The unique riverine ecology of hepatitis e virus transmission in south east asia

2, Jakarta, Indonesia; 2Pasteur Institute, Ho ChiMinh City, Viet Nam; ‘Center-for National Laborato y and Epidemiology, Ministry of Health, Lao PDR; 4Provincial Health Service, Sintang D

TRANSACTIONSOFTHEROYALSOCIETYOFTROPICALMEDICINEANDHYGIENE(1999)93,255-260

The unique riverine ecology of hepatitis E virus transmission in South-East Asia

Andrew L Corwin’, Ngc _ lven T K Tien2 Khanthonn ~~_ ~ ~~~~ l~-.- Bounlu3 Tarot Winarno4, Maid: yP.Putri’,KantiLaras’,

Bia P Larasati’, Nono Sukri’, Timothy’Endy’, H A Sulaiman6 and Kenneth C Hyams’ I US NavalMedical Research Unit No 2, Jakarta, Indonesia; 2Pasteur Institute, Ho ChiMinh City, Viet Nam; ‘Center-for National Laborato y and Epidemiology, Ministry of Health, Lao PDR; 4Provincial Health Service, Sintang District, West Kalimantan, Indonesia;

‘Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand; 6Medical Faculty, University of Indonesia, Jakarta, Indonesia; 7Naval Medical Research Institute, Bethesda, Ma yland, USA

Abstract The ecology of hepatitis E virus (HEV) transmission in South-East Asia was assessed from a review of 6 published and 3 unpublished NAMRU-2 reports of hepatitis outbreak investigations, cross-sectional prevalence studies, and hospital-based case-control studies Findings from Indonesia and Viet Nam show epidemic foci centred in jungle, riverine environments In contrast, few cases of acute, clinical hepatitis from cities in Indonesia, Viet Nam and Laos could be attributed to HEV When communities in Indonesia were grouped into areas of low (<40%), medium (40-60%), and high (>60%) prevalence of anti-HEV antibodies, uses of river water for drinking and cooking, personal washing, and human excreta disposal were all significantly associated with high prevalence of infection Conversely, boiling of river drinking water was negatively associated with higher prevalence (P < 0.01) The protective value ofboiling river water was also shown in sporadic HEV transmission in Indonesia and in epidemic and sporadic spread in Viet Nam Evidence from Indonesia indicated that the decreased dilution of HEV in river water due to unusually dry weather contributed to risk of epidemic HEV transmission But river flooding conditions and contamination added to the risk of HEV infection in Viet Nam These findings attest to a unique combination of ecological and environmental conditions predisposing to epidemic HEV spread in South-East Asia

Keywords: hepatitis E virus, hepatitis E virus antibodies, prevalence, ecology, epidemiology, South-East Asia, Indonesia, Viet Nam, Laos

