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Seasonal incidence of canine leptospirosis in Bangkok
366 TRANSACTIONS OF THE ROYAL SOCIETY OF TROPICAL MEDICINE AND HYGIENE
VOL. 60. No. 3.
SEASONAL
1966.
INCIDENCE
OF C A N I N E
LEPTOSPIROSIS
IN B A N G K O K
BY
B. SUNDHARAGIATI, S. BOONPACKNAVIG, C. HARINASUTA AND
T. P H O L P O T H I
Faculty of Tropical Medicine, Bangkok, Thailand Seasonal variation in the incidence of human leptospirosis has been noted in several countries (TAYLOR and GOYLE, 1931; BROOM, 1951 ; WOLFF and RuYS, 1953; DERRICK et al., 1954). In Thailand the highest incidence was found during and just after the end of the rainy season (SlYl~I)I-IARAGIATIand HARINASUTA, 1964). Seasonal variation .in canine leptospirosis has also been reported; in Germany BREDE(1951) found the highest incidence in autumn and winter. He thought that his finding might account for a similar seasonal incidence of human cases. In England, however, ALSTO~Iand BROOM (1958) reported the incidence of canine leptospirosis to be much the same throughout the year. In this paper we report a study of the seasonal incidence of canine leptospirosis in Bangkok. M a t e r i a l s and m e t h o d s
Heart blood from 1022 dogs (May 1964 to April 1965) at the Municipality Dogeradication Unit of Bangkok was studied serologically by methods previously reported (SuNDHARAGIATI et al., 1965). An agglutination (lysis) test with a titre of 1:100 or higher was considered as signifying previous infection, and a titre of 1:3000 or higher as representing a recent infection. Results
The results are shown in the Table and the figure. During January to June, when Thailand is mostly dry and the humidity is low, 526 sera were examined and 281 (53%) were positive. Titres of 1:3000 or higher were found in only 16 specimens. During July to December Thailand is mostly wet and the humidity is high. During this period 496 sera were examined and 290 (59%) were positive. Titres of 1:3000 or higher were found in 71 (14.3%) specimens. The incidence of high titres (assumed to represent recent infection) in the wet season is thus 4 times greater than that in the dry season. And it is highest in October. This investigation has been made possible through the support and sponsorship of the U.S. Army Medical Research and Development Command, (Far East): Grant No. DA-CRD-AG-S92-544-64-G25. The investigation was also supported in part by the National Research Council of Thailand. We thank the Municipality Dog-eradication Unit of Bangkok for their cooperation, Professor B. G. Maegraith and Dr. H. A. Reid for their help and our technicians for their assistance.
B. S U N D H A R A G I A T I ~ S. B O O N P A C K N A V I G ,
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Seasonal Incidence of Canine Leptospirosis in Bangkok.
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367
C. H A R Y N A S U T A A N D T. P H O L P O T H I
A
Percentage of dogs with -, a titre of 1 : 100 or higher \ \ in each month (General Incidence). Percentage of dogs with a titre of 1:3,000 or higher in each month (Recent Infections).
/% ~°x° \o
/
d I.[ILy
of
S[:PT
\ °x
"~
NOV
TABLE
No. of sera tested
Month
January February March April May
i
June
July August September October November December
:
i
44 51 58 60 145 168 104 153 50
53 88 48
General incidence of positive sera wth a titre of 1:100 or higher
Recent infections with a tit_re of 1:3000 or higher ~,
No.
%
14 26 31 24 88 98 83 89 29 31 40 18
31.8 50.9 53 "4 40.0 60.7 58 "3 79.8 58" 1 58-0 58.5 45.4 37 "5
No.
