Mycoplasma Bovis

Also known as

Mycoplasma agalactia var bovis, Mycoplasmosis

Description

Mycoplasma bovis is one of 126 species of the genus Mycoplasma. It is the smallest living cell and anaerobic (thriving in environments without oxygen). These bacteria do not have a cell wall, and are therefore resistant to penicillin and other antibiotics that contain a beta-lactam ring in their molecular structure (these include penicillin derivatives and cephalosporins),

Mycoplasma bovis mainly affects cattle and bison, and has little effect on other livestock. It does not affect horses or pets, but a few other animals can carry these bacteria. North American pronghorn are affected--with high mortality rates. M. bovis causes many diseases, including mastitis in dairy cows, arthritis in cows and calves, pneumonia in calves, and infections that may cause late-term abortion. Not all infected cows get sick. Some shed these bacteria without signs, with risk for transmission between farms if apparently healthy cows are moved.

Mycoplasma bovis was first identified in the U.S. in 1961 from the milk of a cow with mastitis. It was initially named Mycoplasma agalactia var bovis because of its association with bovine mastitis (Mycoplasma agalactia is a serious disease in sheep and goats). Later research found it to be a different species and it was renamed Mycoplasma bovis.

Today Mycoplasma bovis is recognized as a primary pathogen in bovine respiratory disease. In diagnostic laboratory data, M. bovis is the most prevalently isolated bacteria from the lungs of calves dying from pneumonia. It is found more often than Mannheimia Haemolytica, Pasteurella multocida, or Histophilus somni.

Similar to other bovine respiratory pathogens, Mycoplasma is a normal resident in nasal and upper respiratory tract of cattle and only causes disease in certain circumstances.
Susceptibility to Mycoplasma infection increases during times of stress, such as at weaning.

Mycoplasma infection of the joints and ear are not uncommon. Tenosynovitis (inflammation of a tendon and its sheath) and arthritis (inflammation of a joint) typically occurs in or above the knee and hock, rarely in the lower leg. Ear and/or joint infections may occur without lung involvement but often these infections come along after or during an episode of pneumonia.

Diagnosis of Mycoplasma bovis in previously disease-free countries has increased concerns about this pathogen. In the UK there has been steady increase in diagnosed cases. From January 2006 to December 2017, there were 1,102 diagnoses of M. bovis associated with respiratory disease, mastitis and arthritis, and 86.4% were associated with respiratory disease. The proportion of respiratory cases attributed to M, bovis has increased steadily.

The economic cost of M. bovis in cattle is difficult to determine. In the U.S., one report estimated costs to the U.S. beef industry of $32 million per year as a result of loss of weight gain and carcass value, and $108 million per year to the U.S. dairy industry as a result of M. bovis mastitis.

Lack of accurate prevalence figures makes economic analysis difficult, but costs of this disease include reduced production, drugs and labor for treatment, death and culling losses, financial impacts of implementation of diagnostic and control measures.

Costs per case are typically high, relative to other pathogens. M. bovis also contributes significantly to antimicrobial usage on farms and feedlots.

Occasional outbreaks of respiratory disease in bison caused by Mycoplasma bovis have occurred over the years in North America, and a study of feedlot bison in Alberta identified this pathogen as a primary cause of respiratory disease—and one of the most significant aspects of economic loss to bison producers.

This pathogen in cattle is usually a secondary invader, but a Canadian study begun in 2010 found that M. bovis is a significant primary respiratory pathogen. It can move to other parts of the body, but the lung is the primary target organ.

The disease starts high in the respiratory tract but moves into the lung and from there it can travel to any organ of the body--kidneys, lymph nodes, uterus, etc. In bison cows this pathogen is a primary cause of abortion, and losses can be significant—both in death loss in the cow herds, and in abortion rates.

Bison are more susceptible to harmful effects of M. bovis than cattle are. M. bovis will kill a bison, but usually just debilitates cattle. Some bison herds have experienced 25 to 30% death loss in the cow herd as a result of M. bovis infections, and a 3 to 5% death loss in feedlot bison is common.

In bison, this disease causes chronic lung damage; typical signs in bison include emaciation even though the animal is bright and continues to eat and may not feel sick. Necropsy after the animal dies generally reveals 70 to 80% of the lung tissue destroyed.

Signs

Infected cattle show signs of one or more of these conditions:

• Mastitis
• Arthritis
• Eye problems
• Respiratory disease
• Sometimes abortion

Cause

Mycoplasmas belong to the class Mollicutes and are distinguished by their lack of a cell wall. They are generally host-specific with 13 species identified in cattle, although not all are implicated in disease. The ability of M. bovis to produce biofilms and also change surface proteins allows it to colonize and persist on mucosal surfaces and also evade host immune responses.

