Equine Infectious Anemia Quiz

LA Infectious Diseases of Hemolymphatics

• Infectious agents affecting the hemolymphatic system are discussed. Learning objectives include describing organism types, transmission methods, clinical significance, treatments, and reportability.
• Key infectious agents include Equine Infectious Anemia (EIA), Bovine Leukemia Virus (BLV), Anaplasma, Piroplasma (Babesia/Theilaria), Corynebacterium pseudotuberculosis, and Streptococcus equi ssp. equi (Strangles).

Equine Infectious Anemia (EIA)

• EIA is caused by a retrovirus.
• EIA has a simple RNA genome of 8 kb.
• Retrovirus characteristics include gag, pol, env genes.
• Macrophage/monocyte cell lines are affected.
• Systemic effects arise from cytokine secretion.
• EIA is reportable.

Coggins Test

• A Coggins test is required for sale/movement of horses in the US.
• The test is performed yearly by a USDA Category II-accredited veterinarian.
• The Coggins test is used to detect antibodies.
• AGID (Agar Gel Immunodiffusion) is the gold standard for testing EIA antibodies,
• The test will shows precipitation lines between test sample/antiserum and EIA antigen.
• Prevalence of this disease is low in the US, particularly in the Gulf Coast region.

Infection Transfer

• Infection can happen through insect vectors, such as flies and mosquitoes.
• Iatrogenic transmission is also possible through needles, surgical instruments, dental floats, and bits.

Clinical signs of Acute EIA

• Sudden, high fever (104-108°F).
• Anorexia and depression.
• Weight loss.
• Petechiae (indicates thrombocytopenia).
• Jaundice (signifies hemolytic anemia).
• Ventral edema.

EIA Abnormalities

• Thrombocytopenia is an early and consistent abnormality.
• The disease encompasses intravascular and extravascular hemolysis, additionally affecting erythropoiesis.
• Glomerulonephritis/vasculitis is caused by antibody/antigen complexes.

EIA: Cyclical Alterations

• Acute/subacute form is the most common type.
• Chronic disease includes periods of illness followed by remission and potentially recurrence.
• Inapparent carriers show no clinical signs.

Managing Positive EIA Horses

• A positive test indicates a lifelong infection.
• Quarantining affected horses along with those within a 200 yard radius is a common practice.
• Euthanasia or permanent quarantine may be necessary.

Bovine Leukemia Virus (BLV)

• BLV belongs to the Deltaretrovirus genus and Retroviridae family.
• BLV is characterized by lifelong infection and a blood-borne nature, infecting lymphocytes.
• BLV progression can follow distinct stages, as seen in the diagram.

BLV Disease Progression

• Healthy B-cells can be infected.
• Aleukemic occurs; this phase is characterized by absence of leukemic cells in blood.
• Persistent lymphocytosis: marked increase in the lymphocytes in the blood is noted.
• Tumors are sometimes seen.

BLV Significance

• BLV has high prevalence in the US, especially in dairy herds with some occurrences in beef herds.
• Carcasses of affected animals are condemned.
• BLV is associated with a significant portion of condemned carcasses.

BLV Testing

• Antibody testing (AGID or ELISA) is employed for animals with no observed signs of the disease.
• Lymph node sampling is necessary for clinical cases.
• These types of tests are reportable.

BLV Transmission

• Blood-borne/fluids are important for disease transmission.
• BLV can be transmitted via milk, in utero (in about 1/20 cases), nasal secretions, and insects.
• Iatrogenic spread is possible when needles aren't properly disinfected.

Babesia and Theileria in LA

• These are tick-transmitted protozoa.
• These disease-causing organisms also manifest differently in cattle and other animals.
• Specifically, these protozoa differ in their behavior and presentation in these animals compared to other species like dogs.

Anaplasma

• Anaplasma is obligate intracellular bacteria.
• Organisms exhibit a coccoid to ellipsoidal shape.
• They reside/replicate in vacuoles within the cytoplasm of eukaryotic cells.

Anaplasma Transmission

• Ixodid ticks of specific types are responsible for transmission.
• Certain species of ticks found in the eastern, western USA and other areas can lead to infection.

Anaplasma phagocytophilum - Horses

• This pathogen infects neutrophils and eosinophils, forming colonies termed “morulae”.
• Clinical signs includes fever, lethargy/inappetence, limb edema, icterus, ataxia, and stiff gait.
• Clinical signs in adults tend to be more severe than in younger horses.

Anaplasma marginale

• Affecting erythrocytes.
• Can cause extra-vascular hemolytic anemia.
• Clinical signs are often significant, including fever, pale mucous membranes, lethargy, icterus, gastrointestinal issues, significant weight loss, decreased milk production, abortion, and eventual death.
• Affected younger animals tend to exhibit milder signs.

Anaplasma Testing and Treatment

• Testing methods include blood smears (for intracellular organisms), antibody tests, and PCR.
• Tetracyclines are an antibiotic treatment option
• This pathogen is a reportable disease in LA

Corynebacterium pseudotuberculosis

• A gram-positive, facultative intracellular coccobacillus.
• Primarily found in goats and sheep, also affecting horses.
• Caseous lymphadenitis (CL) is frequently reported in goats and sheep whereas Pigeon fever is associated with the same disease in horses.

CL Pathogenesis

• Entry points for this pathogen are through wounds and mucous membranes.
• Virulence factors include an exotoxin (phospholipase D) which damages endothelium and promotes spread, and a lipid coating offering protection from digestion, which contributes to sustained persistence of infection in cells.

CL Clinical Signs

• Abscess formation (both internal and external) is a characteristic.
• Progressive weight loss is another critical clinical symptom.
• Lymphangitis can also be a present clinical sign.

CL Diagnosis

• Suspected cases are often initially diagnosed using Lymph Node (LN) aspiration and serology.
• Definitive diagnosis is confirmed using pus bacterial cultures. Other possible abscess-causing bacteria are also identified in this process.

CL Treatment Options

• Treatment options for CL range from culling afflicted animals, surgery to lance/drain abscesses and lavage procedures or LN resection, to administration of long-term penicillins combined with rifampin, or topical or systemic tulathromycin.

CL Prevention

• Biosecurity and isolation measures are crucial in CL prevention.
• Ideally, affected animals should be culled.
• If culling isn't possible, implementing separation from unaffected animals is vital.
• Vaccinations are an option for inclusion in control measures, although they may not fully prevent infection.

Streptococcus equi ssp. Equi (aka Strangles)

• Gram-positive, beta-hemolytic bacteria.
• Key traits include M-protein that resists phagocytosis and facilitates immunogenicity, and a polysaccharide capsule crucial in attachment and evasion of phagocytosis.

Strangles

• A highly infectious disease in horses showing clinical signs such as fever, nasal discharge, regional lymph node swelling, pain in parotid region, stertor or stridor, coughing, and dyspnea.

Strangles Treatment

• Surgical procedures such as lancing and draining abscesses is part of many treatment protocols and in some instances the horse might require a tracheostomy procedure.
• Antimicrobials, like penicillins and ceftiofur, are essential components of the treatment regimen. TMS/rifampin are also included in many treatment plans.

Metastatic Strangles (aka Bastard Strangles)

• A form of strangles that displays signs of infection in areas beyond the initial site.