%
23 16 6 12 7 7
2"3 1"9 1"7 1"7 3"4 4"2 22" 1 10"5 12"0 22"6 7"9 14'6
Discussion
According to PETERSEN and FERRNESTAD (1962), the specific agglutination fitres in dogs surviving L. canicola and L. icterohaemorrhagiae infections usually reach a m a x i m u m o f 1:3000 or higher a few weeks after an acute infection and the titre subsequently falls at a variable rate. One y e a r after infection, titres of 1:300 are commonly found, and fitres of 1:100-1:300 may persist for years. I n Thailand h u m a n leptospirosis begins to increase in July and reaches its highest incidence in October-November (STJIqBHARAGIATI and HARINASUTA, 1964). F r o m M a r c h to June the incidence is low. As expected we found that canine lept ospirosis follows the same seasonal pattern as in h u m a n cases. T h e incidence o f high titres among the total positive reactions indicating recent infection was
368
C ~ N r ~ LEPTOSPIROSIS IN BANGKOK; SEASONAL INCIDENCE
23 •7% during July-December compared with 5.7 % during January-June. These findings, similar to those of KL~FN~I~vI~ (1938) in the Netherlands, and BI~a~D~(1951)in Germany, suggest that in Thailand, also, climate is important in the epidemiology of canine leptospirosis.
Summary Sera from 1022 dogs in Bangkok City were examined for leptospiral antibodies and 56% were found to have a titre of 1:100 or higher. In the wet season the proportion of sera with titres of 1:3000 or higher (indicating recent infection) was 4 times as high as in the dry season. The highest incidence of recent infection occurred in October, and this is similar to our findings in human leptospirosis. REFERENCES ALSTON~J. M. & BROOM,J. C. (1958). Leptospirosis in Man and Animals, p. 261, Edinburgh: E. & S. Livingstone Ltd. BREDE, H. D. (1951). Z. Immun-Forsch., 109, 1. BROOM, J. C. (1951). Brit. reed. J., 2, 689. DERRICK,E. H., GORDON,D., Ross, C. J., DOHERTY,R. L., SINNAMON,C. H., MJkCDONALD, V. M. & KENNEDY,J. M. (1954). Aust. Ann. Med., 3, 85. KLARENBEEK,A. (1938). Zbl. Bakt., 142, 83. PI~TERSON,C. B. & FERRNESTAD,K. L. (1962). Nord. Vet. Med., 14, 609. SUNDHARAGIATI,B. & HARINASUTA,C. (1964). Med. Ass. Thailand, 47, 662. TAYLOR, J. & GOYLE, A. N. (1931). Indian Med. Res. Man. No. 20. WOLFF, J. W. & RuYs, A. C. (1953). Docum. Med. Geogr. Trop., 5, 247.
VOL. 60. No. 3.
SEASONAL
1966.
INCIDENCE
OF C A N I N E
LEPTOSPIROSIS
IN B A N G K O K
BY
B. SUNDHARAGIATI, S. BOONPACKNAVIG, C. HARINASUTA AND
T. P H O L P O T H I
Faculty of Tropical Medicine, Bangkok, Thailand Seasonal variation in the incidence of human leptospirosis has been noted in several countries (TAYLOR and GOYLE, 1931; BROOM, 1951 ; WOLFF and RuYS, 1953; DERRICK et al., 1954). In Thailand the highest incidence was found during and just after the end of the rainy season (SlYl~I)I-IARAGIATIand HARINASUTA, 1964). Seasonal variation .in canine leptospirosis has also been reported; in Germany BREDE(1951) found the highest incidence in autumn and winter. He thought that his finding might account for a similar seasonal incidence of human cases. In England, however, ALSTO~Iand BROOM (1958) reported the incidence of canine leptospirosis to be much the same throughout the year. In this paper we report a study of the seasonal incidence of canine leptospirosis in Bangkok. M a t e r i a l s and m e t h o d s
Heart blood from 1022 dogs (May 1964 to April 1965) at the Municipality Dogeradication Unit of Bangkok was studied serologically by methods previously reported (SuNDHARAGIATI et al., 1965). An agglutination (lysis) test with a titre of 1:100 or higher was considered as signifying previous infection, and a titre of 1:3000 or higher as representing a recent infection. Results
The results are shown in the Table and the figure. During January to June, when Thailand is mostly dry and the humidity is low, 526 sera were examined and 281 (53%) were positive. Titres of 1:3000 or higher were found in only 16 specimens. During July to December Thailand is mostly wet and the humidity is high. During this period 496 sera were examined and 290 (59%) were positive. Titres of 1:3000 or higher were found in 71 (14.3%) specimens. The incidence of high titres (assumed to represent recent infection) in the wet season is thus 4 times greater than that in the dry season. And it is highest in October. This investigation has been made possible through the support and sponsorship of the U.S. Army Medical Research and Development Command, (Far East): Grant No. DA-CRD-AG-S92-544-64-G25. The investigation was also supported in part by the National Research Council of Thailand. We thank the Municipality Dog-eradication Unit of Bangkok for their cooperation, Professor B. G. Maegraith and Dr. H. A. Reid for their help and our technicians for their assistance.
