Equine babesiasis: Epidemiology, control and chemotherapy

Equine piroplasmosis (EP) is a hemoprotozoan disease cased by Babesia caballi and B.equi. It is a tick-borne disease principally characterized by fever, anemia, and icterus. Clinically inapparent babesia carrier horses are important in the dissemination of the disease. Clinical episodes occur under two conditions:

1. When susceptible horse stock is moved into endemic EP areas; and

2. When inapparent babesia carriers are moved into non-endemic areas, then in the presence of certain ticks, babesiasis is spread to the susceptible horse population.

Ticks are the principal vectors of equine piroplasmosis, additionally contaminated hypodermic needles have shown to spread B. equi among horses. In endemic EP areas, it has been shown that babesiasis can cause unthriftyness in foals.Control of babesiasis is principally directed at tick control. Various tickacidal sprays or dips can be used to break the life cycle of ticks.Chemotherapy, using certain aromatic diamidines, is an adjunct to tick control and also facilitates the international relocation of horses and other equidae. Objectives of chemotherapy are divided as follows: 1. In EP endemic areas, the therapeutic aim is to subdue the babesia parasites and leave the host horse in a state of premunition; and 2. In non-endemic areas, complete clearance of babesia organisms from the animal is the objective. Several aromatic diamadine pharmaceuticals are available to veterinarians.During recent years, horses and other equidae have become important in international commerce. Such commerce has focused attention on the international spread of certain infectious and communicable animal disease; among these is equine piroplasmosis (EP).Piroplasmosis is an infectious hemoprotozoan disease characterized by fever, anemia, icterus, and other signs arising from hemolysis caused by Babesia caballi or Babesia equi. The disease has been reported in horses, mules, donkeys, and zebras.⁸     

Equine Piroplasmosis

Equine piroplasmosis (EP) is a tick-borne protozoal disease of horses, mules, donkeys, and zebras that is characterized by acute hemolytic anemia. The etiologic agents are two hemoprotozoan parasites, Theileria equi (Laveran, 1901) and Babesia caballi (Nutall and Strickland, 1910) that are transmitted primarily by ixodid ticks. Equine piroplasmosis is found globally where tick vectors are present and is endemic in tropical, subtropical, and some temperate regions. Horses infected with B. equi remain seropositive for life; horses infected with B. caballi are seropositive for several years to life. Economic losses associated with EP are significant and include the cost of treatment, especially in acutely infected horses; abortions; loss of performance; death; and restrictions in meeting international requirements related to exportation or participation in equestrian sporting events. Equine babesiosis–free countries limit the entrance of Babesia-seropositive horses into their countries. In the United States a few sporadic outbreaks have occurred in recent years but have been limited due to implementation of stringent control methods. The cELISA for both T. equi and B. caballi is currently the recommended test for international horse transport. Different therapies for control and sterilization of the parasites are discussed.     

Molecular characterisation of Theileria equi and risk factors associated with the occurrence of theileriosis in horses of Punjab (Pakistan)

Theileria equi (T. equi) is an obligate intra- and extra-erythrocytic parasite that causes equine theileriosis (ET) in equids. Equine theileriosis is considered a notifiable disease of global significance, a major constraint to the international movement of horses, and endemic in many countries. This disease may be difficult to diagnose, as it can produce variable and nonspecific clinical signs. A cross-sectional study was designed for the molecular characterisation of T. equi and to investigate the associated risk factors of ET accompanied by its consequences on haematological and sero-biochemical parameters. A convenience sampling of 500 blood samples were collected from ET suspect horses from January to December 2017. PCR was performed on all blood samples targeting the 18S rRNA gene of T. equi followed by sequencing; 9% animals tested positive with confirmed sequences. The isolates of this study showed high homology with Cuban, Russian and Brazilian isolates of T. equi (accession numbers KY111762.2 , MG551915.1 and KY952237.1 , respectively). Based on multivariate analysis, the principal risk factors consisted of absence of dogs on the premises and presence of tick infestation. The haemato-biochemical parameters showed a decrease in granulocytes and erythrocytes, and an increase in lymphocytes, monocytes, mean corpuscular volume, mean corpuscular haemoglobin, mean platelet volume, glucose, phosphorus and aspartate aminotransferase in positive horses. This is the first study which identified ET in Punjab (Pakistan) using molecular techniques and risk factors together with the haemato-biochemical variations in horses.     