Introduction

Hepatitis E virus (HEV) transmission occurs predo-

minantly in the developing world First identified during

the 1956 outbreak in India, involving over 29 000 cases,

epidemic and sporadic HEV infections have since been

recognized in many developing regions except for South

America, although antibody to the virus was recently

detectedfromBrazil (VISWANATHAN,~~~~~;BALAYAN,

~~~O;BRADLEY, 1992; PANG etal., 1995; PARANA etal.,

1997) In China, some 120 000 cases of HEV were

associated with an epidemic in Xinjiang during 1986-

88 (AYE et al, 1992) In South-East Asia, HEV in

epidemic form has been reported from Myamnar, Viet

NamandIndonesia (BALAYAN,~~~O;BRADLEY,~~~~;

CORWIN et al., 1996a; MAST et al., 1996)

HEV infections reuorted from develoued countries in

contrast are generally acquired from tiavel-related ex-

posures Only l-2% of US blood donors have been

found to be HEV-seroreactive, and few infections have

been documented in Europe In the USA and Singapore,

acute, clinically recognized hepatitis E has been attrib-

utedtoforeigntravel (BALAYAN,~~~O;BRADLEY,~~~~;

MAST et al., 19%‘)

HEV is a small, single-stranded RNA virus similar in

structure to the caliciviruses HEV spread is generally

water-borne, particularly in epidemics Unlike hepatitis

A virus (HAV), there is little evidence to suggest person-

to-person transmission Because HEV is principally

spread by human and possibly animal faecal contamina-

tion of water resources, transmission is associated with

poor water-related hygiene and sanitary conditions (VIS-

WANATHAN,~~~~~;KANE etaZ., 1984; B~y~N,1990;

BRADLEY, 1992; MAST&ALTER, 1993).Alsoin con-

trast to HAV, HEV is characterized by (i) a longer

incubation period ofup to 9 weeks, (ii) prolonged clinical

course of illness, and (iii) poor protective value of serum

immune globulin Particularly notable and unique rela-

tive to HAV is the high case-fatality rate (CFR) in

pregnant women (1 O-24%) associated with H&V ir&ec-

tions KI-IUROO ~~~O;DECOCK etal 1987: BALAYAN

1990;‘ REYES 8( BA&JDY, 1991; 'BRAD&Y, 1942,

Corresponding author: CDR Andrew Lee Corwin, US NAM-

RU-2, Box 3 Unit 8132, APO AP96520-8132; phone +62 21

421 4457 to 4463, fax +62 21424 4507,

e-mail corwin@smtp.namru:!.go.id

CENTERS FOR DISEASE CONTROLAND PREVENTION, 1993;MAsT&AL~~~,1993)

This review, mostly of the literature as well as a few unpublished research findings from studies conducted or supported by the US Naval Medical Research Unit No 2 (NAMRU-2) in Jakarta, Indonesia, is intended to show that in South-East Asia the epidemic form of HEV transmission may be a function of a unique, predomi- nantly rural, riverine ecology The data also indicate that extremes of rainfall conditions, both flooding and drought, combined with a background of specific river usage practices, contribute to the risk of HEV transmis- sion

Methods and Analysis Examules of both enidemic and sooradic HEV trans- mission ‘were identifieh from our inbestigations of rural and urban settings in South-East Asia First, recognized foci of epidemic HEV transmission in jungle, riverine areas were investigated in Indonesian Borneo (West Kalimantan)and Eastern Java (Bondowoso), and in the

An Giang Province of the Mekong River Delta region of Viet Nam which borders Cambodia (CORWIN et al., 1995,1996a, 1997; unpublished data; HAU et al., 1999) Second, the importance of HEV in acute, sporadic hepatitis was examined in a multi-hospital-based study

of HEV that included the cities of Takarta Indonesia (unpublished data), Hanoi and Ho C& Ming, Viet Nam (CORWIN et al., 1996b) and Vientiane, Lao PDR (BO~NLU et al., 1998) Data from studies conducted in Indonesia, Viet Nam, and Laos were included in the analysis

Epidemiological approach Three approaches were used to investigate HEV transmission in 8 reported studies: (i) outbreak investi- gations; (ii) cross-sectional prevalence studies; and (iii) hospital-based, case-control studies Data pertaining to demographics, the environment, medical history, and risk-related behaviours had been obtained bv use of a standardized questionnaire administered by trained in- terviewers Except for hosnital-based studies and 1 HEV outbreak investigation described from Vie; Nam, the household served as the principal sampling unit Outbreak investigation In Indonesia, an investigation

of a 1991 HEV outbreak was carried out among com-

munities on the Inggar River of Borneo, providing a

