Pasteurellosis

Pasteurellosis is a significant bacterial disease affecting multiple farm animal species caused primarily by bacteria of the Pasteurella and Mannheimia genera. The condition manifests most commonly as respiratory disease but can progress to systemic infection affecting multiple organ systems. In cattle, pasteurellosis is a primary component of bovine respiratory disease complex, commonly known as shipping fever, which represents one of the most economically devastating diseases in the beef and dairy industries worldwide. The bacteria involved, particularly Pasteurella multocida and Mannheimia haemolytica, are opportunistic pathogens that often exist as normal flora in the upper respiratory tract of healthy animals.

This disease affects a wide range of livestock species including cattle, sheep, goats, pigs, poultry, and rabbits, with each species showing somewhat different clinical presentations and disease patterns. In cattle, the disease is most prevalent in young animals, particularly those recently weaned, transported, or experiencing other stressors. Sheep and goats commonly develop pneumonic forms of the disease, especially during periods of environmental stress or following viral infections. Poultry experience fowl cholera, a specific form of pasteurellosis caused by Pasteurella multocida that can cause acute septicemia with high mortality rates in affected flocks.

The economic impact of pasteurellosis on livestock production is substantial, with losses occurring through mortality, reduced growth rates, decreased milk production, treatment costs, and condemnation of affected carcasses at slaughter. In the United States alone, bovine respiratory disease complex, of which pasteurellosis is a major component, costs the cattle industry an estimated one billion dollars annually. Additionally, the disease causes significant animal welfare concerns due to the respiratory distress and systemic illness experienced by affected animals, making rapid detection and treatment essential for maintaining both productivity and animal wellbeing.

Pasteurellosis is generally treatable when detected early and addressed with appropriate antimicrobial therapy and supportive care. However, delayed treatment or failure to recognize early signs can result in chronic lung damage, decreased productivity, or death. The importance of early detection cannot be overstated, as treatment success rates decline significantly once the disease progresses to severe pneumonia or systemic involvement. Prevention through vaccination, biosecurity measures, and stress reduction programs forms the cornerstone of effective pasteurellosis control in commercial livestock operations.

The primary causative agents of pasteurellosis are bacteria belonging to the Pasteurellaceae family, with Pasteurella multocida and Mannheimia haemolytica being the most significant pathogens in farm animals. Pasteurella multocida causes disease across multiple species and is responsible for fowl cholera in poultry, snuffles in rabbits, and contributes to respiratory disease in cattle, sheep, and pigs. Mannheimia haemolytica, formerly classified as Pasteurella haemolytica, is the primary agent of shipping fever pneumonia in cattle and also causes significant respiratory disease in sheep. These bacteria produce various virulence factors including leukotoxins, capsular polysaccharides, and adhesins that enable them to colonize respiratory tissues and evade host immune defenses.

While there is no direct genetic predisposition to pasteurellosis infection, certain breed characteristics may influence disease susceptibility and outcomes. Bos indicus cattle breeds and their crosses often demonstrate greater resistance to respiratory diseases compared to Bos taurus breeds, possibly due to differences in immune response or respiratory tract anatomy. In sheep, some breeds appear more susceptible to pneumonic pasteurellosis, though this may relate more to management practices and environmental factors than true genetic differences. Selection for rapid growth and high production in modern livestock breeds may inadvertently compromise immune function, making these animals more susceptible to opportunistic infections.

Environmental and management factors play a crucial role in the development of pasteurellosis, as the bacteria are typically opportunistic and require predisposing conditions to cause disease. Stress is the single most important factor in disease development, with transportation stress, weaning, commingling of animals from different sources, overcrowding, poor ventilation, extreme temperatures, and nutritional deficiencies all contributing to increased susceptibility. Viral infections such as infectious bovine rhinotracheitis, bovine viral diarrhea, parainfluenza-3, and bovine respiratory syncytial virus damage respiratory epithelium and suppress immune function, allowing Pasteurella and Mannheimia species to invade and establish infection.

Age and production stage significantly influence disease risk, with young animals being most susceptible to pasteurellosis. Calves between two and six months of age are at highest risk, particularly during and immediately following weaning when maternal antibody protection is waning and stress levels are elevated. Newly arrived feedlot cattle face extreme risk during the first few weeks after arrival due to the combination of transportation stress, commingling, dietary changes, and exposure to new pathogens. In poultry, all ages are susceptible to fowl cholera, but mature birds often experience the highest mortality rates during acute outbreaks.

