Contents

Introduction 1

Climate-based forecasting models and early warning systems 2

Recent warning message 2

Tripartite FAO, OIE and WHO recommendations 4

One Health communication and public awareness 5

References 6

to the increased availability of suitable environments and by feeding on infected livestock they transmit the virus to other animals and humans (Linthicum et al., 1999; Turell et al., 2008) (Figure 1).

Sero-surveillance efforts have found significant levels of RVF antibodies in domestic and/or wild ruminants in many African countries across different agro-climatic zones. However, many countries are not aware of the circulation of the virus in their territories because systematic surveillance for confirming the presence and distribution of RVF infection is lacking. Limited focal enzootic circulation of RVF has been documented among domestic and/or wild mammalian species.

The most recent RVF outbreaks occurred in the Republic of Botswana (2008, 2010, 2013 - 2014), the Republic of Kenya (2006-2007), the Republic of Madagascar and Mayotte (2008-2009), the Islamic Republic of Mauritania (2010 - 2011, 2013 - 2014), the Republic of Namibia (2011 - 2012), the Kingdom of Saudi Arabia (2010), the Republic of Senegal (2013-2014), the Federal Republic of Somalia (2006-2007) the Republic of South Africa (RSA) (2008-2011), the Republic of Sudan (2007-2008), the Kingdom of Swaziland (2008) and the United Republic of Tanzania (2007). Based on WHO estimates, RVF outbreaks in the Republic of Kenya, the Federal Republic of Somalia and the United Republic of Tanzania during 2006-2007 resulted in a total of 1 098 human infections with 323 deaths (WHO, 2007). In the Republic of Sudan in 2007, a RVF outbreak resulted in 222 human deaths. The RSA, between 2008 and 2011 filed 708 outbreak reports to the OIE, of which 508 in 2010 alone (OIE, 2014a).

Introduction

Rift Valley fever (RVF) is an arthropod-borne arboviral disease that affects ruminants and humans. Most human

cases develop a mild influenza-like illness while a small percentage of patients develop a much more severe form of the disease. In ruminants it may be associated with high mortality in neonates and young animals as

well as high levels of abortion, resulting in significant socio-economic consequences. The disease is transmitted by mosquitoes of several different species (mainly Aedes and Culex) and through direct contact with tissue of infected animals (Linthicum et al., 1999). Although currently confined to sub-Saharan Africa, and having spread to the Arab Republic of Egypt and the Arabian Peninsula, this disease poses a threat to non-endemic countries in temperate regions where both hosts and potential vectors co-occur (Tran et al., 2013; Xue et al., 2013).

Climatic factors, such as temperature, rainfall and humidity are important drivers of RVF viral activity as they drive vector abundance and population dynamics, thus influencing the risk of disease emergence, transmission and spread. The disease ecology of RVF in East Africa has been investigated. Epidemics occur periodically (from 5 to 15 year cycles) and are significantly associated with climate anomalies such as persistent, unusual, widespread, above-average rainfall and flooding, particularly during El Niño events (Anyamba et al., 2009). Temporarily flooded areas and water pools in low-lying areas, also known as dambos, create the conditions for disease-carrying mosquitoes to breed, including the Aedes species, whose eggs can survive in soil for long dry periods. During persistent heavy rainfall, the dambos become flooded triggering transovarially infected eggs to hatch. This results in increased infected vector population abundance and a greater risk of the disease being transmitted to susceptible ruminant species. Subsequently, as vegetation grows in response to heavy rains, other Culex species of mosquito vectors multiply due

Contributors: Claudia Pittiglioa, Caryl Lockharta, Julio Pintoa, Susanne Münstermannb*, Patrick Bastiaensenb*, Pierre Formentyc**, Stephane de la Rocquec**, Assaf Anyambad, Jennifer Smalld, Kenneth J. Linthicume and Jean-Paul Chretienf

a Food and Agriculture Organization of the United Nations (FAO); b World Organisation for Animal Health (OIE); c World Health Organization (WHO); d National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC); e United States Department of Agriculture (USDA) Agricultural Research Service; f Armed Forces Health Surveillance Center (AFHSC)

VOL 31 — DECEMBER 2014 EMPRES-ANIMALHEALTH@FAO.ORG | WWW.FAO.ORG/AG/EMPRES.HTML

Climate models predict persistent above-average rains and risk of flooding in East Africa: FAO, OIE and WHO warn countries to remain vigilant about Rift Valley fever

empreswatch

* The views expressed in this publication are those of the author(s) and do not necessarily reflect the views or policies of the World Organisation for Animal Health

