Preventive Veterinary Medicine, 6 (1988) 1-8 1 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

Retrospective Study of the Temporal Distribution of Vesicular Stomatitis in Cattle in Costa Rica, 1 9 7 2 - 1 9 8 6

ENRIQUE PEREZ' and BRIGITTE CORNELISSEN 2

'Department of Large Animal Clinics, School of Veterinary Medicine, National University, Heredia (Costa Rica) 2Department of Herd Health and Ambulatory Clinic, University of Utrecht (The Netherlands)

(Accepted for publication 18 November 1987)

ABSTRACT

Perez, E. and Cornelissen, B., 1988. Retrospective study of the temporal distribution of vesicular stomatitis in cattle in Costa Rica, 1972-1986. Prey. Vet. Med., 6: 1-8.

The temporal distribution of vesicular stomatitis in cattle in Costa Rica, from 1972 to 1986, was analysed using the time series analysis. Seasonal fluctuations were observed with the highest occurrence in the dry season. The possible existence of 3-4-year cycles was demonstrated.

INTRODUCTION

Vesicular stomatitis has been reported only in the Western Hemisphere (Johnson et al., 1969) and belongs to the vesicular disease group together with foot and mouth disease, vesicular exanthema, and swine vesicular disease (Callis, 1984).

Many studies of the epidemiological behavior of vesicular stomatitis have been carried out, but still there is great controversy on many aspects (Jonkers, 1967; Mason, 1976; Hanson, 1982; Kramer, 1982; Hansen et al., 1985). The socio-economic importance of vesicular stomatitis is mainly related to the problems of control and differential diagnosis of other vesicular diseases, its capacity to affect human beings and its adverse effect on herd productivity. Epidemiological surveillance systems have been implemented in Latin Amer- ica to support the control and prevention of foot and mouth disease (Astudillo, 1984).

Costa Rica has a passive epidemiological surveillance system for vesicular diseases in collaboration with the United States Department of Agriculture (U.S.D.A.) and the International Organization for Animal and Plant Health (O.I.R.S.A.). This system has allowed the creation of a data bank containing

0167-5877/88/$03.50 © 1988 Elsevier Science Publishers B.V.

the number of farms affected with vesicular stomatitis in Costa Rica over time. The objective of this study was to apply classical time series analysis (Lapin, 1978), using the data of the vesicular stomatitis epidemiological surveillance system to identify possible trends, seasonal and cyclical patterns, which might assist in the epidemiological interpretation of the disease in Costa Rica.

M A T E R I A L S A N D M E T H O D S

The information used for this study was obtained from data supplied by the epidemiological surveillance system for vesicular diseases of the U.S.D.A.-Costa Rica bilateral agreement, in cooperation with O.I.R.S.A., for the prevention of foot and mouth disease. Investigations of cases of suspected vesicular disease were carried out by field personnel of the Costa Rica Ministry of Agriculture and Livestock and private veterinary practitioners. The average time required to respond to these reports of suspected disease made by the livestock owner was 6 days in 1986. In all cases, diagnostic material was collected and submit- ted to the laboratory for the final diagnosis (complement fixation test and virus neutralization test; Convenio Antiaftoso Bilateral, 1986).

A case of vesicular stomatitis was defined as a herd in which vesicular sto- matitis was confirmed by laboratory diagnosis in one or more animals during the period from January 1972 until December 1986. Case date was considered as the date of first clinical report.

Decomposition of these data into trend, seasonal and cyclical factors was accomplished using time series analysis (Lapin, 1978). The mathematical equation to represent this model is as follows:

Yt = T, x C t x S t x I t

where

Yt = original time series data; T = t rend factor; Ct = cyclical factor; St = seasonal factor; It = random factor;

t = time period.

The first step was to calculate the trend factor, using a regression equation in which the independent variable was month and the dependent variable the number of cases reported per month. Developing the equation, the trend value was obtained for each month.

The second step was to calculate the seasonal index as a seasonal component of the original information, using the Microstat statistical computer program (Ecosoft, 1984). The value of Y of each month of 1 year was taken as a pro- portion of the total of Y for that year. These proportions were averaged for a particular month over the period under study (15 years in this instance), re-

suiting in the seasonal index for each month. At this point, the original series of data were divided by the seasonal index to eliminate seasonal fluctuation, leaving as a result the deseasonalized values as a function of Tt, Ct and It. The third and last step was to determine the cyclic factor. Each deseasonalized value was divided by the corresponding trend value and expressed as a per- centage. To eliminate the random factor, a 6-month moving average was calculated.

