equine viral rhinopneumonitis Equine viral rhinopneumonitis: infectious disease. It affects the respiratory system in foals and causes abortions in pregnant mares. Are susceptible horses, donkey and zebra. It is seasonal, and has an incubation period of 2 to 10 days for the respiratory form and 1 to 3 months for abortive form. It is not a zoonosis. epizootiology Equine rhinopneumonitis is an enzootic disease in equine populations worldwide and often appears in frequently despite not incorporated new animals to the rodeo. The causative agent is equi herpesvirus type 1 (EHV-1), responsible for causing abortions, perinatal death, respiratory problems and Neurolytic, the equi herpesvirus type 4 (EHV-4), which affects the airways with rinofaringitis and traquebronquitis. The virus can induce latent infections in some horses, form through which self-perpetuating. It is argued that a high percentage of animals over one year old are latent carriers. Overcrowding, poor diet, transfer, some diseases and all those stressful situations can trigger the multiplication of the virus so far latent and affect susceptible horses by direct contact. Horses, zebras and donkeys are the only receptive to the disease under natural conditions animals.
The respiratory and digestive tract rhinopneumonitis transmitted through aborted fetuses and contaminated with nasal secretions elements. They are susceptible to infection foals between 6 months and 2-3 years of age and pregnant mares, resulting in these abortions after 5 months of gestation, but most often happen between 7 and 11 great weakness, pneumonia and severe liver damage. Death inevitably occurs within a few days of life. Weanling foals have respiratory symptoms. The foals that come from free establishments rhinopneumonitis spread from animals exposed to the virus during training in equestrian venues, exhibitions, etc. The rhinopneumonitis provides immunity for about 3- 4 months. The adult horses reinfected have mild symptoms. EHV-1 is widely disseminated in high density area of equines, infecting susceptible hosts. The existing humoral response to respiratory infections does not protect from all the animals, since they can reinfect despite the presence of neutralizing antibodies. Perhaps this is due to the short time of the aforementioned immunity, so effective protection need reinfection or several of many vaccinations. HEV-1 and EHV-4 are genetically and antigenically very similar. Each virus exists as a single neutralizing serotype. Both viruses have managed to evolve to persist latently in those horses who have suffered from illness.
Hence the suspicion that the reservoir is about half of the total population of horses, latent carriers capable of spreading EHV-1 and EHV-4 intermittently. EHV-1 is held responsible for abortions, birth of sick infants and paralytics tables in adult animals, since it has some affinity for the nervous system. EHV-1 can cause respiratory symptoms simultaneous or abortion of the mare at the end of her pregnancy myeloencephalopathy. The neurological condition may occur in pregnant horses, not pregnant, castrated or integers. There ataxias in the hindlimbs of varying degrees and can be mild or severe enough to prevent the normal movement of the animal, which remains supine. In addition, patients are febrile, with runny nose and edema in the limbs. The anamnesis can raise horses prior contact with aborting or suffered respiratory signs accompanied by fevers. Animals with mild ataxia usually recover within 15 to 30 days. Those who lie supine are reserved prognoses, therapy and prolonged support stricter still needed. EHV-4 is responsible for respiratory symptoms in foals and very rarely get to cause abortions. Other herpes viruses that affect horses are Herpesvirus equi type 2 (EHV-2), isolated frequently and without further clinical relevance, and equi herpesvirus type 3 (EHV-3) causing the rash Genital, venereal disease that affects the penis stallion and the mare’s vulva. Virology Herpesvirus belongs to the Herpesviridae family.
Icosahedral shaped, the nucleic acid is DNA and measures 130-200nm. They can be easily isolated through crushed lung or liver and then infected brain inoculated suckling mice or primary cells of rabbit kidney. They have the ability to remain latent in the host organism after primary infection, reinfection or causing new infections in susceptible animals. Both EHV-1 and EHV-4 have one serotype neutralizer, whereby no antigenic changes that does have Influenzavirus. pathogenesis EHV-1 and EHV-4 cause destruction and nasopharyngeal epithelial exfoliation, trachea and bronchi, which brings about severe inflammation and increased removal of glandular secretions. After replication, the viral agents are transported by macrophages to regional lymph nodes. EHV-1 is usually spread to other organs where endothelia cells affected vessel. It is so vasculitis generated results sequels in the uterus production of abortions, or the central nervous system with neurological conditions. The abortion occurs following anoxia suffering the fetus after rapid separation of the placenta and the endometrium. The broodmare no signs that it will abort. Expels the fetus to the placenta and uterus regresses normally. Le aborted fetus contains a high viral load.
