Rift Valley Fever in Africa

Kariuki Njenga, DVM, PhDCenters for Disease Control & Prevention, Nairobi, Kenya

L. Baringo

L.

Bogoria

Legend: • Livestock confirmed cases

+ Sublocations with confirmed human cases

Solonchak soils

Density map of human and animal cases on

solonchak soil

Munyua et al., Amer J Trop Med Hyg 83 (Supp2), 58-64,2010

Transmitted by infected mosquito bites

– Various species of mosquito

– other biting insects can transmit

Affects sheep, cattle, camel, goats

– Abortions

– bleeding

RVF Disease: Transmission in Livestock

RVF Disease: Transmission in humans

o Direct contact with blood, meat, milk and other

body fluids of infected animals

o Can occur during slaughtering, skinning

o Bite of infected mosquito

Aerosol transmission?

– Generated during slaughter of infected livestock

What are risk factors of acute RVF in humans?

• Touching an aborted fetus [OR = 3.83]

• Consuming or handling products from sick animals

[OR = 2.53]

• Being a herdsman [OR = 1.77]

• Exposure to mosquitoes was not an independent

risk factor

Amwayi et al., Amer J Trop Med, 83 (supp2), 14-21, 2010

19

40

19

50

19

60

19

70

1980

19

90

20

00

20

10

Egypt

Egypt

Mauri

tania

Ma

urita

nia

KS

A/Y

em

en

Egypt

Su

da

nR

SA

/Com

oro

s

RVF activity in East Africa*

RVF Epidemics (1932 – 2011)

RS

AM

adagascar

RS

A

Recent Severe Human RVF OutbreaksYear Countries Estimated

Cases

Reported

Cases

Deaths

1977 Egypt 200,000 18,000 598

1987 Mauritania 1500 300 224

1993 Egypt 1500 ? 20

1997-98 Kenya, Somalia,

Tanzania

89,000 ? 4581

1998 Mauritania 300 150 7

1999 Mauritania ? ? 2

2000 KSA, Yemen 1500

2000

516

1087

87

121

2003 Egypt 300 148 27

2006-07 Kenya, Tanzania,

Somalia

? 700

309

107

158

144

54

2007 Sudan ? 125+ 60+

2008, 2009 Madagascar, RSA,

Comoros

? ? ?

2010,2011 RSA ? 255 26

1Data available from Kenya only

RVF Risk Mapping: Set upRVF – epizootics occur under favorable and persistent eco-climatic conditions

Can be mapped – either as rainfall or

vegetation – NDVI integrates all the required conditions

Algorithm:

– Mapping of potential epizootic areas –

based on literature survey and climate

variable thresholding= potential epizootic

area mask (PEAM) – (C. J. Peters & K.J.

Linthicum in Handbook of Zoonoses)

– NDVI anomaly calculation -- + anomalies >

0.025 threshold (desert calibration) over 3

month period

– Persistently + anomalies must have three

month mean > 0.1

– All “pixels” that meet this criteria and are

within the PEAM are mapped to have

conditions necessary for the occurrence

of RVF activity

Epidemic prediction: Relies on field dataTeamwork

Capacity Building

1

12

21

2

3

17

10

7

6

9

15 8

5

22

14

20

16

4

19

18

11

13

6-

7

14

20

16

19

18

11

13

1

12

21

2

3

17

10

7

6

9

15 8

5

22

14

20

16

4

19

18

11

13

6-

7

14

20

16

19

18

11

13

1951-1955 1997-2007

Murithi et al., Epi Infect 18, 1-9, 2010

Kenya: RVF Spread Over 52

Last 2 epizootics affected 6 of 8 provinces, 38 of 69 districts

Prediction vs. Outbreak Timing: Epi-Curves: 2006 - 2008

Anyamba et al (In Review AJTMH)

What is the inter-epizootic period (IEP)?

IEP

IEP

IEP

IEPMean IEP = 3.6 years

Murithi et al., Epi Infect 18, 1-9, 2010

Based on Kenya Dept Vet Svs Data – 1910 - 2007

Where is RVF virus maintained ?

1. Transovarially in Aedes mosquito spp

2. Endemicity. Cycling between wildlife, livestock and possibly humans within a permissive

ecosystem, mediated by the appropriate vectors.

Cummulative percent of positive samples at each titer level

-20.00

0.00

20.00

40.00

60.00

80.00

100.00

1:12

80

1:64

0

1:32

0

1:16

01:

801:

401:

201:

10

Titer level

% o

f p

osit

ive s

am

ple

s o

f

sp

ecie

s Buffalo

Black rhino

Other

In wildlife

Evans et al, Epid Inf 8, 1-92007

Negative: Lions, giraffes, common zebras

9 of 17 species tested

were positive

- Buffalos, Black rhinos,

- Thompson gazelles,

- Impalas, Elands, Kudus

Rostal et al, Amer J Vet Res 71, 522-6, 2010

In livestock : Kenya during the 1999 – 2006 IEP

Where is RVF virus maintained ?

