Info maladies vectorielles

New equine diseases in training centers due to climate change



Worldwide when there are new disease outbreaks (human or horse), there seems to be a link between climate change and infectious disease risk.  Warmer environment and changing weather patterns influence many factors which encourage disease outbreaks, disease transmission and the emergence of new diseases. Warmer temperatures enable disease-carrying organisms to extend their ranges, have a longer breeding season and generally become more virulent.

Changes in the distribution and abundance of insects are likely to be amongst one the most important and immediate effects of climate change

Changes in average climate conditions are observed between regions. If the conditions in Western and Northern Europe were to be described, those would be shorter and less severe winters and wetter summers. These changes can have a direct impact on the survival and development of arthropod vectors, which today is well demonstrated among ticks but also in some mosquitoes.

 Impact of climate change on ticks

The tick (vector of babesiosis and borreliose) is present in 2/3 of the French territory. It is clearly spreading to the East, and north favoring milder winters. It has now been reported in Belgium, the Netherlands, where cases of babesiosis have become more and more common. It has also been observed in UK, Ireland, Sweden, Germany, Czech Republic, Slovakia, but also in the area of Moscow. These studies conducted in continental Europe have shown that shorter winters have a direct impact on the ecology of ticks. Thus, by observing the activity of the three main tick vectors encountered in Europe over relatively short periods of time, changes are noted. They are all associated with an increase in activity and thus in the risk of transmitting pathogenic agents

But we nevertheless must keep in mind that climate changes are currently still limited and that other human-induced factors co-exist: transport and travel can be considered as well.

Impact of climate change on mosquitoes and sand flies

Culicidae mosquitoes and biting midges are present all over Europe, including in the harshest climates (Scandinavia, Siberia). The risk of transmission of pathogenic agents by mosquitoes is not fully linked to their mere presence but also 1- to his Vector competence (ability to complete the cycle of the pathogenic agent within the vector, followed by trans-mission, and the meteorological conditions enabling the pathogen to complete its extrinsic cycle during the vector’s period of activity), 2- to the presence of the pathogen and 3- of at least one reservoir. Climate change may be reflected by an increase in the number of days of activity per year. Changes in the distribution and abundance of insects are likely to be amongst the most important and immediate effects of climate change.

Which new diseases ?

·        Piroplasmosis

-          Agent and transmission

Babesia caballi (more on the North) and Theilleria. equi (More on the South) are transmitted by ticks, which become infected when they ingest parasites in the blood of infected horses. Equine piroplasmosis can also be transmitted directly between animals by contaminated needles and syringes, or by blood transfusions. After recovery, horses may become carriers for long periods. Animals infected with B. caballi can remain carriers for up to 4 years, but might be able to clear the organism eventually. Equids infected with T. equi appear to remain permanently infected. Parasitemia is often absent in carriers, but can reoccur after immuno-suppression or strenuous exercise. T. equi can be passed to the foal in utero, and some foals can be healthy carriers. The incubation period for equine piroplasmosis is 12 to 19 days when it is caused by T. equi, and 10 to 30 days when it is caused by B. caballi.

-          Symptoms

The clinical signs of piroplasmosis are variable and often nonspecific. T. equi tends to cause more severe disease than B. caballi. More often, piroplasmosis presents as an acute infection, with fever, inappetence, malaise, labored or rapid respiration and congestion of the mucus membranes. The feces may be small and dry, but diarrhea has also been reported. Anemia, thrombocytopenia, jaundice, hemoglobinuria, sweating, petechial hemorrhages on the conjunctiva, a swollen abdomen, and posterior weakness or swaying may also be seen. Subacute cases have similar but less severe clinical signs. The fever may be intermittent, and animals may show weight loss, signs of mild colic, and mild edema of the distal limbs. The mucus membranes in subacute cases can be pink, pale pink or yellow, and they may have petechiae or ecchymoses. In chronic cases and they are probably very common, symptoms include mild inappetence, poor exercise tolerance, weight loss, transient fevers and an enlarged spleen (only palpable on rectal examination).

-          Détection

Equine piroplasmosis can be diagnosed by identification of the organisms in blood. T. equi can often be found in the blood in acute infections, but may be very difficult to find in carrier animals. B. caballi can sometimes be difficult to find even in acute disease. Because organisms can be difficult to detect in carriers, serology is often used for diagnosis. Polymerase chain reaction (PCR) assays to detect DNA are available in some laboratories.

-          Treatment

Imidocarb (Carbesia) at the dose of 2 to 4mg/kg IM can also cause side effects (colic, sweating, diarrhea …) Treatment can suppress clinical signs, but the currently available treatments are ineffective in clearing T. equi from carriers. Some studies have suggested that treatment could eliminate B. caballi from infected horses; however, in a recent study, this organism persisted in carriers after even high dose treatment with imidocarb. Although this drug could temporarily clear the parasites and resulted in transiently negative PCR results, B. caballi DNA was found in horses after the treatment ended. There is no vaccine for either B. caballi or T. equi.

