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ELISA
Equine Herpesvirus EHV 1 AND EHV 4 Antibody Detection (EHV1 + EHV4)(Serology)
In horses, donkeys, mules and zebras, infections with EHV-1 as well as with EHV-4 are caused by droplet infection or direct contact. The severity of the clinical symptoms depends on the age and immune status of the infected animal. Particularly infections with EHV-1 are able to spread beyond the respiratory mucosa and cause severe manifestations of the disease: abortions, perinatal foal death, neurological diseases.
In case of foals infected with EHV-4, morbidity rates of up to 100% are possible, especially during the weaning period. More than 80% of the isolates come from animals with rhinopneumonitis. Once horses are infected with herpesviruses, they remain carriers of the virus throughout their lives, and the virus can be reactivated endogenously under unfavourable conditions (stress, etc.). Lymph organs, the leukocyte fraction and trigeminal ganglion cells are the main latency organs. If the vaccinated horses are also taken into account, seroprevalence in the horse population is high.
In recent years, EHV-1-associated neurological diseases, for which a 'neurotropic' strain of EHV-1 is held responsible, have been reported with increasing frequency and severity of the clinical disease. This much-feared clinical picture is referred to as EHM (equine herpesvirus myeloencephalopathy).
Two different variants of EHV-1 have been described in horses (DNApol D752 vs. DNApol N752). Each is associated with a different level of neuropathogenicity. The D752 variant is associated with most outbreaks of neurological disease and is considered neuropathogenic. However, only a fraction of the horses infected with this virus will develop neurological signs. The N752 variant is most commonly isolated in conjunction with abortions, but also in a smaller number of neurological diseases. The differentiation is particularly interesting from an epidemiological point of view.
Infections with EHV1 and EHV4 primarily cause diseases of the respiratory tract. The relevance of clinical symptoms is depending on age and immune status of the infected animal. Especially infections with EHV1 can spread beyond the respiratory mucosa and cause severe manifestations of the disease: abortions, perinatal death of foals, neurologic disease. Once infected, horses stay carrier of virus lifelong. The virus can be activated endogenously by adverse conditions (stress etc.). Latent organs are the lymphatic tissues and the leucocyte fraction. Including vaccinated horses there is a high sero-prevalence within population. In recent years there are an increasing number of reports about an extremely severe EHV-1 associated form of neurologic disease, which is caused by an neurotropic EHV-1 strain with aggressive replication.
Testing of paired serum at an interval of 10 – 14 days. A clear increase in titre would prove an acute EHV infection. However, in acute cases we recommend direct pathogen detection by PCR (from a nasal swab without medium plus EB) to verify excretion. Vaccine titres cannot be distinguished from infection titres.
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