Sheep Goats

Year

of

birth

No. testedPercentage

positiveNo. tested

Percentage

positive

1999 12 25 5 0

2000 27 11 7 14

2001 17 29 7 0

2002 19 11 10 0

2003 17 18 17 0

2004 29 24 10 10

2005 63 17 15 0

2006 4 0 4 0

Total 188 18* 2/75 3

Northeastern Province of Kenya

December, 1997 December, 2006

Sequential Epidemics in Kenya, Somalia, and Tanzania [1997-8; 2006-7]

Reported Human RVF Cases (Deaths) in Kenya

Wajir

26(12)

Garissa

176(59)

Ijara

131(27)Tana-River

21(8)

Kilifi

73(20)

Malindi

15(4)Taita-Taveta

15(1)

ISIOLO

13(0)

Kajiado

10(6)

Baringo

174(13)

Nakuru

1(1)

Kirinyaga

5(2)

Maragua

4(0)

Thika

2(0)Nairobi

5(2)

NEP333 of 700 (45%)

cases

Baringo174 of 700 (24.8%)

Cases

Kilifi73 of 700 (10.4%)

cases

Confirmed and Probable Rift Valley Fever Cases ,

Kenya 2006/07(N=340)

0

2

4

6

8

10

12

14

16

18

2021/1

1/2

006

28/1

1/2

006

05/1

2/2

006

12/1

2/2

006

19/1

2/2

006

26/1

2/2

006

02/0

1/2

007

09/0

1/2

007

16/0

1/2

007

23/0

1/2

007

30/0

1/2

007

06/0

2/2

007

13/0

2/2

007

20/0

2/2

007

27/0

2/2

007

06/0

3/2

007

13/0

3/2

007

20/0

3/2

007

27/0

3/2

007

Date of Onset

Ca

se

s

Alive

DeadNEP Kilifi

Baringo

RVF Outbreaks in Somalia

First case confirmed 20th January, 2007

Total:107 cases, 54

(50.5%) deaths

RVF Outbreak in Tanzania

First case confirmed Feb 1st, 2007

Total: 309 cases, 144 deaths

Sequential Epidemics: How does the virus spread?

2006-2007 Epidemic

Region 1: Nov 26, 2006

Region 2: Dec 26, 2006

Regions 3,4: Jan 7, 2007

Region 5: Feb 5, 2007

Region 6: Jan 27, 2007

Region 7: Feb 1, 2007

Nderitu et al., J Inf Dis 203, 2011

Ken

ya

2

Ke

nya

1b

Ken

ya

1a

Ta

nzan

ia 1

How do epizootics spread?

Multiple lineages of RVF virus during one epidemic indicate spontaneous

activation of resident virus

Nderitu et al., J Inf Dis 203, 2011; Bird et al, 2008

Number of confirmed RVF cases and deaths by

province, South Africa, 2010- 2011 (latest April 10, 2011)

All cases occurred mid-February – May each year

Province Cases Deaths 2010 2011 2010 2011

Eastern Cape 17 13 1 0

Free State 123 3 11 0

Gauteng 0 0 0 0

KwaZulu-Natal 0 0 0 0

Limpopo 0 0 0 0

Mpumalanga 0 0 0 0

Northern Cape 74 2 11 0

North West 9 0 2 0

Western Cape 4 9 1 0

Total 228 27 26 0

Source: NICD, South Africa

South Africa: RVF Infection Map, April 2011

Source: NICD, South Africa

1st Epizootic / Epidemic 1990 -few cases

Another in 1991

26

#

Antananarivo

Perinet Forest

Epizootic / Epidemic 1990

Epizootic / Epidemic 1991

RVF in Madagascar

Last cases in 2009

Last cases in March 2009

#

Antananarivo

27

Epizootic / Epidemic 2008-2009

Primary Forest of Perinet

Epizootic / Epidemic 1990

Epizootic / Epidemic 1991

Epizootic / Epidemic 2008

RVF in Madagascar

Major Interventions (Eastern Africa)

Social mobilization

Slaughtering ban

– Major religious holiday (Idd festival)

Livestock quarantine

Livestock vaccination

Vector control (minimal)

RVF Outbreak Response 2006 – A Step BehindLivestock vaccination Public Education

Challenges

Poor accessibility: Flooding

Timing: Occurred in peak holiday season

Limited health services in the region

Coordinating surveillance between

livestock and human health