FC To Review Flashcards
There are 5 steps along the pain pathway to alert a patient to a painful stimulus.
Which of the following is the step that turns a noxious stimulus into an electrical signal in nerves, which then along the pathway is perceived as pain?
Transmission
Transduction
Perception
Projection
Modulation
Answer: Transduction
Transduction is the conversion of a stimulus, usually mechanical, thermal, or chemical, into an electrical signal by pain receptors located on nerve endings in the skin, subcutaneous tissues, viscera, etc.
The electrical impulse is transmitted via afferent sensory nerves to the dorsal horn of the spinal cord.
This is where the response to the painful stimulus is directed, when appropriate (e.g., a withdrawal reflex), or amplified, facilitated and/ or suppressed here (i.e., modulation).
The signal is then projected to higher centers, usually via the spinothalamic or the spinoreticular tracts. Further modulation occurs in the thalamus, reticular formation, and limbic system.
Finally, it reaches the cerebral cortex, where perception produces physical and emotional responses.
Which one of the following regional nerve blocks does not affect sensory function but blocks motor function of the upper eyelid, and is indicated to allow complete ophthalmic examination in the horse?
Supraorbital
Ocular
Zygomatic
Auriculopalpebral
Frontal
Answer: Auriculopalpebral
The auriculopalpebral nerve, located along the dorsal zygomatic arch of the eye, provides motor innervation to the upper orbicularis oculi muscle.
Anesthesia of this nerve prevents the horse from being able to blink the eye and facilitates complete ophthalmic examination.
The frontal nerve is a branch of the trigeminal nerve and provides sensory innervation to the upper eyelid.
Click here to see a good summary on ophthalmology surgical emergencies in horses, with images, courtesy of the American College of Veterinary Surgeons (ACVS).
Refs: Smith, Large Animal Internal Medicine, 4th ed. pp. 793-8.
Auriculopalpebral Block in Equine Medicine
Definition
• Auriculopalpebral Block: A local anesthetic technique used to block the auriculopalpebral nerve, facilitating ophthalmic procedures by preventing eyelid movement.
Purpose
• Indications: Used for ocular examinations, minor surgical procedures around the eye, and alleviating blepharospasm. • Mechanism: Blocks motor function of the orbicularis oculi muscle, causing temporary paralysis of the upper eyelid.
Procedure
• Technique: Administer local anesthetic (e.g., lidocaine) near the auriculopalpebral nerve at the zygomatic arch. • Effect: Immediate eyelid immobility lasting for approximately 1-2 hours.
https://www.acvs.org/large-animal/ophthalmology-surgical-emergencies-in-horses/
Which combination is the safest and most humane anesthetic protocol for ovariohysterectomy in a dog or cat?
Midazolam, ketamine, atropine
Lidocaine, carprofen, etomidate
Butorphanol, acepromazine, sevoflurane
Dexmedetomidine, glycopyrrolate,
bupivacaine, hydromorphone
Morphine, diazepam, propofol, isoflurane
Answer: Morphine, diazepam, propofol, isoflurane
Use a combination of an analgesic (e.g., morphine), anxiolytic (e.g., diazepam), intravenous induction agent (e.g., propofol), and inhalant anesthesia (e.g., isoflurane) to provide the safest, most humane protocol for ovariohysterectomy (OHE) in a dog or cat.
Combining multiple agents, known as multimodal anesthesia, greatly improves pain and stress control.
Examples of common analgesics include opioids and non-steroidal anti-inflammatories (NSAIDs). Commonly used anxiolytics include acepromazine, benzodiazepines (e.g., midazolam, diazepam), and alpha-2 adrenergic agonists (e.g., dexmedetomidine).
Remember, not all anxiolytics and anesthetics have analgesic properties. Failure to provide adequate analgesia results in pain and a requirement for higher doses of other anesthetic agents, which increases the risk of cardiovascular side effects.
