SEROLOGICAL PROFILE OF A NELORE HERD PRESENTING ENDEMIC LEPTOSPIROSIS AND SUBMITTED TO VACCINATION

PERFIL SOROLÓGICO DE UM REBANHO NELORE COM LEPTOSPIROSE ENDÊMICA SUBMETIDO A VACINAÇÃO

ABSTRACT

The effect of vaccination on the serological profile of a closed Nelore beef cattle herd, endemically infected by leptospirosis was studied. Serum samples of 100% of the females (= 12 months to 8 years) were collected in Oct/1998 and examined by Microscopic Agglutination test (MAT) using 6 serovars of Leptospira spp.: icterohaemorrhagiae, canicola, pomona, grippotyphosa, hardjo and wolffi. After MAT, the animals were vaccinated and divided in 4 groups: I) hardjo/ wolffi MAT positive and vaccinated; II) hardjo/wolffi MAT positive and non-vaccinated; III) MAT negative and vaccinated and IV) MAT negative and non-vaccinated. The first vaccination was in Dec/1999 with reinforcement in Jan/2000; and revaccination in Out/2000. The 3 mL dose of a commercial vaccine containing the same 6 serovars was given subcutaneously. Serum samples were taken in Mar/2000 and Nov/2000 and examined the same way by MAT. The proportion of reagents in the 3 collections was: 62.5% (120/192), 77.4% (106/137) and 74% (91/123). Geometrical means titers were equal to 2.59, 2.34 and 2.15, respectively. Serological profile considering reagents frequency and pre-vaccination titers showed a bimodal distribution with 39.6% of negative results. After vaccination, there was an increase in the frequency of reactors, probably due to the seroconversion of negative heifers and cows, however, the vaccination did not elicit significant increase in the magnitude of the Hardjo or Wolffi titers. Instead, the geometric means in the whole herd, vaccinated and unvaccinated groups, showed a decreasing tendency. In postvaccination serological monitoring the progressive titer decrease would represent vaccine efficiency.

KEY WORDS:
Bovine leptospirosis; vaccination; serological profile.

RESUMO

Estudou-se o efeito da vacinação sobre o perfil sorológico de um rebanho Nelore fechado, que apresentava leptospirose endêmica. Amostras de soro de 100% das fêmeas (=12meses a 8 anos) foram examinadas (out/98) pela à Soroaglutinação Microscópica (SAM) frente aos sorovares Icterohaemorrhagiae, Canicola, Pomona, Grippotyphosa, Hardjo e Wolffi. Baseado nesses resultados os animais foram vacinados e subdivididos em 4 grupos: I) SAM +, vacinados; II) SAM +, não vacinados; III) SAM -, vacinados e IV) SAM -, não vacinados. Tres mL de uma vacina comercial contendo os mesmos 6 sorovares foram aplicados por via SC, em dez./99, com reforço em jan/00 e revacinação em out/00. Os soros foram colhidos em mar/00 e nov/00 e reexaminados pela SAM. A proporção de reagentes nas 3 colheitas foi de 62,5% (120/ 192), 77,4% (106/137) e 74% (91/123) com médias geométricas dos títulos de 2,59, 2,34 e 2,15 respectivamente. O perfil sorológico, considerando-se a freqüência de reagentes e títulos de aglutininas antes da vacinação, mostrou distribuição bimodal, com 39,6% negativos. Após vacinação, houve aumento na freqüência de reagentes, provavelmente, devido a soroconversão de novilhas e vacas negativas, entretanto não promoveu aumento significante na média geométrica de títulos para Hardjo e Wolffi, ao contrário, houve tendência decrescente. O monitoramento sorológico de um rebanho vacinado pode ser utilizado como ferramenta na avaliação do "status" protetor conferido pela vacina, onde o decréscimo progressivo dos títulos pós vacinação significaria eficiência vacinal.

PALAVRAS-CHAVE:
Leptospirose bovina; vacinação; perfil sorológico.

