The role of leptospirosis in reproductive disorders in horses
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- Hamond, C., Pinna, A., Martins, G. et al. Trop Anim Health Prod (2014) 46: 1. doi:10.1007/s11250-013-0459-3
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Leptospirosis is a zoonotic disease of global importance and has a worldwide distribution. This infection displays clear seasonal nature in some regions of the tropics, where the rainy season is marked by high temperatures. Household and wild animals carry leptospires and contribute to their dissemination in nature. Transmission mainly occurs by contact with water contaminated with the urine of infected animals, and consequently, it is quite widespread especially in times of rain, since many areas are subject to flooding and have poor sanitation. Serological tests demonstrate that Leptospira sp. infection in horses occurs worldwide and that the predominant serovar may vary depending on the region or infection sources. Besides systemic and ocular manifestations, leptospirosis in horses has been recognized as an important disease of the reproductive system, since it leads to the birth of weak foals, stillbirths or neonatal mortality, and mainly to abortion, usually after the sixth month of pregnancy. In this context, this review aims to gather and discuss information about the role of leptospirosis in reproductive disorders in horses.
Leptospirosis is a bacterial disease with worldwide distribution, but its incidence seems to be higher in tropical rather than in temperate areas. Since it affects many domestic animals, wildlife, and also human beings, it is classified as a zoonosis (Lim 2011). It is noteworthy to observe that veterinarians are at risk for leptospirosis and should take measures (individual protection equipment) to decrease potential exposure to leptospires. Diagnostic tests for leptospirosis should also be considered when veterinarians have febrile illnesses of unknown origin (Whitwell et al. 2009).
Leptospires are bacteria belonging to the family Leptospiraceae, order Spirochaetales. The spirochetes are about 0.1 μm in diameter and 6–20 μm in length (Haake and Matsunaga 2010). Structurally, the leptospires have a helical protoplasmic cylinder consisting of nuclear material, cytoplasm, and the cytoplasmic membrane and peptidoglycan cell wall (Slamti et al. 2011), and the major antigenic component of pathogenic Leptospira sp. is lipopolysaccharide (LPS). There are two axial flagella, or axial filaments, each attaching at opposing ends of the organism by plate-like insertion discs. These bacteria are fastidious, with a generation time from 6 to 16 h, optimum growth at pH 7.2 to 7.6, and temperature at 28 to 30 °C (Adler and De La Peña Moctezuma 2010).
According to the serological classification, the genus Leptospira sp. includes saprophytic (Leptospira biflexa sensu lato) and pathogenic (Leptospira interrogans sensu lato) bacteria, with more than 260 serovars of L. interrogans, while the serovars that are antigenically related are grouped into serogroups (Adler and De La Peña Moctezuma 2010). Although still used for epidemiological surveys, this classification is now challenged by a taxonomically more relevant genomic classification which distinguishes 19 genomospecies (Djelouadji et al. 2012).
Equine leptospirosis is commonly manifested by recurrent uveitis (Verma et al. 2012), decreased athletic performance of racing horses (Hamond et al. 2012b), and reproductive disorders as abortions, embryonic absorption, stillbirth or neonatal mortality, and the birth of weak foals (Whitwell et al. 2009). Although serologic evidence of leptospiral infections is common in horses, acute clinical disease is infrequent, and many animals may manifest as having chronic or subclinical disease (Houwers et al. 2011).
In this context, this review aims to gather and discuss information about the role of leptospirosis in reproductive disorders in horses.
