-CoV. It is always a good idea to obtain a good epidemiological history of the patient: where have you been? Where are you coming from? By now, the World Health Organization has decided to put together an emergency committee to discuss the current situation of the MERS-CoV and determine whether it constitutes an international public health emergency. The Hajj is in October.]]>