Vaccination of horses

Protect horses thoroughly in good time - also from West Nile virus 

West Nile virus: back in Germany since September 2018

It is a serious warning for all horse owners: the West Nile virus has appeared in Germany in 2018. At the beginning of September, it was diagnosed for the first time in birds in eastern Germany; in the same month, a horse in Brandenburg died from the pathogen, which the Friedrich Loeffler Institute was able to clearly identify as West Nile virus (WNV). The tricky thing about the virus is that the majority of affected horses do not show any symptoms. However, after an incubation period of three to fifteen days, acute fever attacks and neurological disorders can set in, as is the case with 8% of infected horses; this form of progression is associated with a mortality rate of 30 to 50%. "Surviving horses often show permanent damage," says StIKoVet[i], which now recommends that horse owners vaccinate their horses against West Nile virus.

Vaccination saves horses' lives 

In general and for all important diseases, the following applies: Every unvaccinated horse increases the risk of infection, which can often affect the entire herd. The StIKo Vet therefore emphasises: "Vaccination is the most important measure to prevent infectious diseases and their spread." This concerns senior horses as well as "youngsters", leisure partners as well as show horses - and above all it concerns complete herds. The StIKo Vet divides vaccinations into two components: core and non-core. Core components are those against which a horse must be protected at all times. Non-core components are no less important, but are not significant for every horse at all times.

Core vaccinations: What is compulsory and when?

There are two vaccinations for horses that are compulsory without exception: vaccination against tetanus ("lockjaw") and influenza ("horse flu"). Tetanus is a bacterial infection caused by spore-formers that are found in the soil worldwide and to which horses are particularly sensitive. When infected, a nerve toxin forms in the body that damages the muscle-controlling nerve cells: possible (and frightening) symptoms of an outbreak are uncontrollable cramping of the muscles, sawbuck position, lockjaw and jumpiness. Tetanus carries a very poor prognosis for affected animals. After the basic vaccination from the sixth month of life, the repeat vaccinations must be repeated (depending on the vaccine manufacturer or on the antibody level) at intervals of one to three years in order to maintain the vaccination protection.

"Equine influenza" is a viral disease caused by equine influenza viruses, which is highly contagious via droplet infection and is therefore spread particularly quickly and easily through tournaments and trade. The incubation period is very fast (24 to 48 hours). Symptoms include fever and loss of appetite or affect the respiratory system, e.g. with a strong cough and nasal discharge. Equine influenza usually lasts two to three weeks and may cause long-term damage as well as serious complications due to secondary bacterial infections (e.g. in the lungs). Unprotected herds are thus a major source of danger for true influenza epidemics, which, for example, abruptly bring equestrian activities to a standstill and cause high economic losses. It is problematic that influenza viruses change constantly - an adjustment of the vaccination protection is therefore appropriate. The basic immunisation with three vaccinations is carried out from the sixth month of life and repeat vaccinations are recommended every six to twelve months. Horses that participate in competitions should be vaccinated every six months according to FN guidelines.

The so-called core vaccinations, but without compulsory vaccination, also include vaccination against the herpes virus, which can be responsible for abortions, respiratory diseases or severe neurological damage. In horses all over the world, herpes viruses occur with different disease manifestations. Particularly noteworthy among these are the herpesvirus EHV (Equine Herpesvirus) 1, which is responsible for viral abortion, and EHV 4, which occurs in respiratory infections, primarily in weanling foals and young horses. And even if an infected horse does not become acutely ill, it remains a virus carrier and excretor over a long period of time and thus a source of infection, especially if stress or immune deficiency activate the virus. Depending on the vaccine, the basic immunisation against herpes takes place from the sixth month of life, the repeat vaccination must take place every six months.

Broodmares should receive vaccination protection against all three core vaccinations; this not only protects the health of the mother mare, but also that of the foal, which picks up vital antibodies with its first beest milk.

Vaccine damage vs. vaccine benefit

Of course, vaccine critics warn against vaccine damage and believe that the harm of a vaccination outweighs the possible benefit or that risks are even trivialised. There are excited reports about vaccination complications, but often without any technical background or evidence. If all the basics are taken into account - if the horse is healthy when vaccinated, if hygiene is observed, if the vaccines are used correctly - it is irresponsible from a veterinary and protective point of view not to vaccinate one's horses! It is only through the consistent use of vaccines that infectious diseases, also in humans, have become controllable. Just because fatal epidemics are no longer likely due to the introduction of vaccinations and some diseases (such as polio and diphtheria) have even died out due to vaccination possibilities, this is no reason to reduce the willingness to vaccinate again. Vaccination reactions of modern vaccines are really rare and out of all proportion to the harm caused by serious infectious diseases.

