PRELIMINARY ESTIMATES OF ECONOMIC IMPACT OFLIVER FLUKE INFECTION IN THAILAND AND

THE FEASIBILITY OF IRRADIATION AS A CONTROL MEASURE

Paisan Loaharanu' and Santasiri Sornmanf

IHead, Food Preservation Section, Joint FAOIIAEA Division of Nuclear Techniques in Foodand Agriculture, International Atomic Energy, PO Box 100, A-1400 Vienna, Austria;

2Faculty of Tropical Medicine, Mahidol University, Rajvithi Road, Bangkok,Thailand.

Abstract. Liver fluke infection by Opisthorchis viverrini is the leading cause of food-borneparasitic disease in Thailand. Approximately one third of the population in the northeastern regionof the country, ie, 6-7 million, are infected by this parasite through the habit of consuming rawor insufficiently cooked freshwater fish, especially those of cyprinoid family. A recent surveyshowed that 60% of the work force in the Northeast between the age of 15 and 60 is infected. Theestimated wage loss of this population may be approximately Baht 1,620 million (US$65 million)per annum. The estimated direct cost of medical care may be as high as Baht 495 million (US$19.4million) per annum. Thus, the total direct cost of the infected work force is estimated to be Baht 2115million (US$84.6 million) per annum.

Irradiation of fish flesh infected by metacercaria of 0. viverrini has been demonstrated as aneffective method of control. A minimum dose of 0.1 kGy is effective without changingphysiochemical properties of the fish flesh. This technology, therefore, shows promise as a methodto control infection by 0. viverrini acquired by the habit of consuming raw freshwater fish inthe country. Preliminary economic analyses indicate that the public health benefit from preventinginfection with this parasite could outweigh the investment cost of irradiation facilities. Detailedeconomic feasibility studies should be carried out to demonstrate the practical efficacy and cost-effectiveness of the treatment as a public health intervention measure in the country.

INTRODUCTION

While the world has witnessed tremendoustechnological development in recent years, basicprimary health care has not kept up with thisprogress. For example, the incidence of food-borne disease continues to adversely affect thehealth and productivity of populations in mostcountries, particularly those in the developingworld. The report of a Joint FAOfWHO ExpertCommittee on Food Safety (WHO, 1984) statedthat "illness due to contaminated food isperhaps the most widespread health problemin the contemporary world and an importantcause of reduced economic productivity".

Because food-borne disease is so widespreadand a significant cause of morbidity, the socialand economic impact is considerable in bothdeveloping and developed countries; more infor-mation is available concerning the latter.

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While the economics of food-borne disease isnot clearly established, the estimate in NorthAmerican and European countries shows that itcan be enormous and represents a significantloss to national economies. For example, theUnited States Food and Drug Administrationestimated the occurrence of food-borne diarrhealdisease in the USA is as high as 24-81 millioncases per year. The costs of medical care andlost productivity may amount to US$5-17 billionper year (Archer, 1986). Todd (1989) estimatedthe total number of cases of food-borne diseasein Canada to be 2.2 billion cases per year ofwhich 88% was caused by microbiologicalagents. The estimated economic loss was 1.3billion Canadian dollars in 1985. In the FederalRepublic of Germany, salmoneiiusis costs alonewere estimated to be DM240 million per year(WHO, 1984). Costs of medical treatment andproductivity lost alone for trichinosis, toxo-

projects have also contributed to the sprea~ ofparasites in fish and aquatic animals in the region.

Epidemiology of liver fluke infection

According to Sornmani (1988), 0. viverrini istransmitted through consumption of raw orimproperly cooked freshwater fish, especially ?fthe cyprinoid family which is abundant Innatural waters all over Thailand.

The popular dishes prepared from this fishare "koi pla" and "pla som". "Koi pla" is madfby chopping raw fish into small pieces andmixing it with chili, lemon and other spices. Itis then eaten immediately with glutinous riccT-"PIa som" is also made from fresh cyprinoidfish but it is mixed with boiled rice and otherspices and left to ferment overnight. Metacer-cariae in fish prepared by these methods canretain their infectivity.