B. S U N D H A R A G I A T I ~ S. B O O N P A C K N A V I G ,
!
/
\
/;
\ \
J
Seasonal Incidence of Canine Leptospirosis in Bangkok.
\
i~II~ ~ ~ "e/
/ !
4(
/
"
,./
/
\
\
//
\ \
x,,\
/
V
//
3( 21
J
/
367
C. H A R Y N A S U T A A N D T. P H O L P O T H I
A
Percentage of dogs with -, a titre of 1 : 100 or higher \ \ in each month (General Incidence). Percentage of dogs with a titre of 1:3,000 or higher in each month (Recent Infections).
/% ~°x° \o
/
d I.[ILy
of
S[:PT
\ °x
"~
NOV
TABLE
No. of sera tested
Month
January February March April May
i
June
July August September October November December
:
i
44 51 58 60 145 168 104 153 50
53 88 48
General incidence of positive sera wth a titre of 1:100 or higher
Recent infections with a tit_re of 1:3000 or higher ~,
No.
%
14 26 31 24 88 98 83 89 29 31 40 18
31.8 50.9 53 "4 40.0 60.7 58 "3 79.8 58" 1 58-0 58.5 45.4 37 "5
No.
%
23 16 6 12 7 7
2"3 1"9 1"7 1"7 3"4 4"2 22" 1 10"5 12"0 22"6 7"9 14'6
Discussion
According to PETERSEN and FERRNESTAD (1962), the specific agglutination fitres in dogs surviving L. canicola and L. icterohaemorrhagiae infections usually reach a m a x i m u m o f 1:3000 or higher a few weeks after an acute infection and the titre subsequently falls at a variable rate. One y e a r after infection, titres of 1:300 are commonly found, and fitres of 1:100-1:300 may persist for years. I n Thailand h u m a n leptospirosis begins to increase in July and reaches its highest incidence in October-November (STJIqBHARAGIATI and HARINASUTA, 1964). F r o m M a r c h to June the incidence is low. As expected we found that canine lept ospirosis follows the same seasonal pattern as in h u m a n cases. T h e incidence o f high titres among the total positive reactions indicating recent infection was
368
C ~ N r ~ LEPTOSPIROSIS IN BANGKOK; SEASONAL INCIDENCE
23 •7% during July-December compared with 5.7 % during January-June. These findings, similar to those of KL~FN~I~vI~ (1938) in the Netherlands, and BI~a~D~(1951)in Germany, suggest that in Thailand, also, climate is important in the epidemiology of canine leptospirosis.
Summary Sera from 1022 dogs in Bangkok City were examined for leptospiral antibodies and 56% were found to have a titre of 1:100 or higher. In the wet season the proportion of sera with titres of 1:3000 or higher (indicating recent infection) was 4 times as high as in the dry season. The highest incidence of recent infection occurred in October, and this is similar to our findings in human leptospirosis. REFERENCES ALSTON~J. M. & BROOM,J. C. (1958). Leptospirosis in Man and Animals, p. 261, Edinburgh: E. & S. Livingstone Ltd. BREDE, H. D. (1951). Z. Immun-Forsch., 109, 1. BROOM, J. C. (1951). Brit. reed. J., 2, 689. DERRICK,E. H., GORDON,D., Ross, C. J., DOHERTY,R. L., SINNAMON,C. H., MJkCDONALD, V. M. & KENNEDY,J. M. (1954). Aust. Ann. Med., 3, 85. KLARENBEEK,A. (1938). Zbl. Bakt., 142, 83. PI~TERSON,C. B. & FERRNESTAD,K. L. (1962). Nord. Vet. Med., 14, 609. SUNDHARAGIATI,B. & HARINASUTA,C. (1964). Med. Ass. Thailand, 47, 662. TAYLOR, J. & GOYLE, A. N. (1931). Indian Med. Res. Man. No. 20. WOLFF, J. W. & RuYs, A. C. (1953). Docum. Med. Geogr. Trop., 5, 247.