Hyracoidea

Question 1

Describe the biology and anatomy of hyraxes.

What order and family do hyraxes belong to?

What are their teeth like?

What is unique about their colon?

Where are their testicles located?

What is unique about their iris?

Where are their only sweat glands located?

Do they have a gallbladder?

What type of uterus and placentaiton do they have?

What is their urine like?

Answer 1

Fowler 8 Ch 54 Hyrocoidea - Hyraxes

Biology

• 3 species of hyrax–rock hyrax, gray or yellow spotted hyrax, and the bush or tree hyrax
• Closest living relative is the elephant
• The rock hyrax is the most widely held species in zoologic institutions

Unique anatomy

• Stout and squat with short legs
• Double layered coat with scent gland on the back covered in longer hairs
• Adapted for eating grasses–high crowns and short roots
• Two upper incisors used for grooming are elongated and tusklike and are often mistaken for canines
• Sweat glands only on the plantar surface of the feet
• Simple stomach
• The large intestine is unique to this species. It starts with a cecumlike sac, which has a narrow connecting colon with thick walls and a second connecting colon with wide, thin walls
• The second portion of the colon is where the primary absorption of water and volatile fatty acids takes place. The two connecting colons are followed by a colonic sac with two appendages that ends with a distal colon. The hindgut is important for microbial digestion
• No gallbladder
• Testicles are intra abdominal
• Females have 4 mammae and a duplex uterus
• The eye of the hyrax is unique, as a portion of the iris above the pupil bulges slightly into the aqueous humor to cut off light directly above the animal

Hyraxes (only member of Order: Hyracoidea; Family: Procaviidae)

• 3 major species: cape or rock hyrax (Procavia spp.), gray, yellow-spotted or bush hyrax (Heterohyrax brucei), and tree hyrax (Dendrohyrax spp.)
• Closest extant relatives are elephant, manatee and dugongs
• Herbivores – graze and browse poor quality roughage in semi-arid climates (Africa; Middle East)
• Limited ability to thermoregulate – sunbathe and huddle in groups
• Plantigrade stance – 4 digits on front feet; 3 on hind
• Foot pads contain their only sweat glands
• Unique GI anatomy: Hindgut fermenter with 3 separate areas of digestion (stomach and 2 fermentation chambers w/i extensive LI)
  
  • Colonic sac is site of water and fatty acid absorption – terminates with distal colon
    
    • Thin walled with wide lumen and two tapering appendages
• Do not have gallbladder (like rats)
• Females – duplex uterus, similar to rabbits. Hemochorial and zonary placentation
• Monocytes with bilobed nuclei comprise 1-3% of leukocytes (similar to elephants)
• Efficient intestinal calcium absorption – excess excreted in a cloudy, chalky urine

Question 2

Describe the husbandry and clinical techniques used with hyraxes.

What is their ideal husbandry?

What are their dietary recommendations?

How are they manually restrained?

How are they anesthetized?

What are teh most common venipuncture sites?

What vaccines are recommended?

Answer 2

Housing

• The hyrax is a poor thermoregulator and body temperature fluctuates in relation to the environment
• Important to provide shelter and stable environmental temp and humidity
• Hyraxes spend many hours basking in the sn and will often huddle in groups when the temp drops

Feeding

• Facultative grazers in the wild
• High calcium absorption from the GI tract like rabbits and guinea pigs
• Urine may have a chalky appearance
• Low iron diets recommended due to hemosiderosis

Handling and restraint

• Most are caught by netting, though can be crate trained

Anesthesia and surgery

• Inhalant is preferred, usually iso, though injectable protocols have been used
• Difficult to intubate but can be done

Diagnostics

• Jugular and femoral are most common venipuncture sites
• Rabies and tetanus vaccines recommended

Question 3

Describe the infectious diseases of hyraxes.

What are the most important bacterial diseases of this group?

Herpesviral infection leads to what clincial signs and lesions? What are the inclusion bodies?

What protozoal disease is common in hyraxes? What are the lesions and clincial signs?

Answer 3

Diseases

• Infectious
  
  • Bacterial
    
    • Mycobacteriosis
      
      • All cases either typical or atypical mycobacterium tuberculosis complex
      • A particular variant of MTBC called dassie bacillus has been reported
    • Yersiniosis was a significant problem in one captive colony
  • Viral
    
    • A syndrome involving glossitis and ulceration as will as intranuclear inclusions in tissues is likely due to a herpesvirus
    • A novel alpha herpesvirus was identified in hyrax in 2009, causing blepharoconjunctivitis and blister-like lesions on the tongue, mouth and face
      