Liver fluke infection is known throughoutThailand, but is much more prevalent in thenortheastern region. It is a chronic liver diseaseand the common clinical symptoms are weak-ness, gastrointestinal disturbances and pain theright subcostal region. Jaundice and fever fr0flthe obstruction of bile ducts or cholangitis arealso common. In prolonged and severe cases,the patients may develop biliary fibrosis orcholangiocarcinoma of the biliary system. Aneffective medicine to treat the infectionbecame available recently. Praziquantel, anisoquinolin compound, has been found to behighly effective against the infection. The sideeffects of the treatment are mild and could bereduced or prevented by giving the drug afterdinner. Although an effective drug is availableto control the disease, there are still problemsconcerning the cost of the drug and the highreinfection rate.

IRRADIATION TO CONTROL LIVER FLUKE INFECTION

plasmosis, salmonellosis, campylobacteriosis andbeef tapeworm in the USA were estimatedby the USDA to be over US$l billion per year(Morrison and Roberts, 1985).

Little data are available on the estimatedcosts and economic impact of food-borne para-sitic diseases, especially those commonly occurr-ing in developing countries. Roberts (1985)estimated the costs of lost wages and medicaltreatment of 563 reported cases of trichinosis inthe USA in 1985 as $1.4 million. This paperattempts to make preliminary analysis of economicimpact of liver fluke infections caused byOpisthorchis viverrini, a common parasiticdisease transmitted to man by the consumptionof raw freshwater fish in Thailand. It will alsoattempt to analyze the feasibility of introducingirradiation technology to control the disease inthe country.

LIVER FLUKE INFECTION

Liver fluke infection is widespread amongpopulations in the northeastern region ofThailand. This region has a total population ofapproximately 18 million, one third of the entirecountry. According to the Thai Ministry ofPublic Health, the most common diseases ofthe population in this region are those of therespiratory tract and gastrointestinal tract, withinfection rates of 89.6 and 64.7 per 1000 popu-lation, respectively (Anon, 1985). The popu-lations in this region have a tradition, cultureand habits which differ from those of otherregions. For example, the habit of eating rawmeat and fish allows parasites, such as tape-worms, round worms, liver flukes and otherfood-borne parasites, to gain access into theirbodies. As freshwater fish is the most commonsource of animal protein for the population, themajor causes of their gastrointestinal infectionsare intestinal parasites, especially the liver fluke.In addition, the habit of farmers of defecatingin the field promotes the spread of this disease.The Ministry of Public Health estimated that onethird of the population in the region, ie, 6 millionare infected with liver flukes.

To improve economic productivity of theregion, a number of water resource developmentprojects have been put into operation to improveirrigation and increase fish production. Such

Measures to control infection

The following measures have been con-sidered and introduced for controlling liverfluke infection:

a. Control of intermediate hosts (snail, fish).b. Health education and improvement of

sanitation.c. Prevention of reinfection.d. Treatment.

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FOOD - BORNE PARASITIC ZOONOSIS

The first measure was considered impracticaland uneconomical. The second measure willtake considerable time, especially changing thehabit of the population from eating raw tocooked fish. The same is true for the thirdmeasure, as the only way to become reinfectedis through ingestion of raw fish. Thus, thefourth measure is the only way to control thisinfection in Thailand at present.

Notwithstanding the difficulties facing thecontrol of liver fluke infection, three pilot~rojects were carried out by Sornmani (1988)and his team between 1981 and 1986 in Khon-Kaen Province. The projects covered diagnosis,treatment, health education and sanitationimprovement. The strategies included educationOf mothers, children in school, annual treatmentto reduce reinfection, community participationin diagnosis and payment for the treatment, etc.The projects were quite successful as the numberof infections was significantly reduced duringthis period. Close and constant monitoring ofthe infection is required, however, to evaluatethe degree of reinfection of the parasite.

In principle, there are three defense mecha-nisms to control food-borne illness:

, a. To produce food (eg, fish, meat, vegetables)free from agents which cause infectiousdiseases.

I b. To process food to destroy target organisms(eg, pathogenic bacteria, parasites).

c: To educate consumers to properly handleand cook food.

