Bluetongue

Bluetongue is a serious, non-contagious viral disease caused by the bluetongue virus (BTV), an orbivirus belonging to the Reoviridae family. This arthropod-borne disease primarily affects sheep, though cattle, goats, wild ruminants, and camelids can also become infected. The virus is transmitted exclusively through the bites of infected Culicoides midges, tiny biting insects that serve as biological vectors. Bluetongue is named for the characteristic blue discoloration of the tongue that can occur in severely affected sheep due to cyanosis, though this classic sign is not always present in every case.

Bluetongue occurs worldwide in tropical, subtropical, and temperate regions where competent Culicoides vector species are present. The disease demonstrates clear seasonal patterns, with outbreaks typically occurring during warm, humid months when midge populations peak. There are at least 27 recognized serotypes of the bluetongue virus, with different serotypes predominating in different geographic regions. Sheep are generally the most severely affected domestic species, while cattle often serve as reservoir hosts, maintaining the virus in endemic areas despite showing fewer clinical signs.

The economic and welfare impact of bluetongue can be devastating for sheep producers. Mortality rates in naive sheep populations can reach 70 percent or higher during outbreaks, with survivors often experiencing prolonged recovery periods and reduced productivity. Beyond direct losses from mortality, producers face significant economic consequences from reduced weight gain, decreased wool quality, reproductive failures, and trade restrictions. Bluetongue is classified as a reportable disease by the World Organisation for Animal Health (WOAH), meaning outbreaks must be reported to veterinary authorities, which can trigger immediate trade embargoes and movement restrictions.

Early detection and prompt supportive care are essential for minimizing losses during bluetongue outbreaks. While no specific antiviral treatment exists for this disease, affected sheep can recover with appropriate nursing care if secondary complications are prevented. Understanding vector biology, implementing targeted vector control measures, and utilizing vaccination programs where available are critical components of bluetongue prevention and control strategies. Producers in endemic and at-risk regions must maintain vigilance for early signs of disease and work closely with veterinarians and animal health authorities to protect their flocks.

Bluetongue is caused by the bluetongue virus (BTV), a double-stranded RNA virus belonging to the Orbivirus genus within the Reoviridae family. The virus particle is non-enveloped and displays icosahedral symmetry, containing ten segments of double-stranded RNA that encode seven structural and four non-structural proteins. The outer capsid proteins, particularly VP2 and VP5, determine the serotype of the virus and are the primary targets of neutralizing antibodies. The existence of at least 27 distinct serotypes means that immunity to one serotype does not provide protection against others, complicating vaccination and control efforts.

The exclusive mode of transmission for bluetongue virus is through the bite of infected Culicoides midges, particularly species in the Culicoides imicola complex and the Culicoides obsoletus complex. These tiny biting insects, measuring only one to three millimeters in length, become infected when they feed on viremic animals and can transmit the virus to susceptible hosts after the virus replicates within the midge. The extrinsic incubation period within the midge is temperature-dependent, typically requiring 10 to 15 days under optimal conditions. Midges remain infected for life and can transmit the virus with subsequent blood meals.

Environmental and climatic factors play crucial roles in bluetongue epidemiology. The disease occurs predominantly in areas where average temperatures remain above 15 degrees Celsius during vector-active periods, as midge activity and viral replication within vectors require warm conditions. Wet, humid conditions favor midge breeding in soil, mud, and decaying organic matter. Climate change has contributed to the northward expansion of bluetongue into previously unaffected regions of Europe and other temperate areas, as warming temperatures allow competent vector species to survive and reproduce in new geographic zones.

Risk factors for bluetongue infection include geographic location within vector distribution zones, seasonal timing during peak midge activity, proximity to wetlands or areas with suitable midge breeding habitat, and the presence of cattle or other reservoir species that can maintain viral circulation. Naive sheep populations that have never been exposed to a particular BTV serotype are at highest risk for severe clinical disease. European fine-wool sheep breeds tend to be more susceptible to severe disease than indigenous breeds in endemic regions, which may have developed some degree of genetic resistance through natural selection.

Once a susceptible sheep is bitten by an infected midge, the bluetongue virus replicates initially in regional lymph nodes before disseminating throughout the body via the bloodstream. The virus has a particular affinity for endothelial cells lining blood vessels, and viral replication causes widespread vascular damage resulting in edema, hemorrhage, and tissue necrosis. Viremia in sheep typically develops within three to five days post-infection and can persist for several weeks, during which time the animal can serve as a source of infection for feeding midges. The severity of clinical disease depends on the viral strain, sheep breed, immune status, and various environmental stressors.

