The Prevalence of Parasite Contamination of Vegetables and the Risk Factors in their Transmission in Nsukka Ecological Zone, Enugu State.
ABSTRACT
The prevalence of parasite contamination of vegetables and the risk factors in their transmission were investigated in Nsukka Ecological Zone, Enugu State, Nigeria.
A total of four hundred and eighty-eight (488) samples of six different raw edible vegetable types, from three farms and three markets, were examined between January and October, 2013. It consisted of 241 farm vegetable samples and 247 market samples.
The vegetables included fruit of Solanum marcrocarpon (garden egg), leaf of Solanum species (garden egg leaf), Amaranthus species (spinach or green), Telfairia occidentalis (pumpkin leaf), Ocimum basilicum (scent or basil leaf) and Solanum lycopersicum (tomatoes).
The vegetable samples were washed with normal saline, allowed to stand overnight for sedimentation, and the sediments were examined microscopically, after centrifugation, for the presence of parasites eggs, cysts, oocysts and larvae.
Eighteen samples of irrigation water, six from each farm, were also examined during the dry season, January – March.
The irrigation water was allowed to stand overnight in a straight sided container for sedimentation, and the sediments were examined microscopically after centrifugation and concentration of the parasites.
Modified Zieehl-Neelsen technique was used to detect oocysts of Cryptosporidium parvum in vegetable and irrigation water samples.
The parasites recovered were Entamoeba histolytica cyst, Cryptosporidium parvum oocyst, Taenia species egg, Hymenolepis species egg, Ascaris species egg, hookworm egg, Trichuris trichiura egg, Strongyloides stercoralis larva, Enterobius vermicularis egg and Trichostrongylus species egg.
Ascaris was the predominant parasite found, followed by E. histolytica. C. parvum had the least prevalence 11(4.6%) in farm vegetable samples while E. vermicularis and C. parvum were the least prevalent 9(3.6%) in the market samples.
Trichostrongylus species and Hymenolepis species were the least prevalent 1(5.6%) in irrigation water. Two hundred and fifty-three (51.8%) of the vegetable samples were contaminated with various parasites.
One hundred and thirty-two (53.4%) of market vegetables and 121(50.2%) of farm vegetables were found to have parasitic contamination. The parasites, however, were more prevalent in vegetable samples from farms than those from the markets.
The University of Nigeria, Nsukka (UNN) farm had the highest rate of contamination 47(56.6%) while Nkpologu farm had the least contamination 35(46.1%). Contamination rate among the farms however, did not differ significantly (P > 0.05).
Among the markets, Ikpa had the highest rate of contamination 46(56.1%) whereas Opanda had the least 42(51.9%), but this did not differ significantly (P > 0.05). Pumpkin leaf was the most contaminated vegetable while tomatoes were the least.
The difference was significant (P < 0.05). The month of August recorded the highest rate of contamination while the least were February and January for farm and market vegetable samples respectively.
The difference was not significant (P > 0.05) in farm samples but was significant (P < 0.05) in market samples. The seasonal variability of parasites showed that the rate of contamination was higher in rainy than dry season.
This differed significantly (P < 0.05) in the market samples but was not significant (P 0.05) in the farm samples. Climatic factors were found to influence the prevalence of parasites in vegetables.
The prevalence of some parasites increased as the climatic factors increased while that of others decreased with increase in climatic factors.
The water used by farmers to irrigate vegetables did not meet WHO recommended standard of ≤ 0.1 helminth eggs per litre.
The poor correlation between parasites found in irrigation water and their consequent contamination of vegetables, however, implied that the use of animal manure and environmental contamination with faeces were more important sources of contamination of vegetables in the ecological zone.
Analysis of responses from the questionnaire showed that 92.1% of farmers used animal manure to fertilize vegetables, 72.3% said farmers do not treat it before use, while 94.1% of the respondents agreed to the practice of open defection in the area.
It also showed that all six vegetables are consumed raw without adequate washing. These findings incriminated raw edible vegetables as important vehicle of transmission of both human and zoonotic intestinal parasites in the ecological zone.
The study therefore recommended that untreated animal manure and wastewater should not be used to fertilize and irrigate raw edible vegetables respectively.
It also recommended among others, adequate washing of vegetables before consumption, prevention of environmental pollution with both human and animal faeces, etc.