M. bovis has been recognized as a pathogen in cattle for 60 years, and in experimental infection studies has been demonstrated to cause mastitis, respiratory disease and arthritis (with hot and painful joints).

In naturally occurring infections, M. bovis can be found in cases of mastitis, arthritis, tenosynovitis (tendon and tendon sheath infections), abortion, eye inflammations and pneumonia. In calves, M. bovis is the predominant pathogen isolated from the middle ear of animals with middle ear infections.

In severe cases of mastitis, one or more quarters are tense and swollen but neither hot nor painful. The infected quarters have no milk—just pus. Affected cows usually show no signs of illness although mild respiratory signs and slight discomfort may be seen; this absence of systemic disease is also an indication of mycoplasma mastitis.

In mastitis cases, signs vary from subclinical to very severe and from acute to chronic. Often there is sharp reduction in milk production, along with swelling and firmness of the mammary glands.

The infection generally does not respond to antibiotics. In an infected herd, mastitis usually affects more than 20% of cows, and even dry cows may develop mastitis. The main signs include change in milk consistency (watery or thick pus), and rapid spread of the infection from one udder quarter to the others.

After a few weeks the affected quarters shrink. Most cows do not recover from the disease during that lactation and milk production rarely resumes normal output.

Pneumonia cases caused by M. bovis have been occurring more frequently in recent years. A clinical study (in the UK in 2000) of pneumonia caused predominantly by M. bovis showed that nearly half of dairy calves were shedding mycoplasma at 5 days of age and by 4 weeks more than 90% were shedding these bacteria.

Clinical disease in calves (with up to 10% mortality as a result of severe pneumonia), peaked at 10-15 days of age. Surviving calves showed poor weight gain; other signs included fever, depression, rapid and difficult breathing, nasal discharge, mild to continuous coughing and loss of appetite.

In the UK, incidence of calf pneumonia usually begins in November and peaks around January, but deaths continue to occur in some herds in the spring at pasture due to relapses because of chronic lung lesions.

Arthritis may be a sequel to either the respiratory disease or mastitis--with lameness, swollen joints, slight fever, and no response to antibiotic treatment. In severe cases the animal is off feed and becomes debilitated. Initial signs are reluctance to stand and a stiff gait.

Many cases are mild and the animal usually recovers; in severe cases, lameness becomes more pronounced within a few days. The affected limb is stiff or held stiffly at the affected joint. If the animal moves, the limb may be dragged or swung outwards to avoid moving that joint.

Genital disease caused by M. bovis results in infertility, but rare.

Infected but clinically healthy calves and young cattle shed bacteria via the respiratory tract, acting as the reservoir of infection. Appearance of M. bovis on some farms has been associated with increased severity of respiratory disease and increased mortality.

The infection is usually brought into a herd by clinically healthy calves or young cattle shedding the mycoplasma and once established in a herd this disease is very difficult to eradicate. Cattle can be infected via the teat canal, the respiratory tract and genital tract; artificial insemination with infected semen is another common route.

In calves, infection can also occur via maternal contact and infected milk. Fomite-mediated transmission (bacteria carried on objects or human hands, etc.) can occur. Though these bacteria are killed by drying and sunlight, M. bovis can survive for long periods in cool, humid conditions.

Mycoplasma bovis has been a cause of mastitis in dairy cows for more than 60 years, and infections of various body systems has drastically increased in beef cattle over the past 20 years--but researchers are not sure why.

There are differences in opinions on whether M. bovis should be considered a primary pathogen or a secondary invader. Some scientists think M. bovis can and does cause disease in the absence of other viral and bacterial pathogens and is therefore a primary causative agent. In cases of calf pneumonia, there is usually some form of stress that weakens the calf’s immune system.

There appears to be more correlation between M, bovis and Bovine Viral Diarrhea Virus (BVDV) than any other typically implicated organisms. Studies suggest that BVDV-induced immunosuppression enhances the ability of M. bovis to flourish in the animal.

Prevention

Preventing M. bovis infections can be challenging, since the presence of persistently-infected BVD calves in a herd makes them more susceptible—so herd health programs utilizing vaccination against BVD are important, along with testing and culling any cattle persistently infected with BVD.

Metaphylactic use of antibiotics (giving all animals antibiotics upon arrival at the feedlot, to try to prevent pneumonia) may be beneficial in control of M. bovis but there is some concern that this practice might lead to resistance into the bacteria that could make that class of drug ineffective when a sick calf needs to be treated.

There are also questions about timing of drug use (as well as the type of drug administered), since M. bovis infections occur a week or two later after arrival at the feedlot than the other bacterial pathogens that cause respiratory disease.

