Diagnosis and Treatment Experience of Secondary Infection with Hemotropic Mycoplasma (Eperythrozoon) in Canine Distemper
Canine distemper mainly affects young dogs, and its pathogen is canine distemper virus. Affected dogs are characterized by a biphasic fever pattern, rhinitis, severe digestive tract disorders and respiratory tract inflammation. However, cases of mixed infection of canine distemper and canine hemotropic mycoplasma (Eperythrozoon) are relatively rare.
1 Onset and Symptoms
The affected dog was 8 months old, clinically diagnosed with canine distemper, with a disease course of 1 week, and had already been treated with canine pentavalent serum, antibiotics, etc.
When it came to our hospital for treatment, it was confirmed to have secondary lobar pneumonia, with a body temperature of 40.6 degrees C, showing a biphasic fever pattern (that is, at the beginning of the disease the body temperature rises to about 40 degrees C and lasts for 1-2 d, then drops to normal, and after 2-3 d the body temperature rises again); when the body temperature rose for the second time, respiratory symptoms appeared: the affected dog coughed, sneezed, had serous to purulent nasal discharge, and a dry nasal mirror; the eyelids were swollen, with purulent conjunctivitis, and later corneal ulcers occurred; on the skin of the external auditory canal there were millet-sized red spots, edema and purulent papules; vomiting was common; initially constipation, and soon diarrhea, with foul-smelling feces, sometimes mixed with blood and gas bubbles.
While our hospital continued treatment with hyperimmune serum, it was combined with cephalosporin antibiotics and other drugs as auxiliary treatment, bringing the condition under control.
One week later, the dog was brought to our hospital again by its owner, with a body temperature of 40.3 degrees C, decreased appetite, dry feces, nasal discharge, accelerated heart rate, visible mucous membranes initially congested and later pale, mild jaundice, and yellow urine, similar to pig hemotropic mycoplasma (Eperythrozoon).
2 Laboratory Diagnosis
2.1 Blood Examination
Take 1 drop of venous blood from the forelimb (or anticoagulated blood) onto a glass slide, add an equal amount of normal saline and mix well, cover with a coverslip, and observe under a 400-600x dark-field microscope; the organisms can be seen as spherical, comma-shaped, rod-shaped or granular. A single hemotropic mycoplasma organism has strong motility and can roll or twist forward, backward, left and right; generally the activity of a single large organism is weaker than that of a small one, while those gathered in clusters or close to or attached to red blood cells have weakened or no activity.
If on-site examination is not possible, collect 1 mL of anticoagulated blood (with heparin or sodium citrate added), add 1 mL of 10% formalin solution, mix well, and send it to the laboratory for acridine orange staining examination; the hemotropic mycoplasma organisms can be seen as light to deep orange-yellow.
2.2 Blood Smear Staining Examination
For blood smear examination, collect blood from the forelimb vein of the affected dog (do not wipe with an alcohol cotton ball, to prevent changes in red blood cells), drop it onto a glass slide, spread the smear and stain with Wright's stain; the organisms appear purple-blue, then examine under high power, and the red blood cells can be seen as stellate or serrated, with 1-3 blue-black granules on the surface, and in more severe cases 3-5 or 10; organisms can also be seen in the plasma. Under oil immersion after Giemsa staining, the hemotropic mycoplasma organisms are stained light purple, with a white ring around the periphery; when the fine adjustment screw is turned, the refractility is strong, and the center of the organism is bright, resembling a vacuole. The morphology of canine hemotropic mycoplasma is mostly ring-shaped, round, oval, blunt dot-shaped, rod-shaped and horseshoe-shaped, among other forms, mostly gathered on the surface of red blood cells, at least 3-5 and at most 20-30, with the red blood cell edges not smooth and uneven. The red blood cells lose their spherical shape, with irregular edges, some appearing gear-shaped, stellate, and some appearing as irregular polygons and various other flattened shapes. The hemotropic mycoplasma organisms move freely, able to extend, rotate, and move forward, backward, left, right, up and down.
Microscopic examination should be linked with clinical symptoms and pathological changes to confirm the diagnosis of this disease.
3 Treatment
Xuechongting (yellow pigment), Aokelin, Qidaosu, Tianneng, Baidukuaidian, etc. were respectively injected intramuscularly at a dose of 1 mL/kg, twice a day, and Shengxuebao was injected intramuscularly once a day; after 1 week of treatment, the condition was brought under control. After the above treatment, a follow-up visit 2 weeks later showed the condition was stable, body temperature normal, and appetite returned to normal.
4 Summary and Experience
4.1 Regular Preventive Vaccination
To improve the immune effect, vaccination should be carried out according to the following immunization program. The first immunization for puppies is at 6 weeks of age, the second immunization at 8 weeks of age, and the third immunization at 10 weeks of age. Thereafter, immunize once a year, with each immunization dose of 2 mL, which can achieve a certain immune effect. Since it takes a certain period (7-10 d) after vaccination to produce a good immune effect, and canine distemper is currently rather widespread, some dogs have already been infected with canine distemper virus before immunization but do not show clinical symptoms; under the influence of certain stress factors (changes in living conditions, long-distance transport, etc.), clinical symptoms can still be triggered and the disease can develop. This is one of the important reasons why some dogs still develop canine distemper and other diseases after immunization. To improve the immune effect and reduce the infection rate, when purchasing puppies, it is best to first give the puppies 4-5 mL of canine pentavalent hyperimmune serum, inject once more after 1 week, and then after 2 weeks vaccinate with canine pentavalent vaccine according to the above immunization program; this is both safe and reliable and can reduce the incidence rate.
4.2 Strengthen Veterinary Sanitary and Epidemic Prevention Measures
During the epidemic season of this disease, contact with affected dogs is strictly prohibited.
4.3 Timely Isolation and Treatment
Timely detection of affected dogs, early isolation and treatment, and prevention of secondary infection are the keys to improving the cure rate and reducing the mortality rate. In the early stage of the disease, anti-canine distemper hyperimmune serum (or canine pentavalent hyperimmune serum) or serum (or whole blood) from dogs recovered from this disease can be injected intramuscularly or subcutaneously. The dosage of serum should be determined according to the condition and the size of the dog; usually 5-10 mL per time, used continuously for 3-5 d, can achieve a certain therapeutic effect. While using hyperimmune serum treatment, combined application of Kangduling lyophilized powder for injection can improve the therapeutic effect; its usage and dosage are: before treatment, dissolve Kangduling with 20 mL of sterilized normal saline or water for injection, and for medium-sized dogs administer 2-4 vials by intravenous drip; for younger dogs, the dosage can be reduced as appropriate. In addition, early application of antibiotics combined with symptomatic treatment is of great significance for preventing secondary infection by bacteria and other diseases and for the recovery of affected dogs.
4.4 Strengthen Disinfection
Kennels and exercise yards should be thoroughly disinfected with various disinfectants, such as Baisusha, 1210, Weidao brand disinfectant, sodium hypochlorite, etc.
Canine hemotropic mycoplasma disease was discovered in our hospital for the first time, especially as a secondary infection to canine distemper, which was also discovered for the first time. During treatment, symptomatic treatment measures for canine distemper should be taken as early as possible to prevent decreased immunity and secondary infection by other diseases, including infection by canine hemotropic mycoplasma.