** The author is a staff member of the World Health Organization. The author alone is responsible for the views expressed in this publication and they do not necessarily represent the views, decisions or policies of the World Health Organization

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Climate-based forecasting models and early warning systemsThe availability of near-realtime satellite-based climate data, such as rainfall, temperature and vegetation indices, has provided an opportunity to monitor climatic conditions that are linked to vector abundance and population dynamics. This has facilitated the development of cost-effective Early Warning Systems (EWSs) for vector-borne diseases, including RVF. The aim of such EWSs is to monitor the first signals of a possible increase in vector abundance and RVF risk and provide information for prevention and risk mitigation. The Goddard Space Flight Center (GSFC) of the NASA, FAO and WHO have been monitoring climatic conditions to predict the risk of RVF vector amplification in East Africa for the past several years using a modelling approach developed by the NASA GSFC team (Anyamba et al., 2009). With this approach, near-realtime satellite-derived climate data such as precipitation and the Normalized Difference Vegetation

Index (NDVI) are used to identify and map areas with persistent, heavy, above-average rains and vegetation anomalies over the last three consecutive months. Results are then interpreted and assessed in relation to El Niño and Sea Surface Temperature (SST) indicators and precipitation forecasts and compared with historical data. Warm El Niño conditions and positive SST are significantly associated with persistent and abnormal rains in East Africa, which determine suitable environmental conditions for vector amplification. In 2006-2007 this climate-based model predicted the risk of RVF occurrence in the Horn of Africa several weeks before the first signs of the disease were recorded in livestock and humans. This facilitated strategic preparedness and significantly enhanced field response (Anyamba et al., 2010; FAO, 2006; WHO, 2006).

Recent warning messageDuring September, October and mid-November 2014 the observed conditions of the El Niño Southern Oscillation (ENSO)

decreased from those of a borderline El Niño to a relatively warm ENSO-neutral state (Figure 2). However, most of the ENSO prediction models continue to indicate development of weak El Niño conditions from October to December 2014, reaching a low peak during winter 2014 - 2015 and lasting through most of northern spring 2015. Positive equatorial SST anomalies continue across most of the Pacific Ocean. Some impacts from the current SST anomaly patterns can be observed in the pattern of global convective activity illustrated by the Outgoing Longwave Radiation (OLR) anomaly patterns. From August through October 2014, large positive departures (>+35 watts per meter squared [W/m2]) in OLR across the Republic of Indonesia and coastal southeast Asia indicate drier than average conditions, while large negative departures (<-40 W/m2) across northern China, the western Indian Ocean, central Asia, north-central and northeast Africa, the United Mexican States/Central America, the southwestern United States of America, and the northeastern and southwestern tropical Pacific suggest wetter than average conditions (Figure 3). There was increased rainfall from September through mid-November in East Africa (Figure 4) and above-average precipitation was predicted for the coming months.

Since September 2014, NASA GSFC intensified their monitoring activity to produce biweekly maps of precipitation anomalies and monthly RVF risk maps in response to the predicted and current development of the El Niño event in East Africa. NASA GSFC has recently delivered a warning message to remain vigilant about the risk of RVF occurrence in East Africa in the coming weeks. Although precipitation patterns are currently less persistent and widespread than expected, in some locations the rainfall estimates and anomalies for October and mid-November 2014 are similar to, or above, values observed in 1997/1998 and/or in 2006/2007, when major outbreaks occurred in the Republic of Kenya, the Federal Republic of Somalia and the United Republic of Tanzania (Figure 5). Comparisons between the current cumulative rainfall estimates, historical RVF outbreak reference periods and long-term average estimates have highlighted areas at increased risk of flooding. These include reference meteorological stations Sukari Farm and Marigat in the Republic of Kenya; Belet Weyne in the Federal Republic of Somalia; Manyara Ranch and Magara in the United Republic of Tanzania.

Figure 5 shows the cumulative rainfall anomaly maps for September to mid-November 2014 that reference meteorological stations with rainfall anomalies (pink closed circles). In the Federal Republic of Somalia, a first flood occurred during the

Figure 1. RVF transmission cycle

HEAVYRAINFALLS

Source: FAO

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last week of October in one of the predicted locations, Belet Weyne, forcing 2 500 people to seek safety on higher ground away from the riverbanks. This area was affected by RVF in January 2007. However, except for a few small areas in Southern Sudan, the RVF risk map for October 2014, which is based on NDVI anomalies over August, September and October 2014, does not yet show widespread RVF at-risk areas in East Africa or near the reference sites (Figure 6).

