MIDDLE EAST RESPIRATORY SYNDROME
Middle East Respiratory Syndrome (MERS) is a severe respiratory infection in humans
mainly originating in the Middle East. It is caused by a novel lineage C betacoronavirus called the Middle East
respiratory syndrome coronavirus (MERS-CoV). As of 23 September 2015, MERS-CoV
has caused 1570 infection cases and 555 deaths in over 20 countries worldwide,
with a high case-fatality of more than 30 %.
MERS-CoV
is enzootic in Dromedary Camels (DC) across the Arabian Peninsula and in parts
of Africa, causing mild upper respiratory tract illness in its camel reservoir
and sporadic, but relatively rare human infections. Precisely how virus
transmits to humans remains unknown but close and lengthy exposure appears to
be a requirement. The Kingdom of Saudi Arabia (KSA) is the focal point of origin
of MERS. Most human cases of MERS have been linked to lapses in infection
prevention and control (IPC) in healthcare settings, with approximately 20 % of
all virus detections reported among healthcare workers (HCWs) and higher
exposures in those with occupations that bring them into close contact with
camels. Seasonal introduction of virus to the human population via infected
Dromedary Camels occurs in the camel calving season in the winter months and
this may be a time when there is increased risk to humans of spill-over due to
new infections among naïve DC populations. Juvenile Dromedary Camels appear to
host active infection more often than adult Camels.
The
continuing MERS epidemic in the Middle East is believed to be related to the
failure to control the zoonotic sources, most probably the dromedary camels,
which results in ongoing camel-to-human transmission. The largest
healthcare-associated outbreak occurred in the Republic of Korea in 2015, in
which 186 cases including 36 deaths occurred after the index patient returned
from the Middle East. The high case-fatality rate of MERS and the capability of
MERS-CoV to cause outbreaks in healthcare facilities pose significant threat to
public health worldwide.
Droplet
spread between humans is considered the mechanism of human-to-human
transmission and the need for droplet precautions was emphasized after the Al-
Ahsa hospital, the KSA and the South Korean outbreaks. Aerosol-generating
events involving Dromedary Camels (urination, defecation, and preparation and
consumption of Camel products) also increase the risk of transmission and
spread. House- hold human-to human transmission occurs but is limited.
Educational programs will be essential tools for combating the spread of
MERS-CoV both within urban and regional communities and for the health care
setting.
The primary infection site of MERS is human
respiratory tract. It has been demonstrated that MERS-CoV can effectively
infect and robustly replicate in the human airway epithelium. MERS-CoV infects
non-ciliated bronchial epithelial cells, bronchiolar epithelial cells, alveolar
epithelial cells and endothelial cells of pulmonary vessels. Upon MERS-CoV
infection in ex vivo lung tissues, the uninfected cells undergo massive
apoptosis. The effective infection results in robust viral propagation and
massive induction of apoptosis. These observations provide a pathological basis
of the major pulmonary features of MERS i.e., pneumonia and acute lung injury.
The fact that endothelial cells of blood vessel in human ex vivo lung tissues
are permissive to MERS-CoV may provide a pathological basis of the potential
for virus dissemination hence extrapulmonary organs involvement. Collectively,
MERS-CoV may have evolved multiple antagonistic mechanisms to dampen or
attenuate the host defense, which has contributed to the high pathogenicity in
humans.
Unlike
most other human-pathogenic coronaviruses, which mainly cause self-limiting
upper respiratory tract infections, MERS-CoV is capable of causing severe
disease with lower respiratory tract involvement and extrapulmonary
manifestations. The mean incubation period for MERS is five to six days,
ranging from two to 16 days, with 13 to 14 days between when illness begins in
one person and subsequently spreads to another. Patients with severe MERS often
present with pneumonic symptoms including fever, cough and dyspnoea, with some
progressing to respiratory failure, acute respiratory distress syndrome,
multiorgan failure and death in 20 % to 40 % of those infected. Older males
most obviously suffer severe disease and MERS patients often have co morbidities.
Among those with progressive illness, the median time to death is 11 to 13
days, ranging from five to 27 days. Extrapulmonary manifestations such as renal
failure, hepatic dysfunction and diarrhea have been reported. MERS bears some
resemblance to severe acute respiratory syndrome (SARS) in terms of clinical
manifestation.
Diagnosis
Real Time reverse transcription Polymerase
Chain Reaction (RT-rtPCR) assays as well as virus culture in Vero and LLC- MK2
cells have been employed in the diagnosis of MERS-CoV. However, cell culture is
a slow, specialized and insensitive method while PCR-based techniques are the
preferred method for MERS-CoV detection.
Detection
of MERS-CoV antigen using a monoclonal antibody-based capture ELISA targeting
the MERS-CoV nucleocapsid protein may also be done.
Serological
assays for Dromedary Camel sero-surveys can be transferred to human screening
with minimal re-configuration. A number of commercial ELISA kits,
immunofluorescent assays (IFA) kits, recombinant proteins and monoclonal
antibodies have been developed for use.
Currently,
there is no vaccine to prevent MERS-CoV infection. CDC routinely advises that
people help protect themselves from respiratory illnesses by taking everyday
preventive actions: Wash your hands often with soap and water for 20 seconds,
and help young children do the same. Cover your nose and mouth with a tissue
when you cough or sneeze, then throw the tissue in the trash. Avoid touching
your eyes, nose and mouth with unwashed hands. Avoid personal contact, such as
kissing, or sharing cups or eating utensils, with sick people. Clean and
disinfect frequently touched surfaces and objects, such as doorknobs.
Dr.
Moses Bwana
Post-grad at the University of Nairobi
[Applied Microbiology]
Cell: +254729246187;
Email: bwanamoses@gmail.com
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