The pathophysiology of pasteurellosis involves bacterial colonization of the upper respiratory tract followed by invasion of the lower respiratory tissues when host defenses are compromised. Mannheimia haemolytica produces a potent leukotoxin that destroys bovine neutrophils and macrophages, releasing inflammatory mediators that cause extensive tissue damage. This results in the characteristic fibrinous pneumonia with consolidated lung lobes, pleuritis, and potential abscess formation. In acute septicemic forms, such as hemorrhagic septicemia in cattle or fowl cholera in poultry, bacteria rapidly enter the bloodstream and multiply, causing disseminated intravascular coagulation, organ failure, and death within hours to days of initial infection.

Early warning signs of pasteurellosis are often subtle and require attentive observation to detect before the disease progresses to more severe stages. In cattle, the first indicators typically include mild depression, decreased feed intake, and subtle changes in behavior such as separation from the herd or reduced activity. Animals may show slightly elevated respiratory rates and stand with their heads lowered and necks extended. A mild nasal discharge that is initially serous may be present, along with occasional coughing. Temperature elevation is one of the earliest detectable signs, with affected cattle typically showing rectal temperatures between 104 and 106 degrees Fahrenheit before other clinical signs become apparent.

Clinical presentation varies somewhat between species, reflecting differences in disease manifestation and progression. In cattle, pasteurellosis typically presents as pneumonia with fever, depression, anorexia, and respiratory distress characterized by increased respiratory rate and effort, nasal discharge progressing from serous to mucopurulent, and a moist productive cough. Sheep develop similar pneumonic signs but may also show neurological involvement in some cases. Pigs with pasteurellosis often present with pneumonia as part of a respiratory disease complex, showing coughing, labored breathing, and poor growth. Poultry affected by fowl cholera may show acute illness with sudden death, or chronic disease with localized infections of the wattles, sinuses, or joints.

Behavioral changes are important indicators of pasteurellosis and often precede obvious physical symptoms. Affected animals typically become depressed and lethargic, spending more time lying down and showing reluctance to move when approached. Feed and water consumption decreases noticeably, and animals may stand apart from their herdmates or flockmates. Cattle with respiratory disease often position themselves facing into the wind or seek areas with better air circulation. Social dynamics within the group may change as sick animals are avoided by healthy individuals, making the isolated animals easier to identify during routine observation.

Physical signs of pasteurellosis become increasingly apparent as the disease progresses. Respiratory signs dominate in most species, with affected animals showing obvious labored breathing, flared nostrils, open-mouth breathing in severe cases, and audible respiratory sounds including wheezes and crackles. Nasal discharge becomes increasingly thick and may be tinged with blood in severe cases. The muzzle may appear dry and crusty. Cattle often develop a characteristic grunt on expiration due to pleuritic pain, and they may stand with elbows abducted and be reluctant to move. Dehydration becomes apparent through sunken eyes, decreased skin elasticity, and dry mucous membranes.

Symptom progression in untreated pasteurellosis follows a relatively predictable pattern, with initial mild signs advancing to severe respiratory compromise over several days. In acute cases, particularly hemorrhagic septicemia, progression can be extremely rapid, with death occurring within 24 to 48 hours of first observed signs. More typical pneumonic cases progress from early fever and depression through increasing respiratory distress to consolidation of lung lobes with fibrinous pleuritis. Chronic cases may develop lung abscesses, chronic pleurisy, and permanent lung damage that affects long-term productivity even if the animal survives the acute illness.

Emergency symptoms requiring immediate veterinary intervention include severe respiratory distress with open-mouth breathing, blue or gray discoloration of mucous membranes indicating cyanosis, recumbency with inability to rise, extremely high fever above 107 degrees Fahrenheit, or signs of acute septicemia including rapid deterioration, bloody diarrhea, or petechial hemorrhages on mucous membranes. In poultry flocks, sudden increases in mortality with birds found dead without premonitory signs suggest acute fowl cholera requiring immediate action. Any animal showing neurological signs such as circling, incoordination, or seizures in association with respiratory disease should receive emergency evaluation, as this may indicate septicemia with central nervous system involvement.