Early warning signs of bluetongue in sheep often begin subtly and can be easily overlooked in the initial stages. Affected animals typically develop fever ranging from 40.5 to 41.5 degrees Celsius within five to seven days of infection, which may be the first detectable abnormality. During this early febrile phase, sheep may appear slightly depressed, show reduced appetite, and spend more time lying down than usual. Producers who regularly monitor their flocks may notice that affected sheep are reluctant to move with the group or seem slower than their flockmates. Careful observation may reveal early reddening or hyperemia of the muzzle, lips, and oral mucosa before more obvious lesions develop.

Common symptoms vary in severity between sheep and goats, with sheep typically displaying much more pronounced clinical signs. In sheep, the characteristic presentation includes facial edema affecting the lips, muzzle, and ears, giving affected animals a swollen appearance. The oral mucosa becomes hyperemic and congested, progressing to erosions and ulcers on the dental pad, tongue, gums, and hard palate. Excessive salivation and nasal discharge, initially serous but often becoming mucopurulent, are frequently observed. Goats infected with bluetongue typically show much milder clinical signs and may appear subclinically infected, though they can still develop fever, mild oral lesions, and transient lameness.

Behavioral changes in affected sheep are often pronounced and provide important diagnostic clues. Infected animals frequently separate themselves from the flock, seeking shade and showing reluctance to move. Affected sheep typically go off feed due to painful oral lesions and difficulty swallowing. They may stand with an arched back and lowered head, indicative of general malaise and respiratory distress. Excessive drooling and repeated swallowing attempts are common as animals struggle with oral pain and swelling. Some sheep may exhibit head pressing or other signs of discomfort, and affected ewes may show reduced milk production and maternal attention.

Physical signs of bluetongue extend beyond the head and oral cavity to affect multiple body systems. Coronary band inflammation causes severe lameness, with affected sheep showing reluctance to stand or walk. The hooves may become hot to the touch, and hemorrhages may be visible at the coronary band junction. Skin lesions include hyperemia and crusting, particularly on the face, ears, and around the muzzle. Wool breaks may occur in severely affected sheep due to the febrile episode. Reproductive effects include temporary infertility in rams due to testicular damage and potential pregnancy losses in ewes infected during gestation.

Symptom progression in bluetongue typically follows a predictable course over several weeks. Following the initial fever spike, oral and facial lesions develop progressively over the next three to seven days. The tongue may become severely swollen and cyanotic, protruding from the mouth and developing the blue discoloration that gives the disease its name, though this classic sign occurs in only a minority of cases. Muscle necrosis affecting the skeletal muscles can develop, causing severe stiffness, torticollis, or difficulty rising. Coronitis and lameness often become most severe during the second week of illness. Recovery, when it occurs, is typically slow and may take several weeks to months, with wool shedding and hoof abnormalities persisting long after acute illness resolves.

Emergency symptoms requiring immediate veterinary intervention include severe respiratory distress with open-mouth breathing and cyanosis of mucous membranes. Aspiration pneumonia can develop when severely affected sheep with pharyngeal swelling and weakness inhale saliva or regurgitated rumen contents. Complete inability to rise due to severe muscle damage or lameness represents a welfare emergency. Pregnant ewes showing signs of abortion or severe systemic illness require urgent attention. Any sudden increase in mortality within a flock during bluetongue-risk periods should prompt immediate veterinary investigation and notification of animal health authorities, as bluetongue is a reportable disease with significant regulatory implications.

Clinical examination forms the foundation of bluetongue diagnosis, with veterinarians assessing the characteristic constellation of signs including fever, facial edema, oral lesions, lameness, and respiratory involvement. Physical examination should include careful inspection of the oral cavity for erosions and ulceration, palpation of the coronary bands for heat and swelling, auscultation of the lungs for evidence of pneumonia, and assessment of overall body condition. Temperature monitoring is valuable, as the biphasic fever pattern with initial spike followed by resolution and possible secondary elevation can support clinical suspicion. The seasonal timing during midge activity periods and geographic location within vector zones strengthen clinical suspicion when appropriate signs are observed.