Non-core vaccinations

Protection against so-called non-core components is only necessary for horses in special husbandry conditions or where there is an increased risk of infection. These include, for example, vaccination against druse, equine rotavirus, cutaneous fungus, Lyme disease and, in certain regions of Germany, rabies; and also vaccination against West Nile virus, which is a notifiable animal disease. For all vaccinations that are additionally carried out, the veterinarian is available to advise the horse owner in order to consider the vaccination goal and effectiveness together. If you are concerned or would like to spare your horse the "burden" of vaccinations, you can have an up-to-date vaccination status determined instead of vaccinating routinely.

West Nile virus on the rise

First discovered in 1937 in humans in the West Nile district of Uganda, West Nile virus is now found worldwide. It has been firmly established in the Mediterranean region since the 1960s, and WNV infections occur regularly, especially from southern and south-eastern European countries. In 1999, when the first cases appeared in North America, WNV attracted international attention: the virus spread rapidly from New York - brought in from Tel Aviv - and quickly spread throughout the United States and Canada. Since then, true epidemics with fatalities have been recorded time and again.

The transmission route is exclusively via virus-carrying, blood-sucking mosquito species (especially the Culex mosquito) from infected migratory birds as reservoir hosts to mammals. Humans and horses are susceptible, but they are so-called "dead end hosts". In an infected dead end host, the viruses no longer reproduce to such an extent that it could be sufficient to infect other mosquitoes when they suck blood. The cycle therefore ends in the false host.

Many infected horses remain asymptomatic. However, the West Nile virus can lead to flu-like symptoms up to the most severe clinical courses with inflammations of the brain or meninges, which manifest themselves in clear disorders such as stumbling, hind leg paralysis up to the horses being immobilised. Older horses in particular are susceptible to such a severe outbreak of West Nile fever. There is no specific therapy against infection; only the symptoms can be treated appropriately.

Experience from neighbouring European countries and the USA has taught that it can be assumed that West Nile virus will continue to spread in Germany in the coming years. It is present in the entire bird population in Europe and also in Culex mosquitoes throughout Europe, can overwinter in the mosquitoes and thus lead to infections of birds, horses and also humans in the coming years, especially during the peak mosquito season from July to October. The high temperatures of 2018 have greatly favoured virus replication in mosquitoes in our latitudes.

New: Vaccination recommendation against West Nile virus

The StIKoVet now recommends vaccination against WNV according to the following principles: In already affected areas, vaccination should be carried out from the end of March/beginning of April 2019 at the latest, so that basic immunisation is completed before the next mosquito season, i.e. before the end of May 2019. Basic immunisation against West Nile virus requires two vaccinations at intervals of four weeks from a foal age of five months. In the medium term, the aim is to vaccinate horses nationwide. The manufacturers are prepared for this and there is sufficient vaccine available for these plans. Of three approved vaccines, two are recommended by the StIKoVet (more detailed information can be found in the statement).

Optimal vaccination management in consultation with the veterinarian

A show horse is inevitably under a higher infection pressure than, for example, a horse in an open stable that only comes into contact with a few "colleagues" throughout its life. But in principle, the best protection for each individual horse is a complete and regular vaccination of all horses. Only then are fewer viruses excreted, the infection pressure reduced and thus the probability of falling ill at all - a healthy cycle for the better protection of an entire herd. It is certain that vaccinations help to contain (not only fatal) diseases or even prevent them completely; vaccination is therefore an important way of health prophylaxis, which should not be carried out negligently, but reliably. Long-lasting and resilient immunity is also possible against the West Nile virus. An appropriate vaccination management can and should always be set up in consultation with the veterinarian and carried out sustainably with a view to a healthy horse life.

[1] Statement on WNV immunisation, Permanent Vaccination Commission Veterinary at the Friedrich-Löffler-Institute, as of 22.10.2018.

Many thanks to Bianca Flemm for providing this really great and informative guest post.