It is noteworthy that abortions occurred beyond 6 months of gestation are not autolysed, unlike what happens in cases of Salmonella abortus equi infection. The horses who have endured several exposures to EHV-1 or EHV-4 have no detectable respiratory signs before a new reinfection. When the mare than the disease, neutralizing antibodies protect it until the 4th -5th month, when it can be reinfected. The fetus is better protected when the female has passed several infections. symptomatology Foals are feverish, a situation that usually maintained for 5 to 7 days. No congestion of the nasal mucosa and serous discharge, as pharyngitis and mandibular lymph edema in. The larynx is somewhat inflamed and the animal has a productive cough. There may be enteritis with diarrhea and edema in the limbs. The disease returns in 10 days of no secondary complications. In mares, the infection is spread very quickly. In general, no clinical symptoms. They can get to give birth to their foals, but infected and weak, dying within a few hours of birth.
complications Secondary bacterial infections commonly occur with purulent pharyngitis and adenitis. EHV-1, besides affecting the respiratory system, is responsible for causing invasion to other organs. The consequence of which is the occurrence of sequelae below: If the fetus of pregnant mare becomes infected during the late pregnancy, it is likely to be born alive. However, it has signs of disease or present them within a few hours of birth. The infant does not suck, have extreme weakness, fever, hypoxia and pneumonia. They are also very susceptible to bacterial invasion, and so the prognosis is always very serious with a case fatality rate of almost 100%. Although isolated situations have been detected mieloencefalíticos animals with respiratory disorders such as sequelae of conditions EHV-1. The event appears between 5 to 10 days appeared respiratory signs, incoordination and paraplegics with pictures. Aborting mares may also manifest signs of ataxia. Since the virus has been isolated from nervous tissue, it is supposed to be due to paraplegia vasculitis in small vessels CNS motivated by metabolic changes, with a consequent disorder in the blood supply. To the extent that the sequel does not cause recumbency prognosis is favorable, as this disorder usually returns within a few days.
Animals lying on the floor for more than 2-3 days are more committed. Another sequel of respiratory infections EHV-1 usually has a seat on the eyeball, uveitis and / or chorioretinitis. Even, the situation may worsen with retinal detachment and irreversible blindness in extreme cases. Diagnosis The clinical diagnosis is presumptive because it confused with other respiratory symptoms. The disease occurs in animals up to 2 to 3 years of age and at any time of year. The appearance of abortions in foals makes suspect the presence of Rhinopneumonitis. Moreover, as already noted, the aborted fetus before the 6th month of pregnancy is autolysed, while the reverse is true if the expulsion occurs from the 7th month onwards. The viral phase may go unnoticed, signs appearing before secondary bacterial invasion. Herpesvirus infections show a characteristic decrease of leukocytes with neutropenia at 48 hours after the start viremia. The diagnosis of equine rhinopneumonitis is confirmed by the presence of EHV-1 or EHV-2 in respiratory secretions. From 48 hours of onset of the disease, nasopharyngeal samples serous secretions through a sterile swab taken. The material obtained was placed in a fluid medium with antibiotics refrigerated transport and sent to the laboratory to maintain the viability of the agent.
Another way of shaming Herpesvirus is from white blood cells of the venous blood of horses affected. Within 5-10 days of the onset of infection 20-30 milliliters of blood without anticoagulant are extracted. The sample is sent to the laboratory refrigerated. The increase in titers between paired sera taken in the acute course of illness and convalescence also confirms the diagnosis by complement fixation or Elisa. This last test uses the G glycoprotein as antigen, being highly sensitive and specific for detecting EHV-1 and EHV-4 in infected horses (Kirisawa et al. ). The result is positive as there is an increase of four or more dilutions title of specific antibodies against EHV-1 or EHV-4 between the two samples. Sending the fetus by the placenta to a specialized laboratory allows us to demonstrate acidophilic intranuclear inclusions in hepatocytes and respiratory epithelial cells, pathological lesions typical of herpesvirus. The fluorescent antibody test performed in liver or lungs cutting confirm the diagnosis of Rhinopneumonitis. Differential Necropsy Young animals have edema of lungs with necrotic areas in bronchial and alveolar epithelium. fibrinous exudates in the alveoli and widespread atelectasis, with lungs adopting a purple coloration are observed.