Do not use inhalant anesthesia (i.e., mask induction) alone for induction. It causes increases both in patient stress and risk of significant cardiovascular depression and aspiration pneumonia due to an unprotected airway. Use inhalant agents for anesthetic maintenance following induction with an injectable anesthetic or consider total intravenous anesthesia.
What is the U.S. Drug Enforcement Agency controlled schedule for the anesthetic drug alfaxalone?
Answer: IV
Alfaxalone is a U.S. Drug Enforcement Agency (DEA) schedule IV controlled substance.
Alfaxalone is a neuroactive steroid used in cats and dogs for the induction and maintenance of general anesthesia. It may be administered IV or IM and, similar to propofol, it does not provide any analgesia.
The DEA schedules drugs into one of five categories based on their accepted medical use and the abuse/dependence potential.
Schedule I drugs have a high risk for abuse and are the most restricted. Schedule V drugs have the least potential for abuse.
Which part of a cow’s digestive system has many folds in the lining, like leaves or the pages in a book?
Abomasum
Omasum
Rumen
Reticulum
Cecum
Answer: Omasum
The omasum is composed of many layers of folds, which look like leaves or pages in a book. These increase fluid absorption.
There are four compartments in the ruminant stomach: reticulum, rumen, omasum (together comprising the “forestomachs”), and abomasum.
The rumen and reticulum contain microorganisms to ferment and digest nutrients (hence the term “forestomach” fermenters vs. horses are considered “hindgut fermenters” because their large colon and cecum serve this purpose). The abomasum is a glandular “true” stomach that contains acid for further digestion.
Which part of a cow’s digestive system has many folds in the lining, like leaves or the pages in a book?
Abomasum
Omasum
Rumen
Reticulum
Cecum
Answer: Omasum
The omasum is composed of many layers of folds, which look like leaves or pages in a book. These increase fluid absorption.
There are four compartments in the ruminant stomach: reticulum, rumen, omasum (together comprising the “forestomachs”), and abomasum.
The rumen and reticulum contain microorganisms to ferment and digest nutrients (hence the term “forestomach” fermenters vs. horses are considered “hindgut fermenters” because their large colon and cecum serve this purpose). The abomasum is a glandular “true” stomach that contains acid for further digestion.
A three-year-old Dachshund presents with acute onset of severe thoracolumbar pain, arched back, and hypermetria, ataxia, and weakness in the pelvic limbs. Ambulation is normal in the thoracic limbs.
The cutaneous trunci reflex caudal to T13 is absent on the right and absent caudal to L3 on the left.
Of the following choices, where is the likely location of this dog’s lesion?
T11-12, mostly right side
C7-T1 mostly right side
L7-S1 mostly left side
Cannot determine without more information
L2, mostly left side
Answer: T11-12 mostly right side
This dog’s lesion is roughly at T11-12, mostly on the right. The loss of the cutaneous trunci reflex occurs about 1-4 (usually 2) spinal cord segments caudal to the actual lesion.
Dorsal cutaneous branches do not exit the spinal cord at around
L3-4 so the the loss of the reflex on the left at L3 is normal.
The lateral thoracic nerve, which innervates the ipsilateral cutaneous trunci muscle, exits the spinal cord at C7-1. So with a brachial plexus avulsion you may see an ipsilateral loss of the cutaneous trunci response (“twitching”) while lightly pinching on the skin on the ipsilateral side, however the contralateral side will respond!
Cutaneous Trunci Reflex in Veterinary Neurology
Definition
The cutaneous trunci reflex is a test to assess the integrity of the spinal cord, particularly the thoracolumbar region.
Procedure
• Method: Gently squeeze the skin lateral to the spine with a hemostat, starting from the lumbosacral region and moving cranially. • Normal Response: Bilateral contraction of the cutaneous trunci muscles, resulting in a skin twitch over the thorax and abdomen.
Clinical Significance
• Lesion Localization: Absence of reflex caudal to a lesion, while the reflex remains normal cranial to it. • LMN Involvement: Indicates involvement of the lateral thoracic nerve (C8-T2 spinal segments).
Application
• Use: Useful for diagnosing spinal cord injuries and differentiating them from peripheral nerve injuries.