With regard to liver fluke infection, itappears that only the last defense mechanismis: applicable until now. While the practicabilityand economics would rule out the applicabilityof the first mechanism, it may be worthwhileexploring a technology which could control theinfectivity of liver fluke without compromisingthe safety and quality of treated fish. Such atechnology should be comparable to heat pasteuri-zation of liquid food (eg, milk), which iseffective in controlling milk-borne pathogenswithout significantly altering the nutritional valueor quality of milk.

ECONOMIC IMPACT

In general, the economic impact of food-borne

386

illnesses may be measured by:

a. The loss of business to the food producer,retailer or caterer.

b. Medical care and hospitalization of thepatients.

c. Income lost because of illness or carrierstate.

d. Cost of investigation of the outbreak.e. Cost of recall of infected food from commer-

cial channels, destruction of such food.f. Law suits and prosecution.g. Grief, pain, suffering and death.

In this preliminary analysis of economicimpact or" liver fluke infection in Thailand,attempts were made to estimate only the costs ofmedical care and hospitalization and incomeloss because of illness caused by liver flukeinfection. A number of assumptions were madeto arrive at reasonable estimates.

Based on a previous one year observation onmorbidity of opisthorchiasis in a community inKhon Kaen Province conducted by Sornmani(1988), the following assumptions were madein making an economic analysis:

a. Total population infected by liver fluke inthe northeastern part of Thailand: 6 million.

b. The percentage of the infected populationat active working ages (15-60): 60% (atotal of3.6 million population infected).

c. Each infected person had an average ofthree days of illness during each episode.

d. Parasite treatment per person per treatment:3 tablets of praziquantel at a cost of 25Baht each (3 x 25 = 75 Baht/personlannum).

e. Five per cent of infected persons requiredhospitalization on an average of3 days/ per-son/year. The cost of hospitalization is ap-proximately Baht 250/day (300,000 x 3 x 250= 225,000,000).

f. Official minimum wage of Baht 50/day/person.

From these assumptions, the cost estimatesof medical care and wage loss of liver flukeinfection northeastern Thailand were as follows:

Loss of wages

a. Income per capita innortheast: 50 Bahtlday,

Cost/annum

15,000 Baht(6xl02 US$)

IRRADIATION TO CONTROL LIVER FLUKE INFECTION

25 days/monthb. If 60% of work force is 3.6xl06 persons

infected.c. Each infected person has 3episodes 1,620 x 106

Baht per year of 3 days duration. (65 x )06US$) each(3.6x 106x3x3x50)

Direct cost of medical care

a. Treatment (25 Bahtltab, 3 tab.of praziquantel/person)

b. If 5% of infected personsrequired hospitalization of3 days at Baht 250/day(O.3x106x3x250)

Total direct medical cost:

270x106 Baht(lOo4xl06 US$)225x106 Baht(9x106 US$)

Total direct cost of infectedwork force of 3.6x106 persons

495x106 Baht(1904x106 US$)2, 115x106 Baht(84.6x106 US$)

Using the conservative scenario, wages lostfrom the infection may be as high as Baht 1,620million (US$65 million) per annum. Togetherwith the cost of medical care of Baht 495 million(US$1904 million) the economic impact of wageslost and of medical care of infection caused byliver flukes in northeastern Thailand may be ashigh as Baht 2,115 million (US$84.6 million)per annum.

IRRADIATION TO CONTROLFOOD-BORNE PARASITES

Unlike thermal pasteurization of liquid food,there is no method to "pasteurize" solid foodsfrom animal origin, such as meat, fish, chicken,etc, to ensure their hygienic quality and withoutchanging their physical properties.

In the past decade, radiation treatment of foodhas been increasingly recognized by nationalauthorities as an effective method to ensurehygienic quality of food, especially solid food,and to reduce post-harvest food losses. The safetyof this treatment has been evaluated by severalinternational expert committees appointed byFAO, IAEA and WHO since 1964. In its lastsession, the Joint FAOIIAEAlWHO ExpertCommittee on the Wholesomeness of IrradiatedFoods (WHO, 1981), convened in 1980, con-cluded that "irradiation of any food commodityup to an overall average dose of 10 kGy causes

no toxicological hazard; hence, toxicologicaltesting of food so treated is no longer required."The Committee also stated that such treatmentintroduces no special nutritional and microbio-logical problems in food. In 1983, the CodexAlimentarius Commission, an intergovernmentalbody dealing with worldwide food standards,and represented by 138 governments at present,adopted a Codex General Standard for Irra-diated Food and Recommended InternationalCode of Practice for Operation of Facilities Usedfor Treatment of Food.