      • 10 individuals died in this group, no further outbreaks
  • Fungal disease
    
    • Ulcerative lesions of the squamous epithelium of the tongue, gingiva, esophagus, and stomach of a number of hyraxes have contained large numbers of Candida organisms
    • Unclear if primary or secondary to alpha herpesvirus
  • Parasitic
    
    • Grassinema procavia is a small, white nematode, which is approxi- mately 3 mm in length and may be found in the alimentary canal of the hyrax, especially in the stomach
    • Generalized demodicosis has been reported
    • Cutaneous leishmaniasis has been reported (vector is sandfly)

Terio Short Summary

• Mycobacterium - M. tuberculosis (lassie bacillus), M. microti, M. africanum - wt loss, lameness, pneumonia, repro failure
• Bacterial septicemia - managed animals - gram negative
• Pasteurella multocida - pneumonia, zoo managed
• Grassinema procavia - small nematode - stomach, ulceration w/ severe infestations
• Leishmania tropica and aeithopica - OIE - protozoa - rock hyrax is reservoir host for disease in humans - vector = sandfly
• Toxoplasma gondii - fatal; seen in free-ranging animals in Africa - targets brain/spleen/liver; abortion/stillbirth in pregnant animals
• Babesia thomasi - hyrax in Kenya - protozoa in erythrocytes

Longer Terio Summary

• Mycobacteriosis widely reported in hyrax – specific variant of M. tuberculosis complex called “dassie bacillus” and M. microti-like, as well as M. africanum and M. microti have been reported
• CS: Weight loss, lameness, pneumonia, repro failure and gross granulomas in lungs, liver, spleen, kidney
• Spoligotyping (PCR and genotyping) on fresh material, but antemortem dx insensitive and nonspecific
• Bacterial septicemia (most commonly gram-negative sepsis) and bacterial pneumonia
• Alpha-herpesvirus suspected in outbreak of glossitis and oral ulceration and mortality in rock hyrax
  
  • Amphophilic to basophilic IN inclusion bodies in epithelial cells. Cytomegaly, karyomegaly, syncytia.
  • Grouped into genus Simplexvirus
• Toxoplasma gondii
  
  • fatal toxoplasmosis in pregnant and young rock (cape) hyraxes and tree hyrax and titers have been detected in wild rock hyraxes
  • Disseminates to brain, liver, and spleen -> necrosis; May also see pneumonia, abortion, stillbirths

Question 4

Describe the noninfectious disease of hyraxes.

Cardiomyopathies are farily common - what are the proposed risk factors?

Hemosiderosis can result in what secondary sequelae in these species?

What is Hyracoidea stress syndrome?

Renal disease can result in what secondary metabolic consequences?

What reproductive condition are females prone to in late gestation?

Answer 4

Noninfectious Diseases of Hyrax

• Iron overload has been reported on numerous occasions
  
  • Generally present with anorexia caused by gastric enteritis and hemorrhage
  • Severe degenerative liver changes reported
  • Diabetes mellitus is often a sequela
• Pregnancy toxemia and dystocia have been reported
• Dental disease
• Aggression related trauma often due to overcrowding
• A disease process called hyracoidea stress syndrome was identified in a European journal in 2009A 3-year study on 37 animals concluded that environmental stress factors led to respiratory and nervous symptoms just before death. Cold temperatures leading to pneumonia, gastric ulcerations, and damage to endocrine glands, specifically the pituitary, thyroid, and adrenal glands, were deter- mined to be the primary cause of this syndrome.

Nutritional:

• Cardiomyopathies in multiple species, most notably anteaters, hedgehogs and rock hyrax
  
  • Nutritional factors suggested – potential taurine deficiency, but not confirmed
  • Gross: hypertrophy, hepatomegaly, pulmonary edema and congestion, hydrothorax
  • Histo: myocardial fibrosis and edema; LV myocardial degeneration, necrosis, atrophy, hypertrophy, myofiber disarray
• Hemosiderosis and hemochromatosis from iron overload well-described in hyrax
  
  • Presumably diet related, +/- genetic
  • Histo: Increased cytoplasmic iron in hepatocytes (esp. periportal cells)
  • Hemochromatosis – portal fibrosis, hepatocellular vacuolar change, degeneration
  • Prussian blue stain to detect iron
• Pancreatic fibrosis secondary to low-fiber diets in hyrax; some with diabetes mellitus and hyperglycemia
  
  • Gross: Enlarged, frim pancreas
  • Histo: Fibrosis of pancreatic islets; may efface islets and endocrine cells

Metabolic:

• Metastatic mineralization in captive rock hyrax with renal disease and subsequent hypercalcemia
• Pregnancy toxemia in captive rock hyrax in older, multiparous females – leads to rapid mobilization of fat from adipose stores and see hepatocellular degeneration and lipidosis w/ necrosis