The most devastating ailment that the Sanguinem mutation bestows is a severe anemia such that the afflicted becomes reliant on regular transfusions. You cannot regain hit points as usual during a short or long rest, and must receive at minimum 1 pint of fresh blood each day or suffer a level of exhaustion.
Perhaps by work of Adam Virus, Umbravirales-Sanguinem provides mechanism for this transfusion by way of hypodermic fangs within the jaw of the afflicted.

You gain a natural weapon in the form of a bite with which you are proficient. Your bite is considered a finesse weapon, and deals necrotic damage equal to 1d6 + your strength or dexterity modifier (whichever is higher), and drains 4 ounces of blood from the target, using your choice of dexterity or strength for it's attack and damage rolls. If the target of your bite attack is not a construct, plant, ooze, or undead this damage reduces it's maximum hit points by the same amount until the end of it's next short or long rest, and you may spend a hit dice and recover hit points equal to it's rolled value + your constitution modifier.

Alternatively, you may choose to bite a willing creature, draining blood from their body. The target takes no damage, but instead spends hit dice as they would during a short rest, gaining no hit points. Any hit points the target would normally gain by spending hit dice in this way you gain instead. You drain 1 pint of blood for each hit dice spent

You have disadvantage on attack rolls and on Wisdom (Perception) checks that rely on sight when you, the target of your attack, or whatever you are trying to perceive is in bright light. In addition, you take 1 radiant damage each round while your skin is exposed to direct sunlight. 

Your body is weakened by even relatively low doses of radiant energy. You have vulnerability to radiant damage, and take damage from healing spells with a radiant source equal to the hit points they would normally restore.

A lifetime of avoiding the light has adapted your vision to the dark. You can see in dim light within 120 feet as if it were bright light and in darkness as if it were dim light. You can't discern color in darkness, only shades of gray.

Whatever mutation the disease causes within the brain and body, it seems that those afflicted do not require rest in the same way as normal humans. You do not require sleep, so long as you have received a transfusion of at least a pint of blood in the past 24 hours.

The disease has made you acutely aware of the flow of blood, even within other creatures. You can sense the presence and location of all creatures within 30 ft which have flowing blood.

Something dark and powerful flows within your blood. You gain one of the Blood Feats listed:

Blood of the Heretic
(Constitution 16, Ability to cast at least one spell)
Whether by natural affinity, or heretical study, you have mastered the forbidden rites of blood magic. When you cast a spell, you may use a bonus action to expend a hit dice, and gain one of the following effects:

• Scarlet Binding. By consuming one ounce of a creature's blood and dealing slashing damage to yourself equal to the spell's level + the maximum value of the hit dice spent, you may target that creature from any distance, even if you do not have line of sight.
• Blood Channel. When casting a spell which requires concentration, you may choose to ignore the concentration requirement of the spell and instead take slashing damage equal to the spell's level each round that the spell remains in effect. To willingly end the spell before the end of its duration, you must succeed on a constitution saving throw against your own spell save DC.
• Sanguine Empowerment. You deal slashing damage to yourself equal to the spell's level + the maximum value of the hit dice spent to empower your casting, adding your constitution modifier to your spell attack modifier or spell save DC.

Damage you take as part of this feature cannot be reduced in any way.

Blood of the Beast
(Constitution 16, Strength 15)
Your blood is empowered with a ferocity for battle and a thirst for violence. As a bonus action on your turn you may expend a hit dice and deal slashing damage to yourself equal to the maximum value of that hit dice to release the violent power of your blood, and gain the following effects:

• You have advantage on saving throws against spells and magical effects.
• If a creature within 5 ft of you takes any action other than the disengage action, you may use your reaction to make an opportunity attack against them.
• You gain an additional number of reactions each equal to half your proficiency bonus. These reactions can only be used to make opportunity attacks.

This release lasts for 1 minute or until you are knocked unconscious. At the beginning of each of your turns while this release is in effect, you expend an additional hit dice, and take a slashing damage equal to the maximum value of the hit dice expended. As a bonus action on your turn, you may attempt a wisdom saving throw with a DC equal to 12 + your constitution modifier. On a success, the release ends early.

Damage you take as part of this feature cannot be reduced in any way.

Your specific incarnation of Umbravirales-Sanguinem has heightened some aspect of your body or mind. Choose either Strength, Dexterity, or Charisma. Your ability score for this ability increases by 2.

Your constitution score increases by 2

Those afflilicted by Umbravirales-Sanguinem seem immune to the normal process of cell-death, and are functionally immortal so long as they remain regular blood transfusions.

Although often slightly taller than relatives, infected individuals tend towards the same range of height as normal humans. Your size is medium.

The Sanguinem mutation often grants a level of unseemly quickness to the afflicted in their adult years. Your speed is 40 feet.

Despite unfounded rumours to the contrary, those affected by the mutation have no innate leaning towards evil, or any other alignment.