Food Control 16 (2005) 239–242

www.elsevier.com/locate/foodcont

Prevalence of helminth eggs on raw vegetables used for salads

Esma Kozan a, Bahadir Gonenc b, Oguz Sarimehmetoglu b, Hasan Aycicek c,*

a Department Helminthology, Veterinary Faculty of Afyon Kocatepe University, 03010 Afyon, Turkeyb Department Helminthology, Veterinary Faculty of Ankara University, 06029 Diskapi, Ankara, Turkey

c Department Food Hygiene and Technology, Gulhane Military Medical Academy, 06018 Etlik, Ankara, Turkey

Received 11 October 2003; received in revised form 23 February 2004; accepted 24 February 2004

Abstract

The presence of helminth eggs on raw vegetables, including lettuce, parsley, green onions, cucumbers, carrots, red cabbage,

tomatoes, rockets (Eruca sativa), and green-peppers from wholesalers in Ankara, Turkey was determined. A total of 203 unwashed

and 406 washed samples were assayed by light microscopy. Helminth eggs were detected in 12 (5.9%) of 203 unwashed samples and

not in any washed samples (p < 0:05).Helminth eggs detected in unwashed samples included Taenia spp. (3.5%), Toxocara spp. (1.5%), and Ascaris lumbricoides (1.0%)

eggs. Taenia spp. eggs were recovered to be highest number (n ¼ 130), followed by Toxocara spp. eggs (n ¼ 21). Approximately 11%

of unwashed lettuce and parsley was contaminated compared with only 2.5% of carrot samples. No helminth eggs were detected in

red cabbage, rockets, tomatoes or green-peppers.

These results highlight the potential for transmission of helminth eggs by unwashed salad vegetables in Turkey and the

importance of properly washing/disinfecting raw vegetables before consumption.

� 2004 Elsevier Ltd. All rights reserved.

Keywords: Vegetables; Human pathogens; Helminth eggs; Washing; Disinfecting

1. Introduction

In recent years, studies conducted in countries withwidespread helminthic infections (Amahmid, Asmama,

& Bouhoum, 1999; da Silva, Marzochi, Camillo-Coura,

Messias Ade, & Marques, 1995; de Oliveira & Germano,

1992; Ogunba & Adedeji, 1986; Rude, Jackson, Bier,

Sawyer, & Risty, 1984) have shown that consumption of

raw vegetables and fruits without proper washing or

peeling represents an important potential for the spread

of related infections. The increased demand, globalsourcing and rapid transport of foods, especially soft

fruit and salad vegetables, enhance both the likelihood

of source contamination and survival of the transmissive

stages of parasites pathogenic to man (Slifko, Smith, &

Rose, 2000). In developing countries, especially,

uncontrolled use of water from sources contaminated

with human and animal faeces to irrigate such vegeta-

bles and fruits has been reported to be responsible fortheir high rates of contamination with helminth eggs

*Corresponding author. Fax: +90-312-3042150.

E-mail address: haycicek@gata.edu.tr (H. Aycicek).

0956-7135/$ - see front matter � 2004 Elsevier Ltd. All rights reserved.

doi:10.1016/j.foodcont.2004.02.005

(Guilherme et al., 1999; Takayanagui et al., 2000;

Ulukanligil, Seyrek, Aslan, Ozbilge, & Atay, 2001).

Considering the fact that a part of the vegetables grownin these developing countries are exported to the

developed world, the threat that these contamina-

tions cause to other countries cannot be overlooked

(Robertson & Gjerde, 2001).

Failure to adhere to hygienic standards in the kitch-

ens of institutions like schools, hospitals, restaurants

and hotels that deal in catering services can lead to the

widespread and easy spread of helminthic infections likeA. lumbricoides, hookworms, Enterobius vermicularis,

Trichuris spp. Toxocara spp. and Trichostrongylidae to

humans as a result of consumption of improper washed

vegetables and fresh fruits used as salad ingredients

(Coelho, Oliveira, Milman, Karasawa, & Santos, 2001;

Mesquita, Serra, Bastos, & Uchoa, 1999; Takayanagui

et al., 2001; Vazquez Tsuji, Martinez Barbarosa, Tay-

Zavala, Ruiz Hernandez, & Perez-Torres, 1997).The objective of this study was to determine the

prevalence of helminth eggs on raw salad vegetables

obtained from wholesalers.

240 E. Kozan et al. / Food Control 16 (2005) 239–242

2. Materials and methods

A total of 203 unwashed and 406 washed raw salad

vegetables, including lettuce, red cabbage, cucumbers,

green onions, carrots, tomatoes, parsley, rockets and

green-peppers, were obtained between January 2002 and

June 2003 for assay. The vegetables were collected from

wholesalers in the villages of Ankara during the summer

months and from villages of Antalya, Adana, Mersin,and Hatay in the Mediterranean region during the

winter months. The total of 30–35 samples were col-

lected monthly from five wholesalers. Specific informa-

tion regarding water used to irrigate fields from which

the vegetables were grown could not be obtained. Half

of the samples analyzed before washing and half after

washing/disinfecting.