Laboratory diagnostic tests are essential for confirming bluetongue virus infection and identifying the specific serotype involved. Blood samples collected in EDTA tubes during the viremic phase can be tested using reverse transcription polymerase chain reaction (RT-PCR) to detect viral RNA with high sensitivity and specificity. Virus isolation from blood samples using embryonated chicken eggs or cell culture remains the gold standard for definitive diagnosis, though it is more time-consuming than molecular methods. Serological testing using enzyme-linked immunosorbent assays (ELISA) can detect antibodies to bluetongue virus group antigens, while virus neutralization tests identify serotype-specific antibodies. Paired serology demonstrating rising antibody titers between acute and convalescent samples provides evidence of recent infection.

Differential diagnosis for bluetongue includes other diseases that cause oral lesions, fever, and lameness in sheep. Foot-and-mouth disease produces similar vesicular and erosive oral lesions and must be ruled out immediately given its catastrophic implications. Contagious ecthyma (orf) causes proliferative crusty lesions around the mouth but typically lacks systemic signs. Peste des petits ruminants in goats shares many clinical features with bluetongue. Photosensitization can cause facial swelling and oral lesions but is associated with hepatogenous or primary photosensitizing agents. Foot rot causes lameness but without the systemic illness or oral lesions seen in bluetongue. Polyarthritis from various infectious causes may mimic the lameness of bluetongue.

Herd-level diagnostic approaches are valuable during outbreak investigations to understand the scope of infection and guide control measures. Serological surveys using bulk milk testing or individual blood samples can determine flock exposure rates and identify seropositive animals. Entomological monitoring using light traps to capture Culicoides midges can confirm vector presence and help assess transmission risk. Systematic clinical examination of the entire flock identifies the range of disease severity and helps estimate morbidity rates. Necropsy examination of animals that have died provides valuable diagnostic information, with characteristic findings including hemorrhages in the pulmonary artery wall, cardiac muscle, skeletal muscles, and subcutaneous tissues. Mortality patterns and geographic clustering of cases help define outbreak extent and inform targeted control interventions.

Emergency and immediate treatment for sheep with severe bluetongue focuses on stabilizing affected animals and preventing life-threatening complications. Animals showing respiratory distress require immediate attention, with positioning in sternal recumbency to facilitate breathing and reduce aspiration risk. Severely edematous sheep may benefit from emergency tracheotomy if upper airway obstruction threatens survival, though this intervention requires veterinary expertise. Shock treatment with intravenous fluids may be necessary for critically ill animals showing signs of cardiovascular collapse. Moving affected sheep to shaded, well-ventilated areas reduces heat stress that exacerbates clinical signs.

Medical management of bluetongue is entirely supportive, as no specific antiviral treatments are available for this disease. Non-steroidal anti-inflammatory drugs (NSAIDs) such as flunixin meglumine or meloxicam help reduce fever, inflammation, and pain, improving animal comfort and encouraging feed intake. When using any medications in food-producing animals, strict attention to withdrawal times is mandatory to ensure meat and milk safety. Antibiotics have no effect against the bluetongue virus itself but are frequently administered to prevent or treat secondary bacterial infections, particularly pneumonia and infected oral or skin lesions. Broad-spectrum antibiotics with appropriate withdrawal periods should be selected in consultation with the attending veterinarian.

Surgical intervention is rarely required for bluetongue but may be considered in specific circumstances. Emergency tracheotomy can be lifesaving for sheep with severe pharyngeal swelling causing complete airway obstruction. Hoof trimming and corrective foot care may be needed for animals with severe coronitis and hoof deformities once the acute phase resolves. Debridement of severely necrotic oral or skin lesions is occasionally necessary. Most surgical considerations, however, relate to management of secondary complications rather than direct treatment of the viral infection itself.

Supportive care measures are crucial for optimizing recovery in bluetongue-affected sheep. Providing soft, palatable feeds helps maintain nutrition in animals with painful oral lesions, and soaking hay or offering fresh grass can encourage intake. Access to fresh, clean water at ground level reduces the effort required for drinking. Affected sheep should be housed in shaded areas protected from direct sunlight and biting insects, which reduces stress and ongoing midge exposure. Soft bedding minimizes pressure sores in recumbent animals. Careful monitoring of hydration status and provision of oral or subcutaneous fluids helps prevent dehydration in sheep that are reluctant to drink.