Which one of the following sites would be the most appropriate to place an intraosseous catheter in a bird?
Ulna
Humerus
Synsacrum
Femur
Coracoid
Answer: Ulna
The distal ulna is the site most frequently utilized for an intraosseous catheter in birds. The proximal tibiotarsal bone is another frequent site.
Do NOT use the humerus and femur. They are pneumatized bones and would deliver fluids into the respiratory tract, essentially drowning the bird.
What is clinical significance of the reciprocal apparatus?
Maintains balance when one leg is off the ground
Neuromotor mechanism behind pupillary light reflex
Allows a horse to rest while standing
Ensures coordination of movement between eyes
Flexion in stifle causes flexion in hock
Answer: Flexion in stifle causes flexion in hock
The reciprocal apparatus of the pelvic limb means that flexion in stifle causes flexion in hock. It consists of the fibularis (peroneus) tertius muscle on the cranial aspect of the crus and the superficial digital flexor on the caudal aspect.
Because of these two opposing “cords,” flexion or extension of the tarsus (hock) or stifle will cause a reciprocal flexion or extension of the other joint.
Don’t confuse the reciprocal apparatus with the STAY apparatus, a combination of non-tiring tendons and ligaments on both the fore and hind limbs that allow muscle bellies to bypass tension so that a horse may rest while standing with little fatigue.
Click here to see the stifle locking mechanism of the stay. apparatus, courtesy of the Atlanta Equine Clinic.
Which of the following structures is marked with the yellow circle?
Spermatids
Seminiferous tubule
Tunica albuginea
Leydig cell
Intersitium
Answer: Seminiferous tubule
The entire structure outlined in yellow is a seminiferous tubule of a testis, where spermatogensis occurs. #1 is the lumen of the tubule.
Leydig cells (#7, also called interstitial cells) are located in the intersitium between the seminiferous tubules.
The Leydig cells produce most of the body’s testosterone in response to luteinizing hormone secreted from the pituitary.
Sertoli cells are indicated by #5. These are also called “nurse” cells because they produce hormones and proteins to facilitate spermatogenesis.
What are the anatomic structures that comprise the umbilical o cord in a foal?
Two umbilical arteries, one umbilical vein, and two urachi
One umbilical vein, two umbilical arteries, and one urachus
One umbilical artery, two umbilical veins, and two urachi
Two umbilical arteries, two umbilical veins, and two urachi
Two umbilical veins, one umbilical artery, and one urachus
Answer: One umbilical vein, two umbilical arteries, and one urachus
The umbilical cord of a foal is comprised of one umbilical vein, two umbilical arteries, and one urachus.
The umbilical vein brings nutrient- and oxygen-rich blood from the placenta to the fetus; it enters the fetal liver to join the portal vein.
The umbilical arteries are the vascular return from fetus to dam.
They originate off of the internal pudendal artery and pass ventrally on either side of the bladder.
The urachus is the tubular connection present in the fetus between the bladder and the umbilicus. During gestation, urine flows from the bladder through the urachus into the allantoic sac.
As the fetus gets closer to term, more and more urine flows through the urethra, until ideally at birth all urine exits the bladder through the urethra and the urachus should involute.
Which one of the following organisms is typically implicated in verminous myelitis in horses?
Sarcocystis neurona
Stephanurus dentatus
Cuterebra spp.
Strongylus vulgaris
Baylisascaris procyonis
Answer: Strongylus vulgaris
Strongylus vulgaris is the most common helminth associated with verminous myelitis (aberrant helminth migration) in horses. Signs vary, but are usually acute and asymmetric and may be progressive.
Possible organisms include:
Strongylus vulgaris, Halicephalobus (Micronema) deletrix, and Setaria spp. - horses
Parelaphostrongylus tenuis - sheep, goats, llamas
Hypoderma bovis - cattle
Stephanurus dentatus - pigs
Cuterebra spp. - cats
Baylisascaris procyonis - dogs and humans
Don’t confuse equine protozoal myeloencephalitis (EPM), caused by Sarcocystis neurona (and, less commonly, Neospora hughesi) with verminous myelitis caused by helminths (worms).