retrospective epidemiological evaluation (CORWIN et al.,

1995) Another outbreak of hepatitis, that affected rural

villages along the Balut River in eastern Java, was

investigated in 1998, and subsequently attributed to

HEV (unpublished data) From Viet Nam, an HEV

outbreak investigation was conducted in 1994 among

communities along a 60-km stretch of the Hau River, a

tributary of the Mekong River (CORWIN et al., 1996a)

Cross-sectional seroprevalence studies Communities in

Indonesian Borneo (contiguous to the 1991 outbreak

area described above) located along a 150~km stretch of

the Kapuas River (into which the Inggar River flows)

were surveyed in 1995 Targeted for study purposes was

the affected population from a 1987 HEV outbreak

where HEV was first recognized in Indonesia For com-

parison a population further downstream of the Kapuas

River that was more urban was studied (CORWIN et al.,

1997)

In the Mekong Delta river region of Viet Nam, the

serourevalence of anti-HEV antibodies was studied in I

communities surveyed from the area adjacent to the foci

of epidemic HEV transmission in 1994 (HAU et aZ.,

1999)

Hospital-based, case-control studies of acute hepatitis A

standardized case-control design and data collection

instrument were used to evaluate the HEV infection in

acute, clinically recognized hepatitis, from 4 urban

centres (unpublished data; CORWIN et aZ., 1996b; un-

published data; BOUNLU et aZ., 1998) in 3 South-East

Asia countries: Indonesia, Viet Nam, and Laos The

duration of each study was 12 consecutive months: the

first study began in 1993 and the last in 1997 Cases

(175-200) were selected on the basis of clinical criteria

for suspected acute hepatitis, and controls were selected

to match the demographic characteristics of cases

Serological tests

Laboratory testing was coordinated by the US NAM-

RU-2, Jakarta, Indonesia Serawere tested by commercial

enzyme immunosorbent assay for IgG antibody to HEV

(Abbott Laboratories, Abbott Park, IL) and IgGantibody

to HAV (Abbott Laboratories) Sera from acute hepatitis

studiesalsoweretestedforIgMantibodytoHAVandIgM

antibody to hepatitis B core antigen (HBcAg) (Abbott

Laboratories) Sera from patients with signs and symp-

toms of acute hepatitis that were positive for IgG antibody

to HEV were further tested for IgM antibody to HEV

(Genelabs Diagnostics PTE, Singapore)

HEV transmission had not been\ecoanized in eoidemic form was found to

areas Background be lower than in-outbreak-affected (community-acquired) HEV infec-

Specimens found positive for IgG antibody to HEV were also tested by polymerase chain reaction (PCR) at the Armed Forces Research Institute of Medical Sciences (AFRIMS), Bangkok, Thailand (TAM et al.,

199 1) The oligonucleotide primers used in HEV PCR were HEV I’4653 (5’-TTT-TCA-GGT-GGC-TGC-C- 3’) and HEV P4874 (5’-GGG-CCC-CAA-TTC-TTC- T-3’) for RT-PCR; and HEV I’4704 (5’-ATA-CCG-

GAA-GCG-CAC-GAC-ATC-3’) for nested PCR Re- liability evaluation using positive and negative controls conducted at AFRIMS indicated high test sensitivity and specificity (unpublished data) Additionally, IgM anti- body to HEV was detected from sera using Western blotting as previously described (HE et aZ., 1993) HEV studies in South-East Asia

Indonesia

A 199 1 HEV outbreak in Sintang, West Kalimantan, affected over 2500 neonle An attack rate of 90 cases/ 1000 population and case-fatality rate (CFR) of 14% among pregnant women were estimated (CORWIN

et al., 1995) Notable was the relatively high seropreva- lence of IgG antibody to HEV 2 years following this outbreak Overall, anti-HEV prevalence was 59% among

445 study subjects There was no significant difference (P > 0.05) in HEVprevalence between cases (72%) with

a history of acute jaundice and subjects without jaundice (61%) Similarly, the prevalence of anti-HEV 7 years after the 1987 epidemic was 50% in an area adjacent to the 1991 outbreak (CORWIN et al 1997) (Fig 1) Finally, ‘first time’ epidemic HEV transmission h In- donesia outside of Borneo was recognized March/April

1998 A preliminary attack rate of 13% was estimated, ranging by community from 10% to 19% (unpublished data) However 415 (43%) of the 962 studv subiects surveyed were positive for’IgG antibody to*HEV, of which 49% had serological evidence of a recent infection based on RT-PCR testing

In the area of the 1987 West Kalimantan outbreak, continuinn (snoradic) HEV transmission was found bv comparini I&V infection in the population living (aged