TABLE OF CONTENTS
Title page .. .. .. .. .. .. .. .. .. .. i
Certification .. .. .. .. .. .. .. .. .. .. ii
Dedication .. .. .. .. .. .. .. .. .. .. iii
Acknowledgements .. .. .. .. .. .. .. .. .. iv
Abstract .. .. .. .. .. .. .. .. .. .. vi
Table of contents .. .. .. .. .. .. .. .. .. viii
List of tables .. .. .. .. .. .. .. .. .. .. xi
List of figures .. .. .. .. .. .. .. .. .. .. xiv
List of plates .. .. .. .. .. .. .. .. .. .. xv
List of appendices .. .. .. .. .. .. .. .. .. xvi
CHAPTER ONE: INTRODUCTION AND LITERATURE REVIEW
1.1 Introduction .. .. .. .. .. .. .. .. .. .. 1
1.1.1 Justification of the study .. .. .. .. .. .. .. .. 5
1.1.2 Objectives of the study .. .. .. .. .. .. .. .. 5
1.2 Literature Review .. .. .. .. .. .. .. .. .. 6
1.2.1 Vegetable .. .. .. .. .. .. .. .. .. .. 6
1.2.1.1 Production systems for vegetables .. .. .. .. .. .. 6
1.2.1.2 Global production and trade of vegetables .. .. .. .. .. 7
1.2.1.3 Trends in vegetable consumption .. .. .. .. .. .. .. 8
1.2.1.4 Health benefits of vegetables .. .. .. .. .. .. .. 9
1.2.1.5 Sources of contamination of vegetables .. .. .. .. .. .. 10
1.2.1.6 Decontamination of vegetables .. .. .. .. .. .. .. 15
1.2.2 Guidelines for wastewater use in crop irrigation .. .. .. .. .. 16
1.2.3 Protozoan parasites frequently isolated from raw/fresh vegetables.. .. .. 20
1.2.4 Some helminth parasites frequently isolated from raw/fresh vegetables.. .. 23
1.2.5 Reported outbreak of illnesses associated with vegetables .. .. .. .. 25
CHAPTER TWO: MATERIALS AND METHODS
2.1 Study Area .. .. .. .. .. .. .. .. .. .. 28
2.2 Study Design .. .. .. .. .. .. .. .. .. .. 32
2.3 Sampling Locations/Sites .. .. .. .. .. .. .. .. 32
2.4 Sample Collection .. .. .. .. .. .. .. .. .. 37
2.4.1 Collection of vegetables .. .. .. .. .. .. .. .. 37
2.4.2 Collection of irrigation water .. .. .. .. .. .. .. .. 37
2.4.3 Collection of climatic data .. .. .. .. .. .. .. .. 37
2.5 Parasitological Assay .. .. .. .. .. .. .. .. .. 37
2.5.1 Screening of vegetables .. .. .. .. .. .. .. .. 38
2.5.2 Screening of irrigation water .. .. .. .. .. .. .. .. 38
2.5.3 Modified Zieehl-Neelsen technique .. .. .. .. .. .. .. 39
2.6 Identification of Parasites .. .. .. .. .. .. .. .. 39
2.7 Quantification of Eggs Per Litre .. .. .. .. .. .. .. 40
2.8 Assessment of Risk Factors .. .. .. .. .. .. .. .. 40
2.9 Informed Consent .. .. .. .. .. .. .. .. .. 40
2.10 Statistical Analysis .. .. .. .. .. .. .. .. .. 40
CHAPTER THREE: RESULTS
3.1 Overall Prevalence Rate of Parasite Contamination in Vegetables in Nsukka Ecological Zone . .. 46
3.1.1 Overall prevalence rate of parasite contamination in farms and markets studied .. 46
3.1.2 Overall prevalence rate of parasite contamination in farm and market vegetables studied.. .. 48
3.1.3 Overall monthly prevalence rate of parasite contamination in the farms and markets.. .. 50
3.1.4 Overall seasonal prevalence rate of parasite contamination in the farms and markets .. .. 52
3.2 Distribution of Parasites in Vegetables Collected from Farms and Markets in Nsukka Ecological Zone .. 54
3.2.1 Overall distribution of parasites in the farms and markets .. .. .. 54
3.2.2 Overall distribution of parasites in farm and market vegetables.. . .. 56
3.2.3 Distribution of parasites in farm and market garden egg… .. .. 58
3.2.4 Distribution of parasites in farm and market garden egg leaf.. .. . .. 60
3.2.5 Distribution of parasites in farm and market spinach .. .. .. .. 62
3.2.6 Distribution of parasites in farm and market pumpkin leaf .. .. .. 64
3.2.7 Distribution of parasites in farm and market scent leaf .. .. .. 66
3.2.8 Distribution of parasites in farm and market tomatoes.. .. .. 68
3.2.9 Comparison of parasite distribution between farm and market fruit vegetables.. .. 70
3.2.10 Comparison of parasite distribution between farm and market leafy vegetables.. .. 72
3.3 Seasonal Distribution of Parasites in Farm and Market Vegetables in Nsukka Ecological Zone…. 74
3.3.1 Seasonal distribution of parasites in farm and market garden egg.. .. .. 74
