Leptospirosis

Cattle Diseases

Leptospirosis in Cattle

Also known as: Flabby Bag, Milk Drop Syndrome

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.  The serovar Leptospirosis pomona has not been found  in cattle in the UK or continental Europe, whereas it is important in New Zealand, Australia, North and South America.

Cattle, sheep and goats can get infected, but the disease does not normally manifest itself in sheep and they 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, subclinical or chronic infection manifest as abortion and lowered fertility. These are usually the first symptoms to be noticed.

Milk Drop and Leptospirosis

In dairy cattle, acute disease may be seen as 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). Recovery can take up to 10 days.

Abortion and Leptospirosis

In herds contracting the infection for the first time, up to 30% of the animals may abort (Ellis, 1994)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 fetal serology, as no obvious lesions are associated with the infection.

Infertility and Leptospirosis

The main affect of infection on fertility is low pregnancy rates and subsequent high culling rates. The symptoms vary in a herd depending on the status of the infection:

• In a chronic inactive state, very few signs of poor fertility are seen
• In an 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. 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 1st service conception rates has been reported to be 16-32% (Dhaliwal et al., 1996a).

Prevalence of infection

Based on various surveys undertaken in the UK, it has been estimated that some 70-80% of beef herds and 20-55% of dairy herds are infected with leptospirosis (Bennett et al., 1999; Pritchard, 2001). A recent survey in dairy herds, however, estimates 71.9 % of herds to be infected (Williams and Winden 2014). Risk factors for the presence of leptospirosis were larger herd size, purchasing animals and all year round calving. A survey in Ireland reported a prevalence of infection of 79% in dairy herds, with larger herds more likely to be positive (Leonard et al., 2004). There is no reliable information on the occurrence of clinical episodes in endemically infected herds.

Although the precise prevalence of leptospirosis in cattle in North America is not known, estimates of leptospiral infection in a sample of US dairies and beef cow-calf operations indicated that the overall herd infection prevalence was approximately 35% to 50%—with most of those infections likely caused by serovar L. hardjo (Grooms, 2004, Bolin 2003).

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 fetus of an infected animal or with contaminated water. Clinical signs of the disease are flu-like, with headaches and fever, occasionally progressing into meningitis. Herd owners should be aware of their responsibilities under health and safety regulations to protect the health of dairy staff.

Control and Prevention of Leptospirosis

The major risk factors for Leptospira infection in cattle are herd size, river access, sheep co-grazed with cows (as sheep can act as non-symptomatic carriers), inadequate husbandry practices, hired bulls and purchased animals (Bennett, 1991; van der Kamp et al., 1990; Ryan et al., 2012; van Schaik et al., 2002). The most common approaches to the control of leptospirosis in cattle are based on prevention of exposure, vaccination and selective treatment (Bolin, 2001).

Control of the disease is often complicated by the fact that farmers do not usually know whether their farms are infected or not. A bulk milk sample in dairy cows or a statistical sample in beef animals is a first step to establish the infection status.  Control measures are usually first undertaken when there has been an outbreak and significant losses have been suffered. At this point, the control measures are directed towards minimizing the effects of the infection and usually include combined vaccination and treatment with antibiotics (Ellis, 1999).

In beef herds, both vaccination and non-vaccination policies, combined with the separation of younger age groups of cows from the infected older cows, have been shown to eradicate the disease over a long period of time (i.e., six years) (Kingscote, 1986). While vaccination and treatment alone did not eradicate the disease, combined treatment and vaccination were more efficient than vaccination alone in preventing persistent infections (Kingscote and Proulx, 1986). A similar result was produced in a closed beef herd by vaccination and testing over a five-year period (Little et al., 1992a).

A Dutch model of leptospirosis control in dairy herds suggests that in open herd situations only vaccination and antibiotic treatment after an outbreak is economically attractive. Studies also show that vaccination in infected herds limits the effects of the infection on fertility and abortion rates (Dhaliwal et al., 1996b). In closed herds, however, control by vaccination or by preventing the entrance of infection into the herd by improving biosecurity has been shown to be economically feasible (Bennett, 1991).

Vaccination and Leptospirosis

Immunity is serovar specific so it is important to use the appropriate vaccine for the disease in the region (Bolin, 2001). There are currently two vaccines available in the UK for Leptospirosis control, Leptavoid H (MSD Animal Health) and Spirovac (Zoetis).

In both cases a primary course on vaccination is followed up with annual boosters, preferably given in the spring before the period of highest risk. In the case of Spirovac, calves as young as 4 weeks old can be vaccinated, which may be of note if a farm has a high prevalence of infection and if young replacement heifers are to be protected.

While vaccines are considered a valuable tool against leptospirosis, they do not offer full protection against herd infection in herds that are considered free of infection, and there is some doubt about the length of protection they offer (Ellis, 1999) although  they provide excellent protection (Bolin, 2001). The use of vaccines is further complicated by the fact that the antibody tests for Leptospira do not differentiate between real infection and antibody reaction to vaccine – vaccine antibodies can persist for many years which causes difficulties in differentiating infected from vaccinated animals as well as achieving accreditation.