Use of a Mycoplasma bovis vaccine can be beneficial and there are some commercial vaccines marketed in the U.S. Another option is to have an autogenous (custom) bacterin manufactured at a laboratory, from samples taken from your cattle by your veterinarian.

The disadvantage of an autogenous bacterin is that often the vaccine manufacturer can’t provide much information regarding efficacy, potency, host safety and antigen quality.

Development of commercially-marketed vaccines for M. bovis is challenging due to its ability to change its antigenic make up and its relationship with its host.

In dairy herds, the best way to prevent infection is maintenance of a closed herd. Buying from herds of known disease status is always recommended, but many dairies do not know their Mycoplasma status. On farms where the disease has been identified, control measures are aimed at reducing exposure of calves to the pathogen.

Avoid feeding whole milk to calves unless it is pasteurized. Batch pasteurization of milk at 65°C (150 degrees F) for 10 minutes, 70°C (158 degrees F) for 3 minutes or high temperature (72°C or 162 degrees F) short-time will inactivate M. bovis.

Steps should be taken to minimize spread between calves with clean feeding equipment. Calves with clinical Mycoplasma shed large numbers of bacteria, so isolation of affected animals can help reduce spread. Avoid mixing of age groups.

Pens should be disinfected between calves using an appropriate disinfectant. M. bovis is sensitive to heat as well as chlorine, chlorhexidine and iodine-based disinfectants.

Keeping calves healthy is crucial for a strong immune system. This includes good colostrum management, nutrition and control of diseases such as BVD. Appropriate vaccination programs for respiratory viruses, and controlling other pathogens can help reduce the risk of M. bovis coinfections.

Vaccination can reduce incidence of disease and mortality, and vaccinated cattle seem to respond better to treatment if they do get sick, with less risk for chronic cases. Three doses of vaccine administered in the first 14 days after arrival of a stocker/feeder calf is more effective than only giving one or two doses.

Signs of Mycoplasma pneumonia typically appear during the third week after arrival. Administering the vaccine upon arrival and again on days 7 and 14 seems to do the best job of building an immune response in the calf that will be effective for protection.

M. bovis can alter the proteins on its cell membrane surface, which help the organism evade the host’s immune responses. This raises questions about effectiveness of vaccine-induced antibodies against surface proteins/antigens.

Some studies have found that multiple doses of autogenous vaccines containing multiple isolates of M. bovis may be more effective than a commercial vaccine that only addresses one antigen, but cattlemen have often seen some benefits from adding a commercial vaccine.

For farms that have not experienced cases of this disease, the emphasis should be on preventing introduction through good biosecurity and caution when purchasing stock. For herds where Mycoplasma is already present, steps should be taken to minimize spread and reduce the impact of the disease.

Treatment

Treatment of Mycoplasma can be difficult. Success depends on severity of disease at the time of therapy, the type and dosage of antibiotic, and current status of the calf’s immune response. A few drugs are fairly effective against Mycoplasma based on susceptibility tests, but the organism is efficient at developing resistance to the treating antibiotic.

Some success against M. bovis pneumonia and arthritis in calves was reported in 2001 using valnemulin added to their milk starting at 4 days of age and continued for 3 weeks. Animals in the treated group had fewer clinical signs than the control animals, though the number of animals with nasal discharge was similar, and the animals required a considerable number of individual treatments.

Due to lack of a cell wall, M. bovis possesses resistance to penicillins and cephalosporins that work by damaging cell walls. In addition, its metabolism gives it natural resistance to sulphonamides-trimethoprim. Theoretically effective products that do not act on the cell wall include macrolides, erythromycin, tetracyclines, fluoroquinolones and florfenicol with a number of products containing these active ingredients now licensed for treatment of M. bovis.

Draxxin (Tulathromycin) and Resflor Gold are drugs approved for treating Mycoplasma bovis in cattle but Florfenicol (Nuflor) and Batril can also be used. The normal duration of the treatment is 10–14 days by antibiotic therapy.

However, the nature of the pathogen, including its ability to create biofilms, can reduce effectiveness of treatment. The key to treatment success is early intervention, which means rapid identification of affected animals.

Many veterinarians feel that diseases due to M. bovis are resistant to any therapy. Recent evidence suggests that M. bovis strains are becoming resistant to antibiotics traditionally used for treatment of mycoplasma infections; in particular oxytetracyclines, tilmicosin and spectinomycin. Some of the new triamalides are licensed for use in treating mycoplasma respiratory disease in cattle, and are reported to be effective.

In spite of this, antibiotics are widely used to reduce secondary bacterial infections, but are usually ineffective for the core mycoplasma infections.

The most devastating impact of Mycoplasmosis is in calves that have chronic infection and end up as “poor-doing” animals. Continued antibiotic treatment of this type of calf is costly and counter-productive. Time, feed and water and good supportive care are the main treatments.