Clinical examination forms the foundation of pasteurellosis diagnosis and begins with a thorough history including recent stressors, transportation, commingling events, and vaccination status. Physical examination focuses on respiratory parameters including respiratory rate, effort, and character; auscultation of the lungs for abnormal sounds; and assessment of overall condition including hydration status, body condition, and mental alertness. Rectal temperature measurement is essential, as fever is a consistent finding in early pasteurellosis. The veterinarian evaluates nasal discharge, examines the oral cavity and pharyngeal region, and palpates peripheral lymph nodes for enlargement. In cattle, a systematic approach to examination helps differentiate pasteurellosis from other causes of respiratory disease.

Laboratory diagnostic tests provide definitive confirmation of pasteurellosis and help guide treatment decisions. Bacterial culture and identification remain the gold standard for diagnosis, with samples collected from deep nasal swabs, transtracheal washes, or bronchoalveolar lavage in live animals. In fatal cases, lung tissue samples collected at necropsy yield the most accurate diagnostic results. Antibiotic sensitivity testing on cultured isolates helps guide antimicrobial selection, particularly important given increasing concerns about antimicrobial resistance. Blood tests including complete blood count may reveal elevated white blood cell counts with a left shift indicating acute bacterial infection. Serological testing has limited utility for acute diagnosis but may be helpful in retrospective herd investigations.

Differential diagnosis for pasteurellosis includes numerous other respiratory pathogens and conditions that may present with similar clinical signs. In cattle, infectious bovine rhinotracheitis, bovine viral diarrhea, parainfluenza-3, bovine respiratory syncytial virus, Mycoplasma bovis infection, and Histophilus somni must all be considered. Parasitic lung disease caused by lungworms may mimic bacterial pneumonia in pastured animals. In sheep, other causes of respiratory disease include ovine progressive pneumonia, caseous lymphadenitis, and parasitic pneumonia. Fowl cholera in poultry must be differentiated from highly pathogenic avian influenza, Newcastle disease, and other septicemic conditions. Comprehensive diagnostic workup often identifies multiple pathogens, reflecting the complex nature of respiratory disease in farm animals.

Herd-level diagnostics become important when pasteurellosis affects multiple animals or when developing prevention strategies for high-risk populations. Surveillance cultures from healthy animals can identify carrier status and prevalent serotypes within a population. Necropsy examination of animals that die provides valuable information about disease patterns and pathogen involvement. Serological surveys can assess herd immunity levels and inform vaccination program decisions. Production records analysis may reveal patterns in disease occurrence related to specific sources of animals, time periods, or management events. Comprehensive herd health investigations combining individual animal diagnostics with population-level data help develop targeted prevention and control strategies.

Emergency and immediate treatment of pasteurellosis focuses on rapid initiation of antimicrobial therapy and supportive care to prevent disease progression and death. Treatment should begin as soon as clinical signs are recognized, as delays of even 12 to 24 hours can significantly reduce treatment success rates. Initial antibiotic selection is typically empirical, based on known pathogen susceptibility patterns and local resistance profiles, with adjustments made based on culture and sensitivity results when available. Animals with severe respiratory distress may require oxygen supplementation, and recumbent animals need appropriate bedding and positioning to facilitate breathing.

Antimicrobial therapy forms the cornerstone of pasteurellosis treatment, with several drug classes showing effectiveness against Pasteurella and Mannheimia species. Macrolide antibiotics including tulathromycin, tilmicosin, and gamithromycin provide excellent lung tissue penetration and extended duration of action, making them popular choices for respiratory pasteurellosis. Fluoroquinolones such as enrofloxacin and danofloxacin offer broad-spectrum activity and good efficacy. Cephalosporins, particularly ceftiofur, provide effective coverage with relatively short withdrawal times. Tetracyclines, including oxytetracycline and chlortetracycline, remain useful in some situations. Withdrawal times must be strictly observed for all antimicrobials used in food-producing animals, and producers should maintain accurate treatment records documenting drug, dose, route, date, and animal identification.