Leptospirosis is a zoonosis with worldwide incidence that affects both the urban and the rural human population in countries with tropical (Ko et al. 2009), subtropical, or temperate (Wasiński 2011) climates. This infection displays a clear seasonal nature in some topical regions, where the rainy season is marked by high temperatures (Wasiński 2011). In tropical countries, it has become a serious public health problem, associated with high mortality in animals as well as in human beings (Ko et al. 2009). Livestock and wild animals may carry leptospires and contribute to their dissemination in nature. Transmission mainly occurs by contact with water contaminated with the urine of infected animals, and consequently, it is quite widespread especially in times of rain, since many areas are subject to flooding and have poor sanitation (Perez et al. 2011). Additionally, leptospires can persist for months in nutrient-poor aqueous environments prior to transmission to a mammalian host. Interactions with environmental bacteria and biofilm formation are possible mechanisms of persistence of leptospires in the environment (Barragan et al. 2011).
Serovars of leptospires, in terms of adaptation to the host, are divided into two major groups. One refers to those that are adapted and maintained by the host, determining a milder infection and being transmitted directly (animal to animal) or indirectly (contaminated water sources), as serovar Bratislava, which is considered to be adapted to horses (Ellis et al. 1983). Another group involves the incidental serovars which are held by other domestic or wild species and, after indirect transmission, determine a clinical infection, usually acute and severe.
Knowledge about the most common serovars and maintenance hosts in each region for each species is essential for understanding the epidemiology of the disease. Each serovar tends to be maintained by a specific host, and its occurrence may be influenced by the region and the occurrence of that serovar in animal populations with which incidental hosts have contact (Ko et al. 2009; Lindahl et al. 2011). Leptospirosis should be considered as a significant risk to horses and other animals exposed to flood waters or other contaminated water courses (Hamond et al. 2013).
Animal reservoirs are chronically infected and harbor different serovars of Leptospira mainly in the kidneys, one of the sites of predilection of the bacterium (Athanazio et al. 2008; Perez et al. 2011). Additionally, besides the kidneys, it has been demonstrated in other hosts that leptospires may persist in the genital tract, thereby being excreted by semen and vaginal secretions and therefore potentially transmitted by sexual intercourse or artificial insemination (Ellis et al. 1986; Lilenbaum et al. 2008).
Several animals can act as hosts or reservoirs, and each serovar has one or more hosts with different adaptation levels. The persistence of leptospirosis focuses is due to infected animals, sick or asymptomatic, which are considered permanent sources of infection and environmental contamination (Lindahl et al. 2011). Synanthropic animals and domestic and wild reservoirs are essential for the persistence of outbreaks of infection. The main urban reservoirs are synanthropic rodents of the species Rattus norvegicus (brown rat), Rattus rattus (black rat), and Mus musculus (mouse) (De Faria et al. 2008) that harbor the serovar Icterohaemorrhagiae, as well as other serovars of the same serogroup, as Copenhageni. Likewise, cattle serve as maintenance host for serovar Hardjo (Gamage et al. 2011), dogs for serovar Canicola (Raghavan et al. 2011), and swine for serovar Pomona (Wasiński and Pejsak 2010). More recently, it has been also demonstrated that wild rodents such as capybaras (Hydrochoerus hydrochaeris) (Silva et al. 2009) and marsupials, as opossums (Didelphis albiventris) (Jorge et al. 2012) may have a role as reservoirs of leptospires.
Horses can become infected by direct transmission, via contaminated urine or placental fluids of other infected horses, or indirectly from a contaminated environment in which leptospires have been shed by other animal species (Ebani et al. 2012).
Horses have rarely been reported as important for the transmission of this microorganism to other animals and human beings. Nevertheless, it has been recently demonstrated that, when infected, horses may become carriers, harboring the leptospires in the kidneys and spreading them in the environment, with obvious consequences for other animals (Hamond et al. 2013).
