Equi Pneumonia Research Articles

Serum amyloid A (SAA) as an aid in the management of infectious disease in the foal: comparison with total leucocyte count, neutrophil count and fibrinogen

Differentiation between infectious and noninfectious disease and rapid initiation of accurate treatment are essential in managing diseases in the neonatal and young foal. Identification of useful inflammatory markers for these purposes is, therefore, of great importance. The aim of this study was to compare the responses of the acute phase protein serum amyloid A (SAA) with the responses of fibrinogen and total leucocyte and neutrophil counts in infectious diseases encountered in the young foal, and to assess whether SAA measurements give additional information useful in the management of these diseases. In a prospective study, foals (n = 25) showing clinical signs indicative of infectious disease were blood sampled on admission and then daily or every second day during hospitalisation. The main presenting signs were neonatal weakness (n = 9), pneumonia (n = 6) and diarrhoea (n = 10). SAA and fibrinogen concentrations on admission were higher in foals with bacterial infections (n = 8) than in foals with nonbacterial or uncertain diagnoses (n = 17). On admission, weak foals with negative blood cultures (n = 3) had normal SAA and fibrinogen concentrations and varying total leucocyte and neutrophil counts. Foals with positive blood cultures (n = 2) had markedly increased SAA, decreased or increased fibrinogen concentration and leuco- and neutropenia. Those with ambiguous blood cultures (n = 3) had moderate to markedly increased SAA concentrations and normal fibrinogen concentration, leucocyte and neutrophil counts on admission. All foals with negative or ambiguous blood cultures recovered and had normal or decreasing SAA concentration on discharge. Both foals with a positive blood culture were subjected to euthanasia. One foal born with equine herpesvirus-1 infection had moderately increased SAA and normal fibrinogen concentration and leuco- and neutropenia. Foals with Rhodococcus equi pneumonia had increased concentrations of all parameters on admission. On discharge, recovered foals had normal SAA concentrations, whereas fibrinogen and total white blood cell count and neutrophil counts were still increased. There were no consistent inflammatory changes in the parameters measured in diarrhoeic foals and there was no statistical difference between rotavirus-positive (n = 4) and -negative (n = 6) foals in this respect. The results of this investigation suggest that SAA might be an aid in the differential diagnostic procedure of neonatally weak foals and in foals with diarrhoea as the main presenting clinical sign and that SAA measurements could add information in the monitoring of treatment in Rhodococcus equi pneumonia by responding more rapidly than the markers used to date.

Gas exchange during intense exercise in Standardbreds with earlier Rhodococcus equi pneumonia.

It is not known if pulmonary function and gas exchange during exercise are altered after pyogranulomatous pneumonia caused by Rhodococcus equi infection in the foal. The aim was to evaluate whether pulmonary gas exchange during high intensity exercise was altered in mature Standardbreds with a history of R. equi pneumonia as foals. In 7 foals, R. equi pneumonia was confirmed and treated. At age 3 years, when these horses were subjected to professional training, an inclined treadmill exercise test including 4 speeds was performed. Samples were collected when a steady state in VO2 was obtained. Red cell volume, heart rate, respiratory rate, and systemic and pulmonary mean arterial pressures were measured and cardiac output calculated. Oxygen and carbon dioxide tensions in arterial and mixed venous blood were analysed. The alveolar ventilation and the alveolar-arterial oxygen tension difference were determined. Pulmonary gas exchange was assessed and the ventilation-perfusion distribution, VA/Q, was estimated by the multiple inert gas elimination technique. Ventilation-perfusion mismatch and shunt were determined and diffusion limitation calculated. The gas exchange in Standardbred trotters previously infected with R. equi and successfully treated was not compromised during intense treadmill exercise compared with reference values for healthy, fit Standardbreds. We conclude that adult Standardbreds trotters with diagnosed R. equi pneumonia as foals, can achieve an adequate gas exchange at a workload close to VO2peak.

Pharmacokinetics of azithromycin in foals after i.v. and oral dose and disposition into phagocytes.

