Thrombotic Meningoencephalitis (cattle)

Thrombotic meningoencephalitis, commonly abbreviated as TEME, is a severe and often fatal infectious neurological disease primarily affecting cattle, caused by the bacterium Histophilus somni (formerly known as Haemophilus somnus). This condition represents one manifestation of the broader Histophilus somni disease complex, which can affect multiple organ systems including the respiratory tract, reproductive tract, joints, and heart in addition to the central nervous system. The neurological form develops when bacteria invade the bloodstream and cause septic thrombi that lodge in small blood vessels of the brain and meninges, producing areas of infarction, hemorrhage, and inflammation that result in severe neurological dysfunction.

Thrombotic meningoencephalitis predominantly affects feedlot cattle in North America, though the disease has been recognized in cattle populations worldwide. Young cattle recently transported to feedlots are at highest risk, with disease typically occurring within the first several weeks to months after arrival. The stress of weaning, transport, commingling, and dietary changes compromises immune function and allows opportunistic bacterial invasion. The disease can occur sporadically as individual cases or in outbreaks affecting multiple animals within a feedlot population. Prevalence varies considerably between operations and years, with some feedlots experiencing regular losses while others rarely encounter the condition.

The economic and welfare impact of thrombotic meningoencephalitis on cattle operations is substantial due to high case fatality rates and the loss of valuable young cattle with significant growth potential ahead of them. Animals affected with the neurological form frequently die despite treatment, and survivors may have residual deficits limiting their productive potential. The acute, dramatic nature of the disease with animals found recumbent or dead causes significant distress for producers and animal caretakers. Economic losses include the direct value of affected animals, treatment costs, and the broader impact on feedlot health programs when outbreaks occur.

Early detection before severe neurological involvement and immediate aggressive antimicrobial treatment offer the best chance for survival in animals developing thrombotic meningoencephalitis. However, the rapid progression of disease means that many animals present with advanced neurological signs by the time illness is recognized, limiting treatment success. Prevention through vaccination, management of risk factors, and attention to overall animal health represents the most effective approach to reducing losses from this devastating disease.

The primary cause of thrombotic meningoencephalitis is infection with Histophilus somni, a gram-negative pleomorphic bacterium that is an opportunistic pathogen of cattle. Histophilus somni is considered part of the normal flora of the bovine respiratory and reproductive tracts, residing in the upper respiratory passages and genital tracts of many apparently healthy cattle. The organism becomes pathogenic when host defenses are compromised by stress, concurrent infection, or other factors that allow bacterial multiplication and systemic invasion. Once in the bloodstream, Histophilus somni has a particular tropism for vascular endothelium and can cause vasculitis and thrombosis in various tissues, with the brain being a common target in the neurological form of disease.

Genetic and breed predisposition to thrombotic meningoencephalitis has not been clearly established, with management factors and exposure circumstances being far more important than genetics in determining which animals develop disease. All breeds of cattle appear susceptible when exposed under conditions favoring disease development. Individual variation in immune response to Histophilus somni may exist, potentially influenced by prior exposure, vaccination history, and general immune competence, but specific genetic markers for susceptibility have not been identified. Hereditary transmission of susceptibility is not recognized.

Environmental and management factors play dominant roles in the epidemiology of thrombotic meningoencephalitis, particularly the stressors associated with modern beef production systems. The classic risk scenario involves young cattle shipped long distances, commingled with animals from various sources, introduced to new environments and diets, and subjected to processing procedures including vaccination and parasite treatment. Each of these stressors can compromise immune function independently, and their combination creates high-risk situations for opportunistic infections including histophilosis. Feedlot conditions with close animal proximity facilitate respiratory transmission of the organism between animals.

Specific risk factors for thrombotic meningoencephalitis development include recent transport, young age, concurrent respiratory disease, and environmental stress. Cattle recently arrived at feedlots within the first one to four weeks are at highest risk, corresponding to the period of maximum stress and immune suppression. Animals under two years of age are more commonly affected than older cattle. Concurrent bovine respiratory disease complex, which often involves many of the same predisposing factors and may share some of the same pathogens, frequently precedes or accompanies histophilosis. Cold weather, wet conditions, and overcrowding increase stress and disease risk. Previous vaccination may provide some protection, though breakthrough cases can occur.

