Hemagglutinating encephalomyelitis virus (HEV) infection in piglets
Josepha DeLay, Catherine Templeton
Piglets were submitted for postmortem examination from a 1,200 gilt (P1) herd with increased piglet mortality. Piglets were clinically normal at and immediately following birth, but began to fade and waste at 5-14 days of age. No consistent gross lesions were identified in the piglets to explain the clinical signs. Histologically, nonsuppurative encephalitis was present in 5 of 7 piglets. Lesions were limited to brainstem and predominantly involved gray matter. Hemagglutinating encephalomyelitis virus (HEV) nucleic acid was identified by PCR from brain samples of all piglets, confirming the diagnosis of HEV encephalitis as the cause of mortality in this group.
HEV is a group 2 coronavirus, and is antigenically unrelated to other porcine coronaviruses such as TGEV, PEDV, and porcine respiratory coronavirus. Neurologic signs are typically seen in 4-7 day old piglets infected with HEV. In slightly older piglets (4 days-2 weeks), clinical signs of anorexia and vomiting are more common (‘vomiting and wasting disease’). Clinical disease is uncommon in older pigs.
Clinical signs in this group were limited to wasting / fading, with no evidence of vomiting or of overt neurologic deficits. Lack of sufficient anti-HEV antibody in colostrum from naïve gilts was a significant contributing factor to the outbreak in this herd. HEV infection in mixed-parity sow herds is usually self-limiting, with a 2-3 week clinical course, and infection wanes with stimulation of maternal immunity. In this P1 herd, the clinical problem lingered for 12-14 weeks but was eventually controlled using strict feedback protocols pre-breeding and at 5-7 weeks prior to farrowing to stimulate and boost gilt immunity and colostral antibody levels.
Histologic lesions support a diagnosis of HEV and the most diagnostically significant lesions are in brain, which highlights the importance of sampling brain in piglet mortality cases. Diagnosis of HEV infection is confirmed by PCR testing on nasal swabs from live pigs, or on samples from brain, tonsil, and stomach from dead animals.
Reprinted with permission, National Pork Board, USA.