Leptospirosis

Leptospirosis

Leptospirosis is a zoonotic disease, caused by bacteria of genus Leptospira. The disease that affects cattle (and man) in the UK is caused by two serogroups of the serovar Leptospira hardjo.
Cattle, sheep and goats can get infected, but the disease does not normally manifest itself in sheep that remain carriers. In cattle, after the first phase of the infection, the bacteria localise in the uterus and sex glands and in the kidneys. The early symptoms of infection are often so transient that in breeding cattle abortion and lowered fertility are usually the first symptoms to be noticed.
Milk drop
In cattle, the first symptom is often a drop in milk yield in all infected animals. This can be accompanied by transient fever, mastitis-like changes in the milk and sudden loss of all milk with flaccid udder (flabby bag).
Abortion
The abortion usually occurs 6-12 weeks after the initial infection. If the infection occurs in the late gestation, an infected calf may be born. Diagnosis of leptospiral abortion is difficult and based on maternal and foetal serology, as no obvious lesions are associated with the infection.
In herds contracting the infection for the first time, up to 30% of the animals may abort (Ellis, 1994). In endemically infected herds, a 5% abortion rate is suggested (Anon, 1986).
Infertility
The main manifestation of the effect of the infection on fertility is low pregnancy rates and high culling rates for fertility. The manifestation of these symptoms varies in a herd depending of the status of the infection. In a chronic inactive state, very few signs of poor fertility are seen, but during the initial infection of the herd, or when the herd infection becomes active acute infection, the symptoms are more apparent. What changes the health status of a herd from chronic inactive to acute active is not well understood, apart from in cases where a susceptible animal is introduced to an infected herd and is infected.
Whilst a natural immunity is established in a herd after the initial infection phase, all new animals that enter the herd are susceptible and suffer from an acute infection with the associated symptoms. So do animals that were not present in the infected herd during the initial infection but join later (e.g. dry cows). Consequently the abortions and infertility problems can go on for quite a while, causing major losses. In endemically infected herds, the drop in 1^st service conception rates has been reported to be 16-32% (Dhaliwal et al., 1996).
Prevalence of infection in the UK
Reports on the prevalence of Leptospira infection in the UK vary (Pritchard et al., 1989; Anon, 1986; Pritchard et al., 1987; Ellis et al., 1982). Based on various surveys, it has been estimated that some 70-80% of beef herds and 20-55% of dairy herds are infected with leptospirosis (Bennett, 1999). There is no reliable information on the occurrence of clinical episodes in endemically infected herds.
Leptospirosis is a notifiable disease in man, and farmers/farmworkers, abattoir workers and vets have been found to be the main risk groups in the UK. The disease in man is usually acquired from contact with the urine, placental material or aborted foetus of an infected animal or with contaminated water. Clinical signs of the disease are flu-like, with headaches and fever, occasionally progressing into meningitis.