Surgical intervention is rarely indicated for pasteurellosis but may be considered in specific circumstances. Chronic lung abscesses that develop following severe pneumonia occasionally require drainage, though this is uncommon in production settings. Thoracocentesis may be performed to relieve pleural effusion in cases of severe pleuritis. In most situations, medical management is preferred, and surgical approaches are reserved for cases where medical therapy has failed to resolve complications.

Supportive care significantly improves treatment outcomes and should accompany antimicrobial therapy. Affected animals should be moved to a clean, well-ventilated area with minimal environmental stressors. Providing fresh water and palatable feed encourages continued intake during illness. Anti-inflammatory drugs such as flunixin meglumine or meloxicam help reduce fever, decrease inflammation, and improve animal comfort, which often improves appetite and recovery. Fluid therapy may be necessary for dehydrated animals, administered intravenously in severe cases or subcutaneously for milder dehydration. Maintaining appropriate environmental temperatures and protecting animals from weather extremes supports recovery.

Herd treatment protocols become necessary when pasteurellosis affects multiple animals within a group. Metaphylactic treatment, or mass medication of at-risk animals upon arrival or following a disease trigger event, can reduce morbidity and mortality in high-risk situations such as newly arrived feedlot cattle. This approach involves administering antimicrobials to all animals in a group rather than waiting for individual animals to become sick. While effective at reducing disease incidence, metaphylaxis must be used judiciously due to antimicrobial stewardship concerns. Mass medication through feed or water may be appropriate in some situations but generally provides less reliable therapeutic drug levels than individual animal treatment.

Treatment decisions in production settings must balance animal welfare, treatment costs, prognosis for recovery, and economic value of the individual animal. Animals detected and treated early in the disease course have good prognosis for complete recovery and return to normal production. However, animals with severe or chronic disease, multiple treatment failures, or obvious lung damage may have poor prognosis and may be candidates for salvage slaughter or euthanasia rather than continued treatment. Veterinarians work with producers to establish treatment protocols, define treatment endpoints, and make appropriate decisions for individual animals and the herd. Economic analysis comparing treatment costs against potential returns helps guide these decisions in commercial operations.

Recovery timeline for pasteurellosis varies depending on disease severity, promptness of treatment, and individual animal factors. Animals treated early in the disease course with appropriate antimicrobials typically show improvement within 24 to 48 hours, with fever reduction often being the first sign of response. Complete clinical recovery in uncomplicated cases generally occurs within five to seven days, though some animals may require extended treatment courses. Severely affected animals or those with complications such as lung abscesses or chronic pleuritis may require weeks to months for full recovery, and some may never return to previous production levels due to permanent lung damage.

Post-treatment care and monitoring are essential to ensure complete recovery and detect any relapses or complications. Animals should be observed closely for several days following apparent clinical recovery, with daily temperature monitoring helping detect treatment failures or secondary infections. Feed and water intake should return to normal within a few days of effective treatment, and failure to resume normal consumption suggests ongoing illness. Respiratory rate and effort should normalize, though some animals may retain mildly elevated respiratory rates due to residual lung pathology. Treatment records should be completed with outcome information to help evaluate protocol effectiveness.

Prognosis for pasteurellosis depends on multiple factors including time from disease onset to treatment initiation, severity of lung involvement at time of diagnosis, presence of complications, and the animal's overall health status. Animals treated within the first one to two days of illness have excellent prognosis with greater than 90 percent survival rates in most studies. Delayed treatment, severe bilateral pneumonia, or presence of complications such as pleuritis or abscessation significantly worsens prognosis. Repeated episodes of respiratory disease in the same animal suggest either ongoing immune compromise or development of chronic lung pathology and carry a guarded long-term prognosis.

Return to production considerations vary by species and production system. Cattle recovering from pasteurellosis should be allowed adequate time for full recovery before returning to stressful activities such as transport or processing. Growth performance in feedlot cattle is typically reduced in animals that experienced respiratory disease, even those that appeared to recover fully. Dairy cattle may show decreased milk production following illness. In breeding animals, return to reproductive function following recovery is generally expected, though severe illness during pregnancy may affect fetal development. Withdrawal times for any medications used must be strictly observed before animals enter the food chain, with appropriate records maintained to document compliance.

