Rev. Inst. Med. trop. São Paulo
31 (2): 103-109, rnarço-abrü, 1989
RELATIONSHIP BETWEEN THE PREVALENCE OF ANTIBODIES TO ARBOVIRUS AND HEPATITIS B VIRUS IN THE VALE DO RIBEIRA REGION, BRAZIL
C l á u d i o S é r g i o P A N N U T I ( 1 , 3 ) , L y g i a B u s c h I V E R S S O N ( 2 ) , J o ã o S i l v a d e M E N D O N Ç A ( 3 ) ,
A m é l i a P . A , T R A V A S S O S D A R O S A (4) & C e l s o F r a n c i s c o H c r n a n d e s G R A N A T O ( 5 ) .
S U M M A R Y
2 8 0 students, between 6 and 1 4 years old, residents in the Iguape county, southern coast of the State of S ã o Paulo, were studied in order to identify the existence of a possible association between the prevalence of specific antibodies to the hepatitis B virus and the exposure to haematophagous mosquitoes, evaluated indirectly through the prevalence of antibodies to 17 arboviruses isolated in Brazil.
The children were from 4 areas with different topographical characteristics: 89 of the children were from the urban zone of the town of Iguape, 89 were from the p e r i u r b a n zone, 3 0 were from the rural area with extensive banana plantations, and 7 2 were from the jungle zone. Previous studies had shown significantly higher prevalence of antibodies to different arboviruses in the cultivated zone and the jungle zone, when compared to the urban and peri urban zones of Iguape. T h e detec¬ tion of antibodies to the H B V surface antigen ( H B s A g ) was done through the radioimmunoassay (Ausab, Abbott Laboratory). T h e cases considered positive were confirmed through the presence of anti-core H B V antibodies (anti H B c E I A Roche). A significantly higher prevalence of anti H B V antibodies was observed in chil¬
dren from the jungle zone ( 2 6 / 7 2 = 3 6 , 1 % ) when compared to those from the urban
zone (5/89 = 5 , 6 % ) , peri-urban (6/89 = 6 , 7 % ) or from the cultivated zone ( 0 / 3 0 =
0r% ) .
T h e result suggest the existence of a common factor in the dissemination of the arboviruses and the hepatitis B virus, supporting the hypothesis that mosquitoes may play an important role in the H B V transmission in tropical forested region.
K E Y W O R D S : Hepatitis B transmission; Hepatitis B seroepidemiology. Arbovirus and Hepatitis B
I N T R O D U C T I O N
The higher prevalence of hepatitis B virus regions3 3 4 suggested that, along with
conven-( H B V ) markers in h u m a n populations in tropical tional t r a n s m i s s i o n m e c h a n i s m s observed in
(1) I n s t i t u t o de M e d i c i n a T r o p i c a l e L I M d o H o s p i t a l d a s C l í n i c a s d a F a c u l d a d e d e M e d i c i n a d a U n i v e r s i d a d e de S ã o P a u l o . S ã o P a u l o . S P , B r a s i l .
(2) F a c u l d a d e d e S a ú d e P ú b l i c a d a U n i v e r s i d a d e d e S a o P a u l o , S ã o P a u l o , S P , B r a s i l . (3) H o s p i t a l d o S e r v i d o r P ú b l i c o d o E s t a d o d e S ã o P a u l o . S ã o P a u l o . S P , B r a s i l . (4) I n s t i t u t o E v a n d r o C h a g a s . M i n i s t é r i o d a S a ú d e . B e l é m , P a r á , B r a s i l .
(5) I n s t i t u t o A d o l f o L u t z . S e c r e t a r i a d o E s t a d o d a S a ú d e d e S ã o P a u l o , S ã o P a u l o , S P . B r a s i l .
other parts of the world, additional modes of transmission might be present in the tropics.
The high prevalence in some of these regions of diseases t r a n s m i t t e d b y h a e m a t o p h a g o u s arthropods and the low frequency of blood trans-fusion or injections among their inhabitants, raised the first suspicion of H B V transmission via mosquitoes and other insects as reported by B L U M B E R G et al.4
. Detection of H B Ags in various species of mosquitoes and other
haematopha-gous arthropods captured in tropical regions6
8. i7, 27. 35, 40, 41. 42 a n cj e ve n urban areas of the
United States1 3, has somehow corroborated this
hypothesis. Experimental studies showed that
when various species of mosquitoes2 6 7 2 8 3 0
3i, 38a n d 0t h e r haematophagous arthropods
1 2 2 6
3i, 37, 39, 40w er e fe cj blood containing H B s A g , it
was possible to detect this marker in mosquitoes for approximately up to 4 days, in most of the studies, and for periods up to several weeks in the other arthropods. I t was observed, however, that the H B s A g disappears once the blood is fully digested, indicating that no viral replica-tion occurred in the a n i m a l6 , 7-3 1.
