General Hospital actress Barbara Tarbuck dies of human mad cow disease at 74

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Actress Barbara Tarbuck died on Monday at the age of 74 after contracting a human version of mad cow disease

Barbara Tarbuck, a regular on the iconic soap opera General Hospital, has died of human mad cow disease at the age of 74.

The rare, fatal brain disorder affects fewer than 300 people a year in the United States.

While it can be contracted from contaminated meat, 85 percent of cases have no known cause. Recent studies suggest it could lie dormant for years after eating contaminated meat. 

At first, victims of the illness (Creutzfeldt-Jakob disease) experience memory loss, behavior changes, blurred vision and issues with coordination.

Within days their mental deterioration becomes more severe, leading to blindness, spasms, bodily weakness, and sometimes a coma. 

CJD typically leads to death within a few weeks or months of symptoms arising. 

Tarbuck's daughter, producer Jennifer Lane Connolly, announced the news of her mother's death on Friday. The Hollywood veteran died in her Los Angeles home on Monday. 

Tarbuck's 14-year run on the ABC soap, from 1996 until 2010, was that of Lady Jane Jacks, the mother of Jax Jacks (Ingo Rademacher). 

She also had regular roles on two other soap operas during the 1980s, CBS's Falcon Crest and NBC's Santa Barbara.

Signature role: Tarbuck's most prominent turn on screen was as Lady Jane Jacks for 14 years. Here, she was seen with co-stars (left-to-right) Ingo Rademacher, Laura Wright and Aaron Refvem

Tarbuck's career was still thriving shortly before her death, having appeared on five episodes of American Horror Story in 2012 as nun Mother Superior Claudia, the mother of Elsa Mars (Jessica Lange).

CJD is notoriously difficult to diagnose.

It is done by clinical observation and a process of elimination, ruling out other possible causes for the patient's symptoms. 

The only real way to confirm a diagnosis is through an autopsy or brain biopsy.

It is not clear what form of CJD Tarbuck contracted. 

There are four kinds: Sporadic CJD, Familial CJD, Variant CJD, and Iatrogenic CJD. 

The most common is sporadic CJD, which accounts for 85 percent of cases. There is no known cause for this strain. 

The familial strain, caused by a genetic mutation inherited from a parent, accounts for about 10 percent of cases. 

The other two forms are caused by contaminated meat. 

Recent studies suggest the illness could lie dormant for up to 50 years, which could explain how some people get the illness seemingly for no reason. 

Indeed, evidence collected by Britain's Health Protection Agency (HPA) in 2011 suggested that one in 4,000 people who were eating meat before 1996 is probably carrying CJD.

After that date, cattle infected with mad cow disease in Britain were, theoretically, removed from the food chain.

That could mean that as many as 15,000 people in Britain could be affected, and possibly many more in the United States. 

And experts fear CJD might be more prevalent in older people.

Mad cow disease, or bovine spongiform encephalopathy (BSE), first emerged in the mid-1980s as a result of 'cannibalism' - giving cows (natural grass-eaters) beef offal.

The proteins, called prions, that cause BSE were found in large quantities in the brains, spinal cords and spleens of cattle.

When animal carcasses were ground down to form feed stuff for other cattle, prions were passed on.

These prions then colonised the brains of the cattle which ate them.

Finally, when these cows were factory farmed and turned into offal for school dinners or baby food, the prions were passed to humans.

That is when the disease transformed into something else. 

In humans, the prions developed a new form of fatal human dementia called new variant CJD (or, vCJD).

The illness was first identified in 1996. 

These prions are entirely new infectious agents, completely different from viruses, bacteria or parasites.

They are faulty versions of healthy proteins in brain and nervous tissue that then induce their neighbours to become faulty. 

All signals are disrupted or shut down completely, leading to almost certain death.

As a medical examiner investigates Tarbuck's illness, tributes have flooded in for the actress. 

A veteran of virtually every medium, Tarbuck racked up credits in TV, film, stage and radio, starting at the age of nine, when she had a recurring role on Storyland, a Detroit radio show aimed at kids.

In addition to her signature roles on the aforementioned series, Tarbuck sported a vast and impressive TV resume, having appeared on prominent 1970s staples such as Charlie's Angels, Dallas, Little House on the Prairie, The Incredible Hulk and The Waltons.

Tarbuck continued to work steadily through 1980s with parts on programs including Cagney & Lacey, L.A. Law, M*A*S*H, Moonlighting, Newhart and The Golden Girls.

Master of her craft: Tarbuck's work as a performer spanned seven decades and virtually all mediums. Here, she was seen with Laura Wright in a scene from General Hospital in 2009

Steady work: Tarbuck racked up credits on dozens of prominent shows, with her last major role coming on the FX series, American Horror Story

In recent years, she had made appearances on programs such as Dexter, Glee, Mad Men and Nip/Tuck.

She maintained semi-regular work in movies as well, with roles in films such as Big Trouble, Curly Sue, Short Circuit, The Tie That Binds and Walking Tall.

She brought her talents to The Great White Way with roles in the Broadway stage productions of the Neil Simon classic Brighton Beach Memoirs; and The Water Engine/Mr. Happiness.

The actress had lifelong ties to education as well as entertainment, as she was an acting teacher at UCLA. 

After her 1963 graduation from Wayne State University, she earned a master's degree at the University of Michigan and later received a Fulbright Scholarship that paved the way for her to study at the London Academy of Music and Dramatic Art.

Tarbuck is survived by Connolly; her son-in-law Samuel Chawinga; and two grandsons, Cianan and Cuinn Chawinga.

Well-remembered: Fans took to Twitter to pay memorial to the venerated actress 

Gone but not forgotten: Fan sites revered the versatile performer, who appeared on five episodes of American Horror Story