27: Equine Immunodeficiencies

THE most common equine immune deficiency

Failure of transfer of passive immunity (FTPI)

Immunologically speaking, how are foals born

Immunologically competent, but totally immunologically naive

Why don’t foals get antibodies from the mare before birth

Due to the mare’s diffuse epitheliochorial placentation

When is colostrum likely to be of poorer quality

Short days (watch those early winter foals!)

Factors that can decrease colostrum quality

• Mare gets sick in peripartum period

• Older mares

• Standardbred mares

• Placentitis → leaks all the colostrum out

• Fescue toxicosis

Causes of FTPI

• Inadequate intake

• Poor quality colostrum

• Poor absorption of colostrum

Diagnostic for FTPI

IgG stall side test

If a foal tests low for IgGs, what do you assume

Assume they are septic until proven otherwise

Why do FTPI foals often have signs of sepsis

They have no IgGs

CS of sepsis in a foal

Shocky and hypothermic

Treatment for FTPI

• Colostrum (if <24 hrs old)

• Plasma

• Aggressive antibiotics

• IVF

• Nutritional support

• Monitor CBC

• BP support

Severe combined immunodeficiency pathogenesis

Complete lack of functioning B cells and T cells due to a stem cell maturation defect

What type of disease is SCID

Autosomal recessive genetic disease

Breed disposition for SCID

Arabians

Demographic for a horse presenting with SCID

2-4 month old foal, likely an Arabian

Why do SCID foals typically present at 2-4 months old

The mare’s antibodies start to drop around 1-3 months

CS of a SCID foal

Poor doers that get infections that normal, healthy foals don’t get

Diagnostics for SCID

• CBC: stress leukogram with a persistent lymphopenia

• Chem: low globulins

What does a globulin test look like for a normal foal that hasn’t nursed yet

They will have IgMs, which are normally produced in utero

What does a globulin test look like for a SCID foal that hasn’t nursed yet

There will be no IgMs

If you are testing globulins on a foal after it has nursed, when will the IgM count drop

2-4 weeks

Necropsy findings consistent with SCID

Small thymus and grossly normal lymphoid organs with microscopic defects

Treatment for SCID

None really, one case of a bone marrow transplant that worked

Prevention for SCID

Client education: don’t breed heterozygotes!

Definition of Selective IgM deficiency

Absent IgM or more than 2 standard deviations below normal

Three types of presentations for Selective IgM Deficiency

• <10 most with severe infections

• <2 years with repeat infections that respond to antibiotics

• 2-5 years with lymphadenopathy → lymphoma

Breed disposition for Selective IgM Deficiency

Arabians and QHs

CS of a foal with Selective IgM Deficiency

Foal >5 months old with severe respiratory infections, enteritis, or septic arthritis

Cs of an older horse with Selective IgM Deficiency

Presents for weight loss and ADR with palpable lymphadenopathy → lymphoma on histology

Clin path findings consistent with Selective IgM deficiency

• Persistently low/absent IgM with normal IgG/A

• Normal lymphocyte count

• WBCs consistent with infection status

Prognosis for IgM deficiency

Quite grave

Pathogenesis of X-linked Agammaglobulinemia

Complete B cell dysfunction with normal cell mediated immunity

Demographic for X-linked Agammaglobulinemia

Male thoroughbreds, standardbreds, and QHs

How old do horses with X-linked Agammaglobulinemia present

2-6 months of age

CS of X-linked Agammaglobulinemia

• Repeat infections

• No response to vaccination

• No Igs after maternal Abs are gone

Breed disposition for Foal Immunodeficiency Syndrome

Fell ponies and Dale ponies

What type of disease is Foal Immunodeficiency Syndrome

Autosomal recessive gene

How old do Foal Immunodeficiency Syndrome foals present

1 month

Pathogenesis of Foal Immunodeficiency Syndrome

B cell lymphopenia and non-regenerative anemia

CS of Foal Immunodeficiency Syndrome

• Anemia

• Hyperkeratosis of the tongue

• Diarrhea

• Resp disease

• Odd opportunistic infections

Clin path abnormalities associated with Foal Immunodeficiency Syndrome

• Severe non-regenerative anemia

• Normal or low globulins

• Low B cells

• No plasma cells

• Low MHC II expression

Prognosis for Foal Immunodeficiency Syndrome

Dead by 3 months

Pathogenesis of Common Variable Immunodeficiency

B cell lymphopenia with impaired development and impaired Ab function

How old does a horse with Common Variable Immunodeficiency present

2-23 years of age

Prognosis for Common Variable Immunodeficiency

Can be managed for a few years, but eventually succumbs to chronic infections