 ·         Leptospirosis

-          Agent and transmission

Leptospirosis is a zoonotic (transmitted between animals and man) bacterial disease found worldwide that can affect any mammalian species, including humans, wildlife, rodents, livestock, and horses. The disease is caused by leptospires, which are motile (capable of moving) bacteria called spirochetes. Transmission occurs either through direct contact with an infected animal or through indirect contact with soil or water contaminated with urine from infected animals. The incubation period for leptospirosis in horses is one to three weeks.

-          Symptoms

Horses might experience a variety of clinical signs, including fever, loss of appetite, swelling of the eyes, light sensitivity, tearing, ocular discharge, eye cloudiness, and redness around the eye, as well as lethargy and mid- to late-term abortion. Adult horses have been known to develop jaundice and even die from kidney and/or liver failure.

Diagnosis of leptospirosis can often be overlooked because the clinical signs of the disease are common to other diseases. The primary conditions associated with leptospirosis in horses are chronic uveitis (moon blindness) and abortion. Chronic uveitis occurs when the leptospira bacteria enter the eye, creating an immune reaction. The clinical signs, as touched on above, are ocular inflammation, redness, cloudiness, tearing, light sensitivity, and strong muscle spasms closing the eyes. In severe cases, it can cause a calcification of the cornea, permanent blindness, atrophy (wasting away) of the eye, and glaucoma (an increase in intraocular pressure that can cause blindness). Leptospirosis-induced uveitis is often a painful condition for the horse, and it is s recommended that treatment begin as soon as possible.

Detection: Only laboratory tests of blood or urine can confirm if leptospirosis is present. It needs 2 different serological tests with the second samples showing a huge increase. More than 80 % of horses show positive serology. PCR is very promising.

-          Treatment

Drugs of choice are antibiotics (oxytetracycline, streptomycin, or penicillin). Although leptospirosis vaccines are available for dogs, cattle, and pigs, there are no approved vaccines for horses. Cattle vaccines have been tried in horses, but they are not proven to be effective and might produce negative side effects.

-          Prevention.

Prevention is the best option available at this point. Good management techniques at the farm can help reduce the risk of infection. Keep wildlife away from feed sources and do not allow standing water to accumulate (or at least do not allow the horses to drink from stagnant water sources). Standing water might be contaminated with leptospirosis-tainted urine from wildlife or cattle. Good desinfection programs will help reduce the risk of exposure to leptospirosis (and many other diseases).

·         Erhlichiose (Anaplasmose)

-          Agent and transmission

Equine Anaplasmosis (formerly Ehrlichiosis) is an infectious, non contagious, seasonal (late fall-to-spring) disease reflecting the activity of ticks (mostly Ixodes) The agent is named Anaplasma Phagocytophilum. Equine anaplasmosis has been seen with increasing frequency over the past few years in Southern countries. It affects horses of all ages, and the symptoms are usually appearing suddenly. Unlike many diseases, this condition causes less severe symptoms in horses that are less than three years old. Equine Anaplasmosis is transmitted by ticks of the Ixodes family known as deer ticks.

-          Symptoms

After being infected, horses will be normal for 10-20 days prior to developing clinical signs.

After clinical signs develop, the horse will deteriorate rapidly and often will show mild signs of colic and become jaundiced over the next 3-4 days. Most horses will survive after 10-14 days of severe illness, but some will develop subclinical infection.

-          Detection

Demonstration of the characteristic cytoplasmic inclusion bodies in a standard blood smear is diagnostic. However, inclusion bodies are difficult to see in the first day or two of fever. PCR can detect A phagocytophilum DNA in unclotted blood. An indirect fluorescent antibody test can detect rising antibody titers to A phagocytophilum.

-          Treatment

-          Oxytetracycline is extremely effective against A phagocytophilum, and tetracycline, 7 mg/kg, IV, sid for 8 days, has eliminated the infection. Penicillin, chloramphenicol, and streptomycin have no inhibitory effect. Horses with severe ataxia and oedema may benefit from short-term corticosteroid treatment (dexamethasone, 20 mg, sid for 2–3 days). Recovered horses are solidly immune for ≥2 yr and are not believed to be carriers. A recent finding suggests persistence of infection with some European strains, but further verification is required.

-          Prevention

Tick control measures are mandatory for control of disease. There is no vaccine.

·         Borreliosis: Lyme disease (LD) has been recognized for about 40-50 years. It is now the most commonly reported tick-borne illness in the US and Europe and is also found in Asia.

