LA PIEDAD-MICHOACAN VIRUS (LPMV) / BLUE EYE DISEASE
LEVELS: Highly unlikely: No controls necessary; Highly unlikely: No evidence of non-foodborne zoonotic transmission; Highly effective: Routine on-farm biosecurity measures are effective in preventing farm-to-farm transmission; Moderate: Clinical signs not unique but existing tests available at local/regional laboratory(s); Substantial: Unsustainable acute or chronic losses related to severe clinical signs in a high prevalence of animals; Negligible: Little or no market disruption when disease occurs on one or more farms; Minimal risk: Agent inherently unlikely to develop clinically important resistance to antibacterial or antiviral treatments; Minimal risk: Antibacterial or antiviral treatments rarely occur, or are typically limited to short-course individual animal therapy; No availability: Effective treatments not currently available in the US (or have not been developed); Available but uncertain efficacy: Commercial or autogenous vaccines exist in the US but protection may be inconsistent; Highly likely: Can be eradicated using existing tools and knowledge
OVERVIEW
La Piedad-Michoacan virus (LPMV), also known as blue eye paramyxovirus or porcine rubulavirus, is a paramyxovirus in the genus Orthorubulavirus that causes blue eye disease (BED) in pigs. First recognized in 1980 during an outbreak of encephalitis and corneal opacity in piglets at a commercial farm in La Piedad, Michoacán, Mexico, LPMV has remained geographically restricted to central Mexico where it is endemic with seroprevalence of 9-23%. The disease is characterized by central nervous system disturbance in young piglets (with mortality up to 90% in affected litters), reproductive failure in sows, orchitis and epididymitis with permanent infertility in boars, and the characteristic corneal opacity ("blue eye") that gives the disease its name. Distinct viral strains circulate with varying pathogenicity—highly neuropathogenic strains (PAC8, PAC9) cause neurological outbreaks while less neuropathogenic strains (PAC2, PAC3) are associated primarily with respiratory or reproductive disorders. LPMV has never been reported outside of Mexico despite decades of endemic circulation. Two commercial inactivated vaccines are available in Mexico for use in breeding animals and piglets. The virus poses no public health significance and is not infectious for humans.
FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Highly unlikely: No controls necessary
LPMV does not have any public health significance. The chapter explicitly states the virus "is not infectious for humans." No foodborne transmission has been documented, and there is no evidence that consumption of pork products from LPMV-infected pigs poses any risk to human health. The virus is restricted to pigs as the only species known to be clinically affected following natural exposure.
NON-FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Highly unlikely: No evidence of non-foodborne zoonotic transmission
LPMV is not infectious for humans through any route. Despite decades of endemic circulation in Mexican swine populations with extensive occupational exposure of farm workers, veterinarians, and slaughterhouse personnel, no human infections have been documented. Experimental studies confirm that while the virus can affect mice, rats, and chick embryos, it does not cause clinical disease in rabbits, dogs, or cats (though rabbits and cats can seroconvert). The virus appears to have strict host specificity for clinical disease in pigs.
EFFECTIVENESS OF ON-FARM BIOSECURITY IN PREVENTING FARM-TO-FARM TRANSMISSION
Level: Highly effective: Routine on-farm biosecurity measures are effective in preventing farm-to-farm transmission
LPMV is transmitted primarily by nose-to-nose contact between infected and susceptible pigs. The virus is disseminated mainly in nasal secretions and urine, with transmission through semen also documented—virus can be recovered from semen for 5-45 days post-infection and from reproductive tissues for up to 142 days. Fomites (people, vehicles) may contribute to spread, and fruit bats have been suggested as potential vectors given the close genetic relationship between LPMV and Mapuera virus from fruit bats. Importantly, the disease is self-limiting in closed herds—sentinel pigs introduced 6-12 months after an outbreak do not seroconvert, and seropositive animals moved to seronegative herds do not spread the virus. This indicates relatively poor environmental survival and limited transmission efficiency compared to highly contagious pathogens. Standard biosecurity measures including controlled animal movement, quarantine of replacements, and serological/PCR testing can effectively prevent introduction. However, the prolonged shedding period (especially from boars) and potential for subclinical carriers create some bypass risk.
DIFFICULTY OF DETECTING AND CONFIRMING INFECTION
Level: Moderate: Clinical signs not unique but existing tests available at local/regional laboratory(s)
Clinical presentation is distinctive when the full syndrome occurs: encephalitis in piglets, corneal opacity across age groups, and orchitis/epididymitis in boars. However, clinical signs vary with pig age, virus strain, and immune status, requiring laboratory confirmation. Corneal opacity alone is not pathognomonic as it can occur without other signs and resolves spontaneously. Histopathology provides strong support—nonsuppurative encephalomyelitis affecting gray matter, intracytoplasmic inclusion bodies in neurons, and characteristic ocular and testicular lesions. Laboratory diagnosis uses hemagglutination inhibition (HI) with properly treated chicken erythrocytes, virus neutralization, immunofluorescence, or ELISA for serology; paired samples 15 days apart are recommended. Virus detection uses PCR (qRT-PCR targeting phosphoprotein or nucleoprotein genes is most sensitive), virus isolation in PK-15 cells (produces syncytia), or direct immunofluorescence on tissues. Olfactory bulb, midbrain, lung, and tonsil are preferred specimens. Differential diagnosis must consider pseudorabies (Aujeszky's disease) and PRRSV, though only LPMV produces corneal opacity combined with orchitis/epididymitis.
