Rhodococcus Infection in Horses [Foal Pneumonia]
The cause of pneumonia in foals: Rhodococcus equi (R equi). If not complicated by sepsis, most causes of foal pneumonia have a good prognosis, but not the bacteria R equi. R equi has an insidious onset and by the time something is distinctly wrong, a lot of permanent damage is done to the lungs.
The presence of nodular lung lesions and mediastinal lymphadenopathy in foals 1-5 mo of age is highly suggestive of R equi .
One of the most common diseases in foals six months and younger is pneumonia. Though many different organisms can cause foal pneumonia, Rhodococcus equi is considered the most common culprit in a severe case. A nationwide survey indicated that respiratory disease is the third-leading cause of disease in foals and ranks second as a cause of death, following injury or wounds.
The disease process begins with increased diffuse bronchial sounds, often accompanied by a cough. This develops into wheezes, which may be localized to a small area of the lungs (most often the anteroventral area), in some cases unilaterally. Pyrexia (>102F [39C]) follows over the next few days, with an increased respiratory rate (>40/min) and abdominal 'tucking' on inspiration. Bronchovesicular sounds are increased over the large airways, and wheezing occurs over the small airways. Untreated foals develop progressive crackles that can be heard over the entire lung field, often accompanied by stridor. Coughing becomes more severe and intense. Foals commonly remain bright, alert, and vigorous, despite severe lung involvement, often until in the late stages of the disease. Neutrophilic leukocytosis, monocytosis, and marked fibrinogenemia occur. Mucopurulent nasal discharge is common, but lymphadenopathy of the throat region is absent. Eventually, untreated foals may become cyanotic and collapse. There may be severe respiratory embarrassment and fever up to 106F (41C) when the lungs are extensively abscessed and consolidated. On farms where the infection is endemic, morbidity may be 90% and mortality in untreated foals as high. Where the disease is not endemic, foals probably often experience subclinical pneumonia, with perhaps development of a solitary small abscess in the lungs as the only manifestation of disease. In some cases, R equi causes severe diarrhea due to granulomatous colitis and mesenteric lymphadenitis from swallowing infected sputum. Terminally, foals may become bacteremic and develop osteomyelitis or hypopyon.
R equi infection is slowly progressive with acute to subacute clinical manifestations. Clinical signs of disease are difficult to detect until pulmonary lesions reach a critical mass resulting in decompensation of the foal. Pulmonary lesions are relatively consistent and include subacute to chronic suppurative bronchopneumonia, pulmonary abscessation, and suppurative lymphadenitis. At the onset of clinical signs, most foals are lethargic, febrile, and tachypneic. Cough is a variable clinical sign; purulent nasal discharge is less common. Thoracic auscultation reveals crackles and wheezes with asymmetric/regional distribution. Pulmonary regions with marked consolidation lack breath sounds and exhibit dull resonance on thoracic percussion. Diarrhea is observed in many foals due to colonic microabscessation.
Intestinal and mesenteric abscesses are the most common extrapulmonary sites of infection. Foals with abdominal involvement often present with fever, depression, anorexia, weight loss, colic, and diarrhea. Intestinal lesion are characterized by multifocal, ulcerative enterocolitis and typhlitis involving Peyer’s patches with granulomatous or suppurative inflammation of the mesenteric and/or colonic lymph nodes. The prognosis for foals with abdominal forms of R equi is less favorable than for those with pulmonary disease. Septic physitis and osteomyelitis are less common extrapulmonary sites of infection. Vertebral osteomyelitis may result in pathologic vertebral fracture and spinal cord compression, and is a devastating manifestation of R equi osteomyelitis. Panophthalmitis, guttural pouch empyema, sinusitis, pericarditis, nephritis, nonseptic uveitis and synovitis, and hepatic and renal abscessation with R equi have been reported.
The bacterium is a soil saprophyte; its growth is considerably enhanced by constituents of herbivore manure (eg, acetic acid) and by high temperatures. Under ideal conditions (eg, high summer heat), it may multiply thousands of times in soil. In addition, R equi will grow to large numbers in the intestine of foals <12 wk old, but its presence in the feces of older horses represents pasture acquisition. It resists sunlight and dessication and is relatively resistant to most disinfectants. Thus, over the years, infection may progressively build up on breeding farms that have large numbers of foals or allow manure to accumulate in the immediate environment.