The pathophysiology of thrombotic meningoencephalitis involves bacteremia followed by localization in the brain vasculature with characteristic lesion development. Following systemic invasion, Histophilus somni adheres to vascular endothelial cells and induces platelet aggregation and thrombus formation. The organism produces factors that damage endothelium and interfere with host immune responses. Septic thrombi occlude small blood vessels in the brain and meninges, causing ischemia and infarction of dependent tissue. Hemorrhage occurs both from direct vascular damage and secondary to infarction. The resulting lesions appear grossly as multiple small hemorrhagic foci throughout the brain, particularly in the gray matter, creating the characteristic pathological appearance that confirms diagnosis at necropsy.

Early warning signs of thrombotic meningoencephalitis may be subtle and can overlap with signs of other feedlot diseases, making early detection challenging. Initial signs may include mild depression, decreased feed intake, slight fever, and subtle gait abnormalities that could be attributed to various causes. Some animals may show signs of respiratory disease before or concurrent with neurological involvement. Careful observation of feedlot cattle, particularly recently arrived animals, for any behavioral or locomotor abnormalities improves the chance of identifying affected animals before severe neurological deterioration occurs. Animals that are slow to come to feed, stand apart from penmates, or show any head tilt or visual abnormalities warrant closer examination.

The classic symptoms of established thrombotic meningoencephalitis reflect the multifocal nature of brain involvement and can be highly variable between animals depending on which brain regions are most affected. Common presentations include severe depression ranging to obtundation or coma, giving rise to the alternative name sleeper syndrome for animals found lying quietly and unresponsive. Blindness may be partial or complete. Head tilt, circling, and other signs of vestibular involvement are common. Weakness and ataxia progress to recumbency, with affected animals unable to rise. Seizures may occur. The variable presentation reflects the scattered distribution of vascular lesions throughout the brain.

Behavioral changes in cattle developing thrombotic meningoencephalitis typically involve progressive depression and disconnection from normal activities. Early in disease, animals may stand apart from penmates, fail to come to feed, and appear dull or unaware of their surroundings. As disease progresses, affected cattle become increasingly obtunded, standing with lowered heads and minimal response to external stimuli. Some animals develop aggressive or bizarre behavior if particular brain regions are affected. The characteristic sleeper presentation involves animals lying quietly in lateral or sternal recumbency, minimally responsive or completely unresponsive to stimulation, appearing almost comatose.

Physical signs of thrombotic meningoencephalitis include both neurological abnormalities and systemic indicators of infection. Fever is typically present, often high in the range of 104 to 107 degrees Fahrenheit. The neurological examination reveals abnormalities reflecting the specific brain regions involved, which vary between animals. Abnormal pupil size or responsiveness, absent menace response indicating blindness, head tilt, nystagmus, ataxia, circling, and abnormal postures may be observed in various combinations. Proprioceptive deficits are common. Cranial nerve abnormalities other than vision may be present. Signs of concurrent respiratory disease may be apparent in some animals.

Symptom progression in thrombotic meningoencephalitis is typically rapid, with animals deteriorating from subtle initial signs to severe neurological dysfunction over hours to a few days. Some animals are found dead without previously observed illness, indicating that progression can be fulminant. Others may be noticed as slightly dull one day and found recumbent or moribund the next. Once recumbent, animals rarely recover without aggressive treatment, and even with treatment, many do not survive. Seizure activity may increase in frequency and severity as the disease progresses. Terminal stages include coma, respiratory depression, and death.

Emergency symptoms requiring immediate veterinary intervention include recumbency with absent or minimal response to stimulation, seizure activity, high fever above 105 degrees Fahrenheit, severe obtundation or coma, and any rapidly progressive neurological deterioration. Animals found down and unresponsive in feedlot settings should be considered potential TEME cases and evaluated promptly. Given the poor prognosis once severe neurological signs develop, early identification and treatment of animals with milder signs offers the best opportunity for survival.