Herd treatment protocols during bluetongue outbreaks involve systematic assessment and triage of affected animals. All sheep should be carefully examined to identify those requiring treatment versus those with mild or subclinical infection. Grouping affected animals separately facilitates monitoring and treatment while reducing stress on the flock. Implementing insect control measures including insecticide application to animals and housing structures helps reduce ongoing transmission. Restricting movement minimizes stress on affected animals and reduces spread to new areas. Systematic record-keeping of clinical signs, treatments, and outcomes supports outbreak management and informs future prevention efforts.

Treatment decisions in commercial sheep operations must balance individual animal welfare against economic realities and practical constraints. Mildly affected sheep often recover with minimal intervention and careful management, making extensive treatment unnecessary. Severely affected animals with poor prognosis, including those with extensive muscle necrosis, aspiration pneumonia, or complete inability to eat or drink, may be candidates for humane euthanasia on welfare grounds. The decision to treat versus cull individual animals should consider disease severity, likelihood of recovery, treatment costs, residual productivity, and overall herd health management goals. Valuable breeding animals may warrant more intensive treatment efforts than commercial stock destined for market.

Recovery timeline for bluetongue varies considerably depending on disease severity, with mildly affected sheep often recovering within two to three weeks while severely affected animals may require months for full recovery. The acute febrile phase typically resolves within seven to ten days, with gradual improvement in appetite and activity levels following. Oral lesions usually heal within two to four weeks, though complete resolution of mucosal damage may take longer. Lameness associated with coronitis can persist for weeks to months, and permanent hoof deformities may develop in severely affected animals. Muscle damage, when present, resolves slowly, and some animals may retain permanent stiffness or weakness.

Post-treatment care and monitoring should continue for several weeks following apparent clinical recovery. Recovered sheep should be kept in a quiet, low-stress environment with easy access to feed and water. Body condition scoring helps track nutritional recovery, as weight loss during acute illness often requires extended realimentation. Monitoring hoof health is important, as delayed effects of coronitis may become apparent weeks after acute illness. Observation for wool breaks and skin abnormalities helps assess the full impact of infection. Recording individual animal recoveries informs future management decisions and helps predict productivity following recovery.

Prognosis for bluetongue recovery depends on multiple factors including initial disease severity, promptness of supportive care, development of secondary complications, and individual animal resilience. Sheep with mild to moderate disease typically recover fully and return to normal productivity, though prolonged recovery periods may result in reduced weight gain and delayed breeding. Animals with severe oral lesions may have difficulty maintaining body condition during recovery due to feeding difficulties. Aspiration pneumonia significantly worsens prognosis and often proves fatal despite treatment. Extensive muscle necrosis can result in permanent disability or necessitate euthanasia. Pregnant ewes that recover may still experience late-term abortions or deliver weak lambs due to transplacental infection.

Return to production considerations are important for commercial sheep operations managing bluetongue recovery. Recovered ewes typically resume normal reproductive function, though temporary infertility may persist for one to two breeding cycles. Rams may experience prolonged reduction in semen quality due to testicular damage, and semen evaluation before returning to breeding is advisable. Wool quality may be compromised for one or more shearing cycles due to wool breaks caused by febrile illness. Recovered sheep develop immunity to the infecting serotype but remain susceptible to other BTV serotypes. Movement restrictions imposed during outbreaks may affect marketing schedules and require coordination with animal health authorities. Documentation of recovery and veterinary clearance may be required before resuming normal flock operations or movements.

Vaccination protocols form a cornerstone of bluetongue prevention in endemic and at-risk regions. Both modified live virus (MLV) and inactivated vaccines are available, each with distinct advantages and considerations. Inactivated vaccines are generally preferred in non-endemic areas because they cannot revert to virulence or spread to unvaccinated animals, but they require booster doses and provide shorter-duration immunity. Modified live vaccines stimulate stronger, longer-lasting immunity but carry risks of vaccine virus transmission by midges and potential reversion. Vaccination must target the specific serotypes circulating in the region, as cross-protection between serotypes is limited. Timing vaccination to achieve protective immunity before peak midge season maximizes effectiveness. Pregnant ewes should ideally be vaccinated before breeding to avoid potential fetal effects.

Biosecurity measures for bluetongue focus primarily on vector control rather than direct animal-to-animal transmission prevention. Housing sheep in screened enclosures during peak midge activity periods, particularly around dawn and dusk, can significantly reduce exposure to infected vectors. Fans that create air movement can deter midge entry, as these weak fliers avoid windy conditions. Treating animals with approved insecticides and repellents reduces midge feeding success, though efficacy varies and repeated applications are typically necessary. Avoiding low-lying wet areas where midges breed and improving drainage around sheep housing reduces local vector populations. Removing decaying organic matter and managing manure properly eliminates midge breeding habitat.