According to these results, infections of H B V via arthropods would be the result of mechanical t r a n s m i s s i o n . I n this mode of t r a n s m i s s i o n , which was already been described for several ty-pes of plant and animal viruses, such as the
my-x o m a virus in rabbits and certain arboviruses1 1
, the virus would remain viable in the structure of the sucking apparatus of the arthropods and might be transmitted passively from a contami-nated host to a susceptible one, of the refeeding time for the mosquito, or when it completed a
feeding which had been interrupted5. A s is the
case with certain viruses such as the Venezuelan
equine encephalitis1 1 or Rift Valley fever viruses
which reach very high concentration in blood; the likehood of mechanical transmission of H B V , which is highly infectious and highly resistant
to inativation3 6
, appears possible.
T h i s mechanical transmission should occur more frequently in tropical regions, where there is intensive the activity of h a e m a t o p h a g o u s arthropods.
A seroepidemiologic survey to H B V , carried
out in S ã o Paulo State, B r a z i l2 9, demonstrated
a n u n u s u a l l y h i g h p r e v a l e n c e of a n t i - H B S among children living in a camping area near Serra do Mar, a rural area near the coastal region of the State. T h e study showed a prevalence of 31.2% (10/32) among children whose age ranged from 1 to 5 years, and 48.7% (19/39) among those in the 6 to 11 years group. These children were of low socioeconomical status. However, among the adult population of low socioeconomic status living in the urban area of the city of São Paulo,
the prevalence of a n t i - H B s was only 14.58%2 9
, suggesting that factors other than the socioeco nomic status determined, the high prevalence of immunological markers to H B V in this loca-lity.
I n order to test the hypothesis that wild culi-cidae might be involved in H B V transmission, a seroepidemiologic survey to the H B V was con-ducted in a region with similar ecological charac-teristics, namely the Vale do Ribeira, which is also included in the so called Serra do Mar S y s tern. T h i s area is characterized by an abundant Culicidae fauna1 5 1 6
. Since 1977 the Department of Epidemiology of the Public Health School of the University of S ã o Paulo, in collaboration with Evandro C h a g a s Institute, has conducted seroe-pidemiological surveys for arboviruses in the hu-man population. T h e prevalence of arbovirus an-tibodies should thus provided an indirect indi cator of the risk of infections transmitted by mosquitoes. T h e prevalence of immunological markers of the H B V should be correlated with that of arbovirus antibodies.
M A T E R I A L A N D M E T H O D S
T H E A R E A . T h e serological survey was car-ried out in Iguape, one of the counties of the Vale do Ribeira, located in the coastal area of the State of S ã o Paulo, southeast B r a z i l , in a region still extensively covered by forests.
I n 1976 an epidemic of arbovirus encepha-l i t i s r e s u encepha-l t e d i n a m o r b i d i t y i n d e x o f
717.5/100.000 inhabitants in I g u a p e2 1
. Seroepide-miological studies showed that arbovirus as be-longing to the T o g a v i r i d a e and F l a v i v i r i d a e fa-milies, pathogenic for h u m a n2 2 2 5
, are circulating in the region.
characteristics, were studied. These areas, have
been described in details previously2 5
. T h e y are briefly:
a) Urban Zone: including Iguape, a town lo-cated in the coast and a health resort in a large n e i g h b o u r i n g i s l a n d , w h i c h presents u r b a n structure;
b) Peri-Urban Zone: R o c i o District, in the outshirts of Iguape, with rural characteristics, poor houses sparsely located among the vegeta-tion; grass and small bushes predominate.
c) C u l t i v a t e d Zone: in the coastal plains, with a few areas of residual forest. E x t e n s i v e planting of bananas, and, more recently, of vege-tables and grain, is carried out.
d) Jungle Zone: still extensively covered by forests, made up of tall trees, dense foliage and high degree of heterogenity, where the utiliza-tion of land agricultural and cattle-raising pur-poses is still limited.
C A S E S T U D Y
In the 1981-1982 period, blood samples were collected for an arbovirus seroepidemiological study from 337 students (6 to 14 years old) from Iguape county. These children proved to have different prevalences of H I antibodies to 17 arbo-virus isolated in Brazil, according to the locality where they lived. Among, these 337 sera, preser-ved at -20°C, 280 presented an enough amount that permited the research of H B V immunolo-gical markers. T h e 280 children resided in diffe rent areas: 89 of them lived in the Urban Zone; 89 in the Periurban Zone, 30 in the Cultivated Zone and 72 in the Jungle Zone. T h e majority of the children (70.1%) had lived all their lives in the place at which they were residing at the time of the study. Only 2.8% had lived there for a period of less than one year. T h e 280 children belonged to 233 different families. In 33 families two or more children were examined.