Clinical examination of animals suspected of having thrombotic meningoencephalitis focuses on characterizing neurological abnormalities while assessing for concurrent conditions that might explain the presentation. The combination of high fever, neurological signs, and history of recent feedlot arrival or stress creates a classic clinical syndrome in affected cattle. Neurological examination documents the specific deficits present, including assessment of mentation, vision, pupillary responses, gait, postural reactions, and cranial nerve function. Physical examination should also evaluate for signs of respiratory disease, arthritis, or myocarditis, which may indicate other manifestations of histophilosis or concurrent infections. The pattern of multifocal brain involvement with fever and recent stress history is suggestive of TEME.

Diagnostic testing for thrombotic meningoencephalitis in living animals has limited sensitivity, and definitive diagnosis often relies on post-mortem examination. Blood culture may detect Histophilus somni bacteremia but is not consistently positive, and the organism can be difficult to isolate using standard techniques. Cerebrospinal fluid analysis typically shows increased protein and pleocytosis consistent with bacterial meningitis, but CSF collection in cattle requires specialized facilities. Complete blood count may reveal neutrophilia with left shift consistent with bacterial infection. Advanced imaging such as CT or MRI could potentially demonstrate brain lesions but is rarely available or practical for feedlot cattle. Response to antimicrobial treatment can support the diagnosis retrospectively.

Differential diagnosis for cattle presenting with acute neurological signs must consider the various conditions that can affect the bovine brain. Polioencephalomalacia causes cortical blindness and neurological signs but typically without high fever and in animals on high-concentrate diets with inadequate fiber. Lead poisoning produces similar cortical signs but has become less common with restricted lead use. Listeriosis causes brainstem signs with cranial nerve deficits and may produce fever. Rabies must always be considered in cattle with behavioral and neurological changes. Bacterial meningitis from other organisms including Escherichia coli, Streptococcus, and others can produce similar presentations. Nervous ketosis occurs in periparturient dairy cattle. Tetanus produces rigid paralysis rather than flaccid neurological signs.

Herd-level diagnostic considerations become important when multiple cattle in a feedlot develop neurological disease or when investigating deaths in recently arrived cattle. Necropsy examination of animals that die is invaluable for confirming TEME diagnosis, with characteristic gross lesions of multiple hemorrhagic foci in the brain being virtually pathognomonic. Histopathology confirms vasculitis and thrombosis with bacterial involvement. Bacterial culture from brain tissue at necropsy often recovers Histophilus somni. Investigation of herd health status, vaccination programs, and management factors contributing to stress helps identify intervention points for prevention. Assessment of concurrent respiratory disease in the population may reveal broader histophilosis issues.

Emergency and immediate treatment of suspected thrombotic meningoencephalitis requires aggressive antimicrobial therapy initiated as quickly as possible after disease recognition. Histophilus somni is generally susceptible to multiple antimicrobial classes, and treatment should begin before culture results are available given the rapid progression of disease. Common choices include oxytetracycline, florfenicol, ceftiofur, and sulfonamides, administered at appropriate doses and frequency for the severe systemic infection present. Treatment should be administered intravenously when possible for fastest achievement of therapeutic drug concentrations. Concurrent anti-inflammatory therapy with non-steroidal anti-inflammatory drugs helps reduce fever and inflammation.

Medical management of thrombotic meningoencephalitis continues antimicrobial therapy for an extended course to clear the systemic infection while providing supportive care for the neurologically compromised animal. Duration of antimicrobial treatment is typically five to seven days at minimum, with some protocols extending longer for severe cases. Choice of antimicrobial may be guided by culture and sensitivity results if available, though initial therapy should not be delayed for this information. Anti-inflammatory treatment is continued to manage cerebral inflammation. For food-producing animals, all treatments must be documented with attention to withdrawal times, though severely affected animals may not survive to slaughter considerations becoming relevant.

Surgical intervention is not applicable to treatment of thrombotic meningoencephalitis. The diffuse, multifocal nature of brain lesions precludes any surgical approach to the primary disease. Supportive procedures may be needed for managing the recumbent animal, including positioning, padding, and prevention of secondary complications.