Vaccination protocols form a primary defense against pasteurellosis and should be implemented as part of comprehensive herd health programs. Multiple vaccines are available for cattle targeting Mannheimia haemolytica and Pasteurella multocida, typically combined with viral respiratory pathogen components. Vaccination is most effective when administered before stress events such as weaning, shipping, or commingling, ideally two to three weeks in advance to allow development of protective immunity. Preconditioning programs that vaccinate calves on the ranch of origin before sale substantially reduce respiratory disease incidence compared to vaccinating upon feedlot arrival. Poultry vaccines against fowl cholera are available for breeding and laying flocks in high-risk situations. Killed bacterins and modified live vaccines each have advantages depending on the specific situation.

Biosecurity measures help prevent introduction of virulent pathogen strains and reduce environmental contamination levels. New animals should be sourced from reputable suppliers with known health status and isolated upon arrival for observation before introduction to existing populations. All-in-all-out management reduces pathogen accumulation between production groups. Visitors, equipment, and vehicles can transmit pathogens between premises and should be controlled through appropriate protocols. Dead animals should be promptly removed and properly disposed of to eliminate pathogen reservoirs. Cleaning and disinfection of facilities between groups helps reduce environmental bacterial loads.

Nutritional prevention strategies support immune function and reduce susceptibility to infectious diseases. Adequate energy and protein intake maintains body condition and immune competence during high-risk periods. Trace minerals including copper, zinc, selenium, and manganese play essential roles in immune function, and supplementation may be beneficial in deficient areas. Vitamin E and selenium have particular importance for respiratory defense mechanisms. Avoiding abrupt diet changes reduces stress during high-risk periods. Properly formulated receiving diets for newly arrived animals encourage feed intake and provide nutritional support during adaptation.

Management practices significantly influence pasteurellosis incidence and should be optimized to reduce disease risk. Minimizing stress through gentle handling, appropriate stocking density, and good environmental conditions reduces susceptibility to opportunistic infections. Adequate ventilation in housed animals removes respiratory pathogens and noxious gases while maintaining appropriate temperature and humidity. Dust control in dry conditions reduces respiratory irritation that may predispose to infection. Prompt identification and treatment of sick animals reduces pathogen shedding and exposure of herdmates. Maintaining stable social groups and avoiding unnecessary commingling reduces stress and pathogen transmission.

Quarantine and testing protocols provide additional protection for valuable herds or high-risk situations. New animals should ideally be quarantined for a minimum of two to four weeks before introduction to resident populations, allowing observation for development of disease and reducing direct pathogen introduction. Testing may be appropriate in specific situations, particularly for herds with no history of certain diseases. Sentinel animals can be used to test exposure before introducing valuable breeding stock. Recording the source and health history of all introduced animals creates a database for investigating disease events and identifying high-risk suppliers.

Daily management and monitoring practices enable early disease detection and prompt intervention. Regular observation of animals for signs of respiratory disease should occur at least twice daily, with high-risk groups such as newly arrived or recently stressed animals checked more frequently. Observing animals at feeding time helps identify those with reduced appetite, an early indicator of illness. Training personnel to recognize subtle early signs of respiratory disease improves detection rates and treatment success. Recording observations and abnormalities creates a historical record useful for identifying patterns and evaluating program effectiveness.

Housing and environmental management significantly impact respiratory disease incidence and should be optimized for each production system. Adequate ventilation is essential for housed animals, providing fresh air exchange while avoiding drafts directly on animals. Stocking density should allow sufficient space for animals to rest comfortably and access feed and water without excessive competition. Bedding should be clean, dry, and sufficient to insulate animals from cold or wet floors. Protection from extreme weather helps reduce environmental stress. In open-lot systems, windbreaks and shade structures provide important environmental mitigation.

Herd health programs provide a systematic approach to disease prevention and should include pasteurellosis in respiratory disease risk assessment. Veterinarians work with producers to develop customized protocols addressing vaccination, treatment, and prevention strategies appropriate for the specific operation. Regular veterinary visits allow early identification of emerging problems and program adjustments. Necropsy of animals that die provides valuable diagnostic information and helps evaluate disease patterns. Annual program reviews assess outcomes and identify opportunities for improvement.

Record keeping and monitoring systems support informed management decisions and regulatory compliance. Individual animal identification enables tracking of treatments, outcomes, and withdrawal periods. Treatment records should document animal identification, disease observed, products administered including dose and route, treatment dates, and withdrawal dates. Morbidity and mortality records help identify disease patterns and evaluate prevention programs. Production records may reveal subclinical disease impacts through effects on growth rate, feed efficiency, or milk production. Electronic record systems facilitate data analysis and reporting.