Socioeconomic status was estimated on the basis of the father's profession, and proved to be low, with no significant difference between the areas of residences, since 71(30.5%) of the fathers were agricultural workers, 58(24.9%) were
m a n u a l l a b o r e r s , 27(11.6%) were fishermen, 27(11.6% ) were low level public servants, 13(5.6%) were clerks in commercial establishments, and 4(1.7%) were elementary schoolteachers. I n 33 cases (14.2%) this information was not available. A s to sex, 51.7% (135/261) were male and 48.3 (126/261) were female. I n 19 cases, this informa-tion was not available.
A n t i - H B s A g was determined by radioimmu-noassay (Ausab-Abbott Laboratories).
The positive sera were tested to a n t i - H B c antibodies by an immunoenzimatic technique (Roche Laboratory). T o ensure accuracy in the results, only cases where both markers were pre-sent were considered positive. I n schoolchildren from the Cultivated Zone anti-HBc antibodies were measured in all sera.
R E S U L T S
Of the 280 sera studied, 37 (13.2%) were posi-tive for a n t i - H B s . A prevalence of 27/71 (38.0%) was presented by children of farm workers, 3/27 (11.1%) by children of fishermen and 7/135 (5.2%) by children whose fathers worked at others acti-vities. A s to sex there was no significant diffe-rence (p > 0.05) between prevalence in male (12.6%) and female (15.1%). I n one of the positive cases, this information was not available. A s to age distribution, no statistically significant diffe-rence (p > 0.05) was observed in the prevalence of a n t i - H B s A g antibodies among the groups of 6 to 8 years (11.8%), 9 to 11 years (13.3%) and
12 to 14 years (16.0%).
The prevalence rates of a n t i - H B s A g and ar-bovirus antibodies according to the four diffe-rent geographic areas considered may be seen in T a b l e 1. I n the J u n g l e area, the rate of sera with positive a n t i - H B s was 36.1% (26/72), signifi cantly higher than other zones (p < 0.001). I n the three localities of this J u n g l e area, preva-lence was 36% (9/25) in the P a v o a district, 37.8% (14/37) in the Pé da Serra district, and 30% (3/10) in the Despraiado district.
None of the cases from the B a n a n a l Zone presented anti-HBc or a n t i - H B s antibodies.
anti-H B s prevalences were of 26.7% in the Jungle Zo-ne, 8.2% in the Periurban Zone and 6.1% in Ur-ban Zone showing a significant difference bet-ween J u n g l e Zone and Urban and Periurban Zo-nes ( X2
= 10.5050 p < 0.01).
D I S C U S S I O N
There are significant differences in the pre-valence of H B s antibodies according to the geo g r a p h i c area c o n s i d e r e d . T h e p r e v a l e n c e of
T A B L E 1
Prevalence of H B s A g antibodies (anti-Ags H B ) and H I antibodies against 17 arbovirus in school children, aged 6 to 14 years, for different areas of Vale do Ribeira, São Paulo, Brazil.
Geographic area N?
tested
N? positive (%) A n t i - H B s A g
N? positive (%) Anti-arbovirus
Urban Zone
(Iguape and I l h a Comprida) 89 5 ( 5.6%) 2 ( 2.2%)
Periurban Zone
(Rocio) 89 6 ( 6.7%) 3 ( 3.4%)
Cultivated Zone 30 0 ( 0.0%) 7 (23.3^ )
J u n g l e Zone 72 26 (36.1%) 13 (18.0%)
T o t a l 280 37 (13.2%) 25 ( 8.9%)
x2 - 36.2883 p < 0.001
36.1% in children from 6 to 4 years old, the vast majority of whom (73% ) were children of farmers who lived in the Jungle Zone, is unusual, both in relation to children from other areas of the present study and in relation to the rates obser-ved in the adult population of low socioeconomic status in the city of São Paulo, where the
preva-lence of a n t i - H B s antibodies was 14.58%2 9. T h e
rates were similar to those of high prevalence (48 7%) observed in 6 to 11 year-old children
li-ving in the Serra do Mar region2 9, also in the
southern coast of S ã o Paulo State, which pre-sents climatic and phytological conditions simi-lar to those of the Vale do Ribeira.