RESULTS

From January 1972 through December 1986, 407 cases of vesicular stoma- titis were diagnosed in Costa Rica (Table 1). Of these, 335 (82.3%) corre-

TABLE 1

Number of herds affected by vesicular stomatit is per month in Costa Rica 1972-1986

Year Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec. Total

1972 1 2 4 3 4 1 3 0 1 0 0 1 20 1973 2 1 0 0 1 1 1 3 2 0 0 0 11 1974 0 1 0 0 0 0 0 0 0 0 0 1 2 1975 2 1 0 0 3 0 2 0 0 0 2 1 11 1976 0 3 3 1 2 1 0 0 2 2 2 6 22 1977 7 10 7 15 0 0 5 3 6 4 2 1 60 1978 7 7 1 0 2 3 2 1 1 0 2 1 27 1979 3 2 1 1 0 3 2 3 0 0 1 1 17 1980 11 18 3 4 2 5 4 6 0 2 1 0 56 1981 2 1 2 4 2 1 1 0 0 0 1 1 15 1982 4 1 0 0 5 2 2 1 3 0 0 2 20 1983 5 3 0 0 0 1 1 1 2 0 2 2 17 1984 16 5 2 4 2 0 3 9 6 1 3 3 54 1985 6 0 4 5 3 2 3 1 0 2 0 2 28 1986 2 0 2 1 0 0 5 6 7 2 0 0 25

Total 68 55 29 38 26 20 34 34 30 13 16 22 385"

"In 22 herds, both virus subtypes were isolated.

TABLE 2

Positive laboratory reports per virus and year in Costa Rica 1972-1986

1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 Total

New Jersey 13 11 2 11 22 52 27 11 49 15 21 14 35 27 25 335 Indiana 8 0 0 0 0 23 0 6 13 0 0 3 16 2 1 72

Total 21 11 2 11 22 75 27 17 62 15 21 17 51 29 26 407

No. PRKMISES WITH 00TBREAKS 20

° .

. 4 . . . . . . . . . .

• , . . ° . . . . . . .

1 ~0~TB 180

Fig. 1. Laboratory verified cases of vesicular stomatitis in Costa Rica, 1972-1986. Raw data and trend.

sponded to the New Jersey subtype and 72 (17.7%) to the Indiana subtype. The monthly distribution of affected herds is given in Table 2. A very slight, but statistically significant (P < 0.05 ) increase in the number of reported cases of vesicular stomatitis from 1972 through 1986 was observed (Fig. 1 ). Seasonal and cyclical fluctuations were present. Seasonal changes, expressed as sea- sonal index (Fig. 2 ), showed the greatest values during the months of January and February. The lowest indices were observed in October and November, and the rest of the months were close to the average annual value. Figure 3 shows the cyclical factor as percentage of trend. The existence of 3-4-year cycles was observed with peaks occurring in 1977, 1980 and 1984.

DISCUSSION

The temporal distribution of vesicular stomatitis in Costa Rica was de- scribed in terms of seasonal, cyclical and trend factors. From January 1972

SEASOmAL INDEX 215

20 1 12

Fig. 2. Seasonal index of laboratory confirmed cases (herds) of vesicular stomatitis in Costa Rica, 1972-1986.

until December 1986, the trend factor shows a very slight increase. This could be due to increased reporting of cases and/or the intervention of man in cattle production systems in which the host/virus interaction is in favor of the virus. During the last months of the seventies and early eighties, the Costa Rican government stimulated the dairy production systems by intensification of pro- duction, new production areas and new livestock. In 1986, there were more cattle and more herds than in 1972. Other factors of possible importance are: the movement of animals (Hansen et al., 1985) and a greater number of sus- ceptibles (Walton et al., 1984; Barreto, 1985). The principal region chosen for the new livestock production is located in an ecological area of > 2000 mm annual precipitation, temperatures with a range between 12 and 24 °C and hu- midity of 707-1532 (potential evapotranspiration) (Holdridge, 1978). These conditions are adequate for the presence of possible vectors and the persistence of the virus (Zuluaga and Yuill, 1979; Hanson, 1982 ). This region experienced

6

339 DKS[~SO~AL VALOIS / Tgi~D

\ / 72 73 74 75 78 77 78 79 80 81 82 83 84 85 86

Fig. 3. Cyclic factor for laboratory confirmed cases (herds) of vesicular stomatitis in Costa Rica, 1972-1986.

an increase in the number of cases in the last few years. The seasonal behavior, as measured by the seasonal index, may be explained by changes in host den- sity, management practices, agent survival in the environment, dynamic pop- ulation behavior of vectors and other environmental factors such as precipitation, temperature and humidity. The greatest seasonal indices in Costa Rica are seen during January and February (early summer, dry season). It is possible that arthropod populations play an important role in this phenome- non. The summer months are the months with the highest populations of pos- sible vectors of the disease (Zeledon and Vieto, 1957; Vargas and Travis, 1973 ). Data in this study are in agreement with Mason and Guti6rrez (1984), who reported that a greater number of cases were observed 3 months after the peak of the rainy season in tropical regions (which occurs in October in Costa Rica). Lauermann (1967) and Kunns ( 1962 ), cited by Hanson ( 1982 ), also suggested that the disease incidence increased at the end of the rainy season (November and December for Costa Rica). This was not corroborated by the results of this

s t u d y . C y c l i c c h a n g e s m a y b e a s s o c i a t e d w i t h f l u c t u a t i o n s o f t h e s u s p e c t i b i l i t y