Serological and molecular detection of Theileria equi in sport horses of northeastern Brazil

Theileriosis is a worldwide protozoal tick-borne disease caused by Theileria equi, which may produce a variety of clinical signs and turn infected horses into lifetime carriers. This study has aimed to perform a serological and molecular detection of T. equi and associated factors in sports horses from six areas of northeastern Brazil. In overall, 59.6% horses were positive by indirect immunofluorescence assay and 50.4% by polymerase chain reaction. No significant association was found when presence of ticks, age, gender, anemia or total plasma proteins was analyzed with seropositivity and molecular techniques. Although a significant association of infection was found in two cities. Thus, local risk factors other than presence of ticks, horse age, gender, anemia and total plasmatic proteins may dictate prevalence of T. equi infection in sports horses, even in highly endemic areas with no control of infection prior to horse competitions.     

Review of Equine Piroplasmosis

Equine piroplasmosis is caused by one of 2 erythrocytic parasites Babesia caballi or Theileria equi. Although the genus of the latter remains controversial, the most recent designation, Theileria, is utilized in this review. Shared pathogenesis includes tick‐borne transmission and erythrolysis leading to anemia as the primary clinical outcome. Although both parasites are able to persist indefinitely in their equid hosts, thus far, only B. caballi transmits across tick generations. Pathogenesis further diverges after transmission to equids in that B. caballi immediately infects erythrocytes, whereas T. equi infects peripheral blood mononuclear cells. The recent re‐emergence of T. equi in the United States has increased awareness of these tick‐borne pathogens, especially in terms of diagnosis and control. This review focuses in part on factors leading to the re‐emergence of infection and disease of these globally important pathogens.     

Status of Lipid Peroxidation, Antioxidants, and Oxidation Products of Nitric Oxide in Equine Babesiosis: Status of Antioxidant and Oxidant in Equine Babesiosis

Equine babesiosis is a tick-borne protozoal disease of horses caused by Theileria equi and Babesia caballi. The disease is endemic in most tropical and subtropical areas. The aim of this paper is to assess the antioxidant status, lipid peroxidation, and oxidation products of nitric oxide (NO) in horses and mules naturally infected with T. equi and B. caballi. East and Southeast Anatolian horses and mules living in rural region of the Eastern border of Turkey were used as the material for this study. These animals are used as pack animal (3–7 years of age). Infected animals were in acute or subacute infection period. In the current study, malondialdehyde (MDA), oxidation products of NO (nitrate and nitrite), serum glutathione (GSH), vitamin E, and retinol levels were analyzed in 58 equids (horse and mule) infected with T. equi and B. caballi as well as in 44 healthy equids. Compared with controls, the level of MDA and nitrate increased significantly (P < .01, P < .05, respectively), whereas GSH concentration and levels of vitamin E decreased significantly (P < .01). There was no significant change in the level of nitrite and retinol between two groups. The results of the current study suggest that in equids infected with T. equi and B. caballi, this alteration in the lipid peroxidation, oxidants, and antioxidants may be related to the host's defenses against parasitic infection and may play a central role in the pathologic conditions associated with babesiosis.     