Reports on occurrence of agglutinins anti-Leptospira sp. (MAT) in horses in various countries
N sera tested
Australis and Pomona
Pinna et al. 2007
Bratislava and Icterohaemorrhagiae
Jorge et al. 2011
Bratislava and Icterohaemorrhagiae
Hamond et al. 2012b
Kitson-Piggot and Prescott 1987
Lees and Gale 1994
Icterohaemorrhagiae and Bratislava
Barwick et al. 1998
Icterohaemorrhagiae and Grippothyphosa
Cerri et al. 2003
Bratislava and Icterohaemorrhagiae
Ebani et al. 2012
Bratislava and Pomona
Båverud et al. 2009
Bratislava and Icterohaemorrhagiae
Egan and Yearsley 1986
Bratislava and Copenhageni
Rocha et al. 2004
Australis and Pomona
Blatti et al. 2011
Pyrogenes and Canicola
Desvars et al. 2011
Icterohaemorrhagiae and Canicola
Jung et al. 2010
Sejroe and Bratislava
Odontsetseg et al. 2005
Haji Hajikolaei et al. 2005
Grippotyphosa and Ballum
Roqueplo et al. 2011
Icterohaemorrhagiae and Australis
Although serological data indicate that horses in North America are exposed to a variety of leptospiral serovars, abortion is almost always associated with serovar Pomona type kennewicki. In North America, this serovar is maintained by a variety of wildlife, including raccoons, white-tailed deer, striped skunks, opossums, and red and grey foxes (Timoney et al. 2011). Conversely, in tropical countries, members of Icterohaemorrhagiae serogroup, as Icterohaemorrhagiae and Copenhageni, which are maintained by rodents, seem to be predominant (Desvars et al. 2011; Roqueplo et al. 2011; Hamond et al. 2012b).
It is believed that serovar Bratislava is adapted to horses and transmitted directly in horse-to-horse contact (Ellis et al. 1983). Therefore, the transmission of that serovar is less influenced by environmental conditions and does not require other species for the transmission of the infection. Entry of a horse on a stud should be carried out after a quarantine period since horses from different herds may introduce the bacterium on the susceptible herd. The presence of lakes has also been related with environmental characteristics to the dissemination and maintenance of infection by Bratislava (Pinna et al. 2010).
There is a lack of studies regarding the particularities of the pathogenesis of leptospirosis in horses. Hence, it is usually understood by analogy with human beings and other animals, mainly cattle. Pathogenesis of leptospirosis includes active penetration of the leptospires due to the combination of two mechanisms, one due to the secretion of active lytic enzymes (e.g., collagenase and gelatinase) (Adler and De La Peña Moctezuma 2010) and the other related to the active helicoidally movement of the bacterium (Lambert et al. 2012). Leptospires actively penetrate through mucosa, small cuts or abrasions, or wet skin (Adler and De La Peña Moctezuma 2010).
Having overcome the barriers to entry into the body, leptospires spread in the interstitium and organic humors (blood, lymph, and cerebrospinal fluid), and in this leptospiremic phase, they circulate and multiply in the bloodstream for up to 7 days. After the number of leptospires in the blood and tissue reaches a critical level, lesions due to the action of undefined leptospiral toxin(s) or toxic cellular components and consequent symptoms may occur (Adler and De La Peña Moctezuma 2010).
It has been shown that the major antigens of Leptospira recognized by the immune response include LipL32, one of the main membrane lipoproteins, and LipL41 heat shock protein fraction, obtained from the cytoplasm of bacteria (Grassmann et al. 2012). Autoimmune mechanisms have also been implicated in leptospiral disease in horses, particularly in the pathogenesis of equine recurrent uveitis. In this context, LruA and LruB share immunorelevant epitopes with eye proteins, suggesting that cross-reactive antibody interactions with eye antigens may contribute to immunopathogenesis of Leptospira-associated recurrent uveitis (Verma et al. 2010).
If the host immune response is effective to overcome the injuries and consequent functional alterations, the second phase begins, called immune phase, characterized by the circulation of specific antibodies and the presence of leptospires in urine. At this stage, leptospires tend to persist in the renal tubules or the anterior chamber of the eye since in those locations, activity of antibodies is minimal, which leads to a reduced efficiency of immunoglobulins in these sites (Athanazio et al. 2008).