Rhodococcus (Corynebacterium) equi was initially described by Magnusson (1) as a causative agent of primarily purulent pneumonia in foals and represents a serious risk worldwide accounting for greater than 3% of foals deaths.
Inhalation of contaminated dust results in a cranioventral distribution of lung abscesses, which may be more extensive in the right lung than in the left. Granulomatous enteritis and lymphadenitis may follow swallowing of infected sputum. In rare cases, enteritis without pneumonic change may occur. Rhodococcus equi is an opportunistic pathogen; it affects foals when maternal antibody levels decline and their own immune system is immature. In immunocompromised animals (ie, combined immunodeficiency) are at high risk of infection. There may also be a genetic predisposition to disease, particularly in Arabians. The mechanism of pathogenicity remains unknown but relates to the ability of the organism to survive within and eventually destroy alveolar macrophages of young foals. The severity of the disease process appears to be related to the number of organisms inhaled into the lungs. Most foals appear to encounter and successfully resist small numbers of R equi early in life.
The optimal method is by positive culture of transtracheal bronchoalveolar aspirates, but false negative results may occur. Thoracic auscultation may be of limited value early in the course of the disease because airway involvement may not be fully evident. Radiographic lesions of a prominent alveolar pattern characterized by ill-defined regional consolidation is typical; such consolidated lesions are often nodular or cavitary. Mediastinal lymphadenopathy is evident radiographically in advanced cases. In suspected cases, initiation of therapy should be based on radiographic evidence of granulomatous pulmonary disease and clinical signs. Diagnostic serologic tests have been described but are not readily available. Quantitative fecal culture, demonstrating >106 R equi /g of feces, using selective media may be useful.
Intracellular gram-positive bacteria> R.equi
Routine laboratory evaluation of CBC and serum chemistry reveals nonspecific abnormalities consistent with infection and inflammation. Neutrophilic leukocytosis and hyperfibrinogenemia are common, and the severity of these findings relates to prognosis.
Bacterial culture of transtracheal wash samples is required for definitive diagnosis. Cytologic evaluation of transtracheal wash samples reveals intracellular coccobacilli, identification of which indicates initiation of appropriate antimicrobial therapy pending culture results.
The lung contains multifocal pyogranulomas
The colonic and cecal lymph nodes are inflamed and enlarged (lymphadenitis).
As the infection progresses, the foamy histiocytes accumulate lamellar calcified basophilic staining cytoplasmic bodies containing a central crystalline core surrounded by a less dense peripheral zone, Michaelis-Gutmann bodies
Thoracic auscultation may be of limited value early in the course of the disease because airway involvement may not be fully evident. Radiographic lesions of a prominent alveolar pattern characterized by ill-defined regional consolidation is typical; such consolidated lesions are often nodular or cavitary. Mediastinal lymphadenopathy is evident radiographically in advanced cases. In suspected cases, initiation of therapy should be based on radiographic evidence of granulomatous pulmonary disease and clinical signs.
Pneumonia due to Rhodococus equi, lateral projection. Courtesy of Dr. Thomas Lane
Thoracic ultrasonographic examination of a 3 mo old foal with rhodococcal pneumonia. Note pulmonary consolidation with air-filled lung visible in the periphery of the image. Small, fluid-filled abscesses can be identified in the pulmonary parenchyma. Courtesy of Dr. Bonnie R. Rush
Thoracic radiographic evaluation may reveal a pattern of perihilar alveolization, consolidation, and abscessation. The presence of nodular lung lesions and mediastinal lymphadenopathy in foals 1-5 mo of age is highly suggestive of R equi .
