Acute clinical, hematologic, serologic, and polymerase chain reaction findings in horses experimentally infected with a European strain of Anaplasma phagocytophilum.

The research article details an experiment where six horses were intentionally infected with a Swedish strain of Anaplasma phagocytophilum, studying the resultant clinical, hematological, serological, and molecular effects. The study found that despite minor genetic differences, the European strain proved similar to a Californian strain, with Polymerase chain reactions (PCR) providing considerable promise for early diagnosis.

Experimental Procedure and Findings

• The research commenced with six horses being experimentally infected with a Swedish variant of Anaplasma phagocytophilum, administered through horse blood.
• The team discovered that the PCR signal – a primary indicator of the presence of infection – could be consistently perceived between two and three days before any external clinical signs became visible. They also noted that this signal continued for four to nine days after the medical symptoms had subsided.
• Inclusions, which are structures formed inside the cell after infections, first emerged an average of 2.6 days after the fever kicked in.

Comparison with Other Findings

• The clinical signs and hematologic changes observed in the horses closely resembled those previously reported for diseases caused by A. phagocytophilum and other human-derived agents.
• These signs and changes were indistinguishable, suggesting an overall similarity between the European strain and others, despite minor genetic differences.
• There was an initial delay in antibody response, which was noted 12-16 days after inoculation, peaking rapidly within 3-7 days of clinical illness.

Conclusions and Implications

• Although one horse did die during the acute stage of the disease, its initial clinical signs and hematologic changes did not differ from the other horses, further supporting the consistent nature of the infection.
• The researchers concluded that the European equine-derived strain of A. phagocytophilum might be almost as pathogenic as the Californian agent.
• Significantly, the team expressed confidence in the PCR testing ability to enlarge the diagnostic window, enabling diagnosis during the early days when inclusions are not yet visible in blood smears.