27 years: prevalence 53%) during the epidemic with young children born after the event (aged <7 years: prevalence 16%; P < 0.000 1) However, the prevalence

of anti-HEV antibodies in neiahbourine areas where

n Locations of hepatitis E outbreak Fig 1 Geographical distribution of recognized hepatitis E outbreaks, South-East Asia, 199 l-94

HEPATITISEVIRUSINSOUTH-EASTASIA 257

tions in non-outbreak-affected communities surveyed

for comparative purposes in West Kalimantan were

identified in 23% of the population (CORWIN et al.,

1997)

Among the 127 households surveyed after the 199 1

outbreak in West Kalimantan, 112 (88%) had a mini-

mum of 1 anti-HEV reactor However, only 63% of

households had > 1 positive family member There was

no anoarent increased risk of HEV infection associated

w&*&creased family size (CORwIN et al., 1995) Finally,

findings from a survey conducted in 1994 from West

Kalimantan region of the 1987 outbreak provided a more

complete picture of transmission resulting from both

epidemic and sporadic HEV transmission: 94% of 178

households in the outbreak area had > 1 family member

positive for IgG antibody to HAV compared with 52%

for IgG antibody to HEV (P < 0.0001) (CORWIN et aZ.,

1997)

In urban Jakarta, prevalences of background HEV

infections (positive for IgG antibody to HEV) among

cases and control subjects (non-jaundiced, hospital

inpatients) were very low, and differed little: 5%.and

2% resnectivelv (urmublished data) No data are avail-

able for-IgM an&odi to HEV (Tadle)

Indo-china (Viet Nam and Laos)

Another study of epidemic HEV transmission in

South-East Asia involved an outbreak during 1994 in

An Giang Province, Viet Nam (Fig 1) IgG antibody to

HEV was recognized in 76% of cases compared with

36% of matched community and geographical controls

(P < 0.001) As in Indonesia, there was no evidence of

familial clustering of seropositive individuals in Viet Nam

(CORWIN et al., 1996a)

Data presented in Table show low prevalence of anti-

HEV antibodies in acute, clinically recognized hepatitis

from urban settings In Hanoi and Vientiane, 2% of 375

and 4% of 52 acute episodes of suspected hepatitis,

respectively, were attributed to recent HEV infections

(CORWIN~~~Z., 1996b;BOUNLUetaL, 1998).Noserum

sample from hospitalized case subjects in Ho Chi Minh

or Jakarta was positive for IgM antibody to HEV

(unpublished data) Background IgG antibody to

HEV, reflecting previous infections, varied little between

acute jaundiced case and control populations at each

study location in Indo-china Notable was the high

proportion of controls positive for IgG antibody to

HEV similar to cases, from Hanoi and Vientiane: 14%

ofco&rolsvs 12% of&es and 17% ofcontrolsvs 16% of

cases, respectively (CORWIN et al., 1996b; BOIJNLU et al.,

1998)

Role of river ecology

Indonesia

Water use related to hygiene and sanitation was clearly

associated with the risk of HEV infection In the 1991

West Kalimantan outbreak area, HEV prevalence in-

creased with the usage of river water for drinking and

Table Study of acute clinical hepatitis E in South-

East Asia

anti-HEV” anti-HEV Vientiane

Jakarta

Hanoi

Ho Chi

Minh City

(n $16) (n = ;21) 14%

(n 0 187) (n = 6)

‘In the absence of IgM anti-HAV and IgG anti-HBc

bNot available

cooking (P < O.OOl), bathing (P < O.OOOl), and excre- ment disposal (P< 0.001; Fig 2) Conversely, the prevalence of anti-HEV antibodies decreased as the practice of boiling drinking water increased (P = 0.02; Fig 2) (CORWIN et al, 1995)

Adding to the risk of epidemic and sporadic HEV transmission in the 1987 outbreak affected and compari- son study areas of West Kalimantan were the practices of bathing, human waste disposal, drinking, and launder- ing Usage of river water for bathing and human waste disposal was significantly associated with positivity for IgG anti-HEV antibodies in both outbreak and compari- son areas In the comparison area, drinking and washing with river water were found to be strongly associated (P<O.OOOl) with prevalence of IgG anti-HEV anti- bodies (Fig 3) (CORWIN, et aZ., 1997)

There was no evidence from the 1991 outbreak in West Kalimantan that the community-specific preva- lence of HEV declined downstream along the same river,

as the current becomes swifter and waters deeper How- ever, the prevalence of clinical signs and symptoms compatible with acute hepatitis during the actual out- break significantly decreased with community proximity further downriver: ranging from a community high of 35%toalowof<l%(P<O~OOl;Fig.4)(CORWINetal.,