FINANCIAL IMPACT ON FARM'S COST OF PRODUCTION
Level: Substantial: Unsustainable acute or chronic losses related to severe clinical signs in a high prevalence of animals
Initial LPMV outbreaks in naive herds cause devastating losses, particularly in farrowing houses. Approximately 20% of litters farrowed during an outbreak are affected. In affected litters, piglet morbidity is 20-50% and mortality in affected piglets approaches 90%. Piglets 2-15 days old are most susceptible, often dying within 48 hours of clinical sign onset. Mortality in the first cases is rapid; later cases may survive 4-6 days. The outbreak phase typically lasts 2-9 weeks depending on management system. Reproductive losses are substantial: increased returns to estrus, reduced farrowing rate, increased wean-to-service interval, elevated stillbirths and mummified fetuses, and reduced pigs born alive. Reproductive failure may persist for 2-11 months (usually 4 months). Approximately 30% of boars in infected herds show temporary or permanent infertility with decreased sperm concentration, increased abnormalities, decreased motility and viability, and in severe cases azoospermia. Testicular atrophy and loss of libido occur in boars with severe lesions. In pigs older than 30 days, mortality is generally low (<2% affected) unless concurrent infections are present—outbreaks with 20% mortality have occurred in 15-45 kg pigs on poorly managed farms.
EFFECT ON DOMESTIC OR EXPORT MARKETS
Level: Negligible: Little or no market disruption when disease occurs on one or more farms
LPMV is not an OIE/WOAH-listed disease and does not trigger international trade restrictions. The virus has remained geographically confined to Mexico since its discovery in 1980, never spreading to other countries despite decades of endemic circulation. This geographic restriction limits trade implications—importing countries may have specific requirements for Mexican pork, but LPMV does not affect trade between other nations. Within Mexico, LPMV is an endemic production disease with economic impact absorbed into regional production costs rather than causing acute market disruption. The absence of zoonotic risk eliminates food safety concerns that might otherwise affect consumer confidence or market access.
PATHOGEN'S ABILITY TO DEVELOP AND SPREAD RESISTANCE
Level: Minimal risk: Agent inherently unlikely to develop clinically important resistance to antibacterial or antiviral treatments
LPMV is a viral pathogen (negative-sense RNA virus, family Paramyxoviridae) that does not carry, acquire, or transmit antimicrobial resistance genes. The virus poses no AMR concerns. Antigenic variation does occur—genetically and antigenically distinct strains circulate simultaneously in Mexican swine populations, with at least three genetic variants identified and evidence of ongoing viral evolution. This antigenic diversity affects vaccine efficacy but represents viral evolution rather than antimicrobial resistance.
AMR DEVELOPMENT DRIVEN BY DISEASE MANAGEMENT
Level: Minimal risk: Antibacterial or antiviral treatments rarely occur, or are typically limited to short-course individual animal therapy
No antiviral treatments exist for LPMV. Disease management relies on vaccination and biosecurity rather than antimicrobial therapy. Antimicrobials may be used to treat and prevent secondary bacterial infections in affected herds, representing a minor, episodic use pattern. The primary management approach is prevention through vaccination of breeding stock, not treatment of clinical cases. This does not create significant antimicrobial selection pressure.
AVAILABILITY OF EFFECTIVE TREATMENT OPTIONS
Level: No availability: Effective treatments not currently available in the US (or have not been developed)
No specific antiviral treatments exist for LPMV infection. Piglets with severe central nervous signs generally die regardless of intervention. Pigs with corneal opacity frequently recover spontaneously without treatment. Antimicrobial therapy addresses secondary bacterial infections but does not alter the course of LPMV disease. Management is entirely preventive (vaccination, biosecurity) or involves elimination of clinically affected animals. Supportive care has limited value in severe cases.
AVAILABILITY OF EFFECTIVE VACCINES OR BACTERINS
Level: Available but uncertain efficacy: Commercial or autogenous vaccines exist in the US but protection may be inconsistent
Two commercial inactivated virus vaccines are available in Mexico for use in pregnant sows, gilts, boars, and piglets. Primary vaccination protects breeding animals, with twice-yearly booster vaccinations recommended for sows. Pre-farrow booster vaccination provides higher and longer-lasting maternal antibody protection for piglets. However, significant limitations exist: (1) Antigenic diversity among circulating LPMV strains means monovalent vaccines may not completely protect against all subtypes—some data indicate incomplete cross-protection between antigenic variants; (2) An experimental recombinant HN protein vaccine showed promise in protecting suckling piglets against lethal challenge via maternal immunity, but this is not yet commercially available; (3) Corneal opacity continues to appear in vaccinated herds, suggesting incomplete protection against all disease manifestations. Naturally infected pigs develop antibodies that usually persist for life, indicating strong natural immunity that vaccines attempt to replicate.
FEASIBILITY OF ERADICATING THE DISEASE FROM THE US
Level: Highly likely: Can be eradicated using existing tools and knowledge
LPMV has never been detected in the United States—the virus remains geographically restricted to central Mexico since its discovery in 1980. The relevant question is whether LPMV could be eradicated if introduced, and whether it can be kept out. Evidence supports feasibility on both counts: (1) The disease is self-limiting in closed herds—virus disappears naturally within 6-12 months without reintroduction of susceptible animals; (2) Environmental survival is poor—sentinel pigs placed in contaminated areas 3+ days after infected pigs were removed did not become infected (based on Menangle virus data with similar paramyxovirus characteristics); (3) Elimination from infected herds has been accomplished through management practices: herd closure, cleaning and disinfection, all-in/all-out production, elimination of clinically affected animals, and serological monitoring with PCR testing; (4) Serological screening and PCR testing of replacement animals can prevent introduction. The absence of wildlife reservoirs in the US (unlike the fruit bat reservoir suggested in Mexico) would further facilitate eradication if introduction occurred. Prevention through import controls and biosecurity is the primary strategy.