Tick Paralysis Caused by Amblyomma maculatum on the Mexican Pacific Coast

Introduction

T ick paralysis (TP) is an entity described in the medical literature particularly in the United States, Australia, South Africa, and Europe (Felz et al. 2000, Pape and Gershman 2006, Diaz 2010). However, there is very little information on these cases in the tropics and specifically in Latin America, where there is a greater diversity of Acari.

TP is a disease that can lead to death if left undetected. The tick toxin affects motor neurons, leading to paralysis of respiratory muscles. If it is identified opportunely and the tick is removed, there is a full recovery within 24–48 h (Felz et al. 2000, Gerpen and Caruso 2005, Pape and Gershman 2006). For this reason, it is important that medical personnel have high index of suspicion, given that it can be confused with diseases involving the peripheral nervous system such as Guillain-Barré syndrome or toxic polyneuropathy (Felz et al. 2000, Pape and Gershman 2006, Diaz 2010).

This disease has been attributed to at least 43 tick species (Acari, Arachnida), both hard (Ixodidae) and soft (Argasiae) ticks, including the tick found on the coast of the Gulf of Mexico Amblyomma maculatum. (Gerpen and Caruso 2005, Pape and Gershman 2006). This species is widely distributed in North and Central America (Sumner et al. 2007). The purpose of this article was to present a case of paralysis associated with A. maculatum, which is apparently the first one reported in Mexico and Latin America.

Case Report

The patient is a 22-year-old male resident from a rural area in Cihuatlan, Jalisco (19°22′30′′ Latitude North, 104°42′30′′ Longitude West) on the Mexican Pacific coast. He sought medical attention with a 2-day history of progressive asthenia and bilateral ascending weakness in his legs, which rapidly progressed to paralysis. He reported having been in contact with cattle at 7 days prior and had later noticed several ticks attached to his feet.

He was first evaluated at a local hospital where flaccid paraplegia and areflexia were observed. His somatic-sensory exam was normal. Symptoms progressed until the patient had difficulty breathing and he was transferred to the Regional Hospital in the city of Colima (RHC) with the diagnosis of Guillain-Barré syndrome. While moving the patient, nursing personnel found two ticks in the bed that were engorged with blood and later identified as adult female A. maculatum. Upon admission to the RHC the patient was conscious with flaccid paraplegia of the legs, loss of deep tendon reflexes, and a normal somatic-sensory exam. Laboratory work-up was normal and included a complete blood count, renal and liver function tests, serum electrolytes, erythrocyte sedimentation rate, hemoculture, Weill-Felix reaction, urinalysis, and cerebrospinal fluid chemistry and cytology. Cranial computed tomography and magnetic resonance of the spinal cord were normal. After his admission to the RHC, the patient began to have spontaneous and progressive recovery of muscle strength and, 48 h later, was able to walk. He was discharged from hospital without receiving any treatment. At a 1-month follow-up, there was no motor deterioration. Five specimens of A. maculatum were found upon visiting the area where the patient worked with cattle.

Discussion

TP in humans generally presents in pediatric patients but can affect any age group. The condition may be less frequent in adults because the effect of the tick neurotoxin is diminished because of greater total body surface (Felz et al. 2000, Vedanarayanan et al. 2002, Gerpen and Caruso 2005, Pape and Gershman 2006). Signs and symptoms begin ∼1 week after the female tick adheres to the skin, presenting as ascending flaccid paralysis. If the etiology is not suspected and the tick is not removed, symptoms can progress to the point of compromising the medulla oblongata, leading to coma and death. The definitive diagnosis is established by finding the tick attached to the patient's skin. There is a rapid, spontaneous response upon its removal (Felz et al. 2000, Gerpen and Caruso 2005, Pape and Gershman 2006, Crawford and Mitchell 2009). It is very difficult to identify this disease without a high degree of suspicion because it is easily confused with polyneuropathies such as Guillain-Barré syndrome, acute spinal cord injury, cerebellar ataxia, poliomyelitis, botulism, myasthenia gravis, hysterical crisis, or toxic neuropathies. There is a reduction in nerve conduction velocity, which can be detected through nerve excitability studies. This can be explained by a reduction in neurotransmitter release from the presynaptic terminal of the neuromuscular junction (Edlow and McGillicuddy 2008), as well by an increase in refractoriness, suggesting recovery from inactivation of Na⁺ channels (Felz et al. 2000, Vedanarayanan et al. 2002, Krishnan et al. 2009). Electromyography study was not carried out on the patient because of his rapid recovery after hospital admission.

In this patient's case, the ticks dropped off spontaneously when the patient was moved from the hospital bed, resulting in a dramatic remission of symptoms. The fact that the patient had no evidence of somatic sensory involvement suggested the diagnosis of TP, as has been previously reported (Gerpen and Caruso 2005, Pape and Gershman 2006). This was confirmed by examining the entomologic specimens obtained from the first hospital where the patient was treated and then from the site where the infestation presumably occurred. This added to the fact that there was spontaneous remission of symptoms as soon as the ticks were detached from the patient. Perhaps the lack of clinical suspicion leads to the absence of reported cases in Latin America. Also, this entity may be more common than is presently thought.

The tick species most frequently associated with this paralysis in humans in North America are Ixodes scapularis, Ixodes pacificus, Dermacentor andersoni, Dermacentor variabilis, A. americanum, and A. maculatum. The latter has a wide distribution in the United States and Central America (Torres and Schlossberg 2001). This species had been described on the coast of the Gulf of Mexico and the present case is apparently the first reported case on the Mexican Pacific coast, thus extending its geographical distribution. This tick is a cattle ectoparasite that causes TP in these animals (Serra-Freire 1983). It sporadically infests humans and can cause TP or rickettsiosis (Gerpen and Caruso 2005, Sumner et al. 2007).

TP should be included in the differential diagnosis of peripheral polyneuropathy in México and other countries in the region. A focused search, especially of the scalp, should be done for these arthropods in all patients with the presumptive diagnosis of Guillain-Barré syndrome or similar diseases who live or work in communities where humans and cattle come into close contact, as is the case of most of the rural and suburban areas of Latin America.