INTRODUCTION

Among reproductive diseases, leptospirosis has been considered worldwide as bein responsible for decreases in milk and meat production, due to infertility and abortion (FAINE et al., 1999; GENOVEZ et al., 2001a; GUITIAN et al., 1999). Leptospira spp serovar Hardjo, once introduced into a bovine population, establishes varying levels of infection which may persist for a long time (HATHAWAY et al., 1986). In leptospirosis control, vaccination has been almost exclusively recommended, mainly in beef cattle herds (ALEXANDER et al., 1989; LITTLE et al., 1992; MARSHALL et al., 1979). Many commercial vaccines are available in Brazil, which are made up of 5 or 6 serovars, which correspond to the most prevalent serovars in the several regions of the country. These vaccines, bacterines, induce serological response that interferes with diagnosis and prevent the progression of the infection from being monitored in the herd, unless isolation and identification of the strains and/or PCR with detection of bacterial DNA are performed (GENOVEZ et al., 2001b). The objective of the present trial was to evaluate vaccinated and revaccinated groups, comparing them with non-vaccinated ones, in order to study the effect of vaccination on the serological profile of an endemically infected herd.

History

A closed herd of approximately 400 Nelore beef cattle (Bos indicus), without any prior vaccination against leptospirosis, managed under extensive conditions on rotational system in pastures of Brachiaria decumbens and receiving mineral salt ad libido,p resented a low reproductive performance, with sporadic abortions, usually 5-6 month gestation and stillborns. Artificial insemination was used, followed by mating with a bull. Animals have free access to streams and water spring, which are formed by a water source that receives water drained from a small pig facility. The pastures that fed these animals were contiguous to a sugarcane plantation, where free-living species (such as capybaras, rodents and wild dogs) could be found. Samples of naturally voided urine collected before and during the trial, submitted to PCR technique, using a 16S rRNA gene sequence, evidenced the presence of Leptospira spp. in this herd. Although Leptospira spp. was not isolated, the detection of its DNA in urine samples assures that it is circulating in the herd (GENOVEZ el al., 2001).

MATERIAL AND METHODS

Serum samples of 100% of the females at reproductive age were collected in Oct/1998 and examined by Microscopic Agglutination test (MAT) using 6 serovars of Leptospira spp.: Icterohaemorrhagiae, Canicola, Pomona, Grippotyphosa, Hardjo and Wolffi. At screening, titers = 50 with 100% agglutination were considered positive; final titer was the greatest dilution able to show 50% of the free leptospires in a serial two-fold dilution. After MAT, the animals were vaccinated and divided in 4 groups: I) Hardjo/Wolffi MAT positive and vaccinated; II) Hardjo/ Wolffi MAT positive and non-vaccinated; III) MAT negative and vaccinated and IV) MAT negative and nonvaccinated. The first vaccination was in Dec/1999 with reinforcement in Jan/2000; and revaccination in Out/ 2000. The 3 mL dose of a commercial vaccine (serovars Icterohaemorrhagiae, Canicola, Pomona, Grippothyphosa, Hardjo and Wolffi) was given subcutaneously. Serum samples were taken in Mar/2000 and Nov/2000 and examined the same way by MAT.

RESULTS AND DISCUSSION

Serological monitoring showed that 58.6% of negative animals in the first serum collection presented seroconvertion in the second; the rest was kept negative until the third collection. The culling rates during the experimental period were 17.5% in 1998; 0.01% in 1999 and 17.9% in 2000.

MAT results showed the serovars Hardjo and Wolffi, both from the Sejroe group, were the most prevalent in this female herd (Table 1) during the period of the 3 serum collections. Geometric means of agglutinin titers in MAT (Hardjo and Wolffi), in 3 collections of whole herd revealed a decreasing tendency when compared to the first evaluation (Table 2). The same occurred in relation to the vaccinated and non-vaccinated groups.

Table 1
Frequency of seroreactors using MAT (Hardjo and Wolffi) in three collections of females from a Nelore beef cattle herd endemically infected by leptospirosis, São Paulo, Brazil, 2001.

	Oct/98*	Mar/00**	Nov/00***
Positive/Total	120/192	106/137	91/123
examined	(62.5%)	(77.4%)	(74%)

Serum collected before vaccination,
• ^**
  Serum collected 4060 days after vaccination and reinforcement,
• ^***
  Serum collected 40-60 days after revaccination.

Table 2
Geometric means of agglutinin titers in MAT (Hardjo and Wolffi), in 3 collections of females from a Nelore beef cattle heard endemically infected by leptospirosis, São Paulo, Brazil, 2001.

Group	Oct/98*	Mar/00**	Nov/00***
Whole herd	2.59	2.34	2.15
I+III (vaccinated)	...	2.36	2.31
II +IV (not vaccinated)	...	2.17	2.12

• ^*
  Serum collected before vaccination,
• ^**
  Serum collected 4060 days after vaccination and reinforcement,
• ^***
  Serum collected 40-60 days after revaccination.

