Effect of viral inoculum size on appearance of clinical signs in equine Getah virus infection.

This research explored how the size of a viral dose affects the severity and manifestation of symptoms in horses infected with the Getah virus (GV). The study found that horses displayed different symptoms based on the size of the viral inoculation, with the larger doses of virus being associated with more severe clinical signs.

Research Methodology and Parameters

• The experiment involved six experimental horses, each infected with the Getah virus, a mosquito-borne virus that affects horses.
• The viral dose, indicated as TCID50, refers to the amount of virus required to infect 50% of a given population or sample. In this research, each horse received an intramuscular injection with a different dose of the virus, ranging from 10(1.3) to 10(6.3) TCID50 of the MI-110 strain of GV.

Observations and Findings

• Every horse that was inoculated with more than 10(3.3) TCID50 of the virus developed a number of symptoms including fever (pyrexia), swelling in the hind legs (edema), runny nose (serous nasal discharge), a lower than normal amount of lymphocytes (lymphopenia), and the presence of the virus in the blood (viremia) in the early stage of the disease.
• Further observations showed that an enlargement of the submandibular lymph node, a symptom of the body’s immune response, was only observed in horses that were inoculated with 10(5.3) and 10(6.3) TCID50 of the virus.
• Interestingly, horses inoculated with 10(4.3) TCID50 or less developed typical skin eruptions, suggesting that smaller doses led to noticeable skin reactions.
• It was also noted that the chance of seeing both skin eruptions and enlargement of the submandibular lymph node in a single horse was rare.

Conclusions

• The study confirms that the size of the viral dose (inoculum) influences the appearance and severity of clinical signs in equine GV infection.
• The results can help to enhance understanding of the pathology of the GV and aid in the development of strategies for the management and treatment of equine diseases caused by this virus.