Nutritional prevention approaches support immune function and overall flock resilience during bluetongue risk periods. Ensuring adequate trace mineral nutrition, particularly selenium, copper, and zinc, supports immune competence and may improve outcomes in infected animals. Maintaining good body condition before periods of high disease risk provides metabolic reserves for mounting immune responses and surviving illness. Avoiding nutritional stress during peak vector season reduces susceptibility to severe disease. Providing high-quality forage and appropriate supplementation ensures that sheep have the nutritional resources needed to recover from infection.

Management practices that reduce bluetongue risk include avoiding introduction of animals from endemic areas during vector season without appropriate quarantine and testing. Scheduling shearing, transport, and other stressful procedures outside peak midge activity periods minimizes immunosuppression when exposure risk is highest. Maintaining closed flocks or using only tested, vaccinated replacements reduces introduction of infection. Coordinating with neighboring properties on vector control efforts improves regional effectiveness. Reporting suspected cases promptly enables rapid response and helps protect the broader sheep population. Staying informed about disease alerts and regional outbreak status allows proactive implementation of preventive measures.

Quarantine and testing protocols are essential when introducing new animals or responding to suspected cases. New arrivals from regions where bluetongue occurs should be quarantined and tested before joining the main flock, with quarantine duration of at least 30 days to allow for detection of incubating infections. During active outbreaks, movement restrictions may be imposed by regulatory authorities to prevent disease spread. Serological testing identifies previously exposed animals and informs vaccination decisions. Regular monitoring and testing as part of herd health programs helps detect subclinical infections and maintain awareness of flock status. Working with veterinarians and animal health authorities ensures that quarantine and testing protocols meet regulatory requirements and effectively protect flock health.

Daily management and monitoring for flocks in bluetongue-risk areas requires heightened vigilance during vector-active periods. Producers should observe their sheep at least twice daily during high-risk seasons, watching for early signs such as fever, nasal discharge, facial swelling, or reluctance to move. Temperature monitoring of sentinel animals can provide early warning of infection in the flock. Checking feet and observing gait during daily handling helps detect early coronitis before severe lameness develops. Recording any abnormalities in individual animals enables rapid response and provides documentation for veterinary consultation and regulatory reporting.

Housing and environmental management significantly impact bluetongue risk and outcomes. Where possible, housing sheep in enclosed buildings during peak midge activity periods, typically dawn and dusk, reduces exposure to infected vectors. Installing fine mesh screening on windows and ventilation openings prevents midge entry while maintaining air flow. Using fans to create air movement deters midge feeding, as these weak fliers avoid windy conditions. Siting sheep housing away from wetlands, streams, and other midge breeding areas reduces local vector populations. Maintaining good drainage and avoiding waterlogged conditions around housing eliminates breeding habitat. Removing accumulated manure and organic debris that provide midge larval habitat is essential.

Herd health programs for bluetongue-risk flocks should integrate vector control, vaccination, and monitoring into a comprehensive approach. Working with veterinarians to develop vaccination schedules appropriate for local serotype risk ensures effective protection. Establishing baseline serological data for the flock helps detect new infections and guides vaccination decisions. Including Culicoides monitoring using light traps in the herd health program provides information on vector activity and species composition. Planning breeding seasons to minimize lamb birth during high-risk periods reduces transplacental infection and congenital abnormalities. Integrating bluetongue prevention with other herd health activities improves efficiency and compliance.

Record keeping and monitoring provide essential data for managing bluetongue risk and responding to outbreaks. Maintaining individual animal identification enables tracking of vaccination status, disease history, and productivity. Recording clinical observations, treatments administered, and outcomes supports veterinary care and informs future management decisions. Documenting movement of animals onto and off the property demonstrates compliance with regulatory requirements. Tracking weather conditions, midge activity observations, and seasonal patterns helps predict risk periods. Mortality records including necropsy findings contribute to understanding disease impact and identifying problems early. Electronic record systems facilitate rapid analysis and reporting when needed.