1995)

Viet Nam The protective value of boiling river water for drinking purposes was suggested during the 1994 HEV outbreak

in An Giang Province: the proportion of subjects positive for IgG antibody to HEV who boiled water for drinking was lower (40%) compared with those who did not (55%) (P < 0.05) (CORWIN etal., 1995a) Inanadjacent non-outbreak area, the practice of boiling river water for drinking was again significantly (P < 0.01) associated with the absence of IgG antibody to HEV

Weather factors Indonesia

In West Kalimantan 91% of study households re- ported unusually dry weather leading up to and during the 199 1 HEV outbreak Trend analvsis of weather data indicated subnormal rainfall in the months leading up to the outbreak period in September 1991 In the months just before the outbreak, only 19 cm of rain were recorded in August 1991, compared with an August meanvalueof209cmforalltheyears 1985-93 (CORWIN

et aZ., 1995)

Viet Nam

In Viet Nam, climatic conditions were also linked to epidemic HEV transmission in the 1994 outbreak How- ever, unusually heavy rainfall occurred during the nor- mally dry months leading up to the outbreak In May

1994 (early in the outbreak), 341 cm of rain fell in the affected area, compared with a monthly (May) mean of

94 cm recorded for the preceding 4 years (1990-93) This was the second highest rate of monthly rainfall throughout the entire 1990-94 period Additionally, significant flooding of the Mekong River was reported earlier in the year and during the outbreak period Flooding in the months preceding the 1994 outbreak,

as reflected by river depth (in meters), exceeded the highest monthly measures recorded for any of the previous 4 years (CORWIN et al., 1996a) Anecdotal reports from local health officials also suggest increased annual occurrence of community-acquired infections during the rainy season

Discussion Populations affected by HEV outbreaks in Indonesia and Viet Nam have been located on major riverine systems in areas best characterized as rural, with a poorly developed sanitary infrastructure (COR~IN et al., 1995; CORWIN et al., 1996a) That the 2 distantly separated

Drinking and Cooking Bathing

Area Prevalence for IgG anti-HEV Area Prevalence for IgG anti-HEV

Excrement Disposal

Area Prevalence for IgG anti-HEV Area Prevalence for IgG anti-HEV

Low: < 40% Medium: 40 - 60% High: > 60%

Fig 2 Percentage of people in the 199 1 Kalimantan hepatitis E outbreak area using river water for various purposes, and prevalence of IgG antibodies against hepatitis E

Case ChUOl

Bathing

(3% Control

Human Waste Disposal

Case Control

Drinking

Case Control CCL% Control

Washing Boiled Water

Fig 3 Percentage of people with IgG antibodies to hepatitis E virus and various risk factors in the 1987 outbreak-affected and comparison study areas of West Kalimantan

outbreaks described in this review shared (i) the same

riverine-type settings, and (ii) water-associated risks

against a background of universal river usage, attests to

the importance of this ecology in HEV spread in South-

East Asia Other outbreaks fi-om within and outside the

region, as in Myanmar and Pakistan, have been attrib-

uted to faecally contaminated water supplies resulting

from temporary sanitary system breakdowns (KANE et

al., 1984)

Epidemic HEV transmission appears relatively con-

fined, occurring in limited areas with definable geogra-

phical borders Also, uniquely separate episodes of

epidemic HEV spread (repeated outbreaks), recognized from the same district (Sintang, West Kalimantan) and 4 years apart, affected 2 contiguous although geographi- cally distinct populations (CORWIN et al., 1995; CORWIN

et al., 1997) This suggests maintenance of over time HEV transmission in an animal and/or human reservoir Study observations suggest that river water is a primary source of HEV infection in South-East Asia In addition

to river usage for fish farming and transportation, populations in outbreak-affected areas of Indonesia and Viet Nam share a dependence on river water for most personal hygiene and sanitary needs In West Kaliman-

HEPATITISEVIRUSINSOUTH-EASTASIA 259

A

High > 60%

Fig 4 (A) Area-specific prevalence of hepatitis E virus, Sintang District, West Kalimantan, September 1993 (B) Percentage of population with signs and symptoms compatible with acute hepatitis in West Kalimantan August/September 199 1