3.3.2 Seasonal distribution of parasites in farm and market garden egg leaf.. .. 76
3.3.3 Seasonal distribution of parasites in farm and market spinach.. .. 78
3.3.4 Seasonal distribution of parasites in farm and market pumpkin leaf…… .. 80
3.3.5 Seasonal distribution of parasites in farm and market scent leaf.. .. .. 82
3.3.6 Seasonal distribution of parasites in farm and market tomatoes.. .. .. 84
3.4 Correlation of Climatic Variables with Parasite Distribution in Different Vegetables in Nsukka Ecological Zone 86
3.4.1 Correlation of climatic variables with parasite distribution in different farm fruit vegetables.. 86
3.4.2 Correlation of climatic variables with parasite distribution in different farm leafy vegetables .. 88
3.4.3 Correlation of climatic variables with parasite distribution in different market fruit vegetables.. .. 90
3.4.4 Correlation of climatic variables with parasite distribution in different market leafy vegetables.. .. 92
3.5 Prevalence of Parasites in Examined Irrigation Water in Nsukka Ecological Zone.. .. 94
3.5.1 Overall prevalence of parasites in irrigation water .. .. .. .. 94
3.5.2 Quantification of parasite count per litre of irrigation water.. .. .. .. 96
3.5.3 Monthly prevalence of parasites in irrigation water.. .. .. .. .. 98
3.5.4 Impact of irrigation water on parasite contamination of vegetables collected from the farms. 100
3.6 Respondents Reported Risk Factors Associated with the Transmission of Parasites via Vegetables in Nsukka Ecological Zone… 102
3.6.1 Demographics of the respondents.. .. .. .. .. .. .. 102
3.6.2 Assessed agricultural practices that increase the risks of parasite contamination of vegetables… 104
3.6.3 Assessed human attitudes that increase the risks of parasite contamination of vegetables.. .. 107
3.6.4 Assessed anthropogenic attitudes that increase the risks of parasite transmission to man via vegetables… 109
3.6.5 Respondents knowledge on raw consumption of vegetables.. .. .. .. 112
CHAPTER FOUR: DISCUSSION, CONCLUSION AND RECOMMENDATIONS
4.1 Discussion.. .. 115
4.1.1 Prevalence of parasites in vegetables.. .. .. .. .. .. .. 115
4.1.2 Correlation of climatic variables with parasite distribution in vegetables.. .. 119
4.1.3 Major sources of parasitic contamination of vegetables in Nsukka Ecological Zone… .. 121
4.1.4 Risks of parasite transmission to man via vegetables in Nsukka Ecological Zone .. 123
4.2 Conclusion .. .. .. .. .. .. .. .. .. .. 125
4.3 Recommendations.. .. .. .. .. .. .. .. .. 126
References
Appendices
INTRODUCTION
Parasites are living organisms that live in or on another living organism (known as the host), deriving nourishment as well as shelter from the host and at the same time causing harm to the host.
They constitute one of the “Nature’s hangmen” because parasitic diseases continue to be a major public health problem all over the world with associated high degree of morbidity, mortality and man-day loss (Alli et al., 2011; Arora and Arora, 2011).
Out of the six major unconquered disease complexes in the world, five are parasitic in the traditional sense (Cheng, 1999).
Globally, parasites cause over two billion infections annually and more than 25% of sixty million deaths are attributed to them (Arora and Arora, 2011).
More than 1.3 billion people worldwide have ascariasis, and 250 million suffer from associated morbidity; trichuriasis, hookworms (Necator americanus and Ancylostoma duodenale) and schistosomes infect over 1 billion, 1.25 billion and 200 million people, respectively (WHO, 2004).
Others include Entamoeba histolytica (50 million) and Giardia lamblia (2.8 million) (Nyarango et al., 2008).
Intestinal parasites are transmitted to humans via the faecal –oral route as a result of poor personal hygiene, and contamination of soil, water and food sources with human excreta (which occurs through indiscriminate sewage disposal (Nyarango et al., 2008).
The potential risks factors for human intestinal parasitic infections involve unhygienic associations with unhygienic environment (Altekruse, 1997).
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