Histophilosis in Cows: Thrombotic Meningoencephalitis and Sudden Neurologic Disease
- See your vet immediately. The nervous form of histophilosis can progress very fast and may cause sudden death within hours.
- Histophilosis is caused by the bacterium *Histophilus somni*, which is common in North American cattle and is also part of bovine respiratory disease complex.
- Affected cattle may show profound lethargy, fever, stiffness, ataxia, blindness, recumbency, behavior change, or collapse.
- Diagnosis often relies on herd history, exam findings, and testing such as PCR, bacterial culture, and histopathology. Early cases can be hard to confirm before death.
- Treatment usually involves rapid antimicrobial therapy and supportive care directed by your vet, but prognosis is guarded once severe neurologic signs are present.
What Is Histophilosis in Cows?
Histophilosis is an infectious disease caused by the bacterium Histophilus somni. In cattle, it can affect several body systems, including the lungs, heart, joints, and brain. The nervous form is often called thrombotic meningoencephalitis, or TME. In this form, the bacteria damage blood vessels in the brain and spinal cord, leading to clot formation, poor blood flow, and sudden neurologic disease.
This condition is especially important in young, recently stressed, transported, or commingled cattle, including feedlot calves. Some animals are found dead before obvious warning signs are noticed. Others first show fever and marked depression, then quickly develop stiffness, incoordination, blindness, recumbency, or collapse.
Histophilosis is common in North American cattle and can overlap with bovine respiratory disease complex. That means a cow may have respiratory signs, sudden death, or neurologic signs depending on which tissues are most affected. Because the disease can move quickly, prompt veterinary involvement matters for both the sick animal and the rest of the group.
Symptoms of Histophilosis in Cows
- Sudden death
- Profound lethargy or severe depression
- Fever
- Stiff gait or muscle stiffness
- Ataxia or incoordination
- Blindness or abnormal awareness
- Behavior changes
- Recumbency or collapse
- Hyperesthesia
- Rapid breathing or respiratory signs
When a cow becomes suddenly dull, stiff, blind, wobbly, or recumbent, treat it as an emergency. Histophilosis can worsen very quickly, and some cattle die before a full workup is possible.
Call your vet right away if more than one animal in a group looks depressed, febrile, or neurologically abnormal. Rapid herd-level assessment matters because this disease often appears in recently stressed groups, and early treatment of additional at-risk cattle may be discussed with your vet.
What Causes Histophilosis in Cows?
Histophilosis is caused by Histophilus somni, a bacterium associated with cattle in North America. It can be part of the normal upper respiratory tract flora in some animals, but under the right conditions it can invade deeper tissues and enter the bloodstream. Stress plays a major role. Common triggers include weaning, shipping, commingling, weather changes, crowding, and concurrent viral or bacterial respiratory disease.
In the nervous form, the bacteria damage the lining of blood vessels. That injury promotes clot formation inside vessels, especially in the brain, which is why the condition is called thrombotic meningoencephalitis. The resulting loss of blood supply can cause sudden neurologic signs, collapse, or death.
Histophilosis does not always stay in the nervous system. The same organism can also contribute to pneumonia, pleuritis, myocarditis, arthritis, reproductive disease, and sudden death syndromes. That overlap is one reason outbreaks can be confusing at first. A cow with fever and depression may look like a respiratory case early on, then develop neurologic disease later.
How Is Histophilosis in Cows Diagnosed?
Your vet will usually start with the history and pattern in the group. Recent arrival, transport stress, respiratory disease, sudden deaths, and rapidly developing neurologic signs all raise concern. On exam, fever, profound depression, stiffness, ataxia, blindness, or recumbency may support suspicion, but these signs are not unique to histophilosis.
Definitive diagnosis often requires laboratory testing. Common approaches include PCR testing, bacterial isolation, and histopathology. In animals that die or are euthanized, necropsy with brain and other tissue sampling can be especially helpful because the characteristic vascular injury and thrombosis may be identified microscopically.
Your vet may also work through other causes of sudden neurologic disease in cattle, such as listeriosis, polioencephalomalacia, lead toxicity, rabies risk situations, severe pneumonia with low oxygen, or other septic conditions. Because early identification can be difficult, treatment decisions are often made before every test result is back.
Treatment Options for Histophilosis in Cows
Spectrum of Care means you have options. Here are treatment tiers at different price points.
Budget-Conscious Care
- Urgent farm call or chute-side exam by your vet
- Early injectable antimicrobial selected by your vet based on label, herd history, and production class
- Anti-inflammatory treatment if appropriate
- Isolation or reduced-stress pen management
- Monitoring of temperature, attitude, gait, and ability to eat and drink
- Discussion of whether additional exposed cattle need observation or group-level intervention
Recommended Standard Treatment
- Full veterinary exam plus targeted herd history review
- Antimicrobial therapy directed by your vet, often using products commonly selected for bovine respiratory pathogens when legal and appropriate for the animal
- Anti-inflammatory medication and supportive nursing care
- Basic diagnostics such as temperature checks across penmates, treatment records review, and selected lab sampling
- Necropsy and sample submission on fresh deaths when available
- Short-term hospital pen or close observation area for down or high-risk cattle
Advanced / Critical Care
- Referral or intensive hospital-level monitoring when feasible
- Aggressive supportive care for recumbent cattle, including fluids, nursing, and frequent reassessment
- Expanded diagnostics such as CBC/chemistry where practical, PCR or culture submissions, and full necropsy with histopathology for herd confirmation
- Detailed outbreak investigation covering sourcing, transport, vaccination timing, pen moves, and concurrent respiratory disease
- Customized prevention plan for the rest of the group, including vaccine strategy review and stress-reduction steps
Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.
Questions to Ask Your Vet About Histophilosis in Cows
Bring these questions to your vet appointment to get the most out of your visit.
- Do this cow's signs fit histophilosis, or are other neurologic diseases more likely?
- How urgent is treatment for this animal, and what signs would make the prognosis worse?
- Which antimicrobial options make sense for this cow's age, production class, and withdrawal requirements?
- Should we test this case with PCR, culture, or necropsy to confirm what is happening in the herd?
- Do other cattle in the group need to be examined, monitored, or treated now?
- Could bovine respiratory disease stressors be contributing to this outbreak?
- What vaccination plan is reasonable for future groups, and when should those vaccines be given?
- What management changes could lower risk during weaning, shipping, and commingling?
How to Prevent Histophilosis in Cows
Prevention focuses on lowering stress and improving herd health around high-risk periods. Work with your vet on weaning plans, transport timing, commingling practices, stocking density, ventilation, and early respiratory disease control. Newly received cattle are often the highest-risk group, so careful observation during the first days to weeks matters.
Vaccination may be part of the plan. Multivalent bacterins that include Histophilus somni are used in some operations and may help reduce illness and death, although protection is not perfect and vaccine performance can vary. Timing also matters. Vaccines tend to work best when cattle receive them before major stress rather than at the peak of an outbreak.
Good prevention also means using records. If your herd has had sudden deaths, myocarditis, pneumonia, or neurologic disease after arrival, ask your vet to review treatment outcomes, necropsy findings, and vaccine protocols. A practical prevention plan is usually a combination of biosecurity, stress reduction, respiratory disease control, and targeted vaccination rather than one single step.