Antibodies predominantly directed against outer envelope epitopes are produced within a few days of infection. Immunity usually is specific to the inciting serovar and closely related serovars although some broadly reactive antigens have also been described (Lin et al. 2011). After opsonization by antibodies, microorganisms are cleared by the reticuloendothelial system. However, in the case of a host-adapted serovar infection, titers of antibodies may remain low, allowing persistent permanence of the bacterium in the organism, mainly in the renal tubules (Sakoda et al. 2012). Fetal infection, especially in the third trimester, may result in a specific antibody response that can be protective. Passive immunity can be transferred by antibodies alone, but cell-mediated immune responses to leptospires also occur (Timoney et al. 2011) although with a minimal role in protection.
The equine epitheliochorial placenta does not allow transfer of maternal immunoglobulins to the fetus, and so, maternal immunoglobulins are received postnatally via colostrums (Sheoran et al. 2000). However, a number of studies have demonstrated partial immunocompetence in the later stage equine fetus. Mixed lymphocyte culture-responsive cells are detected in the thymus and spleen at 100 and 200 days of gestation, respectively. Detectable quantities of IgM but little or no IgG are found at 200 days (Perryman et al. 1980).
The gestational age of the aborted fetus ranges from 3.6 months to full term with a mean of 9 months. The outcome of leptospiral infection varies with the age of the fetus and with the virulence of the leptospires (Sheoran et al. 2000). Some late-term abortions result in the birth of live foals that develop normally. Leptospires are found in the placenta and in the liver, kidney, and other tissues of the foal. It is unknown what proportion of abortions result from placentitis alone or from a combination of placentitis and the effects of direct fetal infection. Sera of fetuses that aborted due to type kennewicki infection had both IgM and IgG and specific agglutinating activity (Poonacha et al. 1994).
The placenta of aborted fetuses can be heavily invaded by leptospires and should theoretically be a source of extended maternal antigenic stimulation via the uterus (Poonacha et al. 1993). Antigenic stimulation of the fetus should also have been adequate and prolonged since the kidneys of aborted fetuses were positive for Leptospira. Therefore, it is more probable that immaturity of the immune system accounts for the inability of the 10-month-old fetus to synthesize the repertoire of immunoglobulin isotypes seen in the adult animal (Sheoran et al. 2000).
There are four well-characterized clinical syndromes in leptospirosis of horses, i.e., clinical hepato–renal acute disease, ophthalmological disease, respiratory disorders, and reproductive syndrome.
Clinical acute disease involves renal and hepatic dysfunction. Hematuria, fever, jaundice, and anorexia are quite rare in horses, being more frequent in foals (Yan et al. 2010). Probably, the most studied syndrome relates to the ophthalmological disease, mainly the recurrent equine uveitis, also known as moonlight blindness (Divers et al. 2008; Verma et al. 2012). Respiratory disorders, including pulmonary hemorrhages and pneumonitis have also been described (Båverud et al. 2009; Hamond et al. 2011; Broux et al. 2012). Although those three syndromes have already been the subject of other reviews (Bernard 1993), there is a lack of studies regarding to the role of leptospirosis in the reproductive disorders in horses (Pinna et al. 2007).
Reproductive clinical findings
Leptospirosis in horses represents an important disease of the reproductive system since it may lead to the birth of weak foals, stillbirth or neonatal mortality, and abortion; although the latter can occur at any moment of the pregnancy, it is more usual after the sixth month of pregnancy (Timoney et al. 2011; Foote et al. 2012). Abortion without prior clinical disease is also common (Whitwell et al. 2009). In some herds, Leptospira sp. can be considered the main agent causing abortion (Williams et al. 1994; Pinna et al. 2007). Notwithstanding, placental infections are responsible for one third of stillbirths and perinatal deaths and in 75% of cases occur due to bacterial infection (Givens and Marley 2008). Abortion related to leptospirosis is a consequence of fetal leptospiremia due to the passage of leptospires through the placenta and can occur at anytime during pregnancy (Whitwell et al. 2009).