-          Agent and transmission

The Lyme spirochete (Borrelia burgdorferi) is a very mobile, corkscrew-shaped bacteria. In nature the cycle of life involves ticks of the Ixodes ricinus with other species used in other parts of the world. Contrary to popular belief, deer are far from the only host for the infected tick, as the different tick species prefer different hosts. Many small mammals are part of the host cycle, from the mouse and rats along with humans and dogs.

-          Symptoms

The most common things we see is lameness that is difficult to specifically identify. Many if not most of the horses show behavioral changes of various sorts, the most usual being lethargy, irritability or lack of interest in their surroundings. Arthritis attacks maybe periodic, and may wax and wane.. The wax and wane of the symptoms may have to do with the ability of the immune system to respond. Studies have shown that the primary factor leading to arthritic inflammation is the health of the immune system. Spirochete levels have been found to be irrelevant to the severity of the disease.

-          Detection

Detection is not easy because spirochetes have developed a high ability of adaptation. Serological test can be used and PCR. Up to 30% of horses can show positive serology with just a few showing any symptom.

The longer the spirochetes are in the body prior to treatment the more adjusted they become to the specific immune situation in that host. An example of how this works is that the spirochetes may stay in the synovial lining of a joint, then evade the immune system or the antibiotic by entering the synovial cells. Once the antibiotics are out of the system or the immune system is weakened, the spirochetes reenter the joint.

-          Treatment

 Even if  antibiotics can be used, the real key to treating Lyme is to help the immune system be as strong as possible, not just during the immediate treatment but over the long term. Due to Lyme’s ability to “recur” the immune system must be ready to go to work at a moment’s notice. Vitamine C, omega-3 fatty acids and some herbal extracts known for their immunestimulation effect can be used. There are no vaccines approved. As it is thought that the Lyme disease pathogen attacks the thyroid which in turn would lower immune system function. Iodine could be a relevant treatment

·         West Nile Virus

-          Agent

The West Nile virus (WNV) is an arbovirus transmitted by mosquitoes, belonging to the Flaviridae family (genus Flavivirus). It has been serologically classified in the Japanese encephalitis (JE) antigenic complex that includes 4 related viruses. The enzootic virus cycle involves transmission between avian hosts and mosquitoes, whereas humans and horses are considered dead-end hosts.

-          Symptoms

The most common signs of WNV infection in horses include

stumbling, uncoordination, weak limbs, partial paralysis, muscle twitching and in some cases, death. Fever has occurred in less than one fourth of all confirmed equine cases.

-          Detection

Serological test and PCR are used

-          Treatment

Nursing care and treatment is important to the recovery process and each animal is assessed according to it's age and health. With animals who are unable to rise, mortality rate is over 65%. Once the horse has demonstrated significant improvement, full recovery within 1 to 6 months can be expected. In 90% of the patients, residual weakness and ataxia appear to be the main problems. The long term effects of the disease in horses are not yet known.

There are 2 approved vaccines available on the European market.

 ·         African horse sickness

-          Agent:

The agent responsible for AHS is the African horse sickness virus (AHSV) is an orbivirus of the family Reoviridae. Nine different serotypes have been described. African horse sickness (AHS) is an infectious but non-contagious viral disease affecting all species of equidae and characterized by alterations in the respiratory and circulatory functions. The disease has both a seasonal (late summer/autumn) and a cyclical incidence with major epizootics during warm-phase events. This is closely related with the air-borne vector transmission of AHS that involved at least two species of mosquitos (Culicoides imicola and C. bolitinos). Recent emergence of Bluetongue virus, which belongs to the same family and genus and shares the same vector for propagation, increases the threat of emergence of the disease in EU countries


There is a a subclinical form with fever (40-40.5°C) and general malaise for 1-2 days, but for thoroughbreds,  the sub-acute or cardiac form (fever, swelling of the supra-orbital fossa, eyelids, facial tissues, neck, thorax, brisket and shoulders , then death usually within 1 week) or   acute respiratory form (fever, dyspnoea, spasmodic coughing, dilated nostrils with frothy fluid oozing out, redness of conjunctivae  and death from anoxia within 1 week) are frequent.

-          Detection

Serology and PCR

-          Treatment

There is no specific treatment for animals with AHS apart from rest and good husbandry. Complicating and secondary infections should be treated appropriately during recovery. No vaccine.

 ·         Leishmaniosis : is quite common in South and Central America, and some cases were related in Spain, Portugal and even south of Germany.

-          Agent: Leishmania infantum is the aetiological agent of leishmaniasis in Portugal, as in other southern European countries, where the dog is the domestic reservoir. Leishmaniosis is a disease caused by protozoan parasites of the genus Leishmania and transmitted through the bites of female phlebotomine sand flies. Considering recent developments in central Europe and particularly in Germany, the occurrence of foci endemic for L. infantum in these regions does not appear as unlikely as originally suspected, Phlebotomines, the potential vectors are obviously more widely distributed.