Supportive care for cattle with thrombotic meningoencephalitis addresses the various needs of severely ill, neurologically compromised animals. Recumbent animals should be positioned on deep bedding in sternal recumbency when possible and turned regularly if lateral recumbency is unavoidable. Fluid therapy supports hydration and cardiovascular function in animals not drinking adequately. Nutritional support may require force feeding or stomach tubing in animals unable or unwilling to eat. Temperature regulation through shading in hot weather or shelter in cold weather prevents additional stress. Protection from self-injury during seizures or abnormal movement is important. Quiet, calm handling reduces stress.

Herd treatment protocols may be considered when multiple cases occur within a feedlot population, suggesting widespread exposure or common risk factors. Metaphylactic antimicrobial treatment of animals in affected pens or arrival cohorts may reduce additional cases when an outbreak is occurring. Such treatment decisions should involve veterinary consultation and consider antimicrobial stewardship principles. Review of vaccination status and administration of Histophilus somni vaccine to at-risk groups may be warranted, though protection from vaccination is not immediate. Addressing management factors contributing to stress and disease risk should accompany any treatment interventions.

Treatment decisions for individual animals with thrombotic meningoencephalitis must balance the potential for recovery against animal welfare and economic considerations. Animals presenting with early mild signs and treated aggressively may have reasonable chance of recovery. Animals presenting recumbent and obtunded have poor prognosis regardless of treatment intensity, with survival rates often below twenty percent in published reports of severely affected animals. The value of feedlot cattle must be weighed against treatment costs and low likelihood of success for advanced cases. Humane euthanasia is often the most appropriate option for animals with severe neurological compromise, preventing prolonged suffering with minimal chance of meaningful recovery.

Recovery timelines for animals surviving thrombotic meningoencephalitis are variable and depend on the extent of brain damage sustained during the acute illness. Animals that respond to treatment and survive the acute phase typically show improvement within the first few days of therapy, with fever resolution often occurring before neurological improvement. Neurological recovery may continue over one to several weeks as inflammation resolves and surviving brain tissue compensates for damaged areas. Complete neurological recovery is possible in animals with limited brain involvement, but residual deficits are common in survivors of severe disease.

Post-treatment care and monitoring continue throughout the recovery period and extend to ensuring the animal is suitable for return to normal production. Ongoing neurological assessment documents resolution of deficits and identifies any persistent abnormalities. Continued antimicrobial therapy as prescribed ensures complete clearance of infection. Animals should be protected from stress and given adequate nutrition to support recovery. Monitoring for relapse or recurrence is important, as some animals may experience worsening if treatment is discontinued too early. Observation for sequelae including residual neurological deficits, chronic infections, or other complications guides long-term management.

Prognosis factors for thrombotic meningoencephalitis recovery relate primarily to severity of neurological involvement at presentation and timing of treatment initiation. Animals with mild signs treated early have significantly better prognosis than those presenting with severe obtundation or coma. Fever response to treatment provides early prognostic information, with persistent high fever despite appropriate antimicrobial therapy suggesting poor outcome. Neurological improvement within the first forty-eight to seventy-two hours is a positive prognostic indicator. Animals that remain recumbent beyond several days of treatment rarely recover meaningful function. The specific neurological deficits present may influence prognosis, with some patterns of involvement suggesting more extensive damage than others.

Return to production considerations for animals recovering from thrombotic meningoencephalitis include ensuring complete recovery, completion of withdrawal times, and assessment of residual deficits that might affect future productivity. Animals recovering with no apparent neurological residua can return to normal feedlot production after appropriate withdrawal periods for administered medications. Those with residual deficits such as mild ataxia, visual impairment, or behavioral abnormalities may have limited productive potential and require individual assessment. Chronic carriers of Histophilus somni may potentially serve as infection sources for other animals, though the practical significance of this in feedlot populations where the organism is common is unclear.

Vaccination protocols against Histophilus somni represent an important component of prevention strategies for thrombotic meningoencephalitis in feedlot cattle. Commercial vaccines containing Histophilus somni antigens are available and are commonly incorporated into feedlot arrival vaccination programs. Ideally, cattle would receive primary vaccination before the stress of weaning and transport, with boosters administered at feedlot arrival, but in practice many cattle arrive unvaccinated and receive their first exposure at processing. Vaccine efficacy appears variable, and breakthrough cases occur even in vaccinated animals, but vaccination likely reduces overall disease incidence and severity. Vaccination should be viewed as one component of a comprehensive prevention program rather than complete protection.

