- Several animals of a herd of silage fed goats are showing signs of circling, dysphagia, and unilateral dropped lip. On your examination, you also note a lack of a menace and palpebral reflex unilaterally in several of these animals. What is the most likely diagnosis?
- The correct answer is listeriosis. The key to answering this question is the unilateral nature of the clinical signs. Because Listeria infection is caused by an ascending infection, usually of the trigeminal nerve, the signs are frequently unilateral. The other big hint was that the animals were fed silage. Listeria is a common inhabitant of spoiled silage because it thrives in a microaerophilic, low pH environment.
- Listeriosis is defined as an acute bacterial meningoencephalitis of ruminants characterized by circling and cranial nerve deficits. The clinical signs typically relate to caudal cranial nerves (V thru XII) .thus affected cattle can usually see. General signs of fever (last 2-4 days), anorexia, depression, excessive salivation may be seen as well. Neurological signs include proprioceptive deficits, head-pressing, depressed consciousness (due to lesions of the reticular activating system), constant or sporadic walking or circling (the latter due to lesions of the basal ganglia). Sometimes the affected animal, because of the desire to circle, gets stuck against a wall or gets stuck in the corner. Spinal reflexes may show mild to moderate hypertonia and hyperreflexia in the limbs contralateral to the lesion. Lesions of the cerebellar peduncles may result in a head tilt opposite of the direction of circling. The primary cranial deficits (many or none may be present) include: dropped jaw and or facial anesthesia (CN V), medial strabismus on the ipsilateral side of the lesion (CN VI), ptosis, loss of menace, absent palpebral reflex, drooped ear, loss of levator nasolabialis muscle function (one open, one semi-closed nostril), decreased lip tone (CN VII), nystagmus (any type and inconsistent) that changes as the position of the head is altered and head tilt to the ipsilateral side of the lesion, a tendency to circle to the side with the lesion (CN VIII), stertorous breathing, dysphagia and paresis or paralysis of the tongue (cranial nerves IX, X, and XII). With unilateral lesions, the tongue may protrude from the side of the mouth ipsilateral to the lesion. If not treated in time, signs will progress to convulsions, coma and death. Diagnosis is presumptive and based on clinical signs and response to therapy. There is usually NOT an inflammatory leukogram. A CSF tap can be helpful. The CSF tends to be a mononuclear pleocytosis (> 12 cells/ul) with a mildly elevated protein (> 40 mg/dl). The organism can be cultured from CSF or microabscesses but requires refrigeration, enrichment and a long incubation time.
Treatment and control
- Treatment can be successful but may take from 1 week to 1 month. Fluids are necessary for those that cannot swallow or have difficulty swallowing. Fluids should be alkalizing because of salivary bicarbonate loss (due to persistent drooling in those that can’t swallow). Several different antibiotics are effective with the standard oxytetracycline @ 10 mg/kg BID IM, IV, or SQ or procaine penicillin G @ 40,000 IU/kg IM 3-4 x day for 1 week followed by half this dose SID for another 1-2 weeks being the drugs of choice. Under hospital conditions, we will use potassium penicillin @ 44,000 IU/kg IV 3-4 x day for 3-5 days and then follow with one of the antibiotics above on valuable and pet animals.
- A 2-year old nonlactating dairy cow in California has a sudden onset of head tilt and drooling. The owner also reports that she appears less active and less interested in feed than normal, and today is circling in one direction in the pen. You examine her and find T=105F (40.6 C), HR=96, and RR=32. There is ptosis, drooped ear, and weakness of the lips on the affected side. You take a lumbosacral spinal tap (see photo), and submit the CSF to your lab. The results show elevated protein and WBCs, with the cell type being mainly monocytes. The lab reports seeing some gram positive bacteria in the monocytes of the CSF. Based on these findings what is the best treatment for this condition?
- The diagnosis is Listeriosis. Listeria monocytogenes can effectively be treated in the early stages of the disease with penicillin, ampicillin, or tetracycline. Intramuscular procaine penicillin for example has a withdrawal of 10 days for slaughter (meat) and 48 hours for milk if the animal is lactating. Other choices of approved antimicrobials would also likely be effective since L. monocytogenes is susceptible to most antimicrobials. For a list of approved animal drugs see www.farad.org/vetgram. FARAD is the United States Food Animal Residue Avoidance Databank which gives withdrawal information as well as a list of prohibited drugs. The other drugs listed as choices here are prohibited and cannot be legally used in food animals in the USA.