-          Symptoms: in all equine cases, Leishmaniosis was a skin-dwelling disease. A percentage of horses living in L. infantum endemic areas present specific humoral and cellular immune responses, suggesting that exposure to the parasite is common.

Cases of equine leishmaniosis are very rare however, indicating that the immune response mounted by horses is generally effective in preventing the development of disease.

-          Detection: Serological tests and histopathology of skin’s lesions.

-          Treatment: Fortunately, many equine leishmaniasis lesions regress spontaneously, but one more time, immune status is the key.

 ·         Equine infectious anemia (EIA):  a no contagious, infectious disease of horses and other Equidae . The most frequently encountered form of the disease is the inapparent, chronically infected carrier.

-          Agent.

It is caused by a virus classified in the Lentivirus genus, family Retroviridae. Under natural conditions, the most important mode of transmission of EIA is by the transfer of virus-infective blood by blood-feeding insects between horses in close proximity. 

Additionally, EIA can be readily transmitted iatrogenically through use of blood-contaminated syringes, needles, or surgical equipment. Once a horse is infected with EIAV, its blood remains infectious for the remainder of its life

-          Symptoms

Three different sets of symptoms occur: acute, chronic and the asymptomatic carrier. With acute infection the horse has fever, depression, and no appetite. The acute horse may be difficult to diagnose because the symptoms are very general and he will not be positive on the EIA test for a month and a half. Approximately one third of infected horses will die of the acute form within a month.

-          Detection

-          The famous Coggins test checks for Equine Infectious Anemia (EIA) antibodies in the horse's blood is a reliable tests for the detection of EIA in horses, except for animals in

the early stages of infection and foals of infected dams..  There are some different others testing procedures, including PCR when some confirmation is needed.

An horse will not become EIA positive unless he develops a serious, febrile illness after contact with a horse of unknown EIA status.

-          Treatment

No treatment and no vaccine.

 ·         Equine atypical myopathy: a frequently fatal condition affecting autumn and/or spring grazing horses.  The disease clinical signs seem to appear after occurrence of specific climatic conditions.

-          Agent

Hypoglycin, a toxin found in specific maple seeds, is, to day, considered as the Atypical Myopathy cause.

-          Symptoms

Acute Myopathy

-          Treatment: symptomatic treatment can be put in force. It will not directly attack the disease causal agent, but will fight and decrease its clinical effects. The treatment focuses on limiting horse suffering stopping muscular destruction, correcting electrolytic imbalances, restoring horse hydration status, supporting renal function and preventing complications.  



Prevention and management

 1) Reduce Ticks and horses’exposure: ticks live in moist and humid environments, particularly in or near wooded or grassy areas.

Ticks can be carried on mammals, wildlife, and birds, and ticks can also be carried into stables by dogs and cats and  on clothing. Prompt tick removal with tweezers is essential to reduce the transmission of pathogens casing TBD.

Manage your stables to reduce tick populations by:

Treating you dogs and cats.

Removing leaf litter, and weeds at the edge of the lawn or pasture.

Cleaning horses feet and pastern when they’re back from the tracks.

Discouraging formation of wildlife habitats on farms by feeding grain in containers and keeping grains in tightly sealed containers. 


2) Reduce mosquitoes and their breeding grounds and reduce your horses' exposure to mosquitoes

Eliminate any unnecessary standing water on your property (tires, wheelbarrows, old buckets, etc.).,make certain roof gutters drain properly and remove any standing water, especially from flat roofs.

Clean out waterers, birdbaths, plant saucers, etc., at least weekly.

Schedules pasture irrigation to minimize standing water.

Keep swimming pools clean and free of water on covers.

Stable horses inside during active mosquito feeding times (dawn/dusk).

Utilize fans, barrier cloths, screens, flysheets, repellent sprays (permethrin, DEET), and insecticide misting systems.

Turn off lights that attract mosquitoes at night, or use fluorescent lights, which do not attract mosquitoes.

Keep screens in stable windows if possible.


3) Keep you horse with a high immune status. There are three main factors that can compromise the delicately balanced immune system and these are stress, nutrition and age.

See this with your vet.


4) Create a quarantine barn for all yearlings, new horses, or horses coming back from rest, and check all these properly.

Have a history file for each and be careful with horses coming from southern areas or from another continent.

Do not neglect all blood test required for travels.



Epidemiosurveillance has become an important part of veterinary and trainers ‘job. In equine medicine, vectorborne diseases have recently become a serious concern in France and in Europe, following the re-emergence of all previously mentioned diseases.

My goal was not to scare you but to encourage you to be careful. All these diseases can have a devastating effect on the profitability of the stables.