Figure 2. Sea Surface Temperature (SST) Anomalies, October 2014.

Above-average SSTs persisted in the equatorial eastern Pacific Ocean along the equator (~1.5°C) and in the equatorial Indian Ocean (~0.5-1.0°C). The tongue-like structure of the SST anomaly off the Peruvian coast is typical of a developing El Niño event.

Source: NASA/GSFC GIMMS GROUP

Figure 3. Outgoing Longwave Radiation (OLR) Anomalies, August-October 2014.

Used to infer tropical precipitation, current OLR anomalies show very dry conditions (brown to red colours) across Indonesia and most of southeast Asia and enhanced precipitation across northern China, the western Indian Ocean, central Asia, north-central and northeast Africa, the United Mexican States/Central America, the southwestern United States of America, and the northeastern and southwestern tropical Pacific.

Source: NASA/GSFC GIMMS GROUP

Erratic and less persistent rainfall occurred during the first weeks of November suggesting the development of less extreme rainfall patterns than those observed in 1997/1998 and 2006/2007 (Figure 4). Nevertheless, because the anomalies increase in positive Western Indian Ocean (WIO) SSTs (Figure 2) and persistent rainfall conditions are still forecast for the coming months, these areas remain at-risk of vector amplification, RVF disease emergence and

spread. Such areas may require early targeted surveillance. In addition areas of the south-western part of the Kingdom of Saudi Arabia and the western part of the Republic of Yemen bordering the Red Sea are advised to enhance targeted surveillance in areas that have received anomalous high rainfall and an increase in NDVI (Figure 3, 5, 6) which can result in an increase in RVF vector mosquito populations.

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Surveillance systems should be strengthened, applying a One Health integrated approach, with an active collaboration and partnership of the national ministries responsible for public health, agriculture and livestock.

Vaccination

The use of vaccination as a control option for RVF is aimed at limiting virus circulation in enzootic areas and preventing epidemics in free areas and is most effective when used in conjunction with other control strategies including surveillance, quarantine and movement controls. Vaccination against RVF in East Africa (mainly in the Republic of Kenya and the United Republic of Tanzania) is undertaken normally in response to the occurrence of RVF outbreaks using a live vaccine prepared from an attenuated strain of the RVF virus (Smithburn strain). Given the side effects associated with the use of live vaccines, uptake has been limited in areas of East Africa where RVF is enzootic.

A new generation of vaccine, Clone 13, currently in use in South Africa, offers high level of protection with less virulence. Recognizing that the Clone 13 vaccine is safe and efficacious against RVF, countries at risk of an incursion of RVF are therefore strongly encouraged to register it.

Mass vaccination is one of the tools for preventing RVF epidemics in animals. However, vaccination is not recommended in the event of known RVF circulation, as inappropriate vaccination can promote the spread of virus transmission.

Specific requirements for RVF vaccine production are available in the Manual of Diagnostic Tests and Vaccines for Terrestrial Animals 2014 Chapter 2.1.1.4. http://www.oie.int/fileadmin/Home/eng/Health_standards/tahm/2.01.14_RVF.pdf

Vector control

Efforts to prevent the transmission of the virus through contact with mosquitoes should be part of the overall One Health approach. The use of insecticides, repellents on animals and humans, mosquito netting and strategic larvicidal treatment for mosquito breeding habitats, can decrease the risk of virus transmission in at-risk areas.

Trade issues

A revised Chapter on RVF (8.13) has been adopted at the General Session in May 2014. The 2014 edition of the Terrestrial Animal Health Code now clearly separates “Country or zone free from RVF virus (RVFV) infection” from “Country or zone infected with RVFV during the inter-epizootic period”. A country or zone may be considered free of RVFV

d) Monitor the NASA/AFHSC/USDA Rift Valley fever Risk Monitoring site for updates at: http://www.ars.usda.gov/Business/Docs.htm?docid=23464

Surveillance in at-risk areas

The communities surrounding the reference meteorological stations where above-average rainfall conditions are predicted in the Republic of Kenya, the Federal Republic of Somalia and the United Republic of Tanzania should be subject to heightened surveillance. This should include increased monitoring of sentinel herds where available and increased surveillance in markets or places where large numbers of at-risk animals are traded or congregate. Focus should be placed on identification and reporting of non-specific clinical signs such as higher than expected numbers of abortions or neonatal mortalities in ruminants in these areas.