Figures 1 to 8 show the serological profiles of this Nelore herd according to the following conditions: previous MAT results, vaccination, revaccination and age.

DISCUSSION

Unless several prophylatic and preventive conditions are applied on a beef herd, vaccination program control should be used indefinitely. This procedure interferes in the serological diagnosis as can be detected by MAT. Once Leptospira spp. were detected by PCR in the urine of several animals (GENOVEZ et al., 2001b) and the prevaccination (Oct/ 1998) whole herd results revealed 62.5% of reactor animals mainly for serovasr Hardjo and Woffi (Table 1 ), and also because many risk factors related to leptospirosis transmission were recognized in that environment and managing conditions, all these facts confirmed that the leptospirosis had been occurring in an endemic way in this herd. Although in Brazil the sorovar Hardjo has been the more prevalent in bovines (FAVERO et al., 2002; GIORGI et al., 1981; SANTA ROSA et al., 1969/70) the serological evidence of serovar Wolffi in this and in other species has being very frequent (FAVERO et al., 2002; GIORGI et al., 1981; SANTA ROSA et al., 1969/70), and in many times associated with Hardjo. But, the sorovar Wolffi has only been isolated from rodents and human beings (GIORGI et al., 1984; CORRÊA et al., 1965/67).

In the analysis of the serological profile before vaccination a bimodal distributionwas observed (Fig. 1), with high points at both the beginning and the end of the graph, which showed that 39.6% of animals were negative; while the rest presented leptospirosis titers ranging from 50 to 1, 600. Heifers = 24 months (Fig. 1 and 2) represented 57.9% of these negative animals in this herd, and therefore, older animals were the main factor responsible for the bimodal distribution. This fact assumes the beef cattle heifers play an important role as sentinels for the circulation of leptospires in this environment, whereas the entrance in the reproductive service seems to be the main risk factor for first contagion. Similar serological profiles were observed by MARSHALL et al. (1998). In an effort to examine the effectiveness of vaccination for controlling leptospirosis, these authors sampled 30 heifers from ten dairy unvaccinated herds and compared the results to ten vaccinated ones. The vaccinated group had a sloping curve from large numbers of negative downwards to a small number of high titers, while most of the unvaccinated group had mean titers consistent with current infection.

Fig. 1
Pre-vaccination titers according to the age.

Fig. 2
heifers (≤24 months) and cows (> 24 months).

Fig. 3
Whole herd: pre-vaccination, after vaccination and revaccination.

Fig. 4
heifers (≤24 months): pre-vaccination, after vaccination and revaccination.

Fig. 5
previously positive animals vaccinated and revaccinated.

Fig. 6
previously negative animals vaccinated and revaccinated.

After vaccination, there was an increase in the frequency of reactors, probably due to the seroconversion of negative heifers (Fig. 4) and cows; which could be responding serologicaly to vaccination and also because few animals could get infected. However, the vaccination did not elicit a significant increase in the magnitude of the Hardjo or Wolffi titers (Figs.3 and 5). Instead, the geometric means (Table 2) in the whole herd, vaccinated and unvaccinated groups, showed a decreasing tendency when compared to the first evaluation, independently of the previous positive status (Group I). Group III was able do respond to vaccination but the titers were not higher than 800, which after revaccination also presented a decreasing tendency (Fig.6). In conclusion, when the serological profiles of the animals in groups I and III were compared, it was observed that the former presented the same distribution from the beginning of the study (Fig. 5), whereas the latter presented low level seroconversion (Fig. 6). During this trial, no change could be observed in Group II or Group IV. Once groups I and II were bred on the same pasture but separated from groups III and IV, the titers decrease in the former and the constant titers in the latter could have been due to the vaccination effect.

Systematic serological monitoring of the herd submitted to a vaccination program against leptospirosis may provide a good tool for evaluation of the protection given by the vaccine. In postvaccination serological monitoring the progressive titer decrease would represent vaccine efficiency; while high titers (>1,600) may mean that another infecting leptospira strain or a new serovar entered in circulation in the herd stimulating high humoral immune responses, and indicating escape from vaccine protection. In this case, a review in the vaccination program and sanitary management of the herd would be necessary.

ACKNOWLEDGMENTS

The authors are thankful to FAPESP - Fundação de Amparo à Pesquisa do Estado de São Paulo for financial support.

REFERENCES

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Publication Dates

• Publication in this collection
  17 June 2024
• Date of issue
  Oct-Dec 2004

History

• Received
  29 Nov 2004
• Accepted
  29 Dec 2004