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

TRANSACTIONSOFTHEROYALSOCIETYOFTROPICALMEDICINEANDHYGIENE(1999)93,255-260

The unique riverine ecology of hepatitis E virus transmission

in South-East Asia

Tarot Winarno4, Maid: yP.Putri’,KantiLaras’,
Andrew L. Corwin’, Ngc lven
_ T. K. Tien2. Khanthonn ~~_Bounlu3.
~ ~~~~--l~-.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 assessedfrom 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published and 3 unpublished NAMRU-2 reports of hepatitis outbreak investigations, cross-sectional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 casesof 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, usesof river water for drinking and cooking, personal washing, and human excreta disposal were
all significantly associatedwith high prevalence of infection. Conversely, boiling of river drinking water was
negatively associatedwith 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 decreaseddilution 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: hepatitisE virus, hepatitisE virus antibodies,prevalence,ecology,epidemiology,South-EastAsia,Indonesia,
Viet Nam, Laos

Introduction

Hepatitis E virus (HEV) transmission occurs predominantly 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 198688 (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 exposures. 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 attributedtoforeigntravel (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 suggestpersonto-person transmission. Because HEV is principally

spread by human and possibly animal faecal contamination of water resources, transmission is associated with
poor water-related hygiene and sanitary conditions (VISWANATHAN,~~~~~;KANE
etaZ., 1984; B~y~N,1990;
BRADLEY, 1992; MAST&ALTER,

1993).Alsoin

1991; 'BRAD&Y,

PREVENTION,

This review, mostly of the literature as well as a few
unpublished research findings from studies conducted or
supported by the US Naval Medical ResearchUnit 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, predominantly 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 transmission.
Methods

and Analysis

Examules of both enidemic and sooradic HEV transmission ‘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.

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 relative to HAV is the high case-fatality rate (CFR) in
pregnant women (1O-24%) associated with H&V ir&ections KI-IUROO. ~~~O;DECOCK etal.. 1987: BALAYAN.
1990;‘ REYES 8( BA&JDY,

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

1942,

Correspondingauthor: CDR Andrew Lee Corwin, US NAMRU-2, Box 3 Unit 8132, APO AP96520-8132; phone +62 21
421 4457 to 4463, fax +62 21424 4507,
e-mail :!.go.id

Epidemiological approach

Three approaches were used to investigate HEV
transmission in 8 reported studies: (i) outbreak investigations; (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 interviewers. 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-


ANDREW L.

256

munities on the Inggar River of Borneo, providing a
retrospective epidemiological evaluation (CORWINet 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 comparison 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
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; unpublished 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.
I

Serological tests

Laboratory testing was coordinated by the US NAMRU-2, Jakarta, Indonesia. Serawere tested by commercial
enzyme immunosorbent assayfor IgG antibody to HEV
(Abbott Laboratories, Abbott Park, IL) and IgGantibody
to HAV (Abbott Laboratories). Serafrom acute hepatitis

studiesalsoweretestedforIgMantibodytoHAVandIgM
antibody to hepatitis B core antigen (HBcAg) (Abbott
Laboratories). Sera from patients with signs and symptoms of acute hepatitis that were positive for IgG antibody
to HEV were further tested for IgM antibody to HEV
(Genelabs Diagnostics PTE, Singapore).

n
Fig. 1. Geographical

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-C3’) and HEV P4874 (5’-GGG-CCC-CAA-TTC-TTCT-3’) for RT-PCR; and HEV I’4704 (5’-ATA-CCGTCA-GAG-CCC-AGG-3’)
and HEV I?4845 (5’-GGCGAA-GCG-CAC-GAC-ATC-3’)
for nested PCR. Reliability evaluation using positive and negative controls
conducted at AFRIMS indicated high test sensitivity and
specificity (unpublished data). Additionally, IgM antibody to HEV was detected from sera using Western
blotting as previously described (HE et aZ., 1993).
HEV studies in South-East
Indonesia

Asia

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 seroprevalence 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 Indonesia 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
HEV transmission had not been\ecoanized in eoidemic
form was found to be lower than in-outbreak-affected
areas. Background (community-acquired) HEV infec-

Locations of hepatitis E outbreak

distribution

CORWINETAL.

of recognized hepatitis E outbreaks, South-East Asia, 199 l-94.


