Monitoring and managing mycotoxins on maize Challenges and opportunities for resolving an emerging public health crisis in Kenya Rebecca Nelson ASM meeting January 2014
Outline • Overview of the problem – in the African context • Assessment – Evidence of pervasive contamination of Kenyan maize • Perception – Who knows; who needs to know? • Management – Management options – The posho mill scheme Photo: S. Mideros
Focus fungi/toxins for this study Feature Aflatoxin Fumonisin Fungus Aspergillus flavus and A. parasiticus Fusarium , esp. F. verticillioides Health issue Hepatitis and liver cancer; growth Esophageal cancer; growth impairment; immunosuppression impairment; neural tube defects Mechanisms DNA damage; gut irritation Sphingolipid interference; gut irrit’n Lifestyle Generalist; weak ear-rot pathogen; Maize endophyte and stronger ear- pre- and post-harvest rot pathogen; pre-harvest Environmental Warmer temps (30 - 43°C); Moderate temps (15 - 37°C) drivers plant stress (drought) Regulatory limit 10 ppb (Kenya) 1,000 ppb Fumonisin B1 Aflatoxin B1 WHO 2000; http://gallery.cimmyt.org; http://www.aspergillusflavus.org/aflavus/; Marasas et al., 2008
Why worry about mycotoxins on maize in Kenya? • Maize as staple – 25% of calories; 25% of cropped area; • Substantial self-provisioning – >70% by 3.5 M smallholders • Climate and other stressors high risk • Most Kenyans HepB seropositive • There are known problems… – Fatal aflatoxicosis in most years; highly toxigenic Aspergillus in E Kenya – Fumonisin also reported • … but there is limited data, awareness or management; methods are limiting
Framework Perception Assessment Response
Framework Perception Assessment Response What is the extent of mycotoxin contamination of Kenyan maize?
2009/2010 study sites 2010 2009 Kenya
Grain mill survey Samuel Mutiga, Vivian Hoffmann et al.
Mycotoxin measurements Biosciences Eastern and Central Africa ILRI, Nairobi • Helica ELISA • Total Aflatoxin Assay: Solid phase direct competitive immunoassay • Range: 1-20 ppb Immunocapture Aflatoxin extraction • VICAM Aflatest Immunocapture • Fluorometer/monoclonal antibody based affinity chromatography; • Range: 0.1‐300 ppb ELISA
Aflatoxin occurrence in eastern vs. western regions Eastern Western 60 2010 2009 % for Western 146 mills 26 mills 50 % for Eastern n=1,500 n=985 40 39% over 15% over legal limit legal limit 30 % 20 10 0 <1 ppb 1-10 ppb >10 ppb Aflatoxin bins S. Mutiga
Districts with sub-humid agroecologies at greatest risk (watch semi-humid and arid too)? Western Eastern Predominant AEZ Semi Arid Semi humid Humid Semi-humid to Semi-arid Sub humid S. Mutiga
Aflatoxin drivers in maize – E. Kenya • 1,500 samples w/questionnaire • Sub-humid most on 31 management factors contaminated (post-harvest?) • 60% samples home-grown • Rainfall during grain filling • 1/3 < 1 ppb significant in semi-humid • More land and yield less • Drivers of +/- (GLM) toxin – Yield, land size, cropping system, – Less crop stress AEZ – More ability to select – Home sorted, preservative • Intercrops less toxin than • Drivers of quantity (> 1 ppb; monocultures mixed model) • Kernel damage poor – Quality, kernel integrity, AEZ indicator • 17% of variance explained by mills w/in AEZ Mutiga and Vermeylen
Fumonisin occurrence in western and eastern Kenya Western Eastern Kenya Kenyan 45 n = 569 n = 270 40 38% over legal 31% over legal limit 35 limit 30 % for 25 Western 20 % for 15 Eastern 10 5 0 <100 ppb 101-1000 ppb >1000 ppb Fumonisin levels S. Mutiga
Contamination with two mycotoxins across AEZs 60 Aflatoxin Fumonisin Percent of samples 50 40 above limit 30 20 10 0 Humid Sub-Humid Semi-Humid Semi-humid to Semi-Arid Semi-Arid Decreasing soil moisture availability
Do fumonisin levels affect child growth? Yellow- Demographic and Health Survey cluster location (n=73 clusters) Blue- mycotoxin sample location Orange- 20 km radius Laura Smith, Becky Stoltzfus
Fumonisin associated with stunting Median fumonisin levels (controlling for FB variance) significantly predicted HAZ ( B=-0.00055; p=0.034 ) and WAZ ( B=-0.0005; p=0.029 ) of children. Controlled for known predictors of poor child growth: Gender, HH income, mother’s education, mother’s height, mother’s weight, diet diversity In a region with a median fumonisin level of 1000 ppb, the international legal limit for fumonisin, the average child is 0.5 Z scores shorter and lighter than a child in a region with no fumonisin. Laura Smith, Becky Stoltzfus
High rates of esophageal cancer in Kenya Fumonisin : big and important Perception Assessment Response What is the extent • Aflatoxin : lots where it is a of mycotoxin known problem; present but contamination of less where not recognized. Kenyan maize? • Overall mean of [aflatoxin] = 3x legal limit
Perception Assessment Response Do people know?