Lessons learned from a strangles outbreak on a large Standardbred farm

Streptococcus equi subspecies (ssp.) equi infection (strangles) remains one of the most frequently diagnosed and costly infectious diseases of horses. Large breeding herds, where a disease outbreak competes for personnel and financial resources needed for foaling management, present a special challenge for equine practitioners. A 15‐month outbreak involving 62 clinical cases of strangles occurred on a large Standardbred breeding farm (average population of 1400 horses). Sixteen asymptomatic horses were found to be PCR (polymerase chain reaction)‐positive for S. equi ssp. equi. During the outbreak, serological samples from 48 clinically normal horses were found to be seropositive for S. equi ssp. equi, confirming herd‐wide exposure. After several clinical cases of strangles had been diagnosed, an intranasal S. equi ssp. equi vaccine was administered to clinically normal horses (n = 558) considered to be at risk of exposure. Strangles complications included 7 fatalities (none in vaccinated horses) and 6 cases of purpura haemorrhagica (4 in vaccinated horses). Midway through the outbreak, injectable, sustained release ceftiofur crystalline free acid (CCFA), given as an initial dose followed by a second dose 4 days later, was used exclusively for systemic antimicrobial treatment of clinically affected and PCR‐positive horses. This antimicrobial regimen coincided with a reduction in disease incidence and eventual resolution of the outbreak. Two horses with persistent guttural pouch infection were endoscopically confirmed as carrier horses. The herd history demonstrated that a strangles outbreak will often result in asymptomatic carrier horses and that identification and treatment of these horses are necessary to eliminate long‐term sources of infection. Ceftiofur crystalline free acid was found to be a suitable antimicrobial due to its activity against S. equi ssp. equi and the efficiencies associated with twice parenteral dosing during a 10‐day treatment period. Occurrence of purpura in 4 vaccinated horses suggests that vaccination should be reserved for healthy seronegative horses and avoided during an active outbreak.     

Ehrlichia equi infection of horses from Minnesota and Wisconsin: detection of seroconversion and acute disease investigation

Equine granulocytic ehrlichiosis (EGE) is caused by infection with Ehrlichia equi. EGE has been reported primarily in northern California, where E equi is transmitted by the tick Ixodes pacificus. Reports of EGE and the emergence of human granulocytic ehrlichia in Minnesota prompted a seroprevalence study of E equi in horses of Minnesota and Wisconsin. Tick (Ixodes scapularis) endemic areas of Minnesota and Wisconsin were compared to nonendemic regions of Minnesota. Indirect fluorescent antibody was used to detect the presence of serum antibodies to E equi. Serum samples from healthy horses, 375 samples from I scapularis endemic counties, and 366 samples from nonendemic counties were screened at a 1:40 dilution. Results demonstrated a seroprevalence of 17.6% in endemic areas versus 3.8% in nonendemic areas. Ehrlichial DNA from 2 samples was successfully amplified by polymerase chain reaction and 919 base pairs were sequenced. The DNA sequence of 1 Minnesota/Wisconsin strain differed from the GenBank strain (M73223) of E equi at positions 84 and 886 and from the MRK strain of E equi at position 84, and was identical to the human granulocytic ehrlichiosis (HGE) agent. The 2nd Minnesota/Wisconsin strain was identical to the 1st with the exception of a substitution of "A" at position 453 that is not present in E phagocytophila, E equi, or HGE agent strain sequences. Based on the results of this study, we concluded that E equi is present and causes infection in horses in Minnesota and Wisconsin. The occurrence of infection is higher in tick endemic regions.     

Comparison of Serum Amyloid A in Horses With Infectious and Noninfectious Respiratory Diseases

The acute phase protein serum amyloid A (SAA) has been shown to be a useful inflammatory parameter in the horse, but studies showing SAA responses to specific respiratory disease etiologies are limited. The goal of this study was to evaluate SAA responses in horses with infectious and noninfectious respiratory diseases as well as healthy, control horses. Two hundred seven horses were grouped into the following categories: equine influenza virus (EIV), equine herpesvirus-4 (EHV-4), Streptococcus equi subspecies equi (S. equi ss equi), inflammatory airway disease (IAD), and healthy controls. Serum amyloid A concentrations were determined for all horses on serum using a stall-side lateral flow immunoassay test. Serum amyloid A levels were found to be significantly greater for infectious respiratory diseases (EIV, EHV-4, S. equi ss equi) and horses with IAD when compared to control horses. There was a significant difference between viral and bacterial infections and IAD. Although SAA values from horses with S. equi ss equi were significantly greater when compared to horses with viral infections (EIV/EHV-4), the wide range of SAA values precluded accurate classification of the infectious cases. In conclusion, SAA is more reliably elevated with infections of the respiratory tract rather than noninfectious airway conditions. This can facilitate early detection of respiratory infections, help track disease progression, and aid practitioners in making recommendations about proper biosecurity and isolation of potentially contagious horses.     