The properties of azithromycin suggest that it may be an alternative to erythromycin for treatment of Rhodococcus equi pneumonia in foals. To investigate this possibility, the disposition of azithromycin in plasma, polymorphonuclear leukocytes (PMN), and alveolar cells was examined after a single administration in foals. Azithromycin suspension was administered orally (p.o.) at a dose of 10 mg/kg to five healthy 2-3-month-old foals. Two weeks later, azithromycin for injection was administered by intravenous (i.v.) infusion at a dose of 5 mg/kg to the same foals. Plasma samples were collected after p.o. and i.v. administration. Peripheral blood PMN and bronchoalveolar lavage fluid and alveolar cells were collected after p.o. administration. Azithromycin concentrations were determined by reverse-phase high-performance liquid chromatography (HPLC) with coulometric electrochemical detection. Azithromycin p.o. absorption was variable with a mean systemic availability of 39% (+/-20%). The plasma half-life was 16 and 18.3 h after i.v. and p.o. administration, respectively. Azithromycin had a very large volume of distribution (V(d)) of 11.6 L/kg [V(d(ss))] and 12.4 L/kg [V(d(area))]. The large V(d) can be attributed to high tissue and intracellular concentrations, exhibited by the high concentration of azithromycin in PMN and alveolar cells. The PMN half-life was 49.2 h. Dosage of 10 mg/kg of azithromycin p.o. once daily for foals with R. equi pneumonia is recommended for further study.

Rhodococcus equi pulmonary infection in a pancreas‐alone transplant recipient: consequence of intense immunosuppression

We report the case of a pancreas-alone transplant recipient who developed Rhodococcus equi pneumonia after receiving multiple courses of antilymphocyte therapy for the treatment of recurrent acute pancreas allograft rejection. We also review and discuss the diagnosis, clinical course, and treatment of 18 cases of R. equi infection reported in solid organ transplant recipients. The lung is the most common primary site of infection, but R. equi infection is difficult to diagnose because of the pleomorphic, gram-positive, and partially acid-fast nature of the organism. Treatment usually involves a combination of antibiotics including rifampin, macrolides, vancomycin, and ciprofloxacin. The optimal duration of therapy is unknown, but relapse is common if the duration of treatment is less than 14 days. The duration of therapy should be guided by clinical recovery, culture results, and radiographic findings. Monitoring levels of immunosuppressive agents-such as tacrolimus and cyclosporine-is needed in order to avoid clinically significant drug interactions with rifampin or the macrolides when these agents are used in order to treat R. equi infection in the transplant population.

Rapid immunohistochemical detection of Rhodococcus equi in impression smears from affected foals on postmortem examination.

The first objective of this study was to develop an immunohistochemical procedure for rapid detection of Rhodococcus equi in impression smears from affected organs of foals on postmortem examination. The second aim was to demonstrate whether R. equi can be detected in smears of tracheal exudates collected from the same foals using an immunohistochemical method. Impression smears and cryostat and paraffin-embedded sections were made from the lungs and mediastinal lymph nodes of three foals (A, B and C) that had died of respiratory disease caused by R. equi, and also from the caudal mesenteric lymph node of foal A. Impression smears were made from the tracheal exudates of all foals. An affinity purified rabbit IgG was used for the immunohistochemical demonstration of R. equi. This antibody reacted with serotype 1 of R. equi in Ouchterlony's immunodiffusion and in the passive haemagglutination test, but not with other serotypes or with Streptococcus equi ssp. equi or Staphylococcus aureus, and failed to give an immunohistochemical reaction with Mycobacterium bovis or M. paratuberculosis. The immunohistochemical method proved to be of identical sensitivity to bacterial culture; moreover, from the lungs and mediastinal lymph nodes of one foal, R. equi could only be detected by this method. R. equi was demonstrated in smears of the tracheal exudates of all three foals. The results of this study indicate that the immunohistochemical method may be used for the rapid detection of R. equi in impression smears from the affected organs, especially abscesses, obtained postmortem, and possibly as a tool for diagnosing R. equi pneumonia in live foals by examining smears of tracheal aspirates.

