Three to five hundred million cases of malaria occurannually, causing over one to two million deaths.1 Plas-modium falciparum is responsible for the majority of deaths,which occur primarily in young children and pregnantwomen. No single method has been found to eradicatemalaria or stop its spread in tropical countries.Many coun-tries including the United States and several CaribbeanIslands have eliminated malaria through intensive, andcostly control programs, using a variety of environmen-tal management approaches. However, in 1967, WHOrealized the global eradication of malaria was impossi-ble, and focus shifted to control. Increasingly, resistanceto readily available and affordable drugs, and decliningeconomic conditions, has led to an overall worsening ofthe global malaria situation.2

Malaria is one of the leading causes of fever result-ing from travel in tropical or subtropical countries. It isestimated that without chemoprophylaxis, 2,300 out of

100,000 people would contract malaria after a 1-monthstay in West Africa.3

In recent years there has been a considerable increasein travel to malarial areas of the world, both for businessand leisure purposes. Consequently, an increased risk ofexposure to malaria now exists for many individualsnormally resident in nonmalarial areas of the world.The risk is especially very high for sailors, who by thenature of their job cannot avoid malarial regions.

The work on seagoing vessels is long associatedwith an increased risk of loss of health and life. This isattributed to specific conditions at sea, poor availabilityand increased delay of medical assistance, lack of possi-ble evacuation from danger,high accident rate, exposureto extreme weather conditions, and mental and physi-cal stress during service.Analyzing morbidity in the sail-ing population, in the last 20 years shows a great decline(from 9.17–3.18%) in morbidity from infectious dis-eases.4 Still,malaria is one of the largest problems in healthprotection in the sailing community.

Materials and Methods

Sources of information for this work were datafrom the files of the Institute of The Public Health,Rijeka, and medical protocols from the Jadrolinija—Port Health Office where sailors were treated.This is oneof the two Port Health Offices that treat Croatian andforeign sailors coming into the Port of Rijeka, Croatia.All sailors employed by the ship owner Losinjska Plovidba

Malaria, a Travel Health Problem in the Maritime CommunityNebojsa Nikoli c, Ivica Poljak, and Biserka Troselj-Vukic

Background:Three to five hundred million cases of malaria occur annually, causing over one to two million deaths. Malariais one of the leading causes of fever, resulting from travel in tropical or subtropical countries. That risk is very high, espe-cially for sailors. By the nature of their job they cannot avoid malarial regions and generally suffer from the lack of medicalhelp aboard, insufficient knowledge of preventive measures, and lack of up-to-date information about chloroquine resis-tant areas.

Methods: Retrospective analysis embraced all cases of malaria among seafarers employed in the years 1990–1993 by theCroatian sea carrier Losinjska Plovidba, and cases treated at the Clinic for Infectious Diseases, Rijeka, in the same period.

Results: In that period, among seafarers treated in our Port Health Office there were registered 23 cases of malaria; 19cases among sailors and 4 among tourists, all of them aboard merchant ships. Among seafarers treated in the Clinic forInfectious Diseases from 1990–1993 there were 13 malaria patients, 12 of them sailors and 1 tourist.

Conclusion:The aim of this work is to study the morbidity of malaria on board ships owned by the Croatian shipping com-pany Losinjska Plovidba in the 4-year period 1990–1993 and point to the lack of a health system for their health protection.It can be concluded that the severity of malaria, the number of complications, the period of disablement for work, per-manent health damage in a marked number of young persons on duty abroad, all clearly demonstrate the individual andsocial costs of this disease in Croatia and the maritime community worldwide.

3 0 9

Nebojsa Nikolic, MD, MSci: College of Maritime Studies,Rijeka; Ivica Poljak, MD, PhD, and Biserka Troselj-Vukic, MD,PhD: Clinical Hospital Center Rijeka–Clinic For InfectiousDiseases, Croatia.

Reprint requests: Dr. Nebojsa Nikolic, Riva Boduli 1, 51000Rijeka, Croatia.

J Travel Med 2000; 7:309–313.

are treated in this office, in the case of any medical needat the level of primary medical care.Every case of malaria,whether it occurred aboard ship or after disembarkation,is first reported to this office and then, if necessary, sentto a specialist at the Clinic for Infectious Diseases at theClinical Hospital, Rijeka. Data from the hospital proto-cols of the same period, when 13 sailors were treated atthe Clinic are included too.