I n the present study, the children had a ho-mogeneous socioeconomical status. Also, there were no significant differences as to sex and age of those infected by H B V (p > 0.05). Thus, it is pro-bable that a factor linked to the geographic area could be influencing the larger dissemination of the H B V in the J u n g l e Zone. T h e fact that similar rates were found in three different localities of the J u n g l e Zone somehow removes the
possi-bility of a local epidemic of infection by H B V , since these populations have almost no contact at all among themselves. Besides even we exclu-de 33 families where two or more children were studied (15 from Jungle zone), the prevalence of positive sera to a n t i - H B s antibodies remains sig-nificantly higher in the J u n g l e Zone than other areas.
Previous study, carried out among these ve-ry same children, also detected a clear pattern in the prevalence of H I antibodies to 17 arbovi-ruses in Brazil, depending on the geographical
area under consideration2 5
. T h e prevalence of ar-b o v i r u s a n t i ar-b o d i e s was s i g n i f i c a n t l y h i g h e r among those living in the rural zone (Jungle and Cultivated Zones) than observed among
chil-dren living in the Urban and Peri-Urban Zones2 5
.
of anthropophilic mosquitoes, extremely
abun-dant in that region1 5 1 6.
N e v e r t h e l e s s , the t r a n s m i s s i o n m e c h a -nisms for both viruses would have totally diffe-rent characteristics. T h u s , is relation to the arbo-viruses, there is a continuous maintenance cy-cle of these agents in the forest, with partici-pation of wild vertebrates, especially mammals and birds, and of haematophagous mosquitoes in which the virus multiplies. When humans enter this ecosystem, they face a high probability of becoming infected. T h e H B V , on the other hand, would be mechanically transmitted by haemato-phagous arthropods; this requires, besides the high density of this arthropods, exogenous intro-duction of the virus by infected humans. T h i s might occur in one area and not in another, even though the second area might be just a few kilo-meters away from the first, due to the fact that this transmission depends on the degree of dis-persion of the mechanical vectors. Furthermore, there are no know animal reservoirs to H B V ex-cept man. T h e association between the preva-lence of arbovirus antibodies and a n t i - H B s , which seem to be directed proportional (the hi gher the prevalence of anti arbovirus antibodies, the higher the prevalence of a n t i - H B s A g antibo-dies), is sharply interrupted in the Cultivated Zone, the very place of highest prevalence of ar-bovirus antibodies.
A reasonable explanation to this discrepan-cy (0% of a n t i - H B s and 23,3% of arbovirus anti-bodies) would be the total absence of H B V car-riers in the Cultivated Zone. T h e total absence
of H B V markers among children in this zone cor-roborates this hypothesis. Should H B V be intro-duced in this locality, the expectation would be for an infection prevalence comparable to that of J u n g l e Zone since in the open areas of the extraforest environment of Iguape there is a high frequency of different species of C u l i c i d a e1 5 1 6.
Additional research directed to this area beco-mes necessary. I n the Urban and Peri-Urban Zo-nes of the town of the Iguape, the epidemiolo-gical behavior would be equivalent to that obser-ved in the Urban Zone of the city of S ã o Paulo.
Other studies have attempted to stablish a correlation between H B V markers and the
pre-sence of mosquitoes1 1 4 2 0 3 2; the results are
con-flicting. However, the different conditions under which these studies were carried out and the different techniques employed for the detection of H B V immunological markers make the com-parison of the results difficult.
Unusually high prevalences of H B V immu-nological markers have been consistently observed among Indian tribes in the western A m a -zon area, varying, in the adult individuals from
60,7% to 100%9 1 0 1 8 1 9. A s for inhabitants of the
rural zone in the Vale do R i b e i r a these popula-tions live in relative isolation, in close contact with the forest. H i g h rates of infection by arbo-virus, such as Mayaro, have also been observed
in the A m a z o n region3 3. E v e n if there is a wide
gap between the Indians of the A m a z o n regions and the inhabitants of the Vale do R i b e i r a area, both populations have something in common: they both live in close contact with the forest environment and its fauna. T h e present study seems to support the hypothesis that mosqui-toes m a y play an important role in the trans-mission of hepatitis B in the tropical forested regions, However, further research becomes ne-cessary to shed further light on the matter.
R E S U M O
Relação entre prevalência de anticorpos para a r b o v i r u s e v i r u s de hepatite B na região do
Vale do R i b e i r a , B r a s i l .
na área florestal apresentaram mais alta preva-lência (26/72 = 36.1%) de anticorpos para hepa-tite B de que os residentes nas áreas urbana (5/89
= 5,6%), periurbana (6/89 = 6.7%) e cultivada (0/30 = 0% ). Os resultados sugerem a existência de fator comum na transmissão de arboviruses e de hepatite B , apoiando a hipótese que nas regiões tropicais com presença de mata mosqui-tos possam desempenhar importante papel na transmissão da hepatite B .
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