Two new variants of the Rhodococcus equi virulence plasmid, 90 kb type III and type IV, recovered from a foal in Japan

This report describes the discovery of two new virulence plasmid types from a crossbred foal with Rhodococcus equi pneumonia in Kumamoto died with severe R. equi pneumonia and ulcerative enteritis. R. equi was isolated in large numbers and isolates from the foal were investigated for the presence of virulence-associated 15–17 kDa antigens (VapA) by colony blotting, using the monoclonal antibody 10G5, and by gene coding for VapA by PCR. Plasmid DNAs extracted from the isolates were digested with restriction endonucleases BamHI, EcoRI, EcoT22I, and HindIII. The digestion patterns that resulted divided the plasmids of these isolates into two closely related types. The digestion patterns were then compared with eight representative virulence plasmid types (85 kb types I, II, III and IV, 87 kb types I and II, 90 kb types I and II), which have already been reported. None of the EcoRI and EcoT22I digestion patterns of the eight representative plasmids matched those of the two plasmid types. We tentatively designated these new plasmid types as 90 kb type III and type IV, since HindIII and BamHI digestion patterns of the two plasmid types were identical with those of a 90 kb type I plasmid. This study, demonstrated that there are at least 10 distinct but closely related plasmids present in isolates from horses in the world.

Application of Sartwell's Model (Lognormal Distribution of Incubation Periods) to Age at Onset and Age at Death of Foals with Rhodococcus equi Pneumonia as Evidence of Perinatal Infection

The distributions of the incubation periods for infectious and neoplastic diseases originating from point‐source exposures, and for genetic diseases, follow a lognormal distribution (Sartwell's model). Conversely, incubation periods in propagated outbreaks and diseases with strong environmental components do not follow a lognormal distribution. In this study Sartwell's model was applied to the age at onset and age at death of foals with Rhodococcus equi pneumonia. The age at onset of clinical signs and age at death were compiled for 107 foals that had been diagnosed with R equi pneumonia at breeding farms in Argentina and Japan. For each outcome (disease and death), these data followed a lognormal distribution. A group of 115 foals with colic from the University of California were used as a comparison group. The age at onset of clinical signs for these foals did not follow a lognormal distribution. These results were consistent with the hypothesis that foals are infected with R equi during the 1st several days of life, similar to a point‐source exposure.

Application of Sartwell’s Model (Lognormal Distribution of Incubation Periods) to Age at Onset and Age at Death of Foals with Rhodococcus equi Pneumonia as Evidence of Perinatal Infection

The distributions of the incubation periods for infectious and neoplastic diseases originating from point-source exposures, and for genetic diseases, follow a lognormal distribution (Sartwell's model). Conversely, incubation periods in propagated outbreaks and diseases with strong environmental components do not follow a lognormal distribution. In this study Sartwell's model was applied to the age at onset and age at death of foals with Rhodococcus equi pneumonia. The age at onset of clinical signs and age at death were compiled for 107 foals that had been diagnosed with R. equi pneumonia at breeding farms in Argentina and Japan. For each outcome (disease and death), these data followed a lognormal distribution. A group of 115 foals with colic from the University of California were used as a comparison group. The age at onset of clinical signs for these foals did not follow a lognormal distribution. These results were consistent with the hypothesis that foals are infected with R. equi during the 1st several days of life, similar to a point-source exposure.

HIV-infected patient with a Rhodococcus equi pneumonia

The case history of a HIV patient with a pulmonary infect of Rhodococcus equi is presented. He recovered after prolonged treatment with antibiotics and lobectomy. The Rhodococcus equi infection was the presenting symptom of his impaired immune status caused by HIV infection. (See Editorial p. 1)

Some Epidemiological Aspects of Rhodococcus equi Infection in Foals in Japan: A Review of 108 Cases in 1992-1998.