Tripartite FAO, OIE and WHO recommendations

Given the predicted risk for potential RVF activity based on abnormally high rainfall in the identified areas of the Republic of Sudan, the Republic of South Sudan, the Federal Republic of Somalia, the Republic of Kenya and the United Republic of Tanzania, FAO, WHO and OIE encourage these countries to:

a) Heighten their level of surveillance for RVF in human and animals in at-risk areas;

b) Increase their level of preparedness, and implement targeted vaccination in known at-risk areas;

c) Raise awareness and communicate with communities the risk of emergence of the disease in animals first and later in humans;

Figure 4. East Africa Rainfall Maps, November 20 2014

Cumulative rainfall anomalies between September 1 and November 20 for the years 1997 (a), 2006 (b), and 2014 (c). Cumulative rainfall between September 1 and November 20 for 2014 (d). Red circles identify areas with increased rainfall anomalies within suitable RVF vector area.

Source: AFHSC/Div GEIS Operations and NASA/GSFC GIMMS.

(a) (b)

(d) (c)

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One Health communication and public awarenessCommunications regarding disease risks and awareness campaigns on risk mitigation are essential to protect livestock and humans from RVF infections by limiting their exposure in particular for livestock farmers and communities, veterinarians and workers involved in slaughterhouse activities.

FAO, OIE and WHO encourage at-risk countries to prepare themselves in cases of an epidemic and specifically encourage veterinary and public health authorities to develop a joint comprehensive health education programme with the aim of informing the public but also targeting at-risk professions (farmers, veterinarians, slaughter house personnel, etc.).

infective period for RVF has been reduced from 6 months to 14 days. This means that even in the presence of disease or infection, the OIE Terrestrial Animal Health Code accepts trade of ruminants and meat from infected countries if certain specific conditions of quarantine, vaccination and maturation of meat are met. This is based on timely and prompt notification of infection or disease to the OIE (OIE, 2014b).

In addition FAO and the International Livestock Research Institute (ILRI), along with relevant technical partners in Eastern Africa, have recently updated the 2010 (Risk-based) Decision-support framework for prevention and control of Rift Valley fever epizootics in the Greater Horn of Africa, providing guidance on how to plan and monitor activities in the different RVF alert stages. The document can be downloaded from the ILRI website: http://hdl.handle.net/10568/21783

on the basis that the disease is notifiable in the whole country and either : i) meets the requirements for historical freedom; or meets the following two conditions: (ii) no evidence of RVFV infection in ruminants for a minimum of ten years demonstrated by an ongoing pathogen-specific surveillance programme and ii) has not had any occurrence of indigenous human cases. A country or zone may be considered infected with RVFV during the inter-epizootic period on the basis that virus activity is present at a low level in the country or zone, while factors predisposing to an epizootic are absent and there are no clinical cases in animals or humans. A third classification is a “Country or zone infected with RVFV, during an epizootic”. In this case, outbreaks of RVF are occurring at an incidence substantially exceeding that of the inter-epizootic period. However, for the purposes of trade, the

Figure 5. Cumulative rainfall anomaly for September 1 – November 20 2014 and meteorological stations (pink open circles) experiencing rainfall anomalies.

Belet Weyne, Federal Republic of Somalia (a); Marigat and Sukari Farm, Republic of Kenya (b & c); Magara and Manyara Ranch, United Republic of Tanzania (d & e). Graphs show cumulative daily rainfall (mm) during 1997 (green line), 2006 (blue), 2014 (pink) and the long term mean (red).

Source: AFHSC/Div GEIS Operations and NASA/GSFC GIMMS (Map) - NOAA/CPC-RFE (Graphics)

(a)

(b)

(c)(d)(e)

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Figure 6. NDVI anomalies and RVF risk maps.

Source: AFHSC/Div GEIS Operations and NASA/GSFC GIMMS.

Public health messages for risk reduction should focus on:

- Reducing the risk of animal-to-human transmission as a result of unsafe animal husbandry and slaughtering practices. Gloves and other appropriate protective clothing should be worn and care be taken when handling sick animals or their tissues or when slaughtering animals;

- Reducing the risk of animal-to-human transmission arising from the unsafe consumption of fresh blood, raw milk or animal tissue. In the epizootic regions, all animal products (blood, meat and milk) should be thoroughly cooked before eating;

- Protecting the individual and the community against the risk of mosquito bites by using impregnated mosquito nets, personal insect repellent if available,

light coloured clothing (long-sleeved shirts and trousers) and by avoiding outdoor activity at peak biting times of the vector species.

