SUMMARY

Listeriosis is an emerging zoonoses requiring continuous surveillance in order to prevent

outbreaks in humans. The disease can develop after consumption of a wide range of foods

such as meat products, dairy products especially in ripened cheeses, delicatessen products,

fish and seafood products and vegetables. It is a rare disease with high hospitalization rates

for those who become ill and high mortality rate.

Consumption of locally processed milk is becoming more popular among low and medium

income earners in Nasarawa state and checking for possible disease agents that could be

ingested in locally processed milk is essential for prevention. This research estimates the risks

of listeriosis associated with consumption of milk products in Nasarawa State and establishes

science-based intervention strategies aimed at reducing these risks. The study determines

association between socio-demographic characteristics of milk vendors and the occurrence of

Listeria species in locally processed milk in Nasarawa State, Nigeria.

Four hundred and twenty (420) milk samples were collected from vendors after administering

questionnaire on milk processing practices.

Milk samples were processed in the laboratory by culture and isolation, biochemical

characterisation, agglutination and Microbact test. Antibiotic sensitivity was also conducted

on samples that tested positive for listeria.

The socio-demographic characteristics of respondents showed that majoritywere within the

age group 20-24 years, they were mostly females (92.4%), traders (53.1%), Muslims

(99.5%); had no formal education (67.4%). Furthermore, majority of them earned between

N6,000-N18,000 monthly (52.1%). Out of 420 samples collected and tested, 10.2% (43

samples) were positive for listeria through culture and isolation. Listeria species found in this

study are 100% susceptible to enrofloxacin and doxycycline; 77.8% to kanamycin but

resistant to Penicillin (93.7%) and Amoxicillin (80%) and Sulphamethazole/trimethoprim

(60%). Borrowing/sharing of milk processing equipment and refrigeration/addition of ice to

processed milk are factors significantly found to be associated with presence of listeria in

milk sample (with odd ratio of 3.07 and 5.54 respectively). Conversely, training on food

safety and supervision during milk processing were found to be significantly protective from

listeria in milk sample (with odd ratio of 0.14 and 0.18 respectively).

Processors of locally processed milk should be encouraged to undergo food safety training,

observe strict supervision during processing of milk and be discouraged from the practice of

adding ice to milk and borrowing or sharing of equipment.

2

CHAPTER ONE

INTRODUCTION

1.1.      Background

Listeriosis caused by Listeria specie is an emerging zoonotic disease requiring continuous

surveillance in order to prevent outbreaks in humans. The invasive form of listeriosis is

observed primarily in high-risk population groups such as the elderly, individuals with

lowered immunity, pregnant women and newborns. Ready-to-eat foods are the most

important source of both sporadic cases and outbreaks of listeriosis in humans.[1] The disease

can develop after consumption of a wide range of foods such as meat products [2], dairy

products especially in ripened cheeses,[3] delicatessen products[4] fish and seafood products[5]

and vegetables.[6]     Animals are also susceptible to listeriosis but can carry Listeria

monocytogenes asymptomatically.

First confirmed human case of listeriosis was reported in Nigeria in 1982,[7] food borne

listeriosis has not been much documented. The organism causes infection (listeriosis) in man

and in different animal species such as cattle, sheep and goats.[8] People at highest risk

included the elderly, the fetuses of pregnant women, and the immunosuppressed. It is unique

among foodborne pathogens since its incubation time is about seven days. Human infection is

therefore more devastating in immunosuppressed individuals, pregnant women, infants,