tan, Indonesia, outhouses over the water on extended

docks are used by individuals, the family unit, and the

community at large; at the same time bathing, washing of

clothes, and drinking of water take place The frequency

of usage of rivers and tributaries for drinking and

cooking, bathing and human excreta disposal was related

to an increased prevalence of anti-HEV antibodies Also,

the practice of regularly boiling river water for drinking

and cooking purposes was associated with decreased

area-specific anti-HEV antibody prevalence (CORWIN er

al., 1995; CORWIN et aZ., 1997) The absence of HEV as a

cause of acute, clinical hepatitis from study cities in

South-East Asia is probably an attribute of improved

sanitary systems that characterize more urbanized areas

Findings from Indonesia show a probable dose-

response effect associated with clinical (HEV) disease

Further upstream, communities in the outbreak area had

attack rates considerably higher, possibly because of

greater concentration of virus from excreta and other

human and/or animal waste products in shallow, slow-

moving river water Reduced dilution added to the

opportunity of exposure (CORWIN et al., 1995) In

outbreaks reported from Somalia, severe morbidity and

high case-fatality rates were also attributed to HEV

inoculum size: greater exposure resulting from poor

dilution in river and well water (BILE et al., 1994)

Negligible familial clustering (compared with anti-

HAV antibodies) of HEV infection indicates that per-

son-to-person contact contributes little to the mechan-

istic spread of HEV, irrespective of epidemic or sporadic

acquired infections (CORWIN et al., 1995; CORWIN et al.,

1997) A similar finding was reported from a comparative

study of intra-familial transmission versus waterborne

spread during a bimodal, waterborne HEV outbreak in

India (AGGARWAL & NAIK, 1994) In urban Rangoon

(Myanmar), however, there was no apparent systems’

breakdown affecting water sanitation, although the

possibility was acknowledged (MYINT et al., 1985)

Outbreaks in other geographical areas indicate a

primary role for river water in HEV transmission Villages in Somalia that depended on river water during the 1988 HEV outbreak had higher attack rates than those relying on pond or well water (BILE et d., 1994) Epidemic conditions in Nepal were also attributed to significant rains (KANE et aZ., 1984; SHRESTHA, 1991; CiAYSON et al., i995)

The nooulation-based nrevalence of anti-HEV anti- bodies in non-outbreak arias adjacent to recognized foci

of HEV transmission, in both Indonesia and Viet Nam, was found to be significantly lower Nevertheless, spora- dic (ongoing) HEV infections in such areas were evident, indicating that unique conditions of decreased dilution

of virus or increased contamination are necessary for an epidemic (CORWIN et al., 1997)

In Viet Nam, recognized clinical disease associated with the 1994 HEV outbreak was principally a male (15-

40 years) phenomenon (CORm et al., 1996a) Simi- larly, the highest attack rates of epidemic HEV spread in Indonesia were among the same adult population (COR- WIN et al., 1995; CORWIN et cd., 1997) This suggests a possible age-related occupational water exposure, and possible gender bias in health care utilization patterns Similar findings relative to adults aged 14-40 years have been reported from the New Delhi (India) and other epidemic experiences (MELNICK, 1957; VISWANA- THAN, 1957b; FAVOROV et al., 1992)

In conclusion, climatic extremes affecting river ecol- ogy: heavy rainfall linked to flooding in Viet Nam, or subnormal rainfall in Indonesia, have probably contrib- uted to the favourable conditions that influenced epi- demic or cyclic HEV spread Anecdotal information from the Mekong Delta Region also indicates a dramatic annual rise in cases during the flooding of the river system (CORWTN et al., 1995; CORWIN et al., 1997) In Nepal, major peaks in epidemic HEV occurrence coincided with monsoon rains (KANE et aZ., 1984) Excessive run-off associated with heavy rains and flooding probably adds to the mixing of contaminated matter with water supplies as

infected human and/or animal waste materials are

washed into rivers and other water sources

In order for HEV epidemics to occur, unique combi-

nations of water-related factors appear necessary

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Received 6 October 1998; revised 4 December 1998; accepted for publication 1 February I999