Mycobacterial infections in equids: Clinical characteristics and diagnostic techniques

Mycobacterial infections in equids are relatively rare but the case report (Charlesworth 2017) detailed in this issue highlights that Mycobacterium bovis infections may still result in clinical signs in this incidental host and have zoonotic potential. Most reported cases of M. bovis in horses have a protracted disease course, with features including pyrexia, weight loss and oedema with a nonspecific inflammatory profile. As such, the clinical features of disease overlap with conditions such as neoplasia, peritonitis, protein‐losing enteropathies and bacterial infections including Rhodococcus equi and Lawsonia intracellularis. In this clinical satellite article, mycobacterial infections in equids are considered in terms of incidence and mode of transmission, key clinical features and perhaps most importantly, in terms of the diagnostic techniques that can be used in order to reach a definitive (ante mortem) diagnosis. The major zoonotic risk to veterinary personnel is likely to occur at the time of post‐mortem examination of infected horses, and awareness of these potential risks remains of the utmost importance.     

Strangles and its complications

Strangles, caused by the Gram‐positive bacteria Streptococcus equi subspecies equi (S. equi), is a highly contagious upper respiratory infection in horses. The infection is transmitted by inhalation or direct contact with mucopurulent discharge from an infected animal, resulting in fever, depression, and submandibular and retropharyngeal lymph node enlargement that can lead to respiratory distress. Complications include secondary cellulitis at external abscessation sites, guttural pouch empyema and its persistence into the carrier state, purpura haemorrhagica, metastatic abscessation, emergency tracheostomies and rarely secondary S. equi pneumonia or myositis. Control of outbreaks requires strict isolation protocols and hygiene measures. Detection methods of the index case and carrier state are constantly being refined to assist in the identification and prevention of disease perpetuation.     

Clinical and Laboratory Findings in Equine Piroplasmosis

The objective of this study was to evaluate equine piroplasmosis (EP) as a cause of morbidity in horses in Sardinia (Italy), describe the clinical signs and altered hematologic and biochemical parameters, and illustrate response to different treatments. Among 44 horses suspected of tick-borne disease, 38 were polymerase chain reaction (PCR) positive for Theileria equi (n = 27) or Babesia caballi (n = 6), whereas five were positive for both protozoans. Typical clinical features of piroplasmosis were seen in some of the horses, whereas others had nonspecific mild symptoms. Hematologic findings revealed involvement of the three blood cell lineages (anemia, leukopenia or leukocytosis, thrombocytopenia), and biochemical variations were related to increased bilirubin, alteration of serum phosphorus, and hypoalbuminemia. We suggest that the two protozoans are the most important causative agents of equine tick-borne disease in this geographic area, and we observe that different clinical features are associated with the disease; in addition to the typical aspects of piroplasmosis, characterized by fever, pale mucous membranes, and icterus, we can signal other nonspecific mild signs such as weight loss, weight loss associated with an insignificant leukopenia, or weight loss associated with depression, anorexia, and mild hyperbilirubin. The study is intended as a practical contribution for veterinary practitioners because it describes different clinical presentations and laboratory findings of EP, suggests diagnostic and therapeutic approaches to the disease, and shows diffusion of the disease in a Mediterranean region.     

Equine ehrlichiosis: A comparison between E. equi and other pathogenic species of Ehrlichia

Ehrlichia equi, etiologic agent of equine ehrlichiosis, is a rickettsia which morphologically closely resembles the agents of bovine petechial fever, tick-borne fever, and canine ehrlichiosis (tropical canine pancytopenia). Natural infections of E. equi have been reported only in horses; however, the experimental host range of E. equi has been broadened to include burros, sheep, goats, dogs, cats, monkeys and baboons. Infection of primates indicates that E. equi may be a zoonotic agent. An indirect fluorescent antibody test employing E. equi-infected granulocytes as antigen has been developed and used to show that infected horses develop a prolonged antibody response to E. equi. Cell-mediated immune responses measured by the leukocyte migration inhibition test were also detected in horses recovered from acute illness. Protective immunity in horses, monkeys and baboons to reinfection is long-lasting. In contrast to the blood of dogs recovered from clinical E. canis infection, the blood of horses and dogs recovered from clinical infection with E. equi is not infectious for susceptible animals. Infection of dogs with E. equi does not provide protection against subsequent infection with E. canis.     