There fluids in the pleural cavity and liver necrosis, hemorrhage in previous airways and laryngeal edema. Aborted fetuses towards the end of gestation not show large lung injury although in certain cases may also exist lungs atelectasis and purple. petechiae are noted in mucous membranes, splenomegaly and jaundice. No separation between allantochorion and endometrium of the mare and edema of the uterine wall. It is believed to be due to reactions that produce cytotoxic substances originating between the virus and the sensitized lymphocytes endometrium. Treatment Implement therapy is individual and depends on a lot of clinical signs of each patient. It is necessary to reduce the febrile and severe inflammation of the respiratory tract. The application of anti-inflammatory analgesics fulfills this function, phenylbutazone can be used in dose 4mg / kg intravenously every 24 hours or flunixin meglumine at a rate of 1mg / kg intramuscularly every 12-24 hours. As prevention of secondary bacterial contaminants one antibiotic therapy is administered broad spectrum. It is useful to use trimethoprim-sulfadiazine in doses of 15 mg / kg intramuscularly or 30 mg / kg, cda 24 hours for 10 days. They are also indicated benzatínicas penicillins or intramuscularly procaínicas penicillins or the sodium or potassium intramuscular or intravenous routes, in all cases at a rate of 20000 IU / kg. other antibiotics used are ticarcilina, in doses of 45 mg / kg intramuscularly every 8 hours or amikacin 20 mg / kg intramuscularly every 24 hours.
In particular cases minor tranquilizers and electrolyte solutions are used to correct water imbalances. The aftermath caused by rhinopneumonitis resolve symptomatically. Infants with severe respiratory disorders require oxygen therapy. Foals with disorders in the nervous system that are recumbent need constant attention. The bed should be soft and avoid remaining wet with urine. You need to change the patient’s position every 3-4hours to minimize complications that occur from prolonged recumbency, as myositis and ulcerations. Gentle massage in areas exposed to pressure, made two or three times a day, usually very helpful. Prophylaxis The eradication of equine rhinopneumonitis rodeos is virtually impossible because of the existence of carrier animals. However, by vaccinations to all groups of animals and effective management practices can reduce largely the onset of this disease, thus reducing the negative economic impact it generates. In foals, maternal antibodies against EHV-1 and EHV-4 decay around 3-4 months of age, which become seronegative and susceptible to Rhinopneumonitis. Therefore, the first vaccination to prevent respiratory form is made at the foot of the mother at the age of 3 months, then revaccinated at weaning and at one year of age. That way, future protection is achieved when the foal must face stressful situation weaning coexistence in new social groups, transport, training and competitions.
Pregnant mares are immunized in the 5th, 7th and 9th month of pregnancy, along with the rest of the horses from the property. sick animals or mares with gestations of more than 9 months not vaccinated. In areas where the disease is endemic, four months vaccination should be performed per year. As already mentioned, the herpesvirus may be stationed in the host after a primary infection and intensify in stressful situations. For that reason, it is very important to the isolation of all animals entering an establishment at least for three to four weeks to recover from stress and as a prevention of any disease. The mares that have aborted must be separated from the challenges of horses. If the abortion was a field, animals will avoid incorporating this sector for at least 30 days. Fetuses have to be incinerated and proceed to disinfect the stable and to remove the bed and any object that has had contact with the sick animal. In short, for effective control of equine rhinopneumonitis, it is essential to apply the following strategy: Vaccinate all horses from the property. Separate pregnant mares from other categories, especially foals. Subdivide pregnant mares for gestational age and small groups. Establish a quarantine not least 3 weeks in all mares entering or re establishment.
Avoid stress in all animals. Perform a thorough disinfection of the pits. Maintaining effective hygienic measures in facilities, utensils and clothing of personnel. Sources