One hundred and eight foals were necropsied and examined for Rhodococcus equi infection from 1992 to 1998 in Hokkaido and Aomori, Japan. Fifty-four of 108 cases had been clinically diagnosed as having R. equi pneumonia, whereas the remaining 54 were diagnosed with non-R. equi pneumonia (23 foals), arthritis (6 foals) and other diseases (25 foals). Pathologically, 104 foals were shown to have suppurative pneumonia with abscesses, and the remaining 3 had intestinal involvement without pulmonary lesions and one had osteomyelitis. Based on the pathology and bacteriology, 108 were classified into 5 disease types: pneumonia (44 cases; suppurative bronchopneumonia), enteritis (3 cases; ulcerative enteritis associated with suppurative lymphadenitis of the intestines), mixed (25 cases; pneumonia, enteritis, and intestinal lymphadenitis), transitional (35 cases; pneumonia and intestinal lymphadenitis), and osteomyelitis (1 case). Eighty-three of the 108 foals (25 foals died due to non-infectious causes) were analyzed for age distributions at the first clinical examination and death. About 75% (62 foals) of the foals showed clinical signs within 2 months of age, peaking at 40 days, and the mean age at the clinical examination was 53.6 days. About 81% (67 foals) died within 3 months of age, peaking at 60 days, and the mean age at death was 77.2 days. About 57% (47 foals) died within 2 weeks after the first clinical examination, and mean days for treatment were 21.7. Mean ages at the clinical signs and death of the 83 foals were compared statistically according to breed, sex, birth month, and disease types, but the difference was not significant. Bacteriologically, virulent R. equi was isolated from lesions of all the 108 foals. Virulent isolates from the foals bred at Hokkaido and Aomori contained an 87-kb type II or a 90-kb plasmid with a different ratio. From this surveillance, it is clear that R. equi infection in foals is still one of the most important diseases in horse-breeding farms in Japan.

Two Cases of Dead Foals Associated with Rhodococcus equi Pneumonia in Turkey.

Rhodococcus equi has been recognized as an equine pathogen since 1923 and is a worldwide pathogen in foals. Up to now, there has been one report on R. equi infection in an Arabian foal in Turkey. We report here two cases of R. equi pneumonia diagnosed in Turkish foals. R. equi was isolated from pure cultures obtained from lung abscesses of two dead foals which were sent to the laboratory from distinct stud-farms in the Izmit district, Turkey, due to the increasing mortality of foals with pneumonia. These isolates were analyzed by plasmid and protein profiles: one isolate had an 85-kb type I virulence plasmid and the other was considered avirulent. Virulent R. equi strains possessing an 85-kb type I or an 87-kb type I were isolated from one of the stud-farms with the problem. These results indicate that the stud-farm was contaminated with virulent R. equi.

Peripheral Blood Lymphocyte Subpopulations and Immunoglobulin Concentrations in Healthy Foals and Foals with Rhodococcus equi Pneumonia

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 (CD41) or cytotoxic (CD81) 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 occurringRhodococcus equipneumonia 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 agerelated changes in the cell‐mediated immune system in horses. Absolute circulating CD41 and CD81 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 withR equipneumonia 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.

Peripheral blood lymphocyte subpopulations and immunoglobulin concentrations in healthy foals and foals with Rhodococcus equi pneumonia.

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.

Infection by Rhodococcus equi in a patient with AIDS: histological appearance mimicking Whipple's disease and Mycobacterium avium-intracellulare infection.

Rhodococcus equi pneumonia with systemic dissemination is being reported increasingly in immunocompromised patients. This is the first case report of disseminated R equi infection with biopsy documented involvement of the...

RHODOCOCCUS EQUI INFECTION IN TRANSPLANT RECIPIENTS

Rhodococcus equi is an opportunistic pathogen that usually causes infection in immunocompromised hosts, mainly human immunodeficiency virus-positive patients, yet solid organ transplant recipients may be affected as well. Infections in this group of patients have not been sufficiently analyzed. We report an R equi pneumonia in a heart transplant recipient and review another 11 cases. Infection appeared a mean of 49 months (range 1-180) after transplantation. Lung was primarily involved in 10 cases (83.3%). The remaining two cases presented with a paravertebral abscess and a purulent pericarditis. Invasive techniques were necessary to reach the diagnosis in nine cases. One patient healed with surgical resection of the lesion; the remaining 11 received antimicrobial agents. Six of them required additional surgical treatment. Three patients died. Clinicians should consider R equi when evaluating a solid organ recipient with an asymptomatic lung nodule. Microbiology laboratories should be alerted in these cases because it could be mistaken for a contaminant diphtheroid and will not respond to the standard empirical therapy.

