Leptospirosis described in 1886 by the German physician Adolph Weil, is currently one of the most widely distributed infectious diseases worldwide, bacteria of the genus Leptospira spp (Adler and de la Peña, 2010).

The frequency of leptospirosis is usually associated with bad hygiene, so its presence is more frequent in regions where activities such as agriculture, the manufacture of products of animal origin, forestry, livestock, mining, etc (Torres et al., 2016).

This disease has relevance for public and animal health, due to the participation of natural and accidental hosts, which are important for maintenance. Rodents are considered the main hosts, in addition to bovines, horses, pigs, sheep, goats, dogs and cats; as well as wild mammals (Andersen et al., 2016). Some of these meet the function of carriers, which may be able to eliminate bacteria by urine as sick individuals do, without presenting detectable clinical signs (Wood et al., 2018; Ellis, 2014; Moral et al., 2014).

In equines, leptospirosis is commonly associated with genitourinary and ophthalmic diseases in which damage to placenta and fetus, kidneys and eyes can be appreciated. In general, the clinical picture is mild or subclinical; however, in the acute way, depression, jaundice, pyrexia, while in severe infections are observed abortions, neonatal diseases or the birth of a healthy pony with antibodies against this bacterium. In some cases, perinatal mortality is presented, as well as respiratory disorders and recurrent uveitis (ERU) or iridocyclitis (Divers, et al., 2019; Arent and Kedzierska-Mięszkowska, 2013; Verma et al.,2010).

Equines are infected when consuming water contaminated with leptospira; as well as any other species when in contact with urine or other fluids of infected animals. These bacteria have the ability to enter the body through mucous membranes, skin abrasions and transplacental route, so that later they can lodge mainly in the renal tubules of animals, where they are colonizing the kidney (Khalili et al., 2019).

In later, bacteria are eliminated by urine, polluting rivers, lakes and other water sources that are used for activities aimed at trade, agriculture, livestock, included for the consumption of the human being, in this way the infection is facilitated in humans and animals (Pulido et al., 2014). In certain occasions some products, fabrics and fluids of these animals can act as a source of infection.

Hamond et al. (2013), it proposes another non-conventional path of disease transmission, through sexual contagion, because it found the presence of DNA, from Leptospira spp in equine semen, in 50% of evaluated samples and frequency of 60% for Leptospira bratislava and Leptospira Copenhageni. It is worth mentioning that, although exposure to leptospira is common, the development of equine disease occurs at rare occasions (Malalana, 2019).

At present it is not accurately known whether the conditions in the horse kidney alter the physiological functions of the bacteria and, therefore, affect their survival, generate reduction of their pathogenesis, or if there are differences in infection between males and females (Hamond et al., 2012a). However, through histopathological studies in young horses’ kidneys, the formation of petechiae and lymphocytic infiltration in the proximal tubules and glomeruli has been observed. It has also been reported that Pomona serovar, in these organs causes fever and acute renal failure (Verma et al., 2010).

The objective of this literature review was to know the frequency of leptospirosis in equines reported in the literature of the last 10 years.

A review was carried out in web search browsers as PubMed, Science Direct, SciELO, from the scientific literature peer-reviewed and published in the last 10 years (2010-2020), the keywords used were frequency, equines, Leptospira spp, leptospirosis, infection, diagnosis, uveitis and combination of these.

Reports of serovariety, country and continent were obtained from the articles consulted; based on this, the overall frequency of positive animals and the frequency of serovars were calculated.

Then the EpiInfo 7® program was used to analyze the data, know the frequencies and 95% of confidence intervals (95% CI) of the information obtained from the scientific peer- reviewed articles (CDC, 2016).

In a representative sample of 21 papers, where any serovar of leptospira was detected at 7218 horses (Table 1). In these, 40 serovarieties were found (Table 2), being Leptospira bratislava the most frequently reported with 11.43% (IC 95%: 6-19.1%), followed by Leptospira icterohaemorrhagiae with 9.52%, (IC 95%: 4.6-16.8% ; which suggests that these serovarieties reported are the ones that are in contact with equines.

