Temporal Viral Infection

A temporal virus is a terrible affliction. It is a rare complication of the little-understood process the physical body goes through during portal travel, wherein a virus that has piggy-backed a "ride" through a portal with the lifeform mutates during the transmogrification phase. During travel between worlds, the virus mutates, sometimes resulting in a strain that bleeds through time constraints on either side of interworld travel: a temporal virus.
It is generally believed that many such viruses go through this and tend to cease to exist almost immediately, because they are lesser lifeforms and cannot tolerate the shearing effect of temporal mutation. However, there is a window of opportunity: if the virus subsequently infects the body carrying it with this temporally enhanced strain, it is almost impossible to detect because the course of illness it causes travels both ways through time. In other words, from the moment you "catch the bug" via portal travel, you grow sick both after you leave the portal *and before you leave*.
Because our own perception of time is linear-directed-forward, we can only perceive what happens as we progress forward in time. If a traveler gets sick from a temporal virus, we can only trace and follow a course of illness in one direction.* We can only observe half of the total course of the illness. More serious effects that can be observed is the almost doubled effects (seen compared to time of recovery) of loss of strength, respiratory capacity, muscle fatigue and ability to generate the same blood cell counts as were measured before travel (there are few records substantiating this, as scans are prohibitively expensive and only the very wealthy would be curious enough to have them done).
*We only know as much as we do about temporal viruses thanks to the observations and assistive research of the Others, a race of alien beings that exist in omniscient time (they exist in the universe of Earth-T-C, a rare spherical world that possesses sentient species beyond its human life conditions).
Imagine passing through a plane in three-dimensional space. The plane acts as a membrane between worlds. On one side of this plane exists one world: it has its own sense of time, its own scale, its own physical laws, and its people - if they are alive and so skilled to create a documented definition of their world - have their own standards by which all things are measured. On the other side of the plane is a different world: again, its own time, scale, physics, measurements. To travel from one world to the other, one passes through a plane. This plane, we call the transmogrification phase -- using the word _'phase'_ from our own interpretation of travel as an occurrence in time and the way that our physical forms must go through a process by which they are adapted to arrive on the other side of a portal. In some extreme cases, we are aware that non-corporeal entities may transmogrify into corporeal form, and vice versa. In many cases where the world we travel to lives in a different momentum, cycles of the seasons, days, and lifetimes do not match up. For these, we assume that a similar shift in the very nature of our being must be altered to adjust to changing movements of time. If not, what is to keep a being that lives on a timeline of velocity X, traveling to velocity Xx10, from dying instantly, speeding through its lifespan in a matter of its first minutes attempting to acclimate?
So, we call this plane a '_phase'_ because that is our understanding bias. But what if this plane a distance and not a moment? (What if it is a combination of both? Or neither?) If so, what is the truth of its reach -- its size, in space or time -- and how can we objectively measure that, given not only the differing systems defined in either world of our hypothetical example, but the multitudinous (perhaps infinite) worlds of the cosmos?
We have yet to determine the answers for certain.
What we do know is this:

For the traveler, this period of time is almost nonexistent, save for a feeling of lost breath, a shimmer of light behind blinking lids, or for a few more sensitive, mild and instant-specific vertigo; however, there are no current methods to measure what happens in this phase or determine the exact length of time that exists within it.

When a virus mutates along the temporal spectrum, it affects the body it occupies along two directions of time, only one perceivable by the species of our world.

A temporal virus may, in rare cases, become lethal. If it is, it is almost impossible to detect through traditional means until it is too late. Either the body deteriorates rapidly into death, or the virus attacks the body slowly but with exponential effects in each wave of attack.

Temporally mutated viruses can only take hold of the recently traveled body that it mutated on or in. So far as we know, viruses of this kind cannot pass through contact. It is presume that they cannot affect those who have never traveled interdimensionally.

The silver lining is that survival of a temporally mutated virus is rare, and a lethal one, even more so. There have only been, in verifiable records, 868 temporal virus afflictions; of those, only 132 known deaths -- in the known history of portal travel.
Most of those non-fatal afflictions present as a common cold of ongoing and indeterminate length. A dozen or so were affinity allergies, typically to an opposing element (mostly affecting waterfae with a mild to moderate allergy to fire ash). The urban legend of the fae traveler who travels through a portal and becomes allergic to his own affinity is fundamentally unlikely and undocumented.
The Protectorate currently recommends that no one travel interdimensionally through portals unless they really need to, but that recommendation stems more from the ongoing conflict than from any ongoing health concern. The Protectorate itself applies for passage through portals routinely for its diplomats and military assignments.
Suffice to say that all exploration comes with risk. A temporal virus has the potential to cause great harm, but for some, it is a risk both uncommon and worth the reward.

Transmission & Vectors

Temporally mutated viruses can only be transmitted within a narrow window of their strain's inception on the host's body shortly after interdimensional travel using a Dolmen portal.

Causes

Unknown cause. The physical changes that occur during the moment of travel via portal, and the nature of the transmogrification of a body from one system of physics, spatial scale and sense of time to another, are unobservable with current technology.

Epidemiology

Temporally-mutated viral infection does not appear to be capable of transmission through contact or near proximity in most cases. There is a likelihood of transmission among a group of travelers, but documentation of probable instances of this have been anecdotal.

Type

Viral

Origin

Mutated

Cycle

Short-term

Rarity

Rare

Affected Species

• Taxonomy of Lifeforms according to Nioshi