The association of erythromycin ethylsuccinate with acute colitis in horses in Sweden.

In Sweden there are several reports of mares developing acute colitis while their foals were being treated orally for Rhodococcus equi pneumonia with the combination of erythromycin and rifampicin. In this study 6 adult horses were given low oral dosages of these antibiotics, singly or in combination. Within 3 days post administration of erythromycin, in one case in combination with rifampicin, 2 horses developed severe colitis (one fatal). Clostridium difficile was isolated from one of the horses, whereas no specific pathogens were isolated from the other. Both horses had typical changes in blood parameters seen in acute colitis. Clostridium difficile was also isolated from the faeces of a third horse given an even lower dosage of erythromycin in combination with rifampicin. This horse developed very mild clinical symptoms and recovered spontaneously. In the fourth horse given erythromycin only, very high numbers of Clostridium perfringens were isolated. The horses given rifampicin only did not develop any clinical symptoms and there were no major changes in their faecal flora. In conclusion, it has been demonstrated that low dosages of erythromycin ethylsuccinate can induce severe colitis in horses associated with major changes of the intestinal microflora. Clostridium difficile has been demonstrated as a potential aetiological agent in antibiotic-induced acute colitis.

Comparison of tracheal aspiration with other tests for diagnosis of Rhodococcus equi pneumonia in foals

The diagnostic value of tracheal aspiration was evaluated through comparison with other diagnostic methods using an experimental model of Rhodococcus equi (R. equi) pneumonia in foals. Pneumonia was induced by spraying of the virulent R. equi strain ATCC 33701 into the trachea of foals. All foals developed fever from 11 to 16 days after bacterial inoculation. One foal was euthanized on day 26 due to its poor prognosis, and other foals euthanized on day 43. During the experiment, some tests for diagnosis of Rhodococcus equi pneumonia such as tracheal aspiration, radiography, serodiagnosis and fecal culture were carried out. R. equi was continually isolated from tracheal aspirates collected via a silicone catheter inserted transnasally on day 8 to day 32 after bacterial inoculation. On the other hand, radiography, serodiagnosis and fecal culture were demonstrated to be valuable diagnostic methods, but to be limited compared with tracheal aspiration. Indirect fluorescent antibody technique (IFA) using a monoclonal antibody against the 15- to 17-kDa virulence-associated antigens (VapA) of R. equi and PCR targeting the structural gene of VapA detected bacteria in tracheal aspirates less sensitively than the isolation technique although they were more rapid. Therefore, we conclude that a combination of tracheal aspiration and bacterial isolation was the most valuable method for routine diagnosis of R. equi pneumonia in foals.

Prevention of Rhodococcus equi pneumonia of foals using two different inactivated vaccines

Two different, inactivated, aluminium salt adsorbed vaccines, one containing a R. equi strain (serotype 1, 10 9 CFU/ml and equine herpesvirus 2 (EHV-2) (1.5 × 10 7 PFU/ml) and another containing R. equi only were used on three studfarms to determine whether the disease can be prevented by vaccination of both pregnant mares and their foals. Pregnant mares received two 3 ml doses of vaccine intramuscularly 6 and 2 weeks before parturition and their foals were vaccinated on two or three occasions at 3, 5 or 7 weeks of age. The efficacy of the vaccines was evaluated on the basis of the clinical signs, serological response (indirect haemagglutination and virus neutralisation tests) and culture of R. equi from sick or dead foals. On studs A and B where the bivalent vaccine was used, 24 and 14 foals were born respectively to the vaccinated mares but no clinical case or death occurred due to R. equi pneumonia, while out of the 10 nonvaccinated control foals (stud B) two succumbed to R. equi pneumonia and 4 other foals had to be treated with antibiotics because of fever, coughing and dyspnea. In stud C, where the vaccine containing R. equi strain alone was used, all 15 vaccinated foals remained healthy but one of the 11 control foals died of suppurative R. equi pneumonia and one foal had to be treated due to R. equi pneumonia. R. equi strains (serotype 1) were isolated from the lungs of all dead foals. The serological response was very weak to both R. equi and the EHV-2 strain. Antibody titres in the colostrum of the vaccinated mares against R. equi (in studs A and B, geometric mean 3.79 ± 1.63 and 4.14 ± 1.46, respectively) were practically not higher than titres in the controls (in stud B geometric mean 2.12 ± 1.96). More antibody was present in the colostrum samples against EHV-2 (geometric mean 6.1 + 1.4 compared to 2.5 ± 1.2). In all foals antibody levels were hardly detectable against both R. equi and EHV-2 until five weeks of age. From the fifth week, antibody levels gradually increased and by the ninth week their reached a titre of 5.5 ± 1.8 (2.7 ± 1.2 in the control foals) against R. equi and 5.2 ± 1.4 against EHV-2. The favorable clinical results and the low antibody titres in the sera of the vaccinated foals during the first week of life suggest that protection probably was due to repeated vaccination of young foals rather than to vaccination of mares.

