A very common horse herpesvirus. It causes airway infections, abortion storms in pregnant mares and a dangerous neurological form, and hides in the body for life.

The most common viral cause of airway infection in horses. Usually a mild fever and runny nose, rarely abortion. Like EHV-1, it stays in the body for life.

A contagious virus spread by breathing and by breeding. Often silent, it can cause fever, swelling and abortion, and some stallions shed it in semen for years.

A bacterial infection spread mainly in urine. In horses it is linked to abortion and recurrent eye inflammation (moon blindness). People can catch it too.

A bird-associated bacterium that can cause late abortion and fatal illness in newborn foals. Infected placentas can give people psittacosis, a serious pneumonia.

Highly contagious 'horse flu' that spreads fast through yards and events. Rarely fatal, but causes fever, harsh cough and weeks off work; vaccination is core in Germany.

A highly contagious bacterial infection of the throat and head lymph nodes. It spreads quickly through yards, and some recovered horses silently carry it for years.

A normal resident of horses' airways and genital tract that causes disease when defences drop. It is a leading cause of pneumonia, womb infection and abortion in horses.

A soil bacterium causing slow-developing pneumonia with lung abscesses in foals aged 1–6 months. It is common on some breeding farms and early signs are easily missed.

A rare, usually fatal brain inflammation of horses in parts of Germany, Austria, Switzerland and Liechtenstein. The virus comes from a wild shrew; infected horses do not pass it on.

Mosquito-borne virus circulating in wild birds, present in Germany since 2018. Most infected horses stay healthy, but some develop severe, sometimes fatal brain and spinal cord disease.

Gut bacteria carried by many animals and the commonest bacterial cause of food poisoning in people. In horses, their role in causing diarrhoea is still unclear.

A gut bacterium whose toxins cause sudden, often severe diarrhoea (colitis). Antibiotics, hospital stays and feed changes raise the risk; young foals can also fall ill.

A normal soil and gut bacterium. Certain toxin-producing strains cause sudden, often bloody diarrhoea that can kill newborn foals within days; adults can develop colitis.

A tiny parasite that can cause diarrhoea in young foals, often without symptoms. It matters because the main type, C. parvum, also infects people.

A common gut parasite of many animals and people. Horses, especially foals, often carry it without signs; illness in horses is rarely reported.

Causes equine proliferative enteropathy: a thickened small intestine leaks protein, so weanlings lose weight and develop swellings. Diarrhoea is not always present; mostly autumn–winter.

The most common viral cause of diarrhoea in foals. It spreads extremely fast on studs and causes watery diarrhoea and dangerous dehydration, mainly in foals under two months.

A gut bacterium causing fever, severe diarrhoea and colic, especially in stressed, sick or hospitalised horses and newborn foals. It spreads easily and can infect people.

Antibiotic-resistant staph bacteria that horses can carry unnoticed in the nose. They can cause hard-to-treat wound and surgical infections and pass between horses and people.

A common, contagious fungal skin infection causing round bald, scaly patches, often under tack. Rarely dangerous, but spores persist for months and people can catch it.

Small redworms occur on practically every horse farm. Heavy worm burdens cause weight loss, diarrhoea or colic, and wormer resistance is widespread, so base worming on dung tests.

A roundworm living in the airways that donkeys carry, usually without signs. Horses grazing with donkeys can develop a stubborn cough that does not respond to antibiotics.

Two tick-borne blood parasites that destroy red blood cells, causing fever and anaemia. Recovered horses often stay carriers, and a few horses have now caught it in Germany.

A tick-borne bacterium that infects white blood cells and causes sudden high fever in horses. Found wherever the castor bean tick lives, including Germany; antibiotics work well.

A tick-borne bacterium that infects many horses, yet proven illness in horses is rare. Documented problems include eye inflammation, nervous system disease and skin lumps.

A herpesvirus that nearly all horses catch as foals and carry for life. Usually harmless; its role in eye inflammation and airway disease is still debated.

A herpesvirus spread mainly by mating. It causes painful blisters and sores on the genitals of mares and stallions, disrupting the breeding season, but is rarely serious.

A herpesvirus most horses carry without problems. In some horses, mainly middle-aged ones, it is linked to a serious lung-scarring disease (EMPF) causing cough and weight loss.

A widespread respiratory virus, often found in healthy horses and usually mild. It can be deadly for foals born with an inherited immune defect (SCID), seen in Arabians.

A blood-borne virus disease with no cure or vaccine. Infected horses carry the virus for life, often without signs, so they are a lasting source of infection.

A parasite of the brain and spinal cord found in the Americas, spread by opossums. Elsewhere, including Europe, it affects only horses that have lived there.