Maize for own consumption : 20% chance of being over the legal limit for aflatoxin Maize for sale : 40% chance of being over the legal limit for afatoxin Hoffmann, Mutiga et al.
Less care taken with maize for sale Post-harvest: people take more care with maize they will eat • 100 people surveyed; 38% sold maize – Keep small-grain local types; sell large-grain hybrid – 50% of sellers take less care in drying, storage – 50% of sellers use pesticides on maize to be sold V. Hoffmann Photo: James Gethi
Emerging concern about aflatoxin in Kenya Maize quality loss Acute aflatoxicosis Year Fatalities 1982 - 1999 15 2000 - 2010 207 • Inadequate surveillance • No proper regulation 2010: 2.3 million bags = 20,700 t condemned
Increasing concern about aflatoxin in research, policy, & Perception funding circles Assessment Response Information Consumers need to asymmetry; know what they are lack of incentive feeding their families for clean maize
Perception Assessment Response What can people do to reduce mycotoxin accumulation and exposure? Pre-harvest Post-harvest Soil fertility Grain sorting resistance resistance management
Genetic resistance to mycotoxin accumulation? Dan Jeffers, CIMMYT CML 269 – derived hybrid Aspergillus ear rot evaluation trial, Mexico, July 2005. Pre-harvest Post-harvest Soil fertility Grain sorting resistance resistance management
Pre-harvest resistance: QTL meta-analysis synthesis of 12 mapping studies Heritability is low to moderate for aflatoxin resistance, Mideros et al., 2013 moderate to high for fumonisin resistance Pre-harvest Post-harvest Soil fertility Grain sorting resistance resistance management
Post-harvest resistance: mature kernel assay 26 diverse inbred maize lines; seed grown in five locations (7 sets) Location Year 1 Year 2 Aurora 2009 Puerto Rico 2007 2008 Missouri 2007 2009 Florida 2007 Blacksburg 2009 Pre-harvest Post-harvest Soil fertility Grain sorting resistance resistance management
Susceptibility of mature kernels to aflatoxin is influenced by grain production conditions Low heritability, H 2 =35% Pre-harvest Post-harvest Soil fertility Grain sorting resistance resistance management
Maize varieties in farmer’s storage conditions Setup Questions Do the following influence • Humid AEZ in Bungoma, W. mycotoxin accumulation in Kenya farmers’ stores? • 182 farmers who grew • Variety/texture major varieties: • Moisture content at harvest – H614 • Storage conditions – H513 • Ear rot/integrity Grain – WH505 Varietal • Preservative – Local # 8 moisture at differences harvest in toxin associated levels in with storage fumonisin H614 S. Mutiga H513 WH505 Local # 8
Mycotoxin levels much higher in posho mills than in grain stores Grain store (N=488) Posho mill (N=324) At mill In storage Aflatoxin % Undetectable Det., under limit Above limit Undetectable Det., under limit Above limit In storage At mill Grain store (N=316) Posho mill (N=125) Fumonisin % Undetectable Det., under limit Above limit Undetectable Det., under limit Above limit
CIMMYT IMAS goal: develop varieties tolerant to low N 403 genotypes KARI Kiboko KARI Embu KARI Kiboko KARI Kiboko Low N Low N Optimal N Optimal N Long Rains Long Rains Long Rains Short Rains Rep 1 Rep 1 Rep 1 Rep 2 Bulked 109 genotypes common to all environments Pre-harvest Post-harvest Soil fertility Grain sorting resistance resistance management
Nitrogen management v. mycotoxins 900 N treatment 800 associated with 700 lower aflatoxin 600 but not lower fumonisin 500 Aflatoxin Fumonisin 400 300 200 100 0 Embu Low N Rep 2 Embu Low N Rep 1 Kiboko Low N Kiboko Optimal Long Kiboko Optimal Short N-treated N-depleted Collaboration with CIMMYT’s Improve Maize for African Soils Project
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