The data was analyzed with standard statistic methods.The diagnosis of malaria was based on case records

and direct examination with thick and thin blood smears.

Results

A retrospective analysis embraced all cases of malariaamong seafarers employed in the years 1990–1993 by theCroatian sea carrier Losinjska Plovidba. In each year anaverage of 145 sailors was employed on the five shipssailing in the endemic zones, and protocols from 80voyages were analyzed. In the period mentioned, a totalof 23 cases of malaria that occurred among seafarers atsea were recorded and analyzed. Two cases had a lethalending. The group, comprised of 23 Croatian citizens,included 19 sailors and 4 tourists (some merchant shipsare still taking a few tourists aboard).

Table 1 summarizes the number of cases in individ-ual years per number of seaman then employed by

Losinjska Plovidba and the incidence rate of malaria per1,000 persons.Table 2 describes the seasonal distributionof malaria cases.

The majority of cases—65.2% (15 cases), werecaused by Plasmodium falciparum and in 1 case two typesof parasites were isolated (P. falciparum and Plasmodiummalariae).Plasmodium vivax was found in 3 cases (12.5%),and in 5 cases the parasite was unknown. In two lethalcases, which happened onboard, the type of parasiteremains unknown.

Most infections originated in Angola (9 cases), butfor the same number of cases it was impossible to estab-lish the geographic origin of infection because of the shortperiod sailors were docked in the various malariousregions.

Chemoprophylaxis is supposed to be obligatoryaboard ships traveling in endemic zones and based onthe data collected from the sailors treated in our PortHealth Office 69 (57%) of them were taking chemo-prophylaxis.On the ships leaving the Port of Rijeka andheading for the tropics, chemoprophylaxis was recom-mended according to the then current recommendationsof WHO. It was not possible to establish the type ofchemoprophylaxis taken,because various health author-ities in different ports also gave instructions for it when,for trade reasons, ships had to change their planed zonesof sailing.

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Table 1 Number of Cases of Malaria among Seafarers Employed by Losinjska Plovidba in the Years 1990–1993 Sailing inMalarial Regions, and Incidence Rate of Malaria

Year Number of Sea Personnel Number of Sick Persons Number of Fatal Cases Incidence Rate of Malaria Cases per 1,000

1990 145 3 0 211991 144 6 1 421992 145 6 1 411993 146 8 0 55Total 560 23 2 55

Table 2 Seasonal Distribution of Malaria Infection on the Ships Sailing in Malarial Regions 1990–1993

Month Number of Sailors Visiting Malarial Regions Number of Malaria Cases among Sailors Percentage

January 843 3 0.36February 634 0 0March 800 7 0.88April 667 4 0.6May 763 0 0June 705 2 0.28July 689 0 0August 518 4 0.77September 557 1 0.18October 768 0 0November 746 1 0.13December 689 1 0.15Total 8,379 23 0.27

According to the answers given, all the sailors weresick for the first time, and no other preventive measureswere used.

In Table 3 data from the Clinic for Infectious Dis-eases of the Clinical Hospital, Rijeka are presented andthey cover the period from 1990 to 1993. In this period,13 patients were treated at the clinic, 12 of them sailorsand 1 tourist (contracted malaria while embarking).

Some of the patients registered in the data of theJadrolinija—Port Health Office—were treated in otherclinics, usually in the towns where they live. Also someof the patients in the clinic were from other offices.Theaverage age was 27.7 years and only 6 (24%) of them werereceiving chemoprophylaxis during the voyage.

Discussion

Since 1963 malaria has been exclusively recognizedin Croatia as an imported disease, and WHO confirmedits eradication in 1973.All the cases of malaria registeredby the Institute of Public Health, Rijeka, and presentedin our study were imported.All of them were sailors andtourists—persons who were visiting endemic malariousregions throughout the year.

By the nature of their job sailors cannot avoid malar-ious regions but the occupational aspects of malaria haverarely been discussed in the literature.5–7 Although malariaprophylaxis is obligatory aboard ships entering malari-ous zones and according to the national and internationalregulations all Croatian ships have to have a ship’s med-icine chest and a medically trained officer aboard,Croa-tian sailors are still acquiring malaria.Twenty-three casesof malaria were registered in our protocols.Two of themdied on board and the cause of death was established afterthe ships had returned to their port of embarkation.Among malaria cases treated in the Clinic for InfectiousDiseases, Rijeka, 11 were sailors and 1 was a tourist.

