OVERVIEW

What is mad cow disease?

Mad cow disease is a colloquial term, its official name is bovine spongiform encephalopathy (BSE). It is a fatal disease caused by infectious prion proteins (also known as prions). Mad cow disease is contagious.

Where was mad cow disease discovered? How widespread is it?

Mad cow disease was first discovered in the UK. Currently, 26 countries worldwide have reported cases, spanning Europe, Asia, and the Americas. The UK is the most severely affected, followed by Ireland and Portugal.

Can humans get mad cow disease?

Humans cannot contract mad cow disease. However, there is a human disease—variant Creutzfeldt-Jakob disease (vCJD)—with symptoms very similar to mad cow disease. The similarities include:

• vCJD is also caused by prion proteins.

• The main manifestation of vCJD is neurological damage, where prions destroy brain cells. Once brain cells are damaged, they cannot regenerate, leading to progressive impairment of functions such as movement and memory (neurodegenerative disorder).

• vCJD has a 100% fatality rate, with an incubation period of up to 15 years. Once symptoms appear, patients typically die within 12–18 months, and there is currently no effective treatment.

• Recent studies suggest a possible link between vCJD and mad cow disease, supported by animal experiments.

There is substantial evidence that vCJD and mad cow disease are caused by the same pathogen—prion proteins. However, other human prion diseases (e.g., classic Creutzfeldt-Jakob disease) are unrelated to mad cow disease or vCJD.

Other known human prion diseases include Kuru, fatal familial insomnia (FFI), and Gerstmann-Straussler-Scheinker syndrome (GSS).

Is mad cow disease (or vCJD) a significant threat?

Despite being highly fatal, these diseases are relatively rare.

Since the discovery of mad cow disease nearly 30 years ago, according to CDC data as of June 28, 2012, there have been 227 global cases of vCJD: 176 in the UK, 27 in France, 5 in Spain, 4 in Ireland, 3 each in the US and the Netherlands, 2 each in Italy, Canada, and Portugal, and 1 each in Japan, Saudi Arabia, and Taiwan.

SYMPTOMS

What are the symptoms of a cow with mad cow disease?

The incubation period of mad cow disease is approximately 4 to 6 years, and the disease course typically lasts 14 to 90 days. Cows infected with mad cow disease experience viral attacks on their nervous system, leading to neurological disorders, abnormal behavior, and lack of coordination. Additionally, the brain tissue of affected cows becomes sponge-like. In the later stages of the disease, infected cows suffer severe weight loss and eventually die.

What are the symptoms of a person with variant Creutzfeldt-Jakob disease?

Rapidly progressing dementia (progressive dementia) is the primary symptom, which may be accompanied by muscle twitching (myoclonus), visual disturbances, unsteady gait (cerebellar dysfunction), generalized muscle dysfunction (pyramidal and extrapyramidal abnormalities), aphasia, and non-intermittent motor inability (akinetic mutism).

CAUSES

What is the cause of mad cow disease?

The occurrence of mad cow disease is related to cattle consuming feed containing meat-and-bone meal infected with prion proteins. This feed includes, but is not limited to, diseased animals such as those with scrapie or mad cow disease, whose carcasses are processed into meat-and-bone meal for feed.

The exact mechanism by which cattle develop the disease after consuming prion-infected feed is not yet fully understood. Current hypotheses suggest the following possible mechanisms:

• After ingestion, prion proteins are not digested. Because they share the same amino acid sequence as normal proteins in the body, they also evade clearance by the immune system.

• When prion proteins come into contact with normal proteins in the body, they induce the conversion of these normal proteins into prion proteins (the detailed mechanism remains unclear). These abnormal proteins cannot be broken down by enzymes, leading to their accumulation in the brain as plaques. This eventually causes the death of central nervous system cells and the formation of spongy, vacuole-like changes in brain tissue.

What is the cause of variant Creutzfeldt-Jakob disease (vCJD)?

Variant Creutzfeldt-Jakob disease is also caused by prion proteins and is believed to be associated with exposure to mad cows or consumption of beef, offal, and related products from cattle infected with mad cow disease.

Can variant Creutzfeldt-Jakob disease spread between humans?

No cases of human-to-human transmission of variant Creutzfeldt-Jakob disease have been documented.