How would you change exposure settings to make an x-ray film lighter?
Increase kVp, decrease mA, increase time
Increase kVp, increase mA, increase time
Decrease KVp, decrease mA, decrease time
Decrease kVp, increase mA, increase time
Decrease the film-focal distance
Answer: Decrease KVp, decrease mA, decrease time
To make a film lighter, decrease kilovoltage (KVp), milliamperes (mA), or time (seconds).
Decreasing milliampere-seconds (mAs) decreases the number of photons hitting the film, which exposes it less.
Lower kVp decreases photon energy (penetrating power of the x-rays through tissue).
Shorter time generates fewer electrons which also decreases exposure and therefore decreases darkness on the X-ray film once it is developed.
A four-year-old male neutered domestic shorthair cat is presented for left thoracic limb lameness. He is an indoor-outdoor cat who was normal four days ago. The owner noted the lameness upon returning from a trip out of town.
Physical exam reveals left carpal swelling, radiographs of the area are shown below.
What pathological process is most likely?
Neoplasia
Congenital malformation
Infection
Osteochondrosis
Projectile foreign body (shotgun pellet)
Answer: Infection
The joint-crossing lytic damage seen between the carpal joint and fourth and fifth metacarpal bones is consistent with osteomyelitis (infection), although biopsy for histopathology and culture is required for definitive diagnosis. Osteomyelitis may be bacterial or fungal in origin.
In chronic osteomyelitis that does not respond to medical management amputation maybe the best Tx option.
Bone tumors, such as osteosarcoma, usually do not cross the joint.
A four-year-old male neutered domestic shorthair cat is presented for left thoracic limb lameness. He is an indoor-outdoor cat who was normal four days ago. The owner noted the lameness upon returning from a trip out of town.
Physical exam reveals left carpal swelling, radiographs of the area are shown below.
What pathological process is most likely?
Neoplasia
Congenital malformation
Infection
Osteochondrosis
Projectile foreign body (shotgun pellet)
Answer: Infection
The joint-crossing lytic damage seen between the carpal joint and fourth and fifth metacarpal bones is consistent with osteomyelitis (infection), although biopsy for histopathology and culture is required for definitive diagnosis. Osteomyelitis may be bacterial or fungal in origin.
In chronic osteomyelitis that does not respond to medical management amputation maybe the best Tx option.
Bone tumors, such as osteosarcoma, usually do not cross the joint.
Which two organisms are most associated with early embryonic
loss and infertility in cattle?
Neosporosis, Listeria monocytogenes
Mycoplasma bovis, Foothill abortion
Actinomyces pyogenes, bovine viral diarrhea
Leptospira hardjo, Aspergillus fumigatus
Tritrichomonas foetus, campylobacteriosis
Answer: Tritrichomomas foetus, campylobacteriosis
Campyplobacteriosis and Tritrichomonas foetus are associated with early embryonic loss and infertility in cattle.
Bovine genital campylobacteriosis (Campylobacter fetus sbsp. venerealis) primarily causes venereal disease that leads to infertility. Occasionally it can cause late abortions too, but most commonly it causes infertility.
Bovine trichomoniasis ( Tritrichomonas foetus) causes early embryonic loss in cattle.
Both diseases have similar presentations.
Which of these organism choices has a reproductive cycle cats ?
Toxoplasma gondii
Haemophilus influenzae
Brachyspira hyodysenteriae
Neorickettsia helminthoeca
Mycobacterium avium sbsp. paratuberculosis
Answer: Toxoplasma gondii
Toxoplasma gondii has a reproductive cycle in cats.
Toxoplasmosis is a multisystemic protozoal disease that affects primarily young animals and the immunosuppressed (think cats with FIV, humans on chemotherapy).
T. gondi is an important cause of abortion in sheep, goats, and sometimes pigs.
This 5-day-old calf was born normally to a primiparous dam, but was found down today.