Biosecurity measures for prevention of thrombotic meningoencephalitis focus on reducing stress and supporting immune function in high-risk cattle rather than excluding the organism, which is ubiquitous in cattle populations. Sourcing cattle from reputable suppliers with good health histories may provide some protection. Avoiding excessive commingling of animals from many different sources reduces stress and pathogen exposure diversity. Quarantine and observation periods allow identification of sick animals before mixing with established populations. These measures align with general best practices for feedlot health management.

Nutritional prevention of thrombotic meningoencephalitis centers on supporting immune function and reducing metabolic stress during the high-risk arrival period. Adequate energy and protein nutrition supports immune response. Appropriate mineral and vitamin supplementation ensures no micronutrient deficiencies compromise immunity. Careful transition to feedlot diets prevents ruminal acidosis and associated stress. Some evidence suggests that adequate selenium and vitamin E status supports immune function against bacterial infections. Ensuring adequate water intake, particularly important during transport recovery, supports overall health.

Management practices offer the greatest opportunity for prevention of thrombotic meningoencephalitis by reducing the stress factors that predispose cattle to histophilosis. Minimizing transport time and distance when possible reduces stress. Preconditioning programs that wean, vaccinate, and start cattle on feed before shipment dramatically improve outcomes compared to shipping freshly weaned calves. Avoiding processing procedures during peak stress periods allows some immune recovery before additional challenges. Adequate rest and recovery time after arrival before intensive processing helps normalize physiological function. Environmental management including adequate shelter, appropriate stocking density, and good air quality reduces respiratory disease pressure.

Quarantine and testing protocols for thrombotic meningoencephalitis prevention focus on identifying and managing high-risk animals rather than detecting carrier status. Close observation of newly arrived cattle during the first several weeks, when risk is highest, allows early detection of illness. Animals showing any signs of depression, fever, or neurological abnormalities should be evaluated promptly. Isolation of sick animals prevents stress to penmates and facilitates treatment. Testing for Histophilus somni carrier status is not practical or particularly useful given the organism's prevalence in cattle populations.

Daily management and monitoring for prevention of thrombotic meningoencephalitis in feedlot settings emphasizes careful observation of high-risk cattle groups. Newly arrived cattle should be observed at least twice daily, with more frequent checks during the first one to two weeks when disease risk is highest. Trained personnel should evaluate animals for depression, decreased feed intake, respiratory signs, gait abnormalities, and any neurological indicators. Animals that fail to come to feed, stand apart from penmates, or show any concerning signs should be identified for closer examination. Early detection and treatment of any illness reduces progression to severe disease including TEME.

Housing and environmental management for prevention of histophilosis including thrombotic meningoencephalitis focuses on reducing stress and supporting cattle health during the vulnerable arrival period. Adequate space prevents overcrowding stress. Good ventilation reduces respiratory pathogen concentration while avoiding excessive drafts. Protection from weather extremes including wind, precipitation, and temperature extremes reduces metabolic stress. Clean, dry bedding areas promote rest and comfort. Easy access to feed and water without excessive competition ensures adequate intake. Hospital pens for sick animals allow focused treatment while reducing stress exposure for penmates.

Herd health programs addressing thrombotic meningoencephalitis integrate vaccination, management of arrival stress, and overall feedlot health protocols. Arrival processing protocols should include Histophilus somni vaccination along with other appropriate immunizations. Preconditioning programs for source cattle, when available, dramatically reduce arrival disease problems. Metaphylactic antimicrobial protocols may be appropriate for very high-risk cattle groups, though antimicrobial stewardship considerations influence such decisions. Working relationships with veterinarians allow rapid response when cases occur and ongoing refinement of prevention strategies. Staff training on disease recognition ensures early identification of affected animals.

Record keeping and monitoring systems support both individual animal management and evaluation of population-level disease patterns. Individual animal records should document arrival source, vaccination and treatment history, and any illness episodes. Population records tracking disease incidence, mortality, and treatment outcomes allow assessment of prevention program effectiveness. Analysis of disease patterns may reveal risk factors specific to certain source groups, arrival periods, or management situations. Necropsy records confirming diagnoses in fatal cases provide valuable information for understanding disease occurrence. These data support continuous improvement in prevention programs.

