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Оглавление

Hypovitaminosis B

BASICS

DEFINITION/OVERVIEW

Hypovitaminosis B generally refers to hypothiaminosis and is a health concern in reptiles that are fed fish—whether live or frozen thawed. Other cases have been reported in herbivorous reptiles and reptiles fed vitamin supplements lacking in thiamine.

ETIOLOGY/PATHOPHYSIOLOGY

In humans, thiamine deficiency can occur rapidly and advance to metabolic coma and death; causes being malnutrition, a diet high in thiaminase‐rich foods (raw freshwater fish, raw shellfish, ferns), chronic gastrointestinal diseases, and diabetes mellitus.

Thiamine derivatives and thiamine‐ dependent enzymes are present in all cells, but the nervous system is very sensitive, leading to nerve fiber myelin sheath degeneration causing necrotizing encephalopathy and peripheral neuritis.

Bilateral vision loss due to optic neuropathy can occur.

Thiamine is a water‐soluble vitamin synthesized by bacteria, fungi, and plants.

Captive fish‐eating garter snakes and semi‐aquatic turtles, and captive and free‐ ranging crocodilians are most commonly affected.

Feeding fish high in thiaminase—goldfish and fathead minnow, improperly thawed fish (thawing too slowly), or fish that has been frozen a long time can all be factors.

Some frozen thawed vegetables containing phytothiaminases lead to thiamine deficiency in green iguanas.

Insectivorous anoles developed thiamine deficiency due to lack of any thiamine in the multivitamin supplement because of extensive storage before use.

Thiamine is a rapidly deteriorating vitamin so it is important to ensure that supplements are stored and used properly.

SIGNALMENT/HISTORY

Fish as primary diet

Thawed frozen vegetables

Using same container of vitamin supplement/powder beyond expiration date or past 6 months after opening.

CLINICAL PRESENTATION

Can present with non‐specific signs such as anorexia, dehydration, and lethargy, but suspicions of thiamine deficiency are greater with torticollis, opisthotonus, muscle tremors, incoordination, blindness, jaw gaping, and sudden death.

RISK FACTORS

Husbandry

N/A

Others

Piscivores

Thawed frozen vegetables

DIAGNOSIS

DIFFERENTIAL DIAGNOSIS

Trauma

Infectious encephalitis

Toxins

Metabolic bone disease

Hepatoencephalopathy

Neoplasia

Cardiac disease

Renal disease

Ruptured aneurysm

DIAGNOSTICS

Usually based upon history, clinical signs, and response to parenteral thiamine (B‐complex vitamins).

PATHOLOGICAL FINDINGS

Cerebral cortical necrosis

• Peripheral neuritis

TREATMENT

APPROPRIATE HEALTH CARE

N/A

NUTRITIONAL SUPPORT

Avoid feeding fish known to have high thiaminase levels, such as goldfish and fathead minnows.

Proper storage of frozen fish by not keeping beyond 6 months of death/freezing.

Rapid thawing for five minutes in 80 degrees C (175 degrees F) water denatures thiaminase or thawing in refrigerator also avoids thiaminase activation.

An added level of protection would be to add thiamine 25 mg/kg fish.

Do not use vitamin supplements beyond expiration date or 6 months after opened.

CLIENT EDUCATION/HUSBANDRY RECOMMENDATIONS

Proper education about expiration dates/ opening dates of vitamin supplements, avoiding certain live fish species and carrying out proper thawing techniques for frozen fish.

Avoidance of too many thawed frozen vegetables.

MEDICATIONS

DRUG(S) OF CHOICE

Thiamine administered at 50–100 mg/kg IM, SC, or PO q24h until resolution of clinical signs.

A vitamin B complex formulation is less ideal but can be used if a thiamine‐only supplement is not available.

PRECAUTIONS/INTERACTIONS

N/A

FOLLOW‐UP

PATIENT MONITORING

Reassess diet

Diet processing/handling

Supplementation at every visit

EXPECTED COURSE AND PROGNOSIS

If thiamine deficiency without concurrent issues, should have immediate response to therapy, although repeated treatments may be needed.

In non‐piscivores, often not considered and diagnosed postmortem on histopathology.

MISCELLANEOUS

COMMENTS

N/A

ZOONOTIC POTENTIAL

N/A

SYNONYMS

Thiamine deficiency

ABBREVIATIONS

IM = intramuscular

PO = per os

SC = subcutaneous