Following these international recommen-dations, 37 governments have approved the useof irradiation for treating one or more fooditems. Twenty-four of these countries are usingthe technology for treating a number of food!food ingredients for commercial purposes. Withregard to control of food-borne parasites, theUS FDA has approved the use of the technologyfor controlling trichinosis in pork, with aminimum dose of 0.3 kGy. There is, however,no practical application for this purpose in theUSA in view of the low incidence of trichinosisin the country. Small scale application of irra-diation to control salmonellosis and trichinosisin "nham" (fermented pork sausages) has beensuccessfully carried out in Thailand in the past4 years (prachasittisak et aI, 1989).

What is food irradiation? What can it do?

Food irradiation is the treatment of food bya certain type of energy similar to heating,freezing and microwaving. The process involvesexposing the food, either packaged or in bulk,to carefully controlled amounts of ionizingradiation for a specific time to achieve certaindesirable objectives. Ionizing radiation whichcan be used for treating food include thefollowing:

a. Gamma rays from the radionuclides 6OCoor 137Cs.

b. X-rays generated from machine sourcesoperated at or below an energy level of 5MeV.

c. Electrons generated from machine sourcesoperated at or below an energy level of 10MeV.

These ionizing radiations cannot add radio-

387

FOOD - BORNE PARASITIC ZOONOSIS

activity to the food regardless of the length oftime the food is exposed or the amount ofenergy "dose" absorbed. In other words, theseradiations are at levels too low to induce radio-activity in any material, including food.

Ionizing radiations act through changes inDNA molecules in living organisms, such asbacteria or sprouting cells, to prevent theirdivision, or cause biochemical reactions in thephysiological processes of plant tissues slowingdown ripening or maturation of certain fruitsand vegetables. The energy level used forirradiation of food to achieve any technologicalpurpose is extremely low. At the maximumenergy level (dose) of ionizing radiation recom-mended by the Codex Alimentarius Commissionfor treating food (10 kGy), the absorbed energyis equivalent to energy of heat which wouldincrease the temperature of water by 2.4° C.Quite often, irradiation of food uses much lowerdoses (0.1 or 1 kGY) which would be equivalentto heat energy of 0.024° C or 0.24° C. Thus,irradiated food remains at the same natural stateafter treatment as it was originally.

Irradiation as a control method

The effect of irradiation on the destructionor' food-borne parasites was recognized some 70years ago (Schwartz, 1921). Gould et al (1955),Gomberg and Gould (1958), and Brake et al(1985) demonstrated the effect of irradiation ata minimum absorbed dose of 0.3 kGy againstTrichinella spiralis in pork. Based on these data,the US FDA approved the use of irradiationfor treating pork to control T spiralis in 1985(FDA, 1985) using a minimum absorbed dose of0.3 kGy (maximum 1 kGy).

Taylor and Parfitt (1959) and van Kooij andBobijns (1968) reported a dose of 6 kGy tocontrol Taenia solium and T. saginata usingevagination as a means to determine whetherthe treated tapeworms were still alive. Verster(1979), however, used the ability to grow andretain scolices as criteria to determine infectivity,and reported a dose between 0.2 and 0.6 kGycould be used to render carcasses infected withcysticerci fit for human consumption. Dubey etal (1986) reported a dose of 0.5 kGy as effectiveto prevent infectivity of Toxoplasma gondiiusing cats and mice for bioassay.

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In the past three years, institutions inArgentina, Belgium, China, Japan, Republic ofKorea, Kuwait, Mexico, Poland, Thailand, Turkeyand USA have collaborated under the scope ofa Coordinated Research Program on the Use ofIrradiation to Control Infectivity of Food-BorneParasites, sponsored by the Joint FAOIIAEADivision of Nuclear Techniques in Food andAgriculture. The results of this coordinatedresearch program are summarized in Table 1.