Hematology and some blood chemical parameters as a function of tick-borne disease (TBD) signs in horses

Two statements provide the context within which this investigation was carried out: (i) Apulia is an enzootic region for tick-borne diseases (TBD); (ii) the principles of enzootic stability and the study of resilient/resistant breeds are among the tools for future pest control strategies. Thus, a trial protocol was established to check the amount of variation in hematologic and biochemical parameters serving as a function of TBD signs in resilient horses. Blood samples were collected from 109 horses belonging to the Apulian native Murgese breed. Hematologic and biochemical parameters were screened and microscopic search for the parasites in the red cells was performed. Differences in clinical manifestations and hematological and biochemical responses were recorded. The following disease classification was used: infection-free horses (class 0), infected horses (presence of Theileria equi and/or Babesia spp in the red cells) without clinical signs (class 1), and horses suffering from clinical disease (class 2). Seventy-one horses (65.1%) showed no TBD signs; hemoparasites were found in 38 horses (34.9%), of which only five (4.6%) showed clinical signs. A significant decreasing trend was shown from class 0 to class 2, where animals with clinical signs presented highly reduced values of some relevant blood parameters. The similarity of the blood values of class 0 and 1 animals is the most striking result of this work and calls for more extensive, detailed research into the mechanisms through which infected horses with no clinical signs of disease can cope with the condition.     

Prevalence and Significance of Parasites of Horses in Some States of Northern Nigeria

This study was conducted to determine the prevalence and significance of parasites of horses in northern Nigeria. Blood and faecal samples were randomly collected from 243 horses from different stables in some states of northern Nigeria for laboratory analyses. Fifty-seven horses (23.5%) were found infected with parasites. The hemoparasites detected, 21 (8.6%), include Theileria equi, Babesia caballi, Trypanosoma vivax and Trypanosoma evansi. The endoparasites encountered, 29 (11.9%) were Strongylus spp., Strongyloides spp., Oxyuris equi, Parascaris equorum, Paragonimus spp. and Dicrocoelium spp., 3 (1.2%) was Eimeria spp. Four horses (1.6%) had mixed infection of hemo- and endoparasites. This preliminary finding shows that parasitism is a problem in the horse stables examined, and calls for proper stable hygiene, routine tick control and regular deworming programme.     

Genetic structure of populations of β-haemolytic Lancefield group C streptococci from horses and their association with disease

The genetic structure of β-haemolytic Lancefield group C streptococci isolated from horses in Australia was examined by multilocus enzyme electrophoresis. The 249 isolates comprised 70 classified phenotypically as Streptococcus equi subspecies equi, 177 classified as S equi subspecies zooepidemicus and two which were unclassifiable. Forty-one electrophoretic types were identified which could be classified into three major clusters, A, B and C. Of the isolates, 178 fell into cluster B (types 4 to 22) and lay within a genetic distance of 0·36. Sixty-nine of the 70 S equi subspecies equi isolates fell into type 12, which suggests that they were members of a single clone, and the isolates from abscesses were significantly more likely to belong to type 12 than those from horses with no clinical signs (P<0·001). There were no other significant associations between electrophoretic types or clusters and the isolation of the organism from particular sites. These data suggested that S zooepidemicus may be the archetypal species from which the clone designated subspecies equi has been derived. If isolates of the subspecies equi from other geographical regions also prove to be members of electrophoretic type 12, this hypothesis would be strengthened.     