However, a similar disease—kuru—has been observed to spread between humans. In certain indigenous tribes in Oceania, where the practice of consuming the organs of deceased relatives exists, outbreaks of kuru have occurred.

DIAGNOSIS

See "Creutzfeldt-Jakob disease" and "new variant Creutzfeldt-Jakob disease" for details.

TREATMENT

What is the treatment for variant Creutzfeldt-Jakob disease?

Currently, there is no effective or targeted treatment for variant Creutzfeldt-Jakob disease, and only symptomatic treatment and enhanced care are generally provided.

DIET & LIFESTYLE

Is mad cow disease prevalent abroad? Are we safe now?

We are currently safe because:

• As of now, no cases of mad cow disease have been found in mainland China, and in May 2014, the World Organisation for Animal Health (OIE) recognized it as having negligible risk for mad cow disease.

• Border inspection and quarantine authorities prevent potentially infected products from entering our country:

  • A complete ban is imposed on beef and processed beef products imported from 23 countries with mad cow disease outbreaks, including the UK, France, Germany, the US, and Japan.

  • Comprehensive health quarantine, quality inspections, and origin traceability systems are implemented for imported live animals, meat, embryos, etc., ensuring the safety of imported animal products.

  • To prevent infection in domestic cattle and sheep: China has completely banned the use of animal-derived feed, such as bone meal and meat-and-bone meal, for feeding ruminants like cattle and sheep that may contract the disease.

Which places require extra caution regarding mad cow disease?

According to China's Ministry of Health, countries with mad cow disease outbreaks include:

The UK, France, the US, Japan, Belgium, Italy, Germany, the Netherlands, Switzerland, Denmark, Oman, Ireland, Sweden, the Czech Republic, Greece, Poland, Finland, Canada, Luxembourg, Spain, Portugal, Austria, Israel, Slovakia, Ecuador, and Liechtenstein.

Brazil is currently classified by the OIE as a country with negligible mad cow disease risk, and China lifted its import ban on Brazilian beef in July 2014.

Taiwan is classified by the OIE as a region with controlled mad cow disease risk.

What should you pay attention to when eating beef?

Since the mad cow disease pathogen is highly resistant to external conditions and ordinary cooking cannot kill it, the most effective way to protect yourself is to avoid consuming potentially infected meat or meat products.

If you are in China, be vigilant when purchasing imported meat:

• Only buy beef from safe origins: Imported beef in the domestic market that meets safety standards mainly comes from countries in Oceania and South America. These products undergo multiple inspections upon entry into China, with clear Chinese labels indicating the type, origin, and quarantine certificates, ensuring quality and safety.

• Avoid beef from high-risk origins: Japanese Wagyu beef and marbled beef from Europe and the US come from countries identified by China's Ministry of Agriculture as mad cow disease outbreak zones. Their import and sale are strictly prohibited. Such beef sold in the market is either smuggled through illegal channels, with unverifiable safety and quality, or falsely labeled as domestic beef.

• Don’t buy beef that’s suspiciously cheap: Avoid purchasing or consuming beef and its products at unusually low prices, as they may have entered the market illegally, lack proper quarantine, and pose significant food safety risks.

• Request quarantine certificates: If in doubt when purchasing beef, ask the seller for quarantine certification. Failure to provide it indicates problematic meat.

If you are abroad:

• Don’t buy beef that’s suspiciously cheap: Avoid purchasing or consuming beef and its products at unusually low prices, as they may have entered the market illegally, lack proper quarantine, and pose significant food safety risks.

• For those working, studying, or traveling in mad cow disease outbreak zones: Choose restaurants that operate legally and meet hygiene standards.

• For those in regions with active mad cow disease outbreaks: Avoid consuming bone-in beef, offal, or minced meat products, as the brain, eyes, spinal cord, skull, and lymph nodes pose higher contamination risks. Minced meat, often used in sausages, may contain these high-risk components.

PREVENTION

How to prevent mad cow disease?

Prevention methods for mad cow disease include:

• Slaughter all infected and suspected infected livestock, and incinerate the carcasses to prevent contaminated beef from entering the market.

• Completely prohibit the use of animal-derived feed such as bone meal and meat-and-bone meal made from animal tissues for feeding ruminants like cattle and sheep, to block transmission routes.