Use of Rhodococcus equi virulence-associated protein for immunization of foals against R equi pneumonia

Abstract Objective To evaluate use of the virulence-associated protein of Rhodococcus equi in immunizing foals against R equi pneumonia. Animals Eight (experimental group) and 6 (controls) mares with their foals. Procedure Virulence-associated protein extracted from R equi was used to prepare an acetone-precipitated, Triton ×-extracted (APTX) antigen. After determination of the efficacy of passive immunization, in untreated foals or in foals given plasma from a horse vaccinated with APTX antigen or from a nonvaccinated horse, a field trial was done to evaluate the efficacy of vaccination of 8 mares, twice with APTX before parturition, and of their foals at ages 3 and 5 weeks; 6 mares and their foals served as unvaccinated controls. All 2-day-old foals were given plasma from local donor horses inoculated with a locally produced bacterin. Serum opsonizing activity produced by vaccination with APTX was determined. Passively immunized foals were challenge exposed with an aerosol of virulent R equi. Foals of the field trial were exposed to enzootic R equi infection. Results Inoculation with APTX resulted in high IgG antibody titers with opsonizing activity. Passive immunization of foals with plasma from an immunized horse enhanced bacterial clearance from the lungs, compared with that in foals not given plasma or given plasma without APTX antibodies. Vaccination of mares and foals exposed to natural infection resulted in development of R equi pneumonia in 4 of 8 vaccinated foals, but in only 1 of 6 unvaccinated foals,. Conclusions Vaccination with APTX antigen led to high-titer, opsonizing antibody. Plasma from a vaccinated horse appeared to enhance clearance of R equi from the lungs of foals. Paradoxically, vaccination of mares and their foals with APTX antigen did not protect foals and may have enhanced R equi pneumonia in the foals. (Am J Vet Res 1997;58:356-359)

Radiologic features of Rhodococcus equi pneumonia in aids

This report outlines the radiological features observed in three cases of Rhodococcus equi (R. equi) pneumonia in AIDS (acquired immunodeficiency syndrome) and reviews another 45 radiological reports published of this emerging opportunistic pneumonia in Human Immunodeficiency Virus (HIV) infected patients. The clinical signs in our three patients consisted in a subacute onset of respiratory symptoms and fever. A low lymphocyte count (<200 cells/mm 3), pulmonary infiltrates, and pleural effusion was present in all three cases. Cavitary pneumonia was observed in two patients, and pericardial effusion in another. In this series CD4 lymphocyte count <200/mm 3 was seen in 29 of the 48 patients (60.4%). All 48 patients had abnormal findings on chest radiographs. Abnormalities involved the upper lobes in 26 of the 48 patients (55%). Cavitation was reported in 37 of the 48 cases (77%). R. equi pneumonia may not be as rare as the paucity of case reports suggest. Consequently, a cavitary pneumonia in HIV infected patients with a low CD4 lymphocyte count (< 200 mm 3) with a subacute onset, an upper lobe predilection, and/or a poor response to conventional antibiotic therapy should be considered as suspect of R. equi infection.