Scientific PapersZentralbl Veterinarmed [B] 1999 Nov;46(9):641-8 Effect of prophylactic administration of hyperimmune plasma to prevent Rhodococcus equi infection on foals from endemically affected farms.Higuchi T, Arakawa T, Hashikura S, Inui T, Senba H, Takai SHidaka Agriculture Mutual Aid Association, Hokkaido, Japan. [Medline record in process]The effect on foals of prophylactic administration of hyperimmune plasma to prevent R. equi infection was investigated on three farms at which R. equi infection was endemic. Sixteen foals between 10 and 39 days of age were intravenously given 1-21 of hyperimmune plasma. ELISA antibody titres against R. equi were significantly increased and maintained at high levels for over 30 days in most of the recipient foals. The prevalence of R. equi infection was 6.3% (1/16) in the foals that received the immune plasma, and 26.3% (5/19) in the control foals not given the immune plasma on the three farms. For 2 years before and after this field trial on the three farms, 18 of 64 foals (28.1%) showed clinical signs of respiratory tract infection and four of them died of R. equi pneumonia. Heavy contamination of horses and their environment with virulent R. equi was detected by colony blotting, and plasmid profiles also suggested that foals on the three farms were constantly exposed to virulent R. equi. The results of this field trial support previous observations by some researchers that the administration of hyperimmune plasma to foals in the early days of life promotes prevention of R. equi infection on endemic farms; however, the mechanism of hyperimmune plasma protection remains unclear. Vet Pathol 1999 Jul;36(4):336-9 Disseminated Rhodococcus equi infection in two goats.Davis WP, Steficek BA, Watson GL, Yamini B, Madarame H, Takai S, Render JADepartment of Animal and Nutrional Sciences, University of New Hampshire, Durham 03824, USA. Rhodococcus equi infection was diagnosed in two goats from the same herd. At necropsy, numerous caseating granulomas were disseminated throughout the liver, lungs, abdominal lymph nodes, medulla of right humerus, and the right fifth rib of goat No. 1, and the liver of goat No. 2. Histopathologic examination confirmed the presence of multiple caseating granulomas in these organs. Numerous gram-positive and Giemsa-positive coccobacilli were identified within the cytoplasm of macrophages. Aerobic bacterial cultures of the liver and lung from both goats yielded a pure growth of R. equi. R. equi antigens were immunohistochemically identified in caseating granulomas from both goats. However, the 15- to 17-kd virulence antigens of R. equi were not detected, suggesting possible infection by an avirulent strain of this organism. J Vet Intern Med 1999 May-Jun;13(3):206-12 Published erratum appears in J Vet Intern Med 1999 Sep-Oct;13(5):504 Peripheral blood lymphocyte subpopulations and immunoglobulin concentrations in healthy foals and foals with Rhodococcus equi pneumonia.Flaminio MJ, Rush BR, Shuman WDepartment of Clinical Sciences, College of Veterinary Medicine, Kansas State University, Manhattan, USA. email@example.com Infectious diseases are common in foals aged 1-5 months. The objectives of this investigation were to evaluate immunologic parameters in foals from birth to weaning to establish reference values for the proportion of circulating lymphocytes that were helper (CD4+) or cytotoxic (CD8+) T cells, or B cells; to measure serum immunoglobulin (IgM and IgG) concentrations; and to compare these immunologic parameters to values in foals with naturally occurring Rhodococcus equi pneumonia and in adult horses. Peripheral blood lymphocyte subpopulations were determined by flow cytometric analysis, and serum IgG and IgM concentrations were determined by radial immunodiffusion. Flow cytometric analysis of lymphocyte subpopulations suggested age-related changes in the cell-mediated immune system in horses. Absolute circulating CD4+ and CD8+ T lymphocytes and B cells increased linearly up to 3 months of age. Circulating B cell concentrations from birth to 6 months of age were greater than values in adult horses and the lymphocyte differences among the age groups are mainly due to variation in B lymphocytes. Both absolute and proportional B cell concentrations were greater in foals with R equi pneumonia than in healthy foals at the same age. The increase in absolute cell counts of each subpopulation was dependent on the increase of absolute peripheral blood lymphocyte count. Serum IgG concentration increased linearly from 1 to 3 months of age, and serum IgM concentrations increased from 1 to 6 months of age. These data suggest age-dependent cell-mediated and humoral development in young