Economic considerations significantly influence bluetongue management decisions in commercial sheep operations. Vaccination costs must be weighed against disease risk and potential losses, with cost-benefit analysis informing optimal protection levels. Investment in vector control infrastructure, including housing modifications and screening, pays dividends through reduced disease losses and treatment costs. Insurance options for disease losses may be available in some regions and can help manage financial risk. Planning marketing schedules around disease risk periods and potential movement restrictions avoids disruptions. Budgeting for enhanced monitoring and veterinary services during high-risk periods ensures resources are available when needed. Maintaining relationships with veterinarians, extension agents, and animal health authorities provides access to expertise and support for economically sound disease management.

High-risk breeds for severe bluetongue disease include European fine-wool breeds that have evolved in bluetongue-free regions and lack the genetic resistance present in indigenous breeds from endemic areas. Merino and Merino-derived breeds are particularly susceptible to severe clinical disease and high mortality rates during outbreaks. British breeds including Suffolk, Hampshire, and Southdown tend to show more severe clinical signs than breeds from regions where bluetongue is endemic. Dorset, Texel, and other improved meat breeds from northern Europe similarly lack evolutionary exposure to the virus and are at increased risk. In contrast, indigenous African breeds such as West African Dwarf sheep and fat-tailed breeds from the Middle East and Central Asia often show subclinical infection or mild disease, reflecting generations of natural selection in bluetongue-endemic environments.

Production type considerations affect both disease susceptibility and management priorities during bluetongue outbreaks. High-producing dairy sheep breeds face compounded challenges, as the metabolic stress of lactation may increase susceptibility to severe disease while illness dramatically reduces milk production. Intensive production systems with high stocking densities may facilitate rapid transmission through local midge populations. Rams used for breeding require particular attention, as testicular damage during infection can cause temporary or permanent infertility. Show and exhibition animals face unique risks due to transport and congregation at events during vector-active periods. Organic and pasture-based operations face greater challenges in vector control due to limitations on chemical insecticide use.

Genetic selection and testing offer long-term approaches to reducing bluetongue impact in sheep flocks. Research has identified genetic markers associated with reduced susceptibility to severe disease, and selective breeding programs could potentially increase flock resistance over time. However, genetic improvement for disease resistance must be balanced against other production traits. Genomic testing may eventually enable identification of more resistant breeding stock. Until genetic tools are widely available, breed selection based on historical performance in endemic regions can inform flock composition decisions. Crossbreeding programs incorporating resistant indigenous genetics into commercial production genetics offer another avenue for reducing susceptibility. Maintaining genetic diversity within flocks provides a buffer against diseases like bluetongue that may differentially affect specific genetic lines.

Commonly co-occurring conditions with bluetongue include secondary bacterial infections that develop as opportunistic pathogens exploit virus-damaged tissues and immunosuppression. Aspiration pneumonia frequently complicates severe bluetongue cases when pharyngeal swelling and weakness lead to inhalation of saliva or regurgitated rumen contents. Secondary bacterial pneumonia can develop independently as damaged respiratory mucosa allows bacterial invasion. Oral infections with bacteria including Fusobacterium necrophorum may cause necrotic stomatitis in conjunction with viral lesions. Foot infections secondary to coronitis can extend to deeper structures, causing septic arthritis or chronic lameness. Myositis and muscle necrosis may become secondarily infected, leading to abscessation.

Conditions with similar symptoms that must be differentiated from bluetongue include several other significant ruminant diseases. Foot-and-mouth disease presents with vesicular lesions of the mouth and feet that can closely resemble bluetongue and must be ruled out immediately due to its catastrophic implications. Peste des petits ruminants in goats causes fever, oral lesions, and respiratory signs similar to bluetongue. Contagious ecthyma produces proliferative crusty lesions around the mouth and can occur concurrently with bluetongue. Photosensitization causes facial edema and oral erosions but is associated with liver damage or ingestion of photodynamic plants. Foot rot causes lameness but without systemic signs. Sheep pox produces skin lesions that may be confused with bluetongue skin manifestations.

Complications and sequelae of bluetongue extend beyond the acute illness to affect long-term health and productivity. Chronic lameness due to hoof deformities from coronitis can persist indefinitely and reduce productive value. Wool breaks from febrile illness result in reduced fleece quality and value at subsequent shearings. Permanent muscle damage causes chronic stiffness or weakness in some survivors. Reproductive complications include extended infertility in rams, pregnancy losses, and congenital abnormalities in lambs infected in utero including cerebellar hypoplasia, hydranencephaly, and limb deformities. Poor doers that fail to regain body condition despite recovery from acute illness may have suffered permanent organ damage. Recovered animals remain susceptible to other BTV serotypes and can develop disease if exposed to novel strains.