Strangles under the microscope in study of Arabian horses in Egypt

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Microscopic examination of Streptococcus equi stained with Gram-stain showing Gram-positive cocci arranged in pairs and chains.
Microscopic examination of Streptococcus equi stained with Gram-stain showing Gram-positive cocci arranged in pairs and chains.

Nearly a quarter of the 490 Arabian horses involved in a 13-month study in Egypt were diagnosed with the bacterial infection strangles, researchers report.

Strangles is an infectious respiratory bacterial disease of horses caused by Streptococcus equi.

Ahmed Neamat-Allah and Hend El Damaty examined the animals at a government-run horse station in Cairo province during weekly visits from January 2015 to February 2016, and took 120 nasal swabs and pus samples for laboratory examination.

The pair, writing in the journal Veterinary World, said 24.48% of the 490 horses were clinically diagnosed as having strangles, with the most common clinical signs including fever and nasal discharge of mucus and pus.

They said S. equi was found in 102 of the samples, for a prevalence rate in which the infective agent was isolated at 20.8%. In the other 18 samples (3.67%) non S. equi isolates were identified.

The researchers said reasons for the failure to identify the presence of S. equi in clinical strangles cases could involve low bacterial shedding according to the stage of the disease, variations in the method of sample collection, or overgrowth of other bacteria, particularly Streptococcus zooepidemicus.

An Arabian horse with strangles, showing a submaxillary lymph node abscess.
An Arabian horse with strangles, showing a submaxillary lymph node abscess.

There was, they said, increasing evidence that S. zooepidemicus can also act as a contagious upper respiratory pathogen in horses.

They said their findings were in agreement with the results of two previous studies in Egypt that found the prevalence rates of strangles in horses was 19.57% and 20.6%, respectively. However, their findings were at odds with another study in which 250 horses were examined, with 113 (45.2%) of them positive for S. equi.

Horses aged under 1 year were the most prone to strangles, at 32.25%, followed by horses aged 1 to 2, at 20%, and then horses aged 2-4, at 11.89%, Neamat-Allah and El Damaty reported.

The pair, from Zagazig University, singled out 20 infected horses in order to monitor blood and biochemical changes during the course of the disease and after 10 days of treatment with procaine penicillin and benzathine penicillin.

The ill horses were found to be anemic, with a range of other significant changes also identified.

A foal with strangles showing a swollen parotid  lymph node.
A foal with strangles showing a swollen parotid lymph node.

In conclusion, they said a higher occurrence of S. equi was recorded in young foals. S. equi, they noted, easily spread from infected to susceptible horses through contaminated water, surfaces and objects.

“Good biosecurity is important if the welfare and economic costs of an outbreak are to be reduced.”

Natural S. equi infection in Arabian horses revealed some changes to blood and biochemical parameters, they noted, but without affecting liver and kidney tissues.

Their tests revealed the presence of respiratory acidosis and an increase of cardiac troponin I in infected horses, which could indicate pneumonia secondary to strangles with risk of heart involvement.

Treatment with procaine penicillin with benzathine penicillin would be useful in this regard, they said.

Neamat-Allah ANF, El Damaty HM (2016) Strangles in Arabian horses in Egypt: Clinical, epidemiological, hematological, and biochemical aspects, Veterinary World, 9(8): 820-826.

The study, published under a Creative Commons License, can be read here

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