Presentation made by Nsonga A1,Mfitilodze W1, Samui K.L.2, Sikawa D1 at the Biennial Conference, 2012

1. 1

2.  In 2006,First EUS outbreak in Africa & Zambezi River
System (ZRS) was reported (FAO, 2009).
 Biodiversity of the Fishery was threatened and posing
Food insecurity to 700,000 people (FAO, 2009).
 Rapid study conducted was too late for anything else
other than impact assessment (Samui et al., 2007)
 In 2007, Fish samples confirmed EUS positive
(Aphanomyces invadans)……Thailand

3.  Further surveillance in 2007, estimated EUS infection
rate at 50% whereas by 2008, it was 5% (FAO, 2009).
 Observation implies decreasing disease intensity with
time.
 Seasonal outbreaks have persisted and not much
epidemiological research carried out to adequately
elucidate factors associated with EUS outbreaks in the
ZRS

4.  Investigate and understand the Epidemiology of EUS on
fish in the Zambezi River System of Zambia.
Specific Objectives
1. Determine Env. & Bio. risk factors associated with
EUS outbreak in the ZRS of Zambia.
2. Determine the infection rate and severity of EUS on
fish spp of the ZRS in Zambia.
3. Determine the spatial distribution of EUS in the ZRS of
Zambia.

5.  An active surveillance and participatory epidemiology
was used for data collection (Corsin,2007).
 Collection of Env. & Fish Data was done btn Jan 2011
through Jan 2012 from Sesheke District-Zambia
 Five (5) Sampling sites chosen; Main river, Backwaters,
Tributary, Lagoon & Non-affected area

6.  Environmental Data collected ;
Water Temp, Ambient Temp, DO2 ,Water pH,
Total alkalinity, Salinity, NH3, NO3- , No2-, waterflow,
waterlevel- site & month of sampling.
- Multiparameter water quality Checker
- Analytical methods
 Rainfall data for 10 previous yrs collected

7. Biological factors;
 At least 320 fish sampled per site using a 12mm
meshed seine net for 3 seasons-(Feb,June & Oct)
 Presumptive diagnosis for lesions done.
Suspect Fish formalinised (10%)- EUS confirmation at
UNZA.

8. Infection Rate and Severity of EUS
 A total of 4,800 fish were sampled and Gross examined
for EUS infection- proportion determined.
 Severity characterised
0- Lesion absent, 1- Red spot, (mild) 2- Deep ulcers ( severe), 3- Healing (Recovery)

9. EUS Distribtion
 Active surveillance
 Participatory epidemiology
- 350 fishers from 7 Districts along ZRS of Zambia
interviewed-checklist.
- fish specimen formalinised (10%)
 GPS (NAVI 1300) used for mapping coordinates of
EUS +ve stations and Districts

10. PCA extraction method
Components 1 2
Factor 1 2 3
Month A temp
site
T alkalinity Water temp
-.099 -.093 .833
Ambien temp .113 .944 .105
Waterflow -.467 .334 .452
Waterlevel -.937 -.236 -.091
Water temp -.483 .839 .012
Oxygen .169 -.912 -.086
3
Site
Water pH .111 -.507 .614
Water pH
Ammonia .895 .189 .085
Nitrite -.174 .682 -.145
Nitrate .023 -.273 -.425
Salinity .890 .232 -.026
Totalkalinity .903 .369 .029
Month .909 -.162 .059

11. Environmental factors
Logistic Regression Analysis ; Sig. Test (ap<0.05) and measures of association with disease.
Env. Cue Sample # Mean S.e Sig a Meas ure
of
association with
EUS Disease
Month 321 6.028 0.1861 0.003 0.922
Site 321 2.996 0.0790 0.049 0.604
Amb. Temperature 321 25.85 0.3058 0.04 0.906
Water Temperature 321 20.94 0.2173 0.02 0.889
Water pH 321 6.4 0.0199 0.016 0.782
Total alkalinity 321 45.13 0.0418 0.007 0.743

12. Rainfall A 10 year rainfall patern for Sesheke district
1200
JUL RF
1000 AUG RF
SEP RF
Rainfall-RF (mm) 800
OCT RF
600 NOV RF
DEC RF
400
JAN RF
200 FEB RF
MAR RF
0
APR RF
1999/2000
2000/2001
2001/2002
2002/2003
2003/2004
2004/2005
2005/2006
2006/2007
2007/2008
2008/2009
2009/2010
2010/2011
MAY RF
JUN RF
TOTAL RF
years

13. Infection rate
.
Infection Mycotic gran. Healing
144 not affected
58
86
4,656
4,800
144 144
4,800
3% 1.2%
1.79% 97%
EUS +Ve

14.  EUS infection on fish showed no size nor species
specificity
 However, of the 15 species sampled Brycinus lateralis,
Serranochromis robustus and Sargochromis giardii
were found more susceptible to EUS than other species.

15. Disease Severity
 Mild infections
Red spots- across spp
Healing wounds Brycinus lateralis with lesion
No mortalities
Histopathology of EUS-infected
Brycinus lateralis
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16. EUS DISTRIBUTION IN ZRS OF ZAMBIA
M
M
M
M
M
M

17. Participatory epidemiology: Fishers’ opinion
 EUS outbreaks have occurred every year since 2006
affecting most fish spps.
 Outbreaks occur every year in their local fishing areas.
 EUS often occurs in lagoons & oxbow lakes not close to
the main river.
 Fish-eating birds and reptiles such as crocodiles might be
transmiting the disease from one place to another.
 Floods play a vital role in disease spread.
 EUS was associated with low temperature and occurred
after periods of heavy rain.
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18. Research implicates a combination of env. factors preceded by rains that compromised the
aquatic environment……….
Control of EUS in wild is difficult but……
- Water quality-Application of agricultural lime in lagoons and oxbow
- Bio-security-Restriction on trans-boundary fish stock transfers
- Regional cooperation- share research outputs, focus more on
preventing disease spread to non affected areas.
- Health and safety- EUS infected fish should not be eaten
- Warning alarm -Rainfall higher than 500mm will lead to flooding
- Capacity building- Epidemiologists to carry out countrywide
surveillance

19. Corsin F.,2007. Surveillance system for Epizootic Ulcerative Syndrome in
Southern Africa
FAO, 2009. Report of the international emergency disease investigation task
force on a serious fish disease in Southern Africa, 18-26 May
2007, FAO, Rome, Italy, 70pp.
FAO, 2009. What you need to know about epizootic ulcerative syndrome
(EUS)- An extension brochure. Rome, Italy.
Samui K.L., Hangombe B, Choongo K., Syachaba M and Phiri H, 2007.
Report on the field expedition to assess the possible causes of the general fish
kill in western Province from 18th september to 1st October 2007. 29pp.
School of Veterinary Medicine, University of Zambia.

20. Thank you
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