Sailors generally suffer not only from the lack ofmedical help aboard and insufficient knowledge of pre-ventive measures, they also lack up-to-date informationabout chloroquine resistant areas.One reason is that the

Public Health Services in countries where malaria iseradicated are not publicly promoting preventive mea-sures against malaria. The other reason is that theirknowledge and information about malaria is formedmainly during training in maritime schools. In the cur-rent programs in Croatia only 2 hours of training on thesubject of infective diseases are in the training program.8

If given, chemoprophylaxis is given by their familyor company physician, and only a few of them have theknowledge of travel medicine, or up-to-date informa-tion about chloroquine resistant areas (only one doctorfrom Croatia is a member of the International Societyof Travel Medicine).9 Even if his doctor has properinformation, in those countries where malaria is eradi-cated, it is difficult to find proper medication for malariachemoprophylaxis. In Croatia, chloroquine is the onlymalaria chemoprophylactic that is covered by the nationalhealth system’s financing.10

In most cases the deck officer who is responsible forseafarers’ health aboard gives the drugs aboard, and as arule their medical knowledge or information aboutchloroquine resistant zones is poor. They do not evenknow that a reliable source of that information exists.

Another big set of problems is waiting for seafarerswhen they come ashore, looking for medical treatment.Because of a low index of suspicion, the diagnosis ofmalaria may be missed or delayed in nonendemic coun-tries. The typical symptoms of malaria—fever, chillsassociated with myalgia, fatigue,anorexia and headache—are often mistaken for more common illnesses such asviral syndromes. Large majorities of patients in theirfamily physician’s office are not sailors and will neverencounter malaria, and if a doctor had graduated aftermalaria had been eradicated, there is a big chance thathe never saw it, and to be honest, simply will not thinkabout it.

The risk of acquiring malaria depends on where onetravels and the duration of stay. Certain regions of trop-ical and subtropical countries are where malaria is mostpresent. Based on reports from our protocols, malaria in9 cases was imported into Croatia from Angola, and in

Nikol i c e t a l . , Malar ia in the Mar i t ime Communi ty 311

Table 3 Number of Malaria Cases Treated at the Clinic for Infectious Diseases, Rijeka in the Years 1990–1993

Year Number of Malaria Cases Treated Number of Fatal Cases Chemoprophylaxis Taken

1990 6 0 *1991 3 0 **1992 1 0 none1993 3 0 noneTotal 13 0

*In one case mefloquine was taken, in one case patient did not know what kind of chemoprophylaxis was taken, and in the rest of cases nochemoprophylaxis was taken.**In one case chemoprophylaxis was taken irregularly but patient did not know what kind it was, and in the rest of the cases no chemoprophylaxis wastaken.

the rest of the cases malaria was imported from Nige-ria, Ekvator-region, the Persian Gulf, and Caribbean. In9 cases the region remains unclear.

The places of acquisition were a result of the inten-sity of malarial endemia and perennial or a seasonaltransmission of the disease in these areas.Malaria is a sea-sonal disease connected to the life cycle of the malariaparasite, but all the same, sailors were acquiring malariathroughout the year. Infection occurred in the firstmonth or after only a few days in an endemic area in partsof West Africa. In all the cases this was the first time thatthey acquired malaria.

The severity of the illness relates to the strain ofmalaria acquired and the promptness and effectiveness ofavailable treatment.

Infection with P. falciparum was observed most fre-quently.Next was P.vivax, and other mixed infections wererare. In the majority of the cases (15 cases, 65.2%) P. fal-ciparum caused the disease, in 3 cases P. vivax, and P.malariae (mixed infection with P. falciparum) in 1 case.Nocases with Plasmodium ovale were registered although in20.8% of the cases the cause was unknown.

P. falciparum infection occurred most frequently inpersons staying in Africa (West), which is in accordancewith projections noted in literature.11

Another major risk factor for acquiring malaria iswhat (if any) prophylaxis has been taken. The objectiveof chemoprophylaxis is to prevent or reduce the effectof malaria infection by the use of medication. It is wellestablished that regular chemoprophylaxis, combinedwith protective measures against mosquito bites, canlargely prevent malaria infection.