Controversies in therapy of infections caused by Rhodococcus equi in foals

Pneumonia caused by Rhodococcus equi is one of the most important causes of disease and death in foals. R. equi can also be cultured from a large variety of extrapulmonary sites of infection. In the absence of an effective vaccine, ultrasonographic screening for early detection of pulmonary lesions has become routine practice at many farms endemic for pneumonia caused by R. equi. Consequently, the most frequently recognised form of R. equi infection at such farms is a subclinical form in which foals develop sonographic evidence of peripheral pulmonary consolidation or abscessation without necessarily manifesting clinical signs. Evidence exists that not all foals with ultrasonographic lesions will progress to develop clinical signs, and treating a large proportion of foals based on subclinical ultrasonographic findings has been linked to emergence of macrolide‐ and rifampin‐resistant R. equi at a horse farm. Selectively treating only those foals with larger lesion scores and monitoring foals with daily physical inspections and weekly thoracic ultrasonography offers an approach that could decrease antimicrobial drug use without significantly increasing mortality. Current evidence continues to support the combination of rifampin with a macrolide (azithromycin, clarithromycin or erythromycin) for treating clinical infections caused by R. equi despite recently described pharmacological interactions between these drugs. When infection with a macrolide‐resistant isolate is confirmed, limited effective alternatives exist.     

Equine coronavirus: An emerging enteric virus of adult horses

Equine coronavirus (ECoV) is an emerging virus associated clinically and epidemiologically with fever, depression, anorexia and less frequently colic and diarrhoea in adult horses. Sporadic cases and outbreaks have been reported with increased frequency since 2010 from Japan, the USA and more recently from Europe. A faeco‐oral transmission route is suspected and clinical or asymptomatic infected horses appear to be responsible for direct and indirect transmission of ECoV. A presumptive clinical diagnosis of ECoV infection may be suggested by clinical presentation, haematological abnormalities such as leucopenia due to lymphopenia and/or neutropenia. Confirmation of ECoV infection is provided by specific ECoV nucleic acid detection in faeces by quantitative PCR (qPCR) or demonstration of coronavirus antigen by immunohistochemistry or electron microscopy in intestinal biopsy material obtained ante or post mortem. The disease is generally self‐limiting and horses typically recover with symptomatic supportive care. Complications associated with disruption of the gastrointestinal barrier have been reported in some infected horses and include endotoxaemia, septicaemia and hyperammonaemia‐associated encephalopathy. Although specific immunoprophylactic measures have been shown to be effective in disease prevention for closely‐related coronaviruses such as bovine coronavirus (BCoV), such strategies have yet not been investigated for horses and disease prevention is limited to basic biosecurity protocols. This article reviews current knowledge concerning the aetiology, epidemiology, clinical signs, diagnosis, pathology, treatment and prevention of ECoV infection in adult horses.     

First Report of Molecular Characterization of Argentine Isolates of Streptococcus equi subsp. equi by Pulsed-Field Gel Electrophoresis

Strangles is one of the most frequently diagnosed equine respiratory infectious diseases in the world. It is caused by Streptococcus equi subsp. equi (S. equi), and it is an acute infection characterized by pyrexia, nasal discharge, pharyngitis, and abscessation of lymph nodes. Frequently, healthy horses might continue to harbor S. equi after clinical recovery. Although the genetic distance between S. equi isolates is short, strains can be differentiated by pulsed-field gel electrophoresis (PFGE) and single locus sequence typing for epidemiological studies. The aim of this study was to characterize by PFGE Argentine isolates of S. equi obtained from horses with acute strangles and those that had recovered. Bacterial isolation and identification of 80 S. equi isolates by phenotypic and genotypic tests were performed using samples from 29 horses with acute strangles and 95 from healthy animals. Also, the isolates were characterized by PFGE using Bsp120I and SmaI. Visual comparison of macrorestriction patterns generated with both enzymes revealed three different DNA fragment profiles with variations of one or two bands. Interestingly, an identical profile was found in isolates from the same horse and from horses that were infected at the same time, and the horses recovered from strangles continue to carry the same strain. Some vaccinated horses have been mild infected for a different strain from that of carriers suggesting other source of infection. This is the first molecular characterization of Argentine isolates of S. equi, which shows the presence of three strains between 2010 and 2013 in Buenos Aires.     

Attempt to infect horses with brucella canis

Five seropositive adult horses were inoculated conjunctivally with Brucella canis and postexposure temperature, hemoculture and serologic determinations suggested that none of the horses became infected. Antibody titers to Actinobacillus equuli generally paralleled those of B. canis, but not those of Corynebacterium equi.