In some studies, seroreactivity to Leptospira was associated with reproductive problems as abortion, embryonic mortality, stillborn foals (Pinna et al. 2007), and embryo recovery rate (Pinna et al. 2012). Pomona and Icterohaemorrhagiae serovars are commonly associated with acute clinical signs and occurrence of outbreaks of leptospirosis in horses. Moreover, the role of serovar Bratislava has been increasingly recognized in the etiology of infection, with serious damage, especially in the reproductive sphere (Pinna et al. 2007). This serovar, which is maintained by horses, may determine reproductive disturbances (Donahue et al. 1995; Pinna et al. 2010) and more often subclinical infections (Ellis et al. 1983). Nevertheless, despite probably representing the most important serovar in equine leptospirosis, this serovar has been poorly described, probably due to difficulties in its bacteriological culturing and reduced number of laboratories specialized in the diagnosis of leptospirosis in animals.
Abortions associated with leptospirosis have been often reported, while only in a few reports, the agent has been isolated and identified. Therefore, the main described isolates of horses are from serogroups Australis, Pomona, and Icterohaemorrhagiae (Ellis et al. 1983) and L. interrogans serovar Pomona Type Kennewicki (Kitson-Piggot and Prescott 1987; Donahue et al. 1991; Poonacha et al. 1993; Donahue et al. 1995). Also observed was the presence of leptospires in fetal kidneys (Poonacha et al. 1993) and in the kidney and liver of stillborn foals (Bernard et al. 1993a, b) by silver impregnation with the Warthin–Starry method. Equine abortion was also diagnosed by immunohistochemistry (Szeredi and Haake 2006; Whitwell et al. 2009).
Placentitis determined by Leptospira is characterized by thrombosis, vasculitis, and inflammatory cells in the stroma with cystic adenomatous hyperplasia and necrosis of the epithelia (Foote et al. 2012). Funisitis is associated with leptospirosis in the placenta, while umbilical cord presenting yellowish throughout its length has been reported (Sebastian et al. 2005), as well as a case of hydrallantois associated with leptospirosis (Shanahan and Slovis 2011).
Besides serology and bacterial culturing, molecular tools such as polymerase chain reaction (PCR) have increasingly been employed for the diagnosis of leptospirosis as a reproductive disease in horses. Therefore, leptospiral DNA has been detected in the tissues (kidney and liver) of a premature foal (Vemulapalli et al. 2005; Léon et al. 2006), kidney and liver of aborted fetuses (Whitwell et al. 2009), thoracic fluid of aborted fetuses (Pinna et al. 2011), gastric juice of an aborted fetus (Hamond et al. 2012a), and semen of stallions (Scarcelli et al. 2001).
Laboratory diagnosis of leptospirosis is mainly based on serological testing or demonstration of immune response against the antigens of the agent, microbiological demonstration of the etiologic agent, or molecular analysis of bacterial genetic material (Adler and De La Peña-Moctezuma 2010).
The microscopic agglutination test (MAT) is the reference test in the laboratory diagnosis of leptospirosis (OIE 2008). The basis of MAT is the agglutination reaction between the antibodies present in the serum of patients and the antigen of the LPS membrane of leptospires. In this test, a serial dilution ratio of the patient serum is reacted with suspensions of living antigens of a battery of serovars of Leptospira sp. It is recommended that the antigen battery includes at least one representative of each serogroup that occurs in the region, which is periodically reported by reference laboratories of each country or region. Then, the reactions are examined microscopically in dark field for titer determination of the agglutination that occurs due to the presence of antibodies against Leptospira sp. in the patient serum (Hernández-Rodríguez et al. 2011). These tests require specialist expertise, are labor-intensive, and provide a retrospective diagnosis (Desakorn et al. 2012), without providing evidence of current active infection.