Although prophylaxis aboard Croatian ships isobligatory before entering malarious regions, from theanalyzed data of the 23 registered malaria cases, only 16of them were taking chemoprophylaxis, which leaves30.43% of the cases without protection.Among the casesof malaria treated in the Clinic for Infectious Diseasesin the period 1990–1993 only 3 (23%) were takingchemoprophylaxis during the voyage and 2 of those 3were taking it irregularly and didn’t know what kindit was.

The reason for sickness in the majority of registeredcases where prophylaxis was taken had to be looked forin fact, that one of the main problems in malaria pre-vention is compliance. Individual prevention againstmalaria was generally neglected. As a rule no mosquitonets, pyrethroid sprays or skin repellants were used.

Many sailors are afraid of serious side effects fromantimalarial drugs. About 50% of mefloquine users and40% of doxycycline users reported illness, or symptomsduring their regimen (dizziness,headache, strange dreams,sleep disturbance, mood change, anxiety, palpitations,

itching, abdominal pain, diarrhea, nausea and vomit-ing).12 There have been media reports about the occur-rence of severe psychotic reactions associated withmefloquine, thereby shaking the confidence in this drug.Daily doxycycline as an alternative to mefloquine isassociated with breakthrough infection after only a sin-gle missed dose.13 Sailors are aware of these unpleasantside effects and as a rule they lack information on chloro-quine resistant areas.Also,many sailors think that chemo-prophylaxis is ineffective, and they often do not knowthat malaria is a disease with a high rate of mortality.

No methods now available for chemosuppression aretotally safe or absolutely effective, and antimalarial drugresistance is an everincreasing problem.The widespreadprevalence of multidrug-resistant P. falciparum complicatesthe choice of an effective prophylactic for malaria. Thespread of existence of resistance to traditional anti-malarials, such as chloroquine and antifolates, and theappearance of resistance to newer drugs, such as meflo-quine and halofantrine,mean, there is an urgent need todiscover and develop new antimalarials.

These factors are thought to result not only in a highmortality rate among seafarers at sea,but also among sea-men when on land, thus shortening the average seafarer’slife span.14 The severity of malaria, the number of com-plications, the period of disablement for work, perma-nent health damage in a marked number of youngpersons on duty abroad,clearly demonstrate the individualand social costs of this disease in Croatia and the mar-itime community worldwide.

References

1. World Health Organization,Weekly Epidemiological Report.1993; 34: 245–252.

2. DuPont H, Stefen R. Textbook of Travel Medicine andHealth. Hamilton, Canada: B.C. Decker Inc., 1997: 101.

3. Huslz D,Schonfeld C,Beuerk N,Bienyle O.Malaria chemo-prophylaxis in German tourists: a prospective study on com-pliance and adverse reactions. J Travel Med 1996;3:148–155.

4. Vuksanovic P.Most frequent illness of seaman.Pomorska med-icina 1979; 30: 297–302.

5. Jaremin B. Some problems in qualifying the state of healthin diseases imported from countries with different climate con-ditions. Medycyne Pracy 1978; 6: 527–532.

6. Tomaszunas S.Epidemiological world malaria situation.BullInst Marit Trop Med Gdynia 1984; 1: 24–26.

7. Jaremin B, et al. Malaria as an occupational disease in Polishcitizens. J Travel Med 1996; 3: 22–26.

8. Narodne Novine,Sluzbeni list Republike Hrvatske.Zagreb:1998; 103: 2594.

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10. Bencaric L. Registar lijekova u Hrvatskoj. Udruga zdravstvaZagreb 1999; 42: 31.

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11. Thor R, Fadet G, Basco LK, et al. Chimiosensibilite duplaudisme d’importation a Plasmodium falciparum en Franceen 1992.Bull Epidemiol Hebdomadaire 1993; 23:104–106.

12. Sanchez JL, De Fraites RF, Sharp TW, Hanson RK. Meflo-quine or doxycycline prophylaxis in US troops in Somalia.Lancet 1993; 341: 1021–1022.

13. Phillips MA,Koss RB.User acceptability patterns for meflo-quine and doxycycline malaria chemoprophylaxis. J TravelMed 1996; 1: 40–45.

14. Jaremin B, Kotulak E, Starnawska M, Tomaszunas S. Causesand circumstances of deaths of Polish seafarers during sea voy-ages. J Travel Med 1996; 3: 91–95.

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Sukhotai, Thailand. Submitted by Patrick E. Olson, MD, MPH.