1. Prvi klinični znak bolezni je ponavadi povišana telesna temperatura (nad 40 °C), ki jo spremljajo depresija, izguba apetita, hitro in težko dihanje ter izločki iz nosu in oči. Prašiči kažejo motnje v koordinaciji in se stiskajo skupaj. Pri svinjah je možno zvrgavanje v vseh fazah brejosti. Pri nekaterih prašičih se lahko pojavi bruhanje ali zaprtost, pri drugih pa krvava driska. Opazna so območja s polnokrvnostjo in krvavitvami v podkožju, še posebej na okončinah in ušesih. Pred smrtjo, ki nastopi en do sedem dni po nastanku kliničnih znakov, lahko nastopi koma. Stopnja obolevnosti in umrljivosti na gospodarstvu je lahko 100 %.
The development of high fever (more than 40 °C) is usually the first clinical sign of the disease, which is accompanied by depression, loss of appetite, rapid and difficult breathing, and discharges from the nose and eyes. Pigs show uncoordinated movements and huddle together. Sows may abort at all stages of pregnancy. Some pigs may show vomiting and constipation, while others may develop bloody diarrhoea. Congested or haemorrhagic subcutaneous areas become evident, in particular at the extremities and ears. A coma may develop before death, which occurs one to seven days after development of clinical signs. The morbidity and mortality rate within a holding may be 100 %.