MAT is the most widely used diagnosis test. Although it is not clearly specific for serovars, it is at least specific for serogroups (Adler and de la Peña Moctezuma 2010). Nevertheless, it cannot discriminate between antibodies resulting from infection or vaccination, which may cause particular problems in animals, for example in screening for disease status for import or export (Hernández-Rodríguez et al. 2011).
Other immunological indirect diagnostic methods have been reported, as enzyme-linked immunosorbent assay. It uses a leptospiral antigen coating the plate (La-Ard et al. 2011), and although have not been reported in horses, it is promising since it can be performed in a greater number of laboratories throughout the tropics (Desakorn et al. 2012). Immunofluorescence has been reported to be very useful in the demonstration of leptospires in tissue samples (Kitson-Piggot and Prescott 1987; Szeredi and Haake 2006; Broux et al. 2012). Direct immunofluorescence on formalin-fixed, paraffin-embedded tissues is a sensitive method for diagnosis of leptospirosis and can be useful to screen archives of histological specimens (D'Andrea et al. 2012). It also observed the presence of leptospires in fetal kidneys (Poonacha et al. 1993) and in the kidney and liver of stillborn foals (Bernard et al. 1993b) by silver impregnation with the Warthin–Starry method. Leptospirosis as a cause of equine abortion was also diagnosed by immunohistochemistry (Szeredi and Haake 2006; Whitwell et al. 2009).
Among the direct methods of disclosure of the agent, the simplest is the direct visualization of leptospires by dark-field microscopy. This technique has very low sensitivity and specificity, requiring intact and preferably viable leptospires. The detection of leptospires in culture is a conclusive diagnosis and has been reported as the optimum method. However, the isolation procedures are cumbersome and time-consuming and require fresh samples with a significant concentration of leptospires. Thus, it does not apply as a routine diagnosis, but it is important for epidemiological purposes (Adler and De La Peña-Moctezuma 2010).
PCR has been used increasingly for the early diagnosis of leptospirosis in man and several animal species, including horses (Pinna et al. 2011; Koizumi et al. 2012). It is highly sensitive and specific and has been described for detection of leptospiral DNA in aqueous humor (Verma et al. 2010), urine (Hernández-Rodríguez et al. 2011; Hamond et al. 2012b; Koizumi et al. 2012), blood, cerebrospinal fluid (Koizumi et al. 2012), semen (Scarcelli et al. 2001; Lilenbaum et al. 2008), vaginal fluid (Ellis et al. 1986; Lilenbaum et al. 2008), and tissues (D'Andrea et al. 2012). However, one of its main limitations is its inability to identify the infecting serovar. While it may not be important for the individual patient, the identification of the infecting serovar is extremely important for epidemiologic and public health studies (Ko et al. 2009). The sensitivity of PCR may vary with the choice of the pairs of primers, standardization of the reagents employed in the art, selection of the biological material, and shape retention and storage time of the sample since the DNA can easily be degraded (Koizumi et al. 2012).
Therapy and prevention
Disease prevention and control of leptospirosis relies primarily in the identification of the infective serovar, or at least the infective serogroup, which allows the understanding of the transmission mechanisms involved in the herd. In general, the control of an outbreak may require the association of management alterations, hygiene, antibiotic therapy, and vaccination of all the animals of the herd (Pinna et al. 2007).
In the case of incidental infections, it is mandatory to investigate how the animals have been exposed to the infecting serovar, identifying natural reservoirs of the agent, such as pigs, rats, or wild animals (Lim 2011). Factors associated to the occurrence of the disease, such as presence of watercourses, management practices, and presence of animals from other herds without a quarantine period must also be investigated since they may be extremely important in the occurrence of leptospirosis determined by incidental strains. Conversely, when the infection is determined by strains maintained by horses, as serovar Bratislava, the control becomes a lot more complex regarding with the treatment, management, and vaccination of the flock (Pinna et al. 2007). All animals that are reactive and/or PCR-positive troops should be treated and vaccinated and make a reinforcement after 60 days. Environmental measures must be made: draining flooded areas, rodent control, and treatment of pool where horses are swimming. When introducing a stallion for breeding, for example, it is important to quarantine for tests such as PCR-specific urine and semen and check if the stallion is a carrier of Leptospira.