Table 1

Author	Animals used in the study (N)
Ali, 2012	409
Alves, 2016	100
Arent and Kedzierska-Mięszkowska, 2013	620
Bedoya et al., 2013	293
De Oliveira et al., 2014	257
Hamond et al., 2012b	119
Hamond et al., 2013	10
Hamond et al., 2015	206
Malalana et al., 2019	Not available
Martins et al., 2017	54
Méndez et al., 2013	24
Peixoto Ribeiro et al., 2018	1640
Pinna et al., 2014	608
Pikalo et al., 2016	314
Rey Riaño et al., 2015	94
Siqueira et al., 2019	1200
Simbizi et al., 2016	663
Troncoso et al., 2013	55
Tsegay et al., 2016	418
Vera et al., 2019	134
Total	7218

Table 2

Leptospira	Frequency	%	% Accumulated	95% confidence	interval
arborea	1	0.95	0.95	0.02	5.19
australis	4	3.81	4.76	1.05	9.47
autumnalis	5	4.76	9.52	1.56	10.76
ballum	2	1.90	11.43	0.23	6.71
bataviae	1	0.95	12.38	0.02	5.19
bataviae (sv. swart)	1	0.95	13.33	0.02	5.19
bratislava	12	11.43	24.76	6.05	19.11
bratislava jez-bratislava	1	0.95	25.71	0.02	5.19
butembo	1	0.95	26.67	0.02	5.19
canicola	6	5.71	32.38	2.13	12.02
celledoni	1	0.95	33.33	0.02	5.19
copenhageni	6	5.71	39.05	2.13	12.02
copenhageni y australis	1	0.95	40.00	0.02	5.19
cynopteri	1	0.95	40.95	0.02	5.19
djasiman	3	2.86	43.81	0.59	8.12
grippothyphosa (sv. duyster)	1	0.95	44.76	0.02	5.19
grippotyphosa	7	6.67	51.43	2.72	13.25
grippotyphosa moska V	1	0.95	52.38	0.02	5.19
hardjo	4	3.81	56.19	1.05	9.47
hardjo bovis	1	0.95	57.14	0.02	5.19
hardjo prajitno	3	2.86	60.00	0.59	8.12
hardjobovis/wolffi	1	0.95	60.95	0.02	5.19
hardjoprajitno H89	1	0.95	61.90	0.02	5.19
hebdomadis	2	1.90	63.81	0.23	6.71
icterohaemorrhagiae	10	9.52	73.33	4.66	16.82
javanica	1	0.95	74.29	0.02	5.19
panama	2	1.90	76.19	0.23	6.71
patoc	1	0.95	77.14	0.02	5.19
poi	1	0.95	78.10	0.02	5.19
pomona	9	8.57	86.67	3.99	15.65
portland-vere sinaloa	1	0.95	87.62	0.02	5.19
pyrogenes	1	0.95	88.57	0.02	5.19
sentot	1	0.95	89.52	0.02	5.19
seramanga	1	0.95	90.48	0.02	5.19
serjoe	2	1.90	92.38	0.23	6.71
tarassovi	3	2.86	95.24	0.59	8.12
tarassovi perepelitsin	1	0.95	96.19	0.02	5.19
topaz	1	0.95	97.14	0.02%	5.19
wolffi	2	1.90	99.05	0.23%	6.71
zanoni	1	0.95	100	0.02%	5.19

From 21 articles analyzed, it was reported that Brazil is the country where more studies have been carried out on equine leptospirosis during the last decade, with 47.62% (IC 95 %: 25.71-70.22%) as shown in Table 3.

Table 3

Country/continent	Frequency	%	% Acumulated	95% confidence interval
Germany/Europe	1	4.76	4.76	0.12	23.82
Brazil/America	10	47.62	52.38	25.71	70.22
Chile/ America	1	4.76	57.14	0.12	23.82
Colombia/ America	2	9.52	66.67	1.17	30.38
Iran/Asia	1	4.76	71.43	0.12	23.82
Italy/Europe	1	4.76	76.19	0.12	23.82
Mexico/America	1	4.76	80.95	0.12	23.82
Northwest England and North of Wales /Europe	1	4.76	85.71	0.12	23.82
Poland /Europe	1	4.76	90.48	0.12	23.82
South Africa /Africa	1	4.76	95.24	0.12	23.82
Southern Ethiopia /Africa	1	4.76	100.00	0.12	23.82
Total	21	100	100

In Table 4, the serovar reported in the literature consulted in equines are shown during the last ten years.