2.1. Evaluation of the unwashed samples

The vegetable samples from wholesalers were brought

to a hospital kitchen. They were transported to the

laboratory for analysis in nylon bags before washing

process. Samples from the outer leaves of lettuce and red

cabbage, and the peeled skins of carrots, tomatoes, and

cucumbers were obtained, whereas parsley, greenonions, rockets, and green-peppers were evaluated in

tact. Portion of the samples (200 g) were weighed into

sterile nylon.

2.2. Evaluation of washed samples

The washing/disinfecting procedure of the vegetables

in the kitchen included:

1. The sorting stage: Before the washing procedure,

crushed and rotten leaves of the fruits and vegetables

were removed and not used.

2. First washing stage: The leaves of leafy vegeta-

bles were separated and washed with tap water.

Thus, mud and dust of these vegetables were re-

moved.3. Chlorination stage: After the first washing stage, the

vegetables were disinfected by submersion in a wash

solution containing 200 ppm active calcium hypo-

chloride for 30 min.

4. The rinsing stage: The chlorinated vegetables were

washed in an automated vegetable–fruit washer

(Electrolux, Mod. LV198N-Italy) to rinse.

5. The slicing–peeling and weighing stage: Skins ofcarrot, tomato, cucumber samples were peeled. After

peeled parts of the samples were weighed (200 g) into

nylon bags. Lettuce, red cabbage, parsley, green

onion, rocket, and green-pepper samples were sliced

and weighed (200 g) into nylon bags.

2.3. Detection of helminth eggs

The washed and unwashed samples that were brought

from the hospital’s kitchen to the laboratory once every

week, were weighed in portions of 200 g. The weighed

samples were placed in a 1.5-l detergent solution (con-

taining 1% sodium dodecyl sulphate, and 0.1% Tween

80) and subjected for 10 min of sonication using a so-

nicator (Bandelin Sonorex, Mod. RK100H, SonorexElectronic, Germany) (Bier, 1991). Later 50 ml of the

liquid obtained from the sonication procedure were

transferred to centrifugation tubes and centrifuged for

15 min at 1500g (Bier, 1991). The sediment was exam-

ined at 10· magnification under a light microscope for

helminth egg content. The eggs were identified at 40·magnification. Thus, the helminth eggs were counted in

200 g each of samples. Eggs that were deformed wereexcluded from the evaluation.

2.4. The statistical analysis

The data were analyzed by with Statsdirect (Statsdi-

rect Ltd., ver. 2, 2.0) statistical software. Helminth egg

contamination percentages of two samples were com-

pared by the ‘‘Test for two proportions’’ procedure. The

number of eggs of two vegetables was compared by

using ‘‘Comparing two counts test’’ at p < 0:05 (Kanji,

1999; Zar, 1996).

3. Results and discussion

Results of helminth egg contamination of unwashedand washed samples are presented in Tables 1 and 2.

Helminth eggs were detected in 12 (5.9%) of 203 un-

washed. However, neither of washed samples have any

eggs (p < 0:05). The helminth eggs recovered from raw

unwashed samples were Taenia spp. (7/203; 3.5%),

Toxocara spp. (3/203; 1.5%), and Ascaris lumbricoides

(2/203; 1.0%). The recovery percentage of helminth eggs

in unwashed lettuce samples was highest rate (11.4%),whereas, the carrot samples had the lowest infestation

rate (2.5%). No infestation was detected on red cabbage,

tomatoes, rockets, and green-peppers. Differences

among the rates of positive samples were not statistically

significant (p > 0:05).The number of helminth eggs detected per 200 g of the

vegetables is presented in Table 2. The greatest number

of eggs after sample was Taenia spp. (n ¼ 130) followedby Toxocara spp. (n ¼ 21). The highest helminth egg

count was found in parsley samples (n ¼ 107), whereas

cucumber samples (n ¼ 4) contained lowest (Table 2)

(p < 0:05). Eggs that were deformed (7, Taenia spp.; 2,

Toxocara spp.) were excluded from the evaluation.

Table 1

Results of the analysis of unwashed vegetables

Sample (n) Taenia spp. Toxocara spp. A. lumbricoides Total

No. (%) No. (%) No. (%) No. (%)

Lettuce (n ¼ 35) 0 (0.00) 2 (5.71) 2 (5.71) 4 (11.42)

Parsley (n ¼ 44) 4 (9.09) 1 (2.27) 0 (0.00) 5 (11.36)

Green onion (n ¼ 15) 1 (6.66) 0 (0.00) 0 (0.00) 1 (6.66)

Cucumber (n ¼ 16) 1 (6.25) 0 (0.00) 0 (0.00) 1 (6.25)

Carrots (n ¼ 40) 1 (2.50) 0 (0.00) 0 (0.00) 1 (2.50)

Red cabbage (n ¼ 14) 0 (0.00) 0 (0.00) 0 (0.00) 0 (0.00)

Tomato (n ¼ 15) 0 (0.00) 0 (0.00) 0 (0.00) 0 (0.00)

Rocket (n ¼ 8) 0 (0.00) 0 (0.00) 0 (0.00) 0 (0.00)