o f h o s t p o p u l a t i o n s a n d t h e i n f e c t i v i t y o f t h e i n f e c t i o u s a g e n t . C o s t a R i c a

s e e m e d to p r e s e n t c y c l e s e a c h o f 3 - 4 y e a r s . T h e d y n a m i c b e h a v i o u r o f t h e c a t t l e

p o p u l a t i o n r e s u l t s in t h e p e r i o d i c a c c u m u l a t i o n o f n u m b e r s o f a d u l t a n i m a l s d u e t o t h e m e a t m a r k e t i n g cyc le , e a c h 3 - 4 y e a r s r e s u l t i n g in a n i n c r e a s i n g

n u m b e r o f s u s c e p t i b l e a n i m a l s . O t h e r f a c t o r s s u c h as s y l v a t i c cyc l e p e r s i s t e n c e o f t h e v i r u s in t h e a n i m a l p o p u l a t i o n s c a n n o t be d i s c o u n t e d ( M a s o n a n d G u -

t i d r r e z , 1984) .

REFERENCES

Astudillo, V.M., Estupifi~n, J.A., Rosenberg, F.J., da Silva, A.J.M. and Dora, J.F.P., 1984. Vesi- cular stomatitis in South America. Description of data taken from the Continental Vesicular Diseases Surveillance System. Proceedings of an International Conference on Vesicular Sto- matitis, 24-27 September, at Mdxico, D.F., Mdxico, pp. 23-86.

Barreto, C.H., 1985. Consideraciones epidemiol6gicas sobre estomatitis vesicular en Centro Amer- ica y Panamd. Carta informativa, Organismo Internacional Regional de Sanidad Agropecuaria 12.

Callis, J.C., 1984. Vesicular stomatitis virus serotypes. Proceedings of an International Conference on Vesicular Stomatitis, 24-27 September, at M~xico, D.F., Mdxico, pp. 401-411.

Convenio Antiaftoso Bilateral, 1986. Vesicular Disease in Costa Rica. Annual Information Avail- able from C.A.B. on request.

Hansen, D.E., Thurmond, M.C. and Thorburn, M., 1985. Factors associated with the spread of clinical vesicular stomatitis in California dairy cattle. Am. J. Vet. Res., 46: 789-795.

Hanson, R.P., 1982. Vesicular Stomatitis. In: E.P.S. Gibbs (Edi tor) , Diseases of Food Animals. Lea and Febiger, Philadelphia, U.S.A., pp. 517-539.

Holdridge, L.R., 1978. Ecologfa basada en zonas de vida, IICA. San Josd, Costa Rica, 216 pp. Johnson, K.M., Tesh, R.B. and Peralta, P.H., 1969. Epidemiology of vesicular stomatitis virus:

some new data and a hypothesis for transmission of the Indiana serot~-pe. J. Am. Vet. Med. Assoc., 155: 2133-2140.

Jonkers, A.H., 1967. Epizootiology of the vesicular stomatitis virus: A reappraisal. Am. J. Epide- miol., 86: 286-291.

Kramer, W.L., Jones, R.H., Holbrook, F.R. and Walton, T.E., 1984. Entomological investigation of a 1982 vesicular stomatitis epizootic in Colorado U.S.A. Proceedings of an International Conference on Vesicular Stomatitis, 24-27 September, at M~xico, D.F., M~xico, pp. 193 219.

Lapin, L.L., 1978. Statistics for Modern Business Decisions. Harcourt Brace Jovanovich, New York, 778 pp.

Mason, J., 1976. Epidemiologia de la estomatitis vesicular: Una revision de literatura para pro- mover futuros estudios de campo. O.I.R.S.A.

Mason, J. and Guti~rrez, G., 1984. Vesicular stomatitis field studies in M~xico. Proceedings of an International Conference on Vesicular Stomatitis, 24-27 September, at M~xico, D.F., M~xico, pp. 276-311.

Vargas, N.V. and Travis, B., 1973. Binomia de los Simulidos (Diptera: Simuliidae) en Costa Rica. IV. Localizacion y Descripcion de los lugares de recoleccion. Rev. Biol. Trop., 21: 143-175.

Walton, T.E., Webb, P.A., Kramer, W.L., Smith, G.E., Davis, T., Holbrook, F.R., Moove, C., Schiefrer, T. and Jones, R.M., 1984. Epidemiological, entomological and virologic investiga- tion during an outbreak of vesicular stomatitis (New Jersey) in Colorado, 1982. Prolo~ m and

epidemiologic studies. Proceedings of an International Conference on Vesicular Stomatitis, 24-27 September, at M~xico, D.F., M~xico, pp. 180-192.

Zeledon, R. and Vieto, V., 1957. Contribucion al Estudio de los Simulidos en Costa Rica (Diptera: Nematocera) I. Sobre el Simulium panamense. Rev. Biol. Trop., 5: 19-33.

Zuluaga, F.N. and Yuill, T.M., 1979. Estudios ecol6gicos de los virus de Estomatitis Vesicular en Antioquia, Colombia. Bol. Sanit. Panam., 87: 389-403.