The animal is stiff, has opisthotonos, and is hyperreactive to tactile, visual, and auditory stimuli.
There is no visual deficit, but the calf has inducible nystagmus which varies with changes in head position.
Movement of the neck triggers tonic clonic convulsions. Rectal temperature is 105.5°F (40.8°C)..[N=101.5-103.5°F, N=37.8-39.7°C].
Which one of the following choices is the most likely diagnosis?
Nervous coccidiosis
Polioencephalomalacia
Neosporosis
Bacterial meningitis
Bovine spongiform encephalopathy
Answer: Bacterial meningitis
Stiffness, inducible nystagmus, and intermittent tonic-clonic convulsions in a 5-day-old calf are indicative of bacterial meningitis.
These cases are hyperreflexive and extremely hyperesthetic.
Although this patient is still visual, blindness is often seen.
The fever is also typical of bacterial meningitis, and may be exacerbated by the seizures.
The causative agent is usually the bacterial organism E. coli which accesses the CNS hematogenously after entrance through the tonsils, especially in colostrum-deprived calves.
Failure of passive transfer is more common in calves born to primiparous dams.
A lumbosacral CSF tap can be performed to confirm the diagnosis.
Nervous coccidiosis is a disease of weaned calves approximately 3 to 5 months of age. The affected animals are usually comatose and non-visual.
This calf is young for polioencephalomalacia (PEM), and is not blind, a common clinical sign in PEM.
If the calf had neosporosis it might resemble this patient, but wouldn’t have a fever or hyperesthesia, and probably would have been born with the condition.
Bacterial Meningitis in Calves - Comprehensive Study Guide
Definition
• Bacterial Meningitis: Inflammation of the meninges due to bacterial infection, often leading to meningoencephalitis.
Causative Agents
• Common Bacteria: Escherichia coli, Streptococcus spp., Klebsiella spp., Salmonella spp., and Histophilus somni.
Pathophysiology
• Mechanism: Bacteria reach the meninges through hematogenous spread from primary infection sites like the umbilicus (navel-ill), respiratory tract, or gastrointestinal tract, causing inflammation, increased intracranial pressure, and neurologic damage.
Symptoms
• Early Signs: Fever, lethargy, poor suckle reflex, stiff neck, and hyperesthesia. • Advanced Signs: Seizures, opisthotonos, ataxia, and coma.
Clinical Changes
• Lesions: Purulent exudate on meninges, cloudy cerebrospinal fluid (CSF).
Diagnosis
• Methods: Clinical signs, CSF analysis (increased WBC count, protein concentration), culture, PCR.
Treatment
• Antibiotics: Broad-spectrum antimicrobials (e.g., ceftiofur, ampicillin) based on sensitivity. • Supportive Care: IV fluids, anti-inflammatory drugs (NSAIDs), and nutritional support.
Prevention
• Management: Good hygiene during birth, prompt treatment of primary infections, adequate colostrum intake, and vaccination where applicable.
A SNAP® heartworm antigen test with a reported sensitivity 96% and specificity of 98% is being used in dogs.
Assuming the prevalence of heartworm in the area is 10%, what is the predictive value negative (PVN) of the test?
99%
88%
92%
85%
80%
Answer: 99%
The predictive value negative (PVN) is 99%.
The trick with this kind of question is to pick an imaginary number of animals that you test, like 1000, and fill out your 2x2 table from there.
Follow the links to see diagrams step by step.
If prev is 10% then there must be 100/1000 dogs with heartworm and 900 dogs that are disease-free.
A 96% sensitive test will correctly call 96/100 positive (box “a”), and IN-correctly call 4/100 negative, (box “c”; these are the false negs).
If 100/1000 animals are infected, then 900/1000 are disease-free.
Your 98% specific test will correctly call 882/900 disease-free (box “d”: 0.98 X 900=882) and IN-correctly call 18/900 positive, (box “b”: these are the false pos).
Now your a,b,c, d boxes are all filled, it is easy to calculate PVN=d/ (c+d=882/882+4)=99%
A skin scrape from a cow with pruritus and crusts around the caudal thighs and perineum shows the organism below.