- Implementing standard precautions in health care settings. A WHO aide–memoire on standard precautions in health care for RVF is available at: http://www.who.int/csr/resources/publications/standardprecautions/en/index.html

References

Anyamba, A., Britch, S. C., Chretien, J.-P., C. J., Erickson, R. L., Formenty,

Linthicum K. J., Richardson, J. H., Schnabel, D. C., Small, J. & Tucker, P. B.

2009. Prediction of a Rift Valley fever outbreak. Proceedings of the National

Academy of Sciences, 106(3): 955-959.

Anyamba A., Linthicum K.J., Small J., Britch S.C., Pak E. & et al. 2010.

Prediction, Assessment of the Rift Valley Fever Activity in East and Southern

Africa 2006–2008 and Possible Vector Control Strategies. The American

Journal of Tropical Medicine and Hygiene, 83: 43-51.

Bailey, C. L., Davies, F. G., Kairo, A., Linthicum, K. J., Patrican, L. A. & Turell, M.

J. 2008. Vector competence of selected African mosquito (Diptera: Culicidae)

species for Rift Valley fever virus. Journal of Medical Entomology, 45: 102-

108.

Baldet, T., Balenghien, T., Calistri, P., Conte, A., Goffredo, M., Tran, A., Ippoliti,

C., Gely, M. & Chevalier V. 2013. A Geographical Information System-Based

Multicriteria Evaluation to Map Areas at Risk for Rift Valley Fever Vector-

Borne Transmission in Italy. Transboundary and Emerging Diseases, 60:

14-23.

Cohnstaedt, L. W., Scoglio, C., Scott, H. M. & Xue, L. 2013. A Hierarchical

Network Approach for Modeling Rift Valley Fever Epidemics with Applications

in North America. PLoS ONE, 8(5), e62049.

FAO. 2006. Possible RVF activity in the Horn of Africa. EMPRES Watch, Vol. 12

(November), Rome.

Linthicum, K. J., A. Anyamba, C. J. Tucker, P. W. Kelley, M. F. Myers, and C. J.

Peters. 1999. Climate and Satellite Indicators to Forecast Rift Valley Fever

Epidemics in Kenya, Science, 285(5426): 397-400.

OIE. 2012. Rift Valley Fever in the Middle East and the Horn of Africa: challenges,

prevention and control. Bastiaensen P. & Münstermann S., eds. Proceedings

of the GF-TADs (FAO & OIE) inter-regional conference, 12 - 15 November

2012, Mombasa, Kenya. English. OIE, Paris (available at http://www.rr-africa.

oie.int/docspdf/en/2012/RVF/REPORT.pdf)

OIE. 2014a. World Animal Health Information Database (WAHID)

Interface (available at http://www.oie.int/wahis_2/public/wahid.php/

Diseaseinformation/Diseasehome). Accessed 9 December 2014.

OIE. 2014b. Chapter 8.13. Infection with Rift Valley Fever Virus.

Terrestrial Animal Health Code (available at http://www.oie.int/index.

php?id=169&L=0&htmfile=chapitre_rvf.htm). Accessed 9 December 2014.

WHO. 2006. Communicable Disease risk assessment and interventions:

Flooding disaster Horn of Africa (November), Rome.

WHO. 2007. Outbreaks of Rift Valley fever in Kenya, Somalia and United Republic

of Tanzania, December 2006–April 2007. Weekly epidemiological record, 82:

169–178.

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FAOHeadquarters (GLEWS coordinator) Dr. Julio Pinto julio.pinto@fao.org

Nairobi office (ECTAD) Dr. B. A. Diop bouna.diop@fao.org

OIE HeadquartersDr. S. Münstermann s.munstermann@oie.int

Nairobi Office Dr. P. Bastiaensen p.bastiaensen@oie.int

WHO Headquarters Dr. P. Formenty formentyp@who.int

Brazzaville Office Dr. N. Ndayimirije ndayimirijen@who.int

NOTES

Technical support

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Recommended citationFAO, OIE, WHO. 2014. Climate models predict persistent above-average rains and risk of flooding in East Africa: FAO, OIE and WHO warn countries to remain vigilant about Rift Valley fever. EMPRES WATCH, Vol. 31, December 2014. Rome.

Photo cover: ©FAO/Eran RaizmanPhotos back cover: ©FAO/Simon Maina

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