Leptospira are gram-negative bacteria and zoonotic agents which belong to the spirochete group. They are very thin, flexible, spiral bacteria with a hook-shaped end. Leptospira can actively move by twisting. Within the genus Leptospira interrogans sensu lato, there are various pathogenic and saprophytic species which cannot be differentiated morphologically, but only serologically or genetically. Since 1989, more than 250 serovars have been described that are currently classified in 24 serogroups.
Transmission of pathogens occurs directly through the urine or blood of infected animals or indirectly through inanimate vectors such as contaminated water, feed and sleeping places or living vectors like rodents. Leptospira best survive in a humid environment at temperatures of 0 – 25 °C.
Clinically, leptospirosis in dogs is initially manifested by anorexia, vomiting, dehydration and fever. Later, animals are apathetic and often show difficulty breathing. The mucous membranes are icteric, anaemia with haemoglobinuria appears and in some cases, as a complication, disseminated intravascular coagulation (DIC). Toxic degradation products lead to haemorrhagic diathesis and necroses. As a result, acute nephritis with azotaemia can arise. In some cases, hepatitis may also occur, which often has a highly acute course. Leptospira are fetotrophic.
Clinically, leptospirosis in dogs is initially manifested by anorexia, vomiting, dehydration and fever. Later, the animals are apathetic and often show difficult breathing. The mucous membranes are icteric, there is anaemia with haemoglobinuria and, as a complication in some cases, disseminated intravascular coagulopathy (DIC). Toxic decay products lead to haemorrhagic diathesis and necrosis. As a consequence, acute nephritis with azotemia may occur. In some cases, an often highly acute hepatitis also occurs. Leptospires are fetotropic.
According to our own research, there has been a shift in the types of serovars over the past years. In dogs, analysed serovars include L. Bratislava, L. Australis, L. Autumnalis, L. Icterohaemorrhagiae, L. Pomona, L. Canicola, L. Saxkoebing, L. Grippotyphosa and L. Sejroe.
Cats seem to show a natural resistance. However, here too, the number of cases with clinical manifestation is increasing. The predominant serovars are L. Grippotyphosa and L. Bratislava, followed by L. Icterohaemorrhagiae, L. Sejroe, L. Autumnalis, L. Australis and L. Javanica.
In reptiles, leptospira antibodies can quite often be detected.
Leptospira infections, which are spread through the urine of rodents, are usually clinically inapparent in horses. Thus, the seroprevalence in healthy horses is high (up to approx. 75%). The pathogen is ingested with feed or water and leads to rather non-specific symptoms in horses, like fever (often intermittent), icterus, inappetence and productivity loss. Abortions have been described as well. Transmission of the pathogen between horses does practically not occur.
Equine recurrent uveitis (ERU) – It is likely that intraocular persistent leptospiral infection contributes to the aetiology of ERU, however, it is not the only possible aetiology. Autoimmune reactions lead from it lead to a progressive deterioration of the inner structures of the eye and may even lead to blindness.
Detection of antibodies (= most sensitive test) or pathogen detection using PCR can be carried out from aqueous humour or tissue of the vitreous body.
Leptospirosis in ruminants can cause economic losses and is, in Germany, a notifiable animal disease in sheep. It is predominantly cattle kept under extensive grazing conditions that get infected. In cattle, fever, anorexia, icteric mucous membranes, anaemia with haemoglobinuria and a decline in productivity are dominant. Diarrhoea and mastitis can also occur. Predominant serovars in our own research are L. Icterohaemorrhagiae, Saxkoebing and Bratislava. The recently emerged serovar L. Hardjo was not detected in any of the samples we examined.
Gravid pigs are especially susceptible to leptospira. The cardinal signs are birth of weak piglets or abortions. Aborted litters normally show different sizes and degrees of decay of the foetuses as the course of the disease is usually protracted.
When testing for antibodies in pigs, we look for serovars specific to this species: L. Canicola, L. Grippotyphosa, L. Saxkoebing, L. Bratislava, L. Sejroe, L. Pomona, L. Copenhageni and L. Tarrasovi.
In Germany, it is notifiable upon diagnosis in pigs.