What is the presumptive diagnosis?
Psoroptic mange
Chorioptic mange
Cutaneous onchocerciasis
Trombiculidiasis
Sarcoptic mange
Answer: Chorioptic mange
A winter presentation in the northeastern U.S. of crusty, pruritic skin disease around the perineum, caudal upper thigh is most likely to be chorioptic mange. Also called “leg mange.”
Rx: pour-on doramectrin or moxidectin, eprinometrin (injectible or pour-on), or lime-sulfur dips a 12 d.
On skin scrape, look for long legs and short UNsegmented pedicles with Chorioptes. In CONTRAST to the short legs and long UNsegmented pedicles of Sarcoptes.
Chorioptic Mange in Cattle - Comprehensive Study Guide
Definition
• Chorioptic Mange (Leg Mange, Foot and Tail Mange, Symbiotic Mange, Barn Itch): Caused by infestation with Chorioptes bovis or C. texanus.
Causative Agents
• Mites: Chorioptes bovis and C. texanus.
Pathophysiology
• Mechanism: Mites live on the skin surface, feeding on skin debris and causing irritation. They do not burrow. • Transmission: Direct contact and fomites; mites can survive off the host for up to 3 weeks.
Symptoms
• Clinical Signs: Nodules, papules, crusts, and ulcers. Lesions typically start at the pastern and can spread to the udder, scrotum, tail, and perineum. Mild pruritus, flaky dermatitis, self-trauma, and alopecia are common. • Seasonal: Lesions and clinical signs appear in late winter and spontaneously regress during summer months.
Diagnosis
• Methods: Clinical signs, microscopic examination of skin scrapings.
Treatment
• Medications: • Pour-on Doramectin • Eprinomectin (pour-on and injectable) • Moxidectin (pour-on) • Hot Lime Sulfur Dips or Sprays: Follow species-specific dilution and repeat at 12-day intervals if needed.
An adult Tennessee Walker gelding is presented for evaluation.
The hooves are pictured below.
The horse stands with the forelimbs stretched out and the hindlimb tucked underneath.
When asked to trot, the horse has an exaggerated leg motion, lifting the forelimbs high off the ground with each step.
The hair on the lower aspect of the forelimbs is curly and the horse is extremely sensitive to palpation of the dorsal pasterns.
What is the name of the illegal practice that has led to this horse?s presentation?
Docking or blocking
Alcohol blocking
Nicking or cutting
Velveting
Soring
Answer: Soring
This presentation is consistent with soring, which is an unethical and illegal practice of intentionally causing pain to exaggerate the leg motion of horses. The outcome is a chest-high stride called the
“big lick,” which unfortunately is desired in many competitions of gaited horses (esp. Tennessee Walkers).
Soring is achieved by application of chemical irritants to the lower limb, +/- use of “action devices” that make the horse pick up the leg faster, or mechanical/physical measures that make the feet incredibly sore.
The special shoes seen on this horse are called “stacks” - and they make the foot heavy to exaggerate the movement; unfortunately they can also hide application of items that cause pain/pressure on the bottom of the hoof.
The Horse Protection Act (HPA) of 1970 made soring illegal. The USDA enforces the HPA by having Designated Qualified Persons and/or Veterinary Medical Officers inspect horses at events. Any suspect cases should be reported to the USDA.
The American Association of Equine Practitioners (AAEP) and American Veterinary Medical Association (AVMA) support a ban on the use of action devices and performance packages in the training and showing of Tennessee Walking Horses.
Docking, blocking, nicking or cutting are are methods of tail alteration in horses, condemned by the AAEP. Alcohol nerve blocks are not illegal per se, but they tend to be long-term.
Velveting refers to the amputation of live growing antlers from cervids. The AVMA says that if velveting occurs, it must be conducted humanely, and within the bounds of a veterinarian-client-patient relationship.
Refs: The AVMA’s Policy Resources and the AAEP’s Policy on Soring. Image courtesy of Todd Behre, USDA APHIS.