StrategiesThermal pasteurization of milk has been

made mandatory by most governments in thepast 50 years to protect consumers' health. Asa result, milk-borne disease has been significantlyreduced or virtually eliminated. Unfortunately,consumers are not yet given the same degreeof protection from other foods of animal origin,especially those intended to be consumed in araw or partially cooked state.

Radiation treatment of such foods againstpathogenic microorganisms and parasites offersa unique opportunity to control infections fromthese biological agents. The liver. fluke issensitive to low dose irradiation. A minimumradiation dose of 0.10 kGy appears to be effectiveto control infectivity of this parasite. Treatedfish will remain in its raw state and can be

..ccI

>-

Table 1Minimum Effective Dose (MED) of radiation to

control infectivity of certain food-borne parasites.

Parasite MED (KGy)

Opisthorchis viverrini

Clonorchis sinensis

0.1

0.1

Angiostrongylus cantonensis 2.0*

Toxoplasma gondii 0.55

Taenia saginata 0.6*

Trichinella spiralis 0.3

• Preliminaryresults

potatoes, garlic and ginger roots against sprout-ing, and "nham" against Salmonella contami-nation, and possibly Trichinella, etc.

IRRADIATION TO CONTROL LIVER FLUKE INFECTION

used for traditional food preparation with-out significant changes in sensory properties.However, for the infection to be effectivelycontrolled by this technology, the followingparameters will have to be considered:

a. Logistics of treating fish soon after catch-ing and distribution in the villages.

b. Population to be made well-aware of healthrisk from consuming raw cyprinoid fish.

c. Populations need to have neutral attitude tofish treated by irradiation.

d. Close cooperation among local health,food control and technical personnel intreating fish by this technology.

Thus, a feasibility study should be carried outto determining the volume of products to betreated, type of facility (whether stationary ormobile unit), its capacity, location and cost.Consumer attitudes will also have to be studiedto ensure success of the project. Ideally, such aproject should be carried out in a model villagewhere the incidence of infection is already knownand the local health authorities are constantlymonitoring it. The impact of irradiation of localfish products on the incidence of infection couldthen be measured.

Once a small scale feasibility study producespositive conclusions, the government (central orprovincial) has to decide in terms of investmentabout an irradiation facility. Irradiation, inthis case, should be considered as an effectivepublic health intervention measure rather thaneconomic benefit to the investment. The costof investment of irradiation facilities (approxi-mately US$800,OOO each) and the treatmentcost should be borne by national authorities inexchange for the cost of medical care and lostproductivity attributable to liver fluke infection.It would also be interesting to conduct a largescale economic feasibility study on installing anumber of facilities in Thailand to treat allcyprinoid fish against this parasite. It may bepossible that the public health benefit wouldfar outweigh the investment cost offacilities.

An added benefit of an irradiation facility isthat it can also be used for controlling theinfectivity of other parasites in raw fish and fortreating other types of food, such as rice anddried fish against insect infestation, onions,

CONCLUSIONS

Radiation treatment has been demonstratedas an effective method to ensure hygienic qualityof food, especially solid food. It is similar tothermal pasteurization, which is effective forthe same purpose in liquid food. Radiationtreatment is unique as a method to controlfood-borne illness in solid food of animal origin(meat, fish) which is traditionally consumed raw>or improperly cooked. The technology showspromise as a method to control liver flukeinfectivity attributable to the habit of consumingraw freshwater fish in certain regions ofThailand. The estimated cost of medical careand lost wages from this illness is approximateBaht 2,115 million (US$84.6 million) per annum.Together with other costs, such as loss of jobsand productivity, possible reduction of lifespan, travel to and from clinics/hospitals, etc,the cost of this food-borne parasitic disease alonerepresents a significant loss to the economy ofthe country. Preliminary analysis indicates thatthe public health benefits from controllinginfectivity of this parasite by irradiation wouldfar outweigh the investment cost of irradiationfacilities. Detailed feasibility studies would haveto be conducted to demonstrate the practicalefficacy and acceptability of the technology bythe local population.

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