Economic considerations influence disease management decisions and program implementation. Prevention programs require investment in vaccines, labor, and management changes, but typically provide positive returns through reduced treatment costs, lower mortality, and improved production. Treatment costs include medication, veterinary services, labor, and reduced productivity. Economic losses from chronic disease effects may exceed acute disease costs through reduced growth, efficiency, and carcass value. Cost-benefit analysis of prevention and treatment protocols helps optimize resource allocation. Insurance and marketing considerations may influence acceptable disease risk levels in specific situations.

Susceptibility to pasteurellosis varies among breeds and species, though management and environmental factors typically outweigh genetic influences on disease risk. In cattle, Bos taurus breeds including many European beef breeds and dairy breeds appear more susceptible to respiratory disease compared to Bos indicus breeds and their crosses. Holstein dairy cattle, bred primarily for milk production, may have increased susceptibility due to the metabolic demands of high production. Purebred cattle sourced from sale barns or multiple origins face higher risk than ranch-raised cattle from known sources due to increased stress and pathogen exposure during marketing.

Production type considerations influence pasteurellosis risk beyond breed effects. Dairy cattle face ongoing stress from high production demands, frequent handling, and intensive management that may increase susceptibility. Feedlot cattle experience high-risk conditions including transportation stress, commingling, diet changes, and exposure to diverse pathogens. Extensively managed beef cattle may have lower overall disease pressure but face challenges with monitoring and early detection. Layer and breeder poultry operations may experience endemic fowl cholera that persists despite treatment efforts. Production systems emphasizing rapid growth may inadvertently compromise immune competence.

Genetic selection and testing offer opportunities to improve disease resistance over time, though specific genetic markers for pasteurellosis resistance are not well defined. Selecting breeding animals from families with good health records may improve offspring resistance to respiratory diseases. Culling animals with poor disease response or repeated illness removes potentially susceptible genetics from the population. Some breed associations track health traits that may be useful in selection decisions. Research continues to identify specific genetic factors influencing respiratory disease susceptibility, with bovine leukocyte antigen genes and other immune-related loci under investigation as potential selection targets.

Pasteurellosis commonly occurs as part of complex disease syndromes involving multiple pathogens and predisposing factors. In cattle, bovine respiratory disease complex typically involves viral pathogens including infectious bovine rhinotracheitis virus, bovine viral diarrhea virus, parainfluenza-3 virus, and bovine respiratory syncytial virus in addition to Pasteurella and Mannheimia bacteria. Mycoplasma bovis and Histophilus somni frequently contribute to respiratory disease alongside pasteurellosis. These co-infections complicate diagnosis and treatment, as multiple pathogens may require different therapeutic approaches. Understanding the complex nature of respiratory disease helps develop comprehensive prevention and treatment strategies.

Several conditions present with similar clinical signs to pasteurellosis and must be considered in differential diagnosis. Other bacterial pneumonias including those caused by Mycoplasma, Histophilus, or Trueperella pyogenes may be indistinguishable on clinical examination. Aspiration pneumonia following improper oral medication or drenching presents similarly to infectious pneumonia. Lungworm infection in cattle and sheep causes respiratory signs that may mimic or complicate bacterial pneumonia. Acute interstitial pneumonia in cattle, caused by various toxins and metabolic factors, produces severe respiratory distress. In poultry, highly pathogenic avian influenza and velogenic Newcastle disease produce acute mortality similar to fowl cholera and have important regulatory implications requiring accurate differentiation.

Complications and sequelae of pasteurellosis extend beyond the acute disease and may cause long-term production impacts. Chronic pneumonia with lung abscessation may persist despite treatment and cause ongoing poor performance. Fibrous adhesions between lung lobes and chest wall restrict normal breathing and lung expansion. Cor pulmonale, or right-sided heart failure secondary to chronic lung disease, may develop in severely affected animals. Chronic pleuritis causes ongoing pain and respiratory compromise. Joint infections may result from hematogenous spread during septicemic phases of disease. These complications highlight the importance of early detection and effective treatment to minimize long-term consequences.