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Archive Number 20091120.3999
Published Date 20-NOV-2009
Subject PRO/AH/EDR> Rift Valley fever virus - South Africa: (NC), novel genotype
RIFT VALLEY FEVER VIRUS - SOUTH AFRICA: (NORTHERN CAPE), NOVEL GENOTYPE
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International Society for Infectious Diseases
<http://www.isid.org>
Dat: Fri 20 Nov 2009
From: Prof. Janusz T. Paweska
<januszp@nicd.ac.za>
A novel Rift Valley fever virus genotype strikes in Northern Cape, South Africa
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In mid October 2009, 4 suspected human cases of Rift Valley fever
(RVF) from the Northern Cape Province of South Africa were
investigated at the Special Pathogens Unit, National Institute for
Communicable Disease of the National Health Laboratory Service. Of
those, 2 were confirmed by serology, virus isolation and nucleic acid
detection as being recently infected with RVF virus. Analysis of
partial sequencing data of the M segment of a virus isolate recovered
from the index case revealed that the patient was infected with a RVF
virus genotype closest related to a 2004 Namibian isolate from the
Caprivi Strip, and clustering with a 1981 South African isolate from
the East Coast, and isolates from Senegal (1993), Central African
Republic (1969) and Guinea (1981, 1984), but not with other South
African isolates recovered from Kwazulu-Natal in March this year
[2009] and from other 4 provinces (Mpumalanga, Limpopo, North West
and Gauteng) during 2008.
RVF outbreaks are associated either with spread of a single genotype
or with simultaneous emergence of multiple genotypes in endemic foci.
RVF virus isolates recovered during the last decade in southern and
eastern Africa, the Arabian Peninsula, Mauritania, and Madagascar
exhibit little genetic diversity, which indicates recent widespread
distribution of very closely related genotypes of the virus over a
vast area. Various isolates recovered from humans, cattle and buffalo
in Mpumalanga, Limpopo, North West and Gauteng in 2008 and in
Kwazulu-Natal in February/March 2009 are genetically almost identical
and very similar to isolates from eastern Africa, the Arabian
Peninsula, Mauritania, and Madagascar, but the recent isolate from
Northern Cape is genetically different. All laboratory confirmed
human cases (n = 25) in 2008-2009 in South Africa had very close
contact with infected animals and/or their tissues, including the 2
most recent cases in Northern Cape. There have been no!
mortalities.
RVF virus was 1st isolated in 1930 following an epizootic on a sheep
farm in the Rift Valley in Kenya and historically was endemic to
sub-Saharan Africa, but in the last 4 decades spread to Egypt, West
Africa and most recently to the Arabian Peninsula and the Archipelago
of Comoros, including the French Department of Mayotte. Humans become
infected from contact with tissues of infected animals or from
mosquito bite, and usually develop asymptomatic, mild or moderate
febrile illness. Severe complications that may be life-threatening
develop only in a small proportion of infected patients, but
substantial numbers of people may succumb to infection during large
outbreaks of the disease in livestock. Large outbreaks of RVF in
domestic ruminants occur at irregular intervals when exceptionally
heavy rains favour the breeding and high abundance of competent
mosquito vectors, and are associated with high mortality among
newborn animals and abortion in pregnant animals.
A major epizootic, which caused an estimated 500 000 abortions and
100 000 deaths of sheep, occurred in 1950-1951 in South Africa. The
2nd major and more widespread outbreak in South Africa caused
extensive losses of ruminants in 1974-1976. Small outbreaks of RVF or
sporadic virus isolations of the virus were recorded in South Africa
in 1981 and 1999 and most recently in 2008-2009. Compared to
historical outbreaks of RVF in South Africa, the recent outbreaks
appear to be very localized and affected relatively small numbers of
animals and humans. This might be due to the low level of endemicity
of RVF in the country, where prolonged dry spells since the 1974-76
have limited virus activity. However, the present cases diagnosed
early in the wet season this year might indicate increasing activity
of the virus in the country.
[Byline: JT Paweska, A Grobbelaar, J Weyer, P Leman, L Blumberg and B
Swanepoel]
--
Prof. Janusz T. Paweska,DVSc, Dr hab.
Head Special Pathogens Unit
National Institute for Communicable Diseases
of the National Health Laboratory Service
Private Bag X4, Sandringham-Johannesburg, 2131
Modderfontein Road 1, Gauteng, South Africa
<januszp@nicd.ac.za>j
[ProMED-mail thanks Professor Paweska and colleagues for providing
ProMED-mail and the wider community with this report describing the
identification of a novel genotype of Rift Valley Fever virus
recently isolated and characterised in South Africa. Although at
present still localised and affecting few animals and humans it needs
to be kept under surveillance lest it herald an imminent resurgence
of Rift Valley fever in southern Africa.
The HealthMap/ProMED-mail interactive map of South Africa can be accessed at:
<http://healthmap.org/r/00vd>, and a map of the provinces of South Africa at:
<http://www.sa-venues.com/maps/south-africa-provinces.htm>. - Mod.CP]