Leptospirosis control in livestock can be considered in two main approaches. One that aims for the complete eradication of the agent on the herd and is based on the progressive identification of carriers and treatment of those animals. Another approach aims to control the effects of the infection on the animals, not eliminating the occurrence of the bacterium among the carriers; this strategy is based on the vaccination of all the animals and occasional antibiotic therapy of the clinically affected animals (Subharat et al. 2012). In both cases, environmental variables that are characteristic of tropical countries must be considered, mainly the high annual rainfall and contact with wildlife. Nevertheless, there are few programs that emphasize the adoption of environmental measures associated with the traditional strategy of vaccination and antibiotic therapy for the control of animal leptospirosis (Pinna et al. 2007; Sykes et al. 2011; Gamage et al. 2011).
There are few reports regarding the successful treatment of leptospirosis in horses. Some recommended antibiotics include penicillin, oxytetracycline, streptomycin, doxycycline, dihydrostreptomycin, erythromycin, enrofloxacin, and cefquinome (Bernard et al. 1993a; Divers et al. 2008; Sykes et al. 2011; Lim 2011; Broux et al. 2012). Penicillin has been administered to pregnant mares with rising leptospiral titers in late gestation, with the delivery of clinical normal foals, although the significance of this is uncertain (Bernard et al. 1993a). A premature neonatal foal with hematuria and leptospiruria was successfully treated with penicillin and amikacin sulfate (Bernard et al. 1993b). In herds where horses presented a high level of abortions, embryonic deaths, and neonatal deaths, reactive horses were treated with dihydrostreptomycin and vaccinated. After 1 year, seroreactivity, abortions and embryonic and neonatal deaths declined (Pinna et al. 2007). Nevertheless, although highly employed, reports on the efficacy of dihydrostreptomycin in eliminating the carrier state in cattle and swine may be variable (Edwards and Levett 2004). Recently, procaine penicillin G associated with streptomycin, 25 mg/kg was successfully used in adult horses for treating respiratory hemorrhage associated to leptospirosis (Hamond et al. 2011) and also for improving the athletic performance of subclinically infected animals (Hamond et al. 2012a, b).
Since in many countries, leptospiral vaccines are not approved for use in horses, limited studies have assessed the response of horses to vaccination with leptospiral bacterins (Rohrbach et al. 2005). Vaccination with inactivated whole-cell preparations (bacterins) has limited efficacy due to the wide antigenic variation of the pathogen (Grassmann et al. 2012).
In Brazil, currently, there are two commercial vaccines for equine leptospirosis (Lepto-Bac® 6, Pfizer, West Ryde, Australia, and Lepto Equus, Vencofarma, Londrina, PR, Brazil). The recommendation is one dose at 4 months of age and a booster dose 30 days later and revaccination each semester. Therefore, studies to develop new vaccines for leptospirosis, such as a DNA vaccine and protein (e.g., Lipl32) vaccine are in development (Grassmann et al. 2012).
Leptospirosis is an important disease of the reproductive sphere in horses, leading to important economic losses due to the costs of treatment, death of the animal, and decrease in the reproductive efficiency characterized by abortion, stillbirth, and embryo recovery rate. Both direct and indirect methods may be employed for its diagnosis, and its adequate control is dependent of the identification of the infective serovar. Based on this, the association of management alterations, hygiene, antibiotic therapy, and vaccination of the herd is applied.
The authors thank Guilherme Brito for the graphic support in Fig. 1. WL is CNPq and FAPERJ fellow. CH and GM are CAPES and CNPq fellows.