A two-year-old Angus cow is presented with weakness of the hind limbs and a staggering gait.
On physical exam, the heart rate and respiratory rate are slow and irregular, and the pupils are dilated.
The cow’s breath and urine smell like the odor of mouse urine.
Suddenly the cow’s pulse becomes rapid and thready, she collapses, and dies of apparent respiratory failure.
Which one of the following plants is most likely to have caused this spectrum of clinical signs?
Tetradymia spp (Horsebrush)
Centaurea spp (Knapweed, Yellow star thistle)
Veratrum spp (False hellebore, Skunk cabbage)
Pinus ponderosa (Western yellow pine)
Conium maculatum (Poison hemlock)
Answer: Conium maculatum (Poison hemlock)
Poisoning with Conium maculatum (Poison hemlock) is responsible for the death of this cow.
At least eight toxic piperidine alkaloids have been isolated from poison hemlock.
Coniine is found in seeds and the mature plants; g-coniceine is found in young growing plants.
Poison hemlock is toxic to all livestock and humans. Signs of toxicity develop one to two hours after ingestion and are usually fatal.
Signs include nervousness, trembling, weakness especially of the hind limbs, weak pulse, irregular heart rate, recumbency, coma and death.
A mousy odor exuding from the urine and breath is pathognomonic.
Ingestion of poison hemlock during gestation causes arthrogryposis and other congenital defects in cattle, goats, and pigs.
This cow is off-feed, icteric and has raw irritated skin over the back, suggesting secondary photosensitization.
What is the underlying toxic agent that typically causes secondary photosensitization?
Gossypol
Aflatoxin
Ptaquiloside
Unconjugated bile acid
Phylloerythrin
Answer: Phylloerythrin
Secondary photosensitization is caused by plant-related hepatic damage, which releases photodynamic substances like phylloerythrin, a breakdown of product chlorophyll.
Failure to excrete phylloerythin due to liver dysfunction or bile duct lesions can lead to a build up in the blood and skin, where phylloerythin can absorb and release light energy,
causing phototoxicity.
Pyrrolizidine alkaloids are one cause of secondary photosensitization due to liver damage.
The plants most often implicated include ragwort (Senecio jacobea), woolly groundsel (Senecio redellii, Senecio longilobus), rattleweed (Crotalaria retusa), and seeds of yellow tarweed (Amsinckia intermedia).
Click here for a nice visual review of bovine skin conditions, courtesy of the Natl. Animal Disease Information Service (UK).
Overview of Photosensitization in Animals - Comprehensive Study Guide
Definition
• Photosensitization: Skin condition caused by interaction of photoactive substances with UV light, producing free radicals and reactive oxygen species leading to skin damage.
Types and Causes
1. Primary Photosensitization (Type I): Caused by ingestion or absorption of photodynamic agents like hypericin from St. John’s wort. 2. Aberrant Pigment Metabolism (Type II): Due to defective heme synthesis enzymes, leading to porphyrin accumulation. 3. Secondary (Hepatogenous) Photosensitization (Type III): Most common, due to impaired hepatic excretion of phylloerythrin, a chlorophyll by-product. 4. Idiopathic Photosensitization (Type IV): Unknown cause or unidentified photodynamic agent.
Pathophysiology
• Mechanism: UV light activates photodynamic agents, forming high-energy molecules that damage skin cells, leading to increased membrane permeability, cellular leakage, and enzyme release causing skin ulceration, necrosis, and edema.
Symptoms
• Clinical Signs: Photophobia, erythema, edema, vesicles, ulcers, necrosis, especially in non-pigmented skin areas.
Diagnosis
• Methods: Based on clinical signs, history, and detection of photodynamic agents or liver dysfunction. Elevated porphyrin levels in blood, urine, or feces confirm diagnosis.
Treatment
• Supportive Care: Shading, housing, corticosteroids for early stages, wound management, and preventing fly strike. Prognosis depends on the type, with primary photosensitization having a better outcome.
