Neonatal Salmonellosis

Studies from the past decades indicate that certain Salmonella serotypes can be carried asymptomatically by the mare in feces and expose the foal at birth and cause clinical salmonellosis in the foal within 12-72 hours of age [1-3].

I. Clinical Presentation [1-3]

1. History

1. Apparently healthy mare
2. Normal pregnancy and parturition
3. Post birth normal parameters, exam and adequate serum IgG.
4. May have multiple cases of diarrhea developing at 12-72 hr of age

2. Clinical signs-foal

1. Scleral injection
2. Depression
3. Fever
4. Watery diarrhea ≥ mild colic
5. Mild limb edema ≥ joint swelling
6. Death

3. Clinical Pathology

1. Initial CBC may be normal
2. Leukopenia-toxic cells, left shift
3. Hyperfibrinogenemia
4. Positive blood culture for Salmonella spp.
5. Fecal culture positive for Salmonella spp.
6. Necropsy enterocolitis, nephritis, endocarditis, Salmonella cultured from multiple organs
7. PCR can be performed from feces and blood.

4. Epidemiology

1. Mares shed Salmonella spp. at time of parturition. They may be fecal culture negative prior to stress of parturition.
2. Mares may ingest a Salmonella spp. in feed that is not pathogenic to adult horses but capable of causing disease in neonates.
   May need to culture mares 5-10 times to detect shedding.
3. Mare defecation at stage 2 labor contaminates perineum and provides source of Salmonella spp to foal during udder sucking and contaminates environment.

II. Control Measures [1]

1. Foals

1. Keep foal from back end of mare until mare washed
2. Feed colostrum milked from mare before foal rises
3. Antibiotic IV starting at 12 hours and continued for 3 days

1. Choose antibiotic based on culture and sensitivity.
2. Aminoglycosides (gentamicin, amikacin) are effective against some Salmonella strains.
3. 3rd and 4th generation cephalosporins (cefotaxime, ceftazidime, cefquinome, and cefepime) have excellent efficacy against most Salmonella strains.
4. Fluroquinolones (enrofloxacin) are even more effective against resistant strains, but they can cause cartilage damage. Client consent is recommended before using this.
5. Carbepenems (imipenem) are the most potent antibiotics available, however, they are very costly ($200/day for 50 kg foal) and should be used very cautiously due to bacterial resistance concerns.

4. Administer anti-endotoxin plasma IV within 12-24 hrs (See Plasma Therapy).
5. Blood culture foal prior to antibiotics and every day for 3 days post antibiotics (See Blood Culture)
6. Additional treatments and prevention for sepsis, shock, endotoxemia. (See Shock (SIRS), Fluid and Electrolyte Balance, How to Prevent the Leading Cause of Death in Neonatal Foals: Opinion, Guidelines for Drug Use in Equine Neonates)

2. Mares

1. Attempts to identify asymptomatic Salmonella shedders based on fecal culture is difficult [4].
2. Mares shed Salmonella intermittently and may shed only at stress of parturition.
3. Prior to expulsion of afterbirth, wrap placenta in plastic sack to minimize contamination of perineum.
4. Complete bathing of mares post-foaling.

1. Hose mare down while standing outside foaling stalls immediately post birth.
2. Betadine scrub bath and towel dry.
3. Keep mare's head in door of stall to observe foal.
4. Completely dry mare and milk out colostrum.

3. Environment

1. Determine level of foaling area contamination by multiple (40 +) cultures of area.
2. Isolate foaling area, use footbaths, hand washing, and/or latex gloves, separate coveralls, limit movement of horses.
3. Disinfect entire area and disinfect stalls post foaling.
4. Pasture track all foals that are fecal culture positive for salmonella to one set of pastures and negative foals to another set of pastures.
5. Fecal shedding should stop after several weeks (monitor a small group of foals for this).

III. Additional Control Measures

1. Salmonella bacterin

1. Prepare from pure culture of isolate.
2. Test bacterin on research horses.
3. Vaccinate mares with owner permission.

2. Vaccinate plasma donor horses with Salmonella bacterin

1. Test antibody response.
2. Harvest plasma by plasmapheresis and administer to newborn foals.