COTH

COTH (cryptic opportunistic terminal histoparasitosis) is an infection of humans and animals by a microscopic parasite agent. The agent persists in the body in a dormant state, usually for life, and causes no symptoms. When the host is dying of another illness or injury, it activates, takes over the body and turns the host into an assimilated organism within days to weeks.

Since 2025 carriage has been close to universal, with more than 95% of people tested carrying the agent in every surveyed region. Active disease is much less common, as it develops only in hosts who come close to death. Most rapid cases follow wounds inflicted by parasite organisms such as the Rupter. COTH was first recorded in 2020.

Signs and symptoms

Carriers are asymptomatic. Active disease follows a consistent course in four phases.

False remission

The first sign of activation is the sudden recovery of a patient who was dying, usually within 24 hours. The remission is most complete in patients dying of infection or of sepsis after a wound: fever and infection resolve, and the patient is alert and well. In patients dying of organ failure the effect depends on the organ involved, and is often partial or absent. The false remission lasts from a few days to several weeks. In cases caused by a severe parasite wound it is brief or absent.

Prodromal phase

The remission ends in a relapse that is usually mistaken for a return of the original illness. Symptoms include:

• dizziness and loss of balance
• confusion and disorientation, worst in the evening
• fatigue and prolonged sleep
• loss of appetite
• headache and sensitivity to light

Acute phase

The acute phase most often begins on waking. The patient is unresponsive and in a stupor, and within hours becomes agitated and aggressive. The aggression resembles the furious form of rabies in animals. Hydrophobia, a defining sign of rabies in humans, does not occur.

Assimilation

Over the following nights memory, speech and personality are lost entirely, and the patient no longer recognises family members or responds to their name. Necrosis of the skin and soft tissue begins at about the same time and progresses for the rest of the host's life.

Cause

COTH is caused by a microscopic organism related to the larger parasites. In carriers it persists in a dormant form in the bone marrow and lymphatic tissue, where it does not divide and is not attacked by the immune system. Activation follows a collapse of the host's immune defences, most often when they are overwhelmed in the final stage of a serious infection or by sepsis after a major wound, and less often in the organ failure of old age.

Transmission

The agent is shed into the air by infested ground and by parasite organisms, and most carriers acquire it by inhalation. It is carried on the wind well beyond infested areas, and the spread of carriage across continents followed prevailing winds downwind of the infested regions. It survives in fresh water, and passes between people through blood, saliva and other body fluids.

These routes cause carriage, but not disease. Active cases arise when a carrier's immune system fails, and the most common cause of rapid cases is a wound from a parasite organism, which delivers a large dose of the agent and the injury that activates it at the same time. Inborn organisms such as the Rupter cause most of these cases, as their attacks are rarely fatal but severe enough to trigger activation. Attacks by larger parasites more often kill outright. Bites and wounds from assimilated humans and animals act in the same way.

Pathophysiology

On activation the agent divides rapidly and spreads through the bloodstream. It displaces the competing infection and takes over the work of the failing immune system, which produces the false remission, and then begins converting host tissue into parasite tissue. In the brain the frontal and temporal lobes are affected first, causing the confusion and the loss of memory and personality. The basal ganglia, cerebellum and brainstem, which control movement, habit and procedural memory, are affected last and least.

As a result, assimilated humans keep much of their learned behaviour. They return to their homes, follow familiar routes, take food from kitchens and shops, sometimes prepare it, and drink water. They also attack people they encounter.

Diagnosis

Diagnosis of active COTH rests on the clinical course and is confirmed by laboratory testing. A false remission, the unexplained recovery of a patient whose condition was expected to be fatal, is the most reliable early sign. Hospitals in most countries test such patients for agent load before discharge.

The agent is undetectable in the blood of carriers and rises sharply within hours of activation, so a blood test for agent load distinguishes active disease from carriage at any phase. MRI during the prodromal phase shows lesions in the frontal and temporal lobes, before cognitive symptoms are obvious.

The prodromal phase must be distinguished from a genuine relapse of the original illness, sepsis-associated encephalopathy, viral encephalitis, rabies, and delirium in the elderly. Before agent-load testing was available, most early cases were misdiagnosed as one of these.

Prevention

The most effective prevention is ordinary medical care, as a patient whose illness or injury is treated before it becomes life-threatening does not reach the point at which COTH activates. Vaccination against common respiratory infections, and early treatment of pneumonia in the elderly, have been shown to reduce cases.

Among soldiers and others working in infested areas, prevention relies on protective equipment against parasite wounds, and on treating wounds that do occur within the first hour. Standard water treatment inactivates the agent.

Treatment

There is no effective treatment after activation. Antiparasitic drugs, high-dose immunotherapy and bone-marrow ablation have all been trialled without effect. Care in the false remission and prodromal phases is supportive, and patients in the acute phase are transferred to secure wards.

Unproven remedies have been sold widely since 2021, including homeopathic preparations, colloidal silver, herbal "immune" supplements and fasting regimens. Several of them claimed to clear dormant carriage, which no treatment has done. In the European Federation their marketing was restricted after a series of consumer-protection cases brought against sellers in 2022 and 2023.

In most jurisdictions, including the European Federation, a patient is legally declared dead once the acute phase has been confirmed.

Prognosis

Activation is fatal to the person in all recorded cases. No patient has recovered from the prodromal or acute phase, and none has kept memory or personality after assimilation.

Assimilated humans are weak compared with other parasite organisms, and most survive for weeks to a few months. Their foraging depends on retained routines, and as homes and shops in an area are emptied, most die of starvation. Others die of untreated injuries or are killed. Other parasites do not reliably recognise them as parasites, and sometimes attack them.

Epidemiology

Carriage spread first through sub-Saharan Africa, where most of the population carried the agent by 2021. Maps of carriage in 2022 and 2023 show it spreading outward from infested regions along the prevailing winds, and reaching populations hundreds of kilometres from the nearest infestation. It has been close to universal worldwide since 2025.

Active disease is far less common than carriage, and deaths from parasites far outnumber assimilations, since a person killed outright is not affected. The elderly and the seriously ill are most at risk of slow cases, and soldiers in infested areas of rapid ones.

COTH affects all mammals that have been tested. Assimilated cattle, sheep, pigs, horses, dogs, wolves and bears have been recorded, and in sub-Saharan Africa so have elephants, the largest assimilated animals known. Assimilated livestock return to their pastures and barns, and herds in infested regions are routinely tested and culled.

History

The first cases were recorded in 2020, many of them among patients recovering from COVID-19. At first they were treated as unexplained recoveries, and the relapses as a return of COVID-19. The agent was identified in 2021, and the clinical name, cryptic opportunistic terminal histoparasitosis, was given to the disease the same year. The abbreviation COTH became the common name.

See also

• Assimilation
• Rupter
• Vagrant