foals. Antonie Van Leeuwenhoek 1998 Jul-Oct;74(1-3):21-5 Diversity of isolates of Rhodococcus equi from Australian thoroughbred horse farms.Morton AC, Baseggio N, Peters MA, Browning GFFaculty of Veterinary Science, University of Melbourne, Parkville, Victoria, Australia. Pulsed field gel electrophoresis of restriction endonuclease digested genomic DNA from a collection of clinical isolates of Rhodococcus equi was used to compare strain diversity on different Thoroughbred horse farms over time. Restricted diversity was found among the isolates tested, as the same strains were detected on multiple farms and in multiple years. Marked variation occurred in strain prevalence with some strains being represented by single isolates, and the most prevalent by 26 isolates. There were dominant strains on some farms and the prevalence of some strains differed between farms. Infection with multiple strains was noted in some cases where multiple isolates from a single foal were examined. Equine Vet J 1998 Nov;30(6):482-8 Clostridium difficile associated with acute colitis in mares when their foals are treated with erythromycin and rifampicin for Rhodococcus equi pneumonia.Baverud V, Franklin A, Gunnarsson A, Gustafsson A, Hellander-Edman AThe National Veterinary Institute, SVA, Uppsala, Sweden. In Sweden, mares sometimes develop acute, often fatal, colitis when their foals are treated orally with erythromycin and rifampicin for Rhodococcus (R.) equi infection. Clostridium (C.) difficile, or its cytotoxin, was demonstrated in faecal samples from 5 of 11 (45%) mares with diarrhoea. By contrast C. difficile was not found in the faecal flora of 12 healthy mares with foals treated for R. equi infection or in 56 healthy mares with healthy untreated foals. No other enteric pathogen was isolated from any diarrhoeic mare. Of 7 investigated treated foals, 4 had a high (1651.0, 1468.3, 273.0 and 88.8 microg/g) faecal concentration of erythromycin. The dams of those 4 foals developed acute colitis, whereas the dams of 3 foals with a lower (26.3, 4.6 and 3.7 microg/g) faecal erythromycin concentration remained healthy, indicating that there might have been an accidental intake of erythromycin by mares. The foals treated with antibiotics were regarded as asymptomatic carriers and potential reservoirs, as C. difficile was found in 7 of 16 foals investigated, while 56 untreated foals proved negative. The isolated C. difficile strains proved resistant to both erythromycin (MIC>256 mg/l) and rifampicin (MIC>32 mg/l), a fact that may have favoured the growth of C. difficile in the foal intestine. All mares found positive for C. difficile were, or had recently been, hospitalised together with their foals, indicating that C. difficile may be a nosocomial infection, in horses. The results emphasise that routine testing for C. difficile and its cytotoxin is recommended when acute colitis occurs in mares when their foals are treated with erythromycin and rifampicin. Preventive measures in order to avoid accidental ingestion of erythromycin by mares from the treatment of their foals are suggested. Comments:Comment in: Equine Vet J 1998 Nov;30(6):450-1 J Am Vet Med Assoc 1998 Aug 15;213(4):510-5 Associations between physical examination, laboratory, and radiographic findings and outcome and subsequent racing performance of foals with Rhodococcus equi infection: 115 cases (1984-1992).Ainsworth DM, Eicker SW, Yeagar AE, Sweeney CR, Viel L, Tesarowski D, Lavoie JP, Hoffman A, Paradis MR, Reed SM, Erb HN, Davidow E, Nalevanko MDepartment of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853-6401, USA. OBJECTIVE: To determine whether physical examination, laboratory, or radiographic abnormalities in foals with Rhodococcus equi infection were associated with survival, ability to race at least once after recovery, or, for foals that survived and went on to race, subsequent racing performance. DESIGN: Retrospective study. ANIMALS: 49 Thoroughbreds and 66 Standardbreds admitted to 1 of 6 veterinary teaching hospitals between 1984 and 1992 in which R equi infection was positively diagnosed. PROCEDURE: Results of physical examination, laboratory testing, and thoracic radiography were reviewed. Indices of racing performance were obtained for foals that recovered and eventually raced and compared with values for the US racing population. RESULTS: 83 (72%) foals survived. Foals that did not survive were more likely to have extreme tachycardia (heart rate > 100 beats/min), be in respiratory distress, and have severe radiographic abnormalities on thoracic radiographs at the time of initial examination than were foals that survived. Clinicopathologic abnormalities were not associated with whether