Economic considerations for thrombotic meningoencephalitis management encompass prevention costs, treatment costs, and losses from mortality and reduced performance. Vaccination costs are modest relative to the value of animals protected and should be considered standard practice for feedlot cattle. Preconditioning programs cost more but provide substantial health benefits that typically justify the investment. Treatment of clinical cases involves antimicrobial and supportive care costs plus labor, with poor success rates in severely affected animals limiting return on treatment investment. Mortality losses include direct animal value plus the foregone performance that animal would have contributed. Prevention through comprehensive health programs is far more economical than managing clinical disease outbreaks.

Breed-specific predisposition to thrombotic meningoencephalitis has not been clearly established, with the condition affecting beef cattle of various breeds when subjected to the stress factors that precipitate disease. Both British and Continental breeds develop TEME in feedlot settings, and no breed appears to have substantially higher or lower risk when other factors are controlled. The predominant appearance of this disease in beef breeds reflects the management systems that create risk rather than inherent breed susceptibility. Dairy cattle can develop histophilosis but less commonly manifest the neurological form, possibly reflecting different management and stress patterns.

Production type considerations strongly influence thrombotic meningoencephalitis risk, with feedlot beef cattle being the classic affected population. The combination of weaning stress, long-distance transport, commingling, and dietary transition that characterizes beef cattle production creates the conditions for disease development. Within feedlot populations, lightweight calves shipped long distances from sale barns or order buyers face highest risk. Heavy cattle started on feed closer to home with less transport stress have lower risk. Cow-calf operations rarely see TEME because animals are not subjected to the accumulated stressors of feedlot placement. Stocker operations represent intermediate risk depending on management intensity.

Genetic selection and testing specifically for thrombotic meningoencephalitis resistance are not practiced, as management factors overwhelm any genetic component of susceptibility. Selection emphasis in beef cattle focuses on production traits, temperament, and general disease resistance rather than specific pathogen resistance. Cattle with excitable temperaments may experience more stress during handling and transport, potentially increasing disease risk, making selection for calm disposition indirectly relevant. Breeding programs should focus on producing cattle adapted to production system demands with robust overall health rather than attempting selection for specific infectious disease resistance.

Commonly co-occurring conditions with thrombotic meningoencephalitis reflect the systemic nature of Histophilus somni infection and the shared risk factors for multiple feedlot diseases. Bovine respiratory disease complex frequently precedes or accompanies histophilosis, with overlapping pathogens and predisposing factors. Other manifestations of histophilosis may be present, including polyarthritis with joint swelling and lameness, myocarditis with sudden death or cardiac failure, and reproductive disease in breeding animals. Concurrent infections with other respiratory pathogens including Mannheimia haemolytica, Pasteurella multocida, Mycoplasma bovis, and respiratory viruses are common in feedlot cattle. The immunocompromise that predisposes to TEME also increases susceptibility to other opportunistic infections.

Conditions with similar clinical presentations must be differentiated from thrombotic meningoencephalitis to ensure appropriate treatment. Other bacterial meningitides caused by various gram-positive and gram-negative organisms can produce similar presentations and require similar treatment approaches even if the specific etiology differs. Listeriosis causes brainstem encephalitis with cranial nerve signs and fever. Polioencephalomalacia produces neurological signs but typically without fever and with different predisposing factors. Rabies should always be considered in cattle with neurological and behavioral changes. Lead poisoning, though less common currently, can produce cortical neurological signs. Brain abscesses from various sources may cause focal or multifocal neurological signs.

Complications and sequelae of thrombotic meningoencephalitis include immediate complications during acute illness and potential long-term effects in survivors. Respiratory failure may occur with severe brainstem involvement affecting respiratory centers. Secondary aspiration pneumonia develops in recumbent animals with impaired swallowing. Pressure sores and muscle damage from prolonged recumbency affect animals surviving the acute phase. Permanent neurological deficits including blindness, ataxia, or behavioral changes may persist in survivors of severe disease. Chronic arthritis or other manifestations of histophilosis may become apparent as animals recover from the acute neurological episode. Recurrence of disease is possible if infection is not completely cleared.