257

HEPATITISEVIRUSINSOUTH-EASTASIA
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 minimum 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 available 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 antiHEV 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 increased with the usage of river water for drinking and
Table. Study of acute clinical
East Asia
Locality
Vientiane
Jakarta

IgG

anti-HEV
16%

hepatitis

IgG

anti-HEV”

E in South-

16%
(n $16)

Hanoi

(n = ;21)
14%

Ho Chi
Minh City

(n 0 187)
(n = 6)

IgM

anti-HEV

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

cooking (P < O.OOl), bathing (P < O.OOOl), and excrement 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 comparison study areas of West Kalimantan were the practices of
bathing, human waste disposal, drinking, and laundering. Usage of river water for bathing and human waste
disposal was significantly associated with positivity for
IgG anti-HEV antibodies in both outbreak and comparison areas. In the comparison area, drinking and washing
with river water were found to be strongly associated
(PThere was no evidence from the 1991 outbreak in
West Kalimantan that the community-specific
prevalence of HEV declined downstream along the same river,
as the current becomes swifter and waters deeper. However, the prevalence of clinical signs and symptoms
compatible with acute hepatitis during the actual outbreak significantly decreased with community proximity

further downriver: ranging from a community high of
35%toalowof1995).
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 reported 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. However, unusually heavy rainfall occurred during the normally 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


258

ANDREW

L. CORWIN

ETAL.

Bathing

Drinking and Cooking

AreaPrevalence
for

Area Prevalence for IgG anti-HEV

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 1991 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

Washing

CCL%

Control

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 SouthEast Asia. Other outbreaks fi-om within and outside the
region, as in Myanmar and Pakistan, have been attributed to faecally contaminated water supplies resulting
from temporary sanitary system breakdowns (KANE et
al., 1984).
Epidemic HEV transmission appears relatively confined, occurring in limited areas with definable geographical 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 geographically 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 sametime 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 absenceof HEV asa
cause of acute, clinical hepatitis from study cities in
South-East Asia is probably an attribute of improved
sanitary systemsthat characterize more urbanized areas.
Findings from Indonesia show a probable doseresponse effect associated with clinical (HEV) disease.
Further upstream, communities in the outbreak areahad
attack rates considerably higher, possibly because of
greater concentration of virus from excreta and other
human and/or animal waste products in shallow, slowmoving 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 antiHAV antibodies) of HEV infection indicates that person-to-person contact contributes little to the mechanistic 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 antibodies in non-outbreak arias adjacent to recognized foci
of HEV transmission, in both Indonesia and Viet Nam,
was found to be significantly lower. Nevertheless, sporadic (ongoing) HEV infections in such areaswere evident,
indicating that unique conditions of decreased dilution
of virus or increased contamination are necessaryfor an
epidemic (CORWIN et al., 1997).
In Viet Nam, recognized clinical disease associated
with the 1994 HEV outbreak was principally a male (1540 years) phenomenon (CORm et al., 1996a). Similarly, the highest attack rates of epidemic HEV spread in
Indonesia were among the same adult population (CORWIN 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; VISWANATHAN, 1957b; FAVOROV et al., 1992).
In conclusion, climatic extremes affecting river ecology: heavy rainfall linked to flooding in Viet Nam, or
subnormal rainfall in Indonesia, have probably contributed to the favourable conditions that influenced epidemic or cyclic HEV spread. Anecdotal information

from the Mekong Delta Region also indicates a dramatic
annual rise in casesduring the flooding of the river system
(CORWTN et al., 1995; CORWIN et al., 1997). In Nepal,
major peaksin epidemic HEV occurrence coincided with
monsoon rains (KANE et aZ., 1984). Excessive run-off
associatedwith heavy rains and flooding probably adds to
the mixing of contaminated matter with water supplies as


ANDREW L. CORWIN ETAL.
infected human and/or animal waste materials are
washed into rivers and other water sources.
In order for HEV epidemics to occur, unique combinations of water-related factors appear necessary.
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Received 6 October 1998; revised 4 December 1998; accepted
for publication 1 February I999