foals did or did not survive. Forty-five of the 83 surviving foals (54%) eventually raced at least once, but none of the factors examined was associated with whether foals went on to race. Racing performance of foals that raced as adults was not significantly different from that of the US racing population. CLINICAL IMPLICATIONS: R equi infection in foals is associated with a decreased chance of racing as an adult; however, foals that eventually go on to race perform comparably to the US racing population. Vet Microbiol 1998 Mar 15;61(1-2):59-69 Detection of virulent Rhodococcus equi in tracheal aspirate samples by polymerase chain reaction for rapid diagnosis of R. equi pneumonia in foals.Takai S, Vigo G, Ikushima H, Higuchi T, Hagiwara S, Hashikura S, Sasaki Y, Tsubaki S, Anzai T, Kamada MDepartment of Animal Hygiene, School of Veterinary Medicine and Animal Sciences, Kitasato University, Aomori, Japan. firstname.lastname@example.org Polymerase chain reaction (PCR)-based assays were developed to detect virulent Rhodococcus equi in transtracheal aspirate samples from sick foals showing respiratory signs. An oligonucleotide primer pair from the sequence of the virulence-associated 15- to 17-kDa antigen gene of the virulence plasmid in virulent R. equi was used to amplify a 564 bp region by PCR, and the result was confirmed by Southern blot hybridization. No positive reaction was seen in DNA from 13 different microorganisms typically found in the respiratory tract. In tracheal aspirates seeded with virulent R. equi, a visible band could detect 10 to 10(2) bacteria per PCR assay (10(3) to 10(4)/ml of the aspirate). Virulent R. equi was demonstrated in 31 of 42 transtracheal aspirates by culture and colony blot analysis, whereas a positive PCR result was observed in only 12 of the 31 culture positive samples. To prevent false-negative results, two methods were developed: a nested PCR and a PCR in combination with enrichment cultures of aspirates in the selective medium to increase the number of bacteria to 10(4)/ml or more. All of the PCR-negative and culture-positive samples were positive by the two methods. These results indicated that PCR-based assays provide a specific and sensitive means to detect virulent R. equi in tracheal aspirates of foals, and they are more rapid than the routine culture procedures for the diagnosis of R. equi pneumonia in foals. J Am Vet Med Assoc 1998 Apr 1;212(7):976-81 Physical and serologic examinations of foals at 30 and 45 days of age for early diagnosis of Rhodococcus equi infection on endemically infected farms.Higuchi T, Taharaguchi S, Hashikura S, Hagiwara S, Gojo C, Satoh S, Yoshida M, Takai SHidaka Agriculture Mutual Aid Association, Hokkaido, Japan. OBJECTIVE: To evaluate results of physical and serologic examinations of foals at 30 and 45 days of age on 3 types of farms with various prevalences of clinical disease (endemic, sporadic, none) caused by Rhodococcus equi and to determine whether evaluations were helpful in early diagnosis and control of the disease. DESIGN: Prospective cohort study. ANIMALS: 144 foals at 30 and 45 days of age. PROCEDURE: During a 2-year period, 36 foals on farms at which R equi infection was endemic, 71 foals on farms at which the disease was sporadically detected, and 37 foals on farms without the disease were examined by means of auscultation of lungs, serum biochemical and hematologic analyses, and determination of antibody titers against R equi, using ELISA. Transtracheal aspirates were obtained from 14 of 32 foals that had clinical signs of disease and 7 of 41 seropositive foals that did not have clinical signs of disease. RESULTS: Prevalences of respiratory tract disease and seropositive conversion rates for 45-day-old foals on endemically and sporadically infected farms were significantly higher than on farms without the disease. Rhodococcus equi was isolated from tracheal aspirates of seropositive foals, even when clinical signs were not evident. CLINICAL IMPLICATIONS: Physical and serologic examinations of foals at 30 and 45 days of age were useful for early diagnosis of R equi infection, especially for foals on farms at which the disease was endemic. J Vet Med Sci 1997 Dec;59(12):1097-101 Isolation of virulent Rhodococcus equi from transtracheal aspirates of foals serodiagnosed by enzyme-linked immunosorbent assay.Higuchi T, Hashikura S, Hagiwara S, Gojo C, Inui T, Satoh S, Yoshida M, Fujii M, Hidaka D, Tsubaki S, Takai SHidaka Agriculture Mutual Aid Association, Hokkaido, Japan. Although isolation of Rhodococcus equi from tracheobronchial aspirates is thought to be a definitive diagnosis of R. equi pneumonia in foals, virulence of isolates from the aspirates of infected