Strangles — why temperature taking and quarantine stop the spread

Strangles — German Druse — is caused by the bacterium Streptococcus equi subspecies equi and is one of the most contagious diseases of the horse at all. It affects the upper airways and the associated lymph nodes and spreads rapidly in herds if it is not recognised early and consistently contained. Exactly for this reason strangles is less a question of treating the individual animal than a question of herd management.

How the infection runs

The pathogen spreads via infectious nasal discharge and via the pus of ruptured abscesses — directly from horse to horse, but above all indirectly via contaminated hands, clothing, grooming kit, drinkers, buckets, headcollars and shared stable areas. A single shared water trough or unchanged grooming kit can infect a whole group. Decisive for the control is a temporal peculiarity: shedding of the pathogen as a rule only begins one to two days after the rise in temperature. Whoever takes temperatures daily can therefore isolate a freshly infected horse before it becomes contagious — a central lever of control.

Leading signs — fever first

The earliest and most reliable sign is fever, which often precedes the rest by one to two days. There follow dullness, loss of appetite, purulent nasal discharge and the eponymous swollen, painful lymph nodes in the throatlatch and between the jowls, which can rupture and discharge pus. Some horses hold the neck extended and swallow with difficulty. The course ranges from mild to severe forms; feared is the spread to more distant lymph nodes.

Biosecurity: isolate, measure, separate

Three simple principles carry the protection. First: every newly arriving horse is isolated before contact with the herd for a period of several weeks and observed during this time — new arrivals are the most common port of entry. Consensus recommendations name an order of magnitude of around three weeks for the isolation of new horses. Second: daily temperature taking, both in new arrivals and in an affected herd, in order to detect new cases before shedding. Third: strict hygiene and separation of care — own buckets, own grooming kit, hand disinfection and protective clothing for the isolated group, as well as a thought-through workflow from healthy to suspect, never the reverse.

The silent carrier problem in the guttural pouch

A part of the horses does not become completely free of the pathogen after the seemingly survived disease: in the guttural pouches — air-filled outpouchings of the Eustachian tube — thickened pus can harden into solid concretions and harbour the pathogen for months to years. Such clinically healthy persistent shedders can shed the pathogen again and again and trigger new outbreaks without seeming ill themselves. They are the reason why an outbreak is not automatically over even after the symptoms have subsided. The tracing of such carriers — for instance via guttural pouch endoscopy and pathogen detection — belongs in veterinary hands and is part of a clean outbreak management.