Practical approaches to Leptospirosis

When decisions are made concerning prevention and control of leptospiral infection in a herd, it is important to find out what the present health status of the herd is. In dairy herds, this can be done simply and cheaply by testing for L. hardjo infection in the bulk tank milk. This test is accurate enough to tell whether the herd has been exposed to the disease and approximately how many animals might be infected (Pritchard, 2001, 1999). Individual blood sampling of suspect animals can then be used to clarify the picture. In beef herds, the herd history may give an indication of the herd status. Otherwise, a representative sample of different parity cows need to be blood-sampled and tested for antibodies. Once the herd’s infection status has been investigated, approaches to control and eradication can be decided upon.

When a herd is known to be free of disease, the main aim should be to keep it that way. As the main route of entrance for Leptospira infection into a new herd is via a purchased animal or contaminated water source, these entrance routes should be controlled. Preferably, the herd should be kept genuinely closed, and no purchased animals should be brought in, as testing for individually infected animals is not totally reliable. However, if animals are purchased, all bought-in cattle should be bought from a Leptospira-free, accredited herd, or must be quarantined for 4 weeks before inclusion in the main herd and tested for Leptospira antibodies. The animals should not have access to any surface water that has passed through another farm or contact with animals of a neighboring farm, unless these are accredited free of leptospirosis. Furthermore, cows should not be grazed together with sheep, unless the health status of the sheep is known and monitored. If these guidelines are carefully adhered to, vaccination against leptospirosis should not be necessary, as the wildlife reservoirs have been shown to be insignificant in the maintenance of infection (Little et al., 1992b). With monitoring and the necessary testing, such a herd can be accredited free of leptospirosis (see Cattle Health Certification Standards (CHEcS).

If herd testing (e.g a statistical sample of breeding cows or bulk tank milk testing) shows that the herd is infected with leptospirosis, it is important to assess the level of infection (Murray, 1999). If the herd has a very low level of infection, the options are eradication and monitoring or monitoring alone to ensure that no changes in this low-level status occur. If a higher level of infection is detected, a vaccination program is likely to be the best option (Ellis, 1999).

Eradication of Leptospirosis

According to CHeCS rules eradication of disease requires that all animals over 12 months are sampled, with positive reactors removed. A second herd test is conducted 6-12 months later and a clear test is required. To show freedom from disease, all cattle older than 1 years old are tested twice 6-12 months apart, followed by annual monitoring of a statistically determined number of animals.

Treating Leptospirosis

Antibiotic treatment or combined antibiotic and vaccination therapy of cows suffering from active Leptospira-infection have been shown to eliminate infection or alleviate clinical signs during an outbreak and in treatment trials (Alt et al., 2001; Gerritsen et al., 1994; Kingscote and Proulx, 1986). Streptomycin and dihdro-streptomycin have been the antibiotics of choice for the treatment (Ellis et al., 1985), but their use at the recommended dose of 25 mg/kg is extra-label in the UK.  Amoxycillin oxtetracycline, tilmicosin and ceftiofur, have shown some promise in treatment (Alt et al., 2001; Smith et al., 1997). Animals entering an accredited herd should be treated with either dihydrostreptomycin or oxytetracycline to eliminate chronic renal infection before they mix with the rest of the herd (Bolin, 2001).

The farm vet should be contacted to decide on the need to treat individual animals during an outbreak. Simultaneously a decision on the commencement of a vaccination strategy on the farm should be taken.

Leptospirosis and Welfare

Welfare considerations associated with leptospirosis in endemically infected herds are linked to the symptoms – abortion, temperature, milk drop and mastitis. During an outbreak, a vet should be contacted and decisions about treatment and vaccination to protect the herd should be taken on his advice.

Good Practice Based on Current Knowledge

Determine the herd health status regarding leptospirosis with a bulk milk sample or by blood sampling. This is important in order to avoid risk to human health and in order to make informed decisions on disease control.

If the herd is free of infection or the antibody status indicates a very low level of infection (only possible in non-vaccinated herds):

• Establish a closed herd policy (if animals are bought in, quarantine for 4 weeks and test for antibodies plus treat with antibiotics as a safety measure)
• Prevent access to shared surface water
• Prevent access to and contact with neighboring herds
• Do not mix cattle with sheep, unless sheep are known to be free of infection
• Consider accreditation for freedom from the disease – particularly if raw milk used or breeding animals sold (CHeCS)
• Consider establishing a monitoring scheme to be aware of any changes in the situation (CHeCS)

If the herd is infected:

• Establish closed herd policy and biosecurity as above and start vaccinating. It is impossible to monitor disease as the tests are incapable of differentiating between infection and reaction to vaccine. It can, however, be expected that the infection will gradually disappear from the herd as young uninfected animals enter the herd and new infections are prevented by vaccine use. If the measures to prevent new infection from outside the herd are good, vaccination can be discontinued after a few years, depending on the herd’s initial situation
• Before discontinuing vaccination, discuss with the farm vet to assess the preventive measures and the local epidemiology of the disease