foals remains obscure. In the present study, transtracheal aspirates were collected from thirty-one 1- to 6-month-old foals, which showed clinical signs of respiratory tract infection, and R. equi isolates were analyzed for the presence of virulence plasmids and virulence-associated antigens. Moreover, this method was compared with a serodiagnosis by an enzyme-linked immunosorbent assay (ELISA) to evaluate the sensitivity of the ELISA. Of the 31 foals, 21 revealed positive cultures for R. equi. Of the 21 foals, 20 (95%) had an ELISA OD value of 0.3 (positive limit of this test) or higher at the initial medical examination. All of the isolates from the aspirates were virulent R. equi, which contained virulence plasmids and expressed virulence-associated antigens. In the remaining 10 foals showing a negative culture for R. equi, 3 foals had positive ELISA titers. Six foals died during the treatment, and necropsy revealed that 5 of the 6 foals had R. equi infection characterized by large abscesses in the lungs, and 3 of the 5 foals also had intestinal lesions. All clinical isolates from the lesions of the foals were virulent R. equi. These results support the assumption that isolates from the transtracheal aspirates of infected foals are virulent R. equi and the sensitivity of ELISA might demonstrate a serodiagnostic value for early diagnosis of R. equi infection in foals. Am J Vet Res 1997 Nov;58(11):1232-7 Nucleic acid amplification for rapid detection of Rhodococcus equi in equine blood and tracheal wash fluids.Sellon DC, Walker K, Suyemoto M, Altier CDepartment of Food Animal and Equine Medicine, College of Veterinary Medicine, North Carolina State University, Raleigh 27606, USA. OBJECTIVE: To evaluate the ability of nucleic acid amplification techniques to detect Rhodococcus equi in equine buffy coat, blood, and tracheal wash fluid and to differentiate between virulent and avirulent strains of the bacteria. SAMPLE POPULATION: Blood anticoagulated with EDTA and tracheal wash fluid from healthy horses. PROCEDURE: Logarithmic dilutions of virulent and avirulent strains of R equi were added to equine buffy coat and tracheal wash fluid samples. The DNA was extracted and amplified by polymerase chain reaction (PCR), using primers specific for the 16S ribosomal subunit gene and the virulence plasmid of R equi. RESULTS: PCR with 16S ribosomal subunit primers amplified a 441-bp segment of DNA from virulent and avirulent strains of R equi, but not from samples containing other species of bacteria. The virulence plasmid primers amplified an 875-bp segment of DNA from virulent strains of R equi, but not from avirulent R equi, or from other species of bacteria. Virulent strains of R equi could be identified by PCR and differentiated from avirulent strains within 12 to 24 hours after sample collection, with as few as 10 to 100 organisms present. CONCLUSIONS: PCR can be used to rapidly and accurately identify R equi in equine blood and tracheal wash fluid samples and can differentiate between virulent and avirulent strains of the organism. CLINICAL RELEVANCE: Because PCR can confirm a diagnosis of R equi infection in horses more rapidly and specifically than use of standard culture techniques, extrapolation of this assay to soil and fecal samples could be useful in epidemiologic studies and studies of environmental disinfection or decontamination.
To prevent buildup of R equi in the environment of young foals, manure should be removed. Loafing paddocks for young foals and their dams should be grassed and rotated. Dusty conditions within stables should be prevented, eg, by concreting walkways and damping them down. Foals should be moved away from heavily infected environments as soon To prevent buildup of R equi in the environment of young foals, manure should be removed. Loafing paddocks for young foals and their dams should be grassed and rotated. Dusty conditions within stables should be prevented, eg, by concreting walkways and damping them down. Foals should be moved away from heavily infected environments as soon as possible. On endemically affected farms, foals should be examined (temperature, respiratory rate, auscultation of lung fields) every 2-3 days during their first 4 mo, and all with suspected disease treated. By this means, mortality can be prevented, but only good management practices will reduce the level of infection. as possible. On endemically affected farms, foals should be examined (temperature, respiratory rate, auscultation of lung fields) every 2-3 days during their first 4 mo, and all with suspected disease treated. By this means, mortality can be prevented, but only good management practices will reduce the level of infection.