Table 4

Author	Country /continent	Serovariety found Leptospira:	Reported frequency (%)	% positive animals 95% confidence intervalal 95%
Ali, 2012	Irán/Asia	pomona	38.9	39.18
		grippotyphosa	32.7	35-43.6
		icterohaemorrhagiae	15.1
		canicola	10.4
		hardjo	1.7
		ballum	1.04
Alves et al., 2016	Brasil/América	patoc	35.7
		butembo	32.1	28.0
		sentot	14.3	20.1-37.5
Arent y Kedzierska-Mięszkowska, 2013	Polonia/Europa	grippotyphosa	11.7
		serjoe	4.5
		bratislava	4.0
		poi	3.7
		pomona	3.6
		icterohaemorrhagiae	2.9
		celledoni	0.9
		cynopteri	0.9	39.0
		ballum	0.6	35.3-43.0
		hebdomadis	0.6
		bataviae	0.5
		hardjo	0.4
		zanoni	0.4
		autumnalis	0.4
		canicola	0.3
		australis	0.3
Bedoya et al., 2013	Colombia/América	bratislava	53.3
		hardjo bovis	28.5
		icterohaemorrhagiae hardjo prajitno	26.3 5.1	66.70
		grippotyphosa	2.8	51.5-79.0
		pomona	2.6
Hamond et al., 2012b	Brasil/América	copenhageni	43.7	71.4
		icterohaemorrhagiae	27.8	62.7-78.8
Hamond et al., 2013	Brasil/América	bratislava	30.0	60
		copenhageni	30.0	31.3-83.2
Hamond et al., 2014a	Brasil/América	australis	54.4	47.8
		icterohaemorrhagiae	43.6	39.5-56.1
Hamond et al., 2015	Brasil/América	australis	46.4	44.7
		pomona	70.5	38.0-51.5
Malalana et al., 2019	Noroeste de Inglaterra y norte de Gales/Europa	bratislava	19.4	51.4
		copenhageni y Australis	6.9	40.0-62.6
		autumnalis	8.3
Martins et al., 2017	Brasil/América	australis	69.2	48.1
		icterohaemorrhagiae	30.8	35.4-61.1
Méndez et al., 2013	México/América	hardjoprajitno H89	12.0	71
		wolffi	12.0	50.8-85.0
		tarassovi perepelitsin	41.0
		grippotyphosa moska V	4.0
		bratislava jez-bratislava	8.0
		portland-vere sinaloa	8.0
		hardjo prajitno	29.0
		icterohaemorrhagiae	12.0
		pomona	42.0
Peixoto Ribeiro et al., 2018	Brasil/América	serjoe	5.9	32.7
		seramanga	5.3	30.5-35.0
		djasiman	3.9
		grippotyphosa	3.9
		icterohaemorrhagiae	3.6
		autumnalis	2.6
Pinna et al., 2014	Brasil/América	bratislava	62.3	44.9
		Copenhageni	37.7	41.0-48.9
Pikalo et al., 2016	Alemania/Europa	icterohaemorrhagiae	11.1	17.20
		bratislava	9.6	13.4-21.8
		grippotyphosa	1.9
Rey et al., 2015	Colombia/América	pomona	41.5
		grippotyphosa	24.5
		canicola	16.0
		javanica	23.4
		hardjo prajitno	10.5
		tarassovi	7.4
		hebdomadis	7.4
		wolffi	2.1
		bratislava	1.1
		icterohaemorrhagiae	40.4
Troncoso et al., 2013	Chile/América	autumnalis	54.5
		bratislava	52.7	65.5
		canicola	20.0	52.2-76.6
		copenhageni	12.7
		hardjo	7.3
Siqueira et al., 2019	Brasil/América	autumnalis	2.3
		bratislava	54.5
		canicola	4.5
		grippothyphosa (sv. duyster)	2.27	8.0
		hardjobovis/wolffi	22.7	6.6-9.7
		copenhageni	2.3
		panama	2.3
		pomona	4.5
		bataviae (sv. swart)	4.5
Simbizi et al., 2016	Sudáfrica/África	bratislava	32.9
		djasiman	25.8	85.0
		arborea	11.0	82.1-87.6
		tarassovi	7.7
De Oliveira et al., 2014	Brasil/América	panama	6.2
		pyrogenes	3.5	7.40
		grippotyphosa	3.5	4.8-11.3
Tsegay et al., 2016	Sur de Etiopia/África	bratislava	34.3
		djasiman	9.8	44.0
		topaz	6.0	39.3-48.8
		pomona	5.3
Vera et al., 2019	Italia/Europa	bratislava	41.8
		canicola	63.6
		tarassovi	28.4	67.2
		copenhageni	17.9	58.8-74.5
		pomona	10.4
		hardjo	2.2

Knowing the true value of the Leptospira spp frequency from the revised articles is very complicated, there was a confidence interval from there to be able to locate 95% with a range of values among which the real value of this agent frequency in the equine population (Molina, 2013). In this study, 40 serovars of Leptospira spp in horses were identified. Although Leptospira bratislava has been the most commonly reported in the equine literature in the last 10 years (Pinna et al., 2014), Leptospira pomona is the one considered to be the specific agent for equidae, since when the individual develops the disease, high titers of antibodies against the latter can be found (Divers et al., 2019).

