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Viral numbers

  • Veterinary

By Emanuela Valle, veterinary surgeon.

The recent Equine Herpes Virusepidemic has reminded all horse owners of the importance of vaccinations. Regular vaccination is a fundamental element of the horse’s care and wellbeing.

Some vaccinations are not actually optional anyway, but rather an essential factor in horse care. This is why it is necessary to arrange routine veterinary appointments for our equine friends, to carry out regular health checks and advise when medication is required.

For horses, just as for humans, there are some very dangerous diseases against which vaccination is important, regardless of whether the animal ever leaves his home premises or not. 

Below list anumerical assessment of the most serious diseases requiring vaccination in Italy. Others may be recommended by your vet when appropriate. 


50-80% deaths from tetanus. These percentages are confirmed by several studies and testify to the fact that tetanus is an extremely dangerous illness for the horse, as it can lead to death. Horses (and also sheep and humans) are very susceptible to infections caused by Clostridium tetani: this bacterium is very common in areas inhabited by horses, and is even present in their intestines. It can contaminate wounds and cuts, producing a neurotoxin, which leads to very serious neurological symptoms such as muscle rigidity which causes the horse to adopt a strange posture. It causes lockjaw, which is when the jaw muscles seize up and prevent the mouth from opening. The affected horse can therefore neither move nor eat, and his face assumes a typical expression in which the third eyelid covers part of the eyes. Unfortunately the prognosis here is highly unpromising.


8 countries on the European continent have to date noted cases of EHV, Equine Herpes Virus: Italy, Spain, France, Switzerland, Slovakia, Belgium, Germany and the United Kingdom. You can see the updated map here https://www.izslt.it/cerme. On the same website you can see that two Italian regions registered cases up to March 19th

As it is a global issue, outbreaks of EHV are logged regularly throughout the world; the most commonly identified strains are EHV1 and EHV4. This disease is commonly termed equine influenza, or equine flu. It affects the respiratory system and can cause spontaneous abortion in pregnant mares, these occurring usually in the third term of the pregnancy.  The neurological form of the virus is caused by the EHV1 strain, and symptoms can be extremely serious, causing paralysis and even death. Unfortunately these cases of the neurological strain of the virus appear to be on the increase: the Istituto Zooprofilattico Sperimentale del Lazio e della Toscana warns “At the present rate, the spread and pathogenicity (disease-producing capacity) of EHV-1 responsible for the current outbreak, are both higher than hitherto has been the norm”

It is important to remember that the Herpes viruses are insidious because of the phenomenon of a time lag, which means they can lie dormant and undetected in the body, until sparked into activity by a stressful event. Horses affected by this time-lag strain remain carriers of it. 

In its respiratory forms of the virus, contagion happens via aerosol, such as coughs and sneezes.  Direct and close contact (around 10 metres, and certainly less than 50 metres) cause airborne transmission, and indirect contact occurs through shared use of buckets and other equipment. 

(horse affected by equine flu - photo La Clubhouse)


11 outbreaks of WND (West Nile Disease) among equids were reported in the most recent update of the summer-autumn 2020 period (Bollettino No.16, 5/11/2020) and were diagnosed in the regions of Lombardy, Emilia Romagna, Piedmont and Sardinia. This demonstrates that this virus is still present in Italy, and therefore requires our careful attention. This virus typically infects wild birds, their natural source, and is transmitted via a mosquito of the Culex genus;  but one of these mosquito bites can also cause the disease in a horse or a human. However, the horse or the human will be a ‘blind host’, in that even though they have the disease, they cannot transmit it to others. Many infections are asymptomatic, but there is a real and concrete risk of developing serious symptoms such as high fever and weakness, or neurological symptoms such as lack of limb coordination, difficulty moving, or muscle tremors. Unfortunately there is a rather high mortality rate, i.e. up to 40% of cases. 


3 days is the average incubation time for equine flu, showing that it is a highly contagious disease. Outbreaks of this disease occur world-wide and the symptoms are similar to those of human influenza: a cough, runny nose, swelling of the lymph nodes in the armpit, as well as the retro-pharyngeal nodes (in the upper throat). Temperature is often very high, and accompanied by depression, loss of appetite, tiredness and muscle weakness.  Secondary infections are common, which aggravate the condition, and the patient can suffer these, together with severe weakness, for several weeks.  


Need to know:

  • Vaccinations are a crucial element of horse management. 
  • All equids must be vaccinated, following a programme and medications prescribed by the vet. 
  • Regular vaccination also helps to protect other equines living close by. 



  • Ribeiro et al., 2018. Tetanus in horses: An overview of 70 cases. Pesquisa Veterinária Brasileira 38(2):285 Link
  • Comunicato stampa IZSLT 8 marzo 2021: segnalazione di un focolaio epidemico di rinopolmonite da EHV-1 in Europa Link
  • Tamba et al.,2009. L’encefalite equina da virus West Nile. Una zoonosi “riemergente”nel bacino del mediterraneo. Praxix Veterinaria vol.XXX - n.2 1-9 Link
  • Influenza equina (IE)
  • Herpesvirus equini 1 e 4