- Abortion or weak newborns, stillbirth
- Galactorrhea, inappropriate milk production
- Agalactia, decreased, absent milk production
- Purulent nasal discharge
- Mucoid nasal discharge, serous, watery
- Dyspnea, difficult, open mouth breathing, grunt, gasping
- Increased respiratory rate, polypnea, tachypnea, hyperpnea
- Coughing, coughs
- Abnormal lung or pleural sounds, rales, crackles, wheezes, friction rubs
- Dull areas on percussion of chest, thorax
- Back pain
- Colic, abdominal pain
- Forelimb pain, front leg
- Hindlimb pain, hind leg
- Dullness, depression, lethargy, depressed, lethargic, listless
- Tail, anal hypoesthesia, anesthesia perineum, anus
- Forelimb hypoesthesia, anesthesia front leg
- Hindlimb hypoesthesia, anesthesia rear leg
- Fever, pyrexia, hyperthermia
- Exercise intolerance, tires easily
- Underweight, poor condition, thin, emaciated, unthriftiness, ill thrift
- Weight loss
- Neck swelling, mass cervical region
- Back swelling, mass back region
- Internal abdominal mass, swellings, adhesions abdomen
- Lymphadenopathy, swelling, mass or enlarged lymph nodes
- Swelling skin or subcutaneous, mass, lump, nodule
- Forelimb swelling, mass in fore leg joint and/or non-joint area
- Hindlimb swelling, mass in hind leg joint and/or non-joint area
- Forelimb lameness, stiffness, limping fore leg
- Hindlimb lameness, stiffness, limping hind leg
- Tetraparesis, weakness, paralysis all four limbs
- Paraparesis, weakness, paralysis both hind limbs
- Inability to stand, downer, prostration
- Dysmetria, hypermetria, hypometria
- Ataxia, incoordination, staggering, falling
- Abnormal proprioceptive positioning, knuckling
- Cyanosis, blue skin or membranes
- Purulent discharge from eye
- Chemosis, conjunctival, scleral edema, swelling
- Conjunctival, scleral, redness
- Conjunctival, scleral, injection, abnormal vasculature
- Lacrimation, tearing, serous ocular discharge, watery eyes
- Hypopyon, lipid, or fibrin, flare, of anterior chamber
- Anorexia, loss or decreased appetite, not nursing, off feed
- Tachycardia, rapid pulse, high heart rate
The combination of erythromycin (25 mg/kg, PO, qid; esters or salts) and rifampin (5 mg/kg, bid, or 10 mg/kg, sid) is the treatment of choice. These antimicrobials may be bacteriostatic, but their activity is synergistic, and the combination has markedly improved survival of foals. Idiosyncratic hyperthermia and tachypnea can occur with erythromycin administration during periods of warm environmental conditions, and anorexia, bruxism, and salivation may be observed. Life-threatening, antibiotic-induced enterocolitis, due to Clostridium difficile , has been observed in the dams of nursing foals treated with erythromycin. Azithromycin is a newer generation macrolide with greater bioavailability than erythromycin. Azithromycin is administered orally (10 mg/kg, sid) with rifampin until clinical signs stabilize, then every other day until resolution of disease. The duration of antimicrobial therapy typically ranges from 4-9 wk.
Supportive therapy includes provision of a clean, comfortable environment and highly palatable, dust-free feeds. Judicial IV fluid therapy and saline nebulization facilitates expectoration of pulmonary exudates. NSAID should be administered as needed to maintain rectal temperature <103.5F (39.7C). Nasal insufflation with oxygen is necessary in foals with severe respiratory compromise. Bronchodilator therapy may or may not improve arterial oxygenation. Prophylactic antiulcer medication is indicated in foals that are stressed by respiratory difficulty, pain, frequent handling, hospitalization, and transportation.
The survival rate of R equi pneumonia is approximately 70-90% with appropriate therapy. The case fatality rate without therapy (or with inappropriate antimicrobial therapy) is ~80%. Parameters for discontinuation of medical therapy include clinical signs, serum fibrinogen concentration, and radiographic resolution of pulmonary consolidation and abscessation.
There are 3 basic strategies to decrease the incidence of R equi pneumonia on endemic farms: decreased exposure to the organism, early detection of clinical cases, and enhanced passive immunity for neonatal foals. Foals should be maintained in well-ventilated, dust-free areas, avoiding dirt paddocks and overcrowding. Pneumonic foals should be isolated and their manure composted. Herd surveillance programs for early detection of pneumonic foals on endemic farms include twice weekly physical examination and auscultation, and monthly CBC and fibrinogen concentration. Foals with WBC count >14,000 cells/L should be further evaluated for R equi . Administration of hyperimmune plasma might reduce the incidence and severity of R equi within the herd, but it is not completely effective in preventing disease. Hyperimmune plasma (1 L) is administered IV within the first week of life, followed by a second liter at approximately 25 days of age.