Green-pepper (n ¼ 16) 0 (0.00) 0 (0.00) 0 (0.00) 0 (0.00)

Total (n ¼ 203) 7 (3.45) 3 (1.48) 2 (0.98) 12 (5.91)

Table 2

Determined egg counts on infected samples

Sample Number of samples infected Egg counts in 200 g of sample

Taenia spp. Toxocara spp. A. lumbricoides

Lettuce (n ¼ 35) 4 0 6, 12 3, 5

Parsley (n ¼ 44) 5 8, 12, 16, 68 3 0

Green onion (n ¼ 15) 1 7 0 0

Cucumber (n ¼ 16) 1 4 0 0

Carrot (n ¼ 40) 1 15 0 0

Total 12 130 21 8

E. Kozan et al. / Food Control 16 (2005) 239–242 241

Studies on helminthological quality of vegetables in

Turkey are insufficient. In previous studies by Ulukan-

ligil et al. (2001) in Sanliurfa (south-east Anatolian

region) in Turkey, A. lumbricoides and Taenia spp. were

detected, in 11.0% and 1.0%, respectively of unwashed

vegetables tested. In our study, the rate of A. lumbrico-

ides was found lower than those of Ulukanligil et al.

(2001), whereas the rate of Taenia spp. was higher. Choiand Lee (1972) found Ascarid eggs in 49.0% of 147

lettuce samples that were collected from markets in

Taegu, Korea.

In various studies (Amahmid et al., 1999; Ogunba &

Adedeji, 1986; Robertson & Gjerde, 2001; Takayanagui

et al., 2001), different rates of helminthic infections were

associated with vegetables and fruits in various coun-

tries. The differences observed in these studies were re-lated to the level of development of the various countries

as well as the differences within same country (Robert-

son & Gjerde, 2001; Takayanagui et al., 2001). The

water used in irrigating these fields especially was

implicated as a major route of direct contamination of

the fruits and vegetables grown on them by parasites

contained in these waters. In addition, in areas where

the hygienic conditions of the canalization system werenot appropriate, the spread of human-borne helminthic

infections especially was apparent (Bergstrom &

Langeland, 1981; Guilherme et al., 1999; Takayanagui

et al., 2000; Ulukanligil et al., 2001).

In Turkey, hydatidosis infection is widespread among

humans and animals (Tinar & Coskun, 1991; Unat,

1991). In this study, some of the eggs thought to be

Taenia spp. were suspected to be Echinococcus granulo-

sus that are indistinguishable from Taenia spp. and are

transmitted through waters contaminated with faeces of

dogs. The high rate of Taenia spp. contamination of

unwashed vegetables indicate that unwashed raw vege-tables are of major importance in the epidemiology of

helminthic infections from Taenia spp.

Eggs thought to be those of A. lumbricoides are very

difficult to distinguish from A. suum. However, swine

production, with which A. suum is associated, is ex-

tremely limited and pork consumption rarely occasion

in Turkey. Therefore, it was suggested that the eggs are

most likely those of A. lumbricoides. This infection, seenespecially in children and which leads to growth retar-

dation, has been reported to be of high prevalence in

Turkey (Yasarol, 1984). Presence of A. lumbricoides and

Taenia spp. in the samples indicates that the canaliza-

tion system as well as the toilet habits in the areas where

these products are grown are not up to the required

standards.

Almost all studies performed on this topic have fo-cused on the rate of parasitic infections carried by veg-

etables and fruits cultivated in the different regions of

various countries for marketing (Amahmid et al., 1999;

Ogunba & Adedeji, 1986; Robertson & Gjerde, 2001;

242 E. Kozan et al. / Food Control 16 (2005) 239–242

Takayanagui et al., 2000) and evaluation of the variousmethods available for obtaining the eggs and larvae of

these parasites from vegetables and fruits (Bier, 1991;

Robertson & Gjerde, 2000; Rude, Peeler, & Risty, 1987).

Besides, studies on the nature of the washing process of

potentially contaminated vegetables and fruits from re-

gions with high rates of parasitic infections and the level

of change of this potential after the washing procedure

are especially important. In present study, absence ofany helminth eggs indicates that washing/disinfecting

procedures are proper in the establishment.

Vegetables from the Mediterranean region are ex-

ported to European and Asian countries. Thus, the

study is also important with regard to this point of view.

The results indicate that irrigation methods of vegeta-

bles fields and protection of these areas against to stray

animals are very poor. Besides, detected helminth eggsare evidence for human-borne and animal-borne con-

taminations. It is certain that irrigation process of these

vegetables fields has been performed using contaminated

water sources. Besides, it suggests that cats and dogs (or

wild canidae) have entered into the fields freely. These

poor conditions should be improved urgently. There-

fore, legal preventive precautions should be forced for

natural water sources and agricultural environments.Frankly, food safety principles from field to table for

vegetables in Turkey need reformation.

Consequently, the data emphasized that if washing

and disinfecting procedures of the raw eaten salad veg-

etables are neglected, they can be important vehicles of

transmission human pathogen helminths.

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