Contagious Bovine Pleuropneumonia - CBPP

[Kvet Forum]

Aetiology

Mycoplasma mycoides subsp. mycoides small colony (SC) (MmmSC) is the cause of the contagious bovine pleuropneumonia (CBPP). MmmSC is very similar culturally and antigenically to the causative organism of caprine contagious pleuropneumonia, but the two can be differentiated culturally and biochemically.

The disease is not communicable to other species.


Epidemiology

CBPP is considered one of the economically most important cattle plagues affecting Africa, and with relaxation of import controls and increase in international trade, it presents a constant risk for disease-free countries. The World Organization for Animal Health (OIE) has categorized CBPP as so-called “List A” disease. CBPP has been identified as the second most common transboundary disease in Africa after rinderpest.

Under natural conditions, CBPP occurs in cattle of the species Bos. Although buffaloes can be infected by artificial means, no cases have been reported in African buffaloes or other wild ruminants. Currently CBPP affects around 30 countries in sub-Saharan Africa, of which several are endemically infected.

Reasons behind the failure to contain CBPP in Africa include the following:

• Changes of ecological/environmental factors, such as availability of water, droughts, and floods, leading to increased movement of livestock over long distances.
• Civil strife and political and economic difficulties complicating the strict movement control of apparently infected cattle.
• Lack or insufficient resources allocated to CBPP control, particularly limited funding for vaccination, livestock movement control, and mass education of farmers and veterinarians.
• Limited potency and field performance of CBPP vaccines.
• Reduced disease surveillance (e.g. serologic screening and abattoir studies).
• Distraction by control and prevention of other economically important diseases (e.g., rinderpest or avian influenza).

Transmission

Transmission occurs from direct and repeated contacts between sick and healthy animals. The principal route of infection is by the inhalation of infective droplets from active or carrier cases of the disease. Infection by contamination of inanimate objects is unlikely under natural conditions.

Cattle may be infected for periods of up to 8 months before the disease becomes apparent, underscoring the importance of sufficiently long quarantine period before a herd can be declared to be free of the disease.

CBPP is usually transmitted through movements of live animals; trade in animal products is not thought to be a significant risk.


Economic Importance

CBPP is one of the most economically important diseases of cattle in Africa. Direct losses are from mortality, reduced milk yield, vaccination costs and disease surveillance.

The indirect costs associated with the chronic nature of the disease are more difficult to assess but include decreased weight gain or loss of body weight, impaired working ability, reduced fertility, losses resulting from quarantine, and losses related to restrictions of trade and cattle movement.


Clinical Findings

There is considerable variation in the severity of clinical disease from hyperacute to acute to chronic and subacute forms.
With acute presentation, high disease incidence of nearly 90% and fatality rates of 50% and higher are observed. Acute disease is the common presentation in outbreaks occurring in previously unaffected regions.
Mild or even subacute forms with low mortality rates are common presentation in zones where the disease in endemic.
Approximately 25% of the infected cattle have been estimated to remain as recovered carriers with or without clinical signs.

Acute Form
After an incubation period of 3 to 6 weeks (in occasional instances up to 6 months), there is a sudden onset of high fever (40° C [105° F]), a drop in milk yield, anorexia, and cessation of rumination. There is severe depression, and the animals stand apart or lag behind a traveling group. Coughing, at first only on exercise, and thoracic pain are evident; affected animals are disinclined to move, standing with the elbows out, the back arched, and the head extended. Respirations are shallow, rapid, and accompanied by expiratory grunting. Pain is evidenced on percussion of the chest. Auscultation reveals pleuritic friction sounds in the early stages of acute inflammation, and dullness, fluid sounds, and moist gurgling crackles in the later stages of effusion. Dullness of areas of the lung may be detectable on percussion. Edematous swellings of the throat may occur, and swelling of the large movable joints may be present. In calves, valvular endocarditis and myocarditis may occur. In fatal cases death occurs after a variable course of disease from several days to 3 weeks. In the per-acute form, affected cattle may die within 1 week after the onset of respiratory distress.

Chronic and Subacute Forms
Recovered animals may be clinically normal but in some an inactive sequestrum forms in the lung, with a necrotic center of sufficient size to produce a toxemia causing unthriftiness, a chronic cough, and mild respiratory distress on exercise. These sequestra may break down when the animal is exposed to environmental stress and may cause an acute attack of the disease. In Africa, up to one-third of acute cases that recover become potential carriers.


Samples for Confirmation
of Diagnosis

• Histology - Formalin-fixed lung (LM, IHC)
• Mycoplasmology - Effusion fluid in serum tube, lung, bronchial lymph node (MCULT, FAT, PCR, C-ELISA)

Treatment

Conventional wisdom in the past held that treatment of clinical cases of CBPP with antimicrobials is counterproductive to contain the disease because it gives rise to persistent infection and may produce symptomless carrier animals. Nevertheless, the use of antimicrobials in affected regions is widespread, mainly because, with limited availability of vaccines, it is considered the only available and effective treatment and control measure.

The major classes of antimicrobials that are effective against mycoplamsas are tetracyclines, macrolides, florfenicol, and fluoroquinolones.

Because of the generally poor treatment response and because these animals present a source of infection for herdmates, clinically affected animals should rather be culled than treated.


Control

There are four essential tools in CBPP control and eradication: livestock movement control, stamping out, vaccination, and treatment.

The possible strategies used for control in affected countries or regions are as follows:

• Slaughter of all sick and in-contact cattle. This requires full cooperation of cattle owners and an adequate and timely compensation system. This strategy is impractical in developing countries with a pastoral economy.
• Slaughter of all sick cattle and vaccination of in-contact cattle. This strategy is used frequently and usually perpetuates the disease.
• Vaccination of healthy cattle with slaughter of sick cattle in an epidemic and revaccination of cattle at risk. This method depends on the ability of the authorities to detect epidemics rapidly, most effectively, by abattoir surveillance and to maintain vaccination for at least 3 years. Vaccination in endemic areas must be done annually, whereas newly infected areas require repeat vaccinations aimed at eradication of the disease.

Vaccination against CBPP has been used in countries where rigorous cattle movement control, quarantine, and stamping out cannot be implemented, as is the case in many African countries that cannot afford the prohibitive costs of culling entire infected herds. Although CBPP vaccination is doomed to fail when used as stand-alone strategy to control CBPP, a systematic vaccination strategy in combination with intense surveillance and removal of infected animals can contribute to the containment of the disease and reduction of the infection prevalence to the point where vaccination can be discontinued and remaining infected animals can be culled to achieve complete eradication of the disease.