In the serological studies in equines, there is identified that there is variation in the frequency of infection by Leptospira (Hamond et al., 2014b); which can be submitted on the four continents reported in the study sample. The most reported infections in the literature in equines of the last 10 years were caused by Leptospira icterohaemorrahagiae, Leptospira pomona, Leptospira bratislava, Leptospira copenhageni and Leptospira grippotyphosa. These data were obtained in accordance with the analyzed papers, derived from studies, both clinical, serological and ecology of the disease, which has allowed knowing the interface between animal-human environment and its importance for the concept of a one single health (Jaeger et al., 2019). On the other hand, Bertelloni et al. (2019) mention that environmental characteristics, such as wetlands, ponds and channels present at the center of Italy, associated with the presence of domestic and wild animals (the latter as reservoirs of leptospiras) enhance the dissemination of this disease, and they are reported frequencies in pigs of 19.74% and bovines of 13.03%. It is known that leptospira are transmitted efficiently through water, being able to survive for long periods in humid environments (Lourerio et al., 2013). For its part, Verma et al., 2019 showed the existence of the interaction between the pathogen and domestic and wild animals, through water settlements, as well as the bacterium presence in kidneys of wild animals. It has been suggested that the adaptation of serovar to the host, as well as, the nearby coexistence with cattle with horses can influence the frequency of exposure (Lowe,2010). Pinna et al. (2014) demonstrate that Leptospira bratislava is adapted to equines, since this has been associated with reproductive problems in mares. However, Leptospira bratislava and Leptospira muenchen, have been associated with cases of infections in pigs, horses, bovines and dogs, and managed to identify similar strains in wild animals (Arent et al., 2016).

Witkswski et al. (2016) mention that Leptospira grippotyphosa and Leptospira pomona are associated with cases of recurrent uveitis in equines. Hashimoto et al. (2007) evaluated the prevalence of leptospirosis in equines without apparent clinical synology, and used weight loss and depression as inclusion criteria, with which they obtained 66.88% of overall frequency; of this value, antibodies represented 23.36% against Leptospira icterohaemorrhagiae and 13.14% by Leptospira grippotyphosa. While Hamond et al. (2012b) found 89.5 seroprevalence in asymptomatic horses.

The disease severity varies with the serovar and the affected animal, when the disease is presented subclinically, animal deterioration is not apparent; however, when the presence of the disease is chronic, the physical and productive deterioration of animals are evident (Ellis, 2015).

Leptospira pomona kennewicki is considered as responsible for most clinical presentations in American horses, is associated with placenta diseases and fetus, kidneys and eyes ((Divers et al., 2019); however, clinical presentation can result in abortion or in a sick colt. This can be due to the gestational mare stage and at the time it was infected with the bacteria, as well as its immunological state (Bernard, 1993). From the clinical point of view, a study conducted in Sweden showed that there is no significant association between the presence of clinical signs of disease and positive titles to Leptospira bratislava or Leptospira Icterohaemorrhagiae with exception with the association between respiratory problems and fatigue with the Leptospira Bratislava (Båverud et al., 2009). . Such is the case of Rocha (2004) in which, by obtaining samples of horse kidneys, isolations and serological typing were achieved, where it determined the presence of Leptospira australis and Leptospira pomona strains, these two strains are the ones that have been most reported in Portuguese horses.

It has been associated with the frequency of infection with Leptospira spp to environmental conditions, including seasonal variations, as an example has to be Leptospira icterohaemorrhagie are presented more frequently between months of October and December, this attributed to the rodents usually invade the stables and houses at the end of summer and autumn. On the other hand, the increase in frequency Leptospira bratislava is presented between April and June and October to December ( Båverud et al., 2009).

Leptospirosis is a neglected zoonosis with a worldwide distribution, affects many species of mammals, including livestock, causing clinical signs of acute character in animals of all ages and productive stages, which significantly affects animal production. The annual incidence of this zoonosis in humans is not well determined due to sub-notification; it is estimated as an example in Uruguay, which is 15 per 100,000 inhabitants. Human disease seems to be associated with infected animals, as well as with rains and floods in endemic regions (Zarantonelli et al., 2018).

In general, the literature consulted allowed knowing the disease frequency and serovars found on horses. Exposure to different serovars may be related to the region in which equines are found, as well as the presence of one or more specific hosts for these serovars which act as a reservoir so that infection is presented. Horses are infected when they consume contaminated water with some leptospira species. While exposure to these agents is common in horses, systemic disease is rare, equines can be asymptomatic or present different clinical signs. Frequently reported leptospira species that can infect horses are, Leptospira bratislava, (11.43%, IC 95%: 6-19.1%) and with Leptospira icterohaemorrhagiae (9.52%, IC 95%: 4.6-16.8%). It is necessary to consider in future studies, the investigation of animal leptospirosis impact in public, animal and environmental health, in order to implement geographically specific prevention and control programs of this disease.