Apparent tick paralysis by Rhipicephalus sanguineus (Acari: Ixodidae) in dogs

Veterinary Parasitology 188 (2012) 325–329

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Apparent tick paralysis by Rhipicephalus sanguineus (Acari: Ixodidae) in dogs Domenico Otranto a,∗ , Filipe Dantas-Torres a,b , Viviana Domenica Tarallo a , Rafael Antonio do Nascimento Ramos a , Dorothee Stanneck c , Gad Baneth d , Donato de Caprariis a a b c d

Dipartimento di Sanità Pubblica e Zootecnia, Università degli Studi di Bari, Valenzano, BA, Italy Departamento de Imunologia, Centro de Pesquisas Aggeu Magalhães, Recife, Pernambuco, Brazil Bayer Animal Health GmbH, Leverkusen, Germany School of Veterinary Medicine, Hebrew University, Rehovot, Israel

a r t i c l e

i n f o

Article history: Received 5 January 2012 Received in revised form 30 March 2012 Accepted 1 April 2012 Keywords: Rhipicephalus sanguineus Tick paralysis Dogs

a b s t r a c t Certain tick species including Ixodes holocyclus can inoculate neurotoxins that induce a rapid, ascending flaccid paralysis in animals. Rhipicephalus sanguineus, the most widespread tick of dogs, is recognized as a vector of several pathogens causing diseases in dogs and humans. A single report suggests its role as cause of paralysis in dogs. This study presents the clinical history of 14 young dogs heavily infested by R. sanguineus (intensity of infestation, 63–328) in an endemic area of southern Italy. During May to June of 2011, dogs were presented at the clinical examination with neurological signs of different degrees (e.g., hind limb ataxia, generalized lethargy, and difficulty in movements). All animals were treated with acaricides and by manual tick removal but ten of them died within a day, displaying neurological signs. The other 4 dogs recovered within 3 days with acaricidal and supportive treatment. Twelve dogs were positive by blood smear examination for Hepatozoon canis with a high parasitemia, two also for Babesia vogeli and two were negative for hemoparasites. Low-grade thrombocytopenia, hypoalbuminemia, and pancytopenia were the haematological alterations most frequently recorded. Other causes of neurological disease in dogs were excluded and the diagnosis of tick paralysis by R. sanguineus was confirmed (ex juvantibus) by early and complete recovery of 4 dogs following acaricidal treatment and tick removal. © 2012 Elsevier B.V. All rights reserved.

1. Introduction Along with fleas, sand flies and mosquitoes, ticks (Acari: Ixodidae) are the most important ectoparasites infesting dogs globally and they are recognized as efficient vectors of many pathogens. Rhipicephalus sanguineus, commonly known as the “brown dog tick” or the “kennel tick”, is the most widespread tick infesting dogs. Also due to its adaptability to survive under diverse climatic conditions

∗ Corresponding author. Tel.: +39 080 4679839; fax: +39 080 4679839. E-mail address: [email protected] (D. Otranto). 0304-4017/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.vetpar.2012.04.005

and ecological contexts, this tick species has a cosmopolitan distribution in tropical, subtropical and even temperate regions (Dantas-Torres, 2008). Its medical and veterinary importance mainly relies on its role as a vector of canine (e.g., Ehrlichia canis, Babesia vogeli and Hepatozoon canis) and human (e.g., Rickettsia conorii and Rickettsia rickettsii) pathogens. Certain tick species (e.g., Ixodes holocyclus) can inoculate neurotoxins (secreted by their salivary glands during blood feeding) that induce a rapid, ascending flaccid paralysis in animals. These neurotoxins may interfere with acetylcholine release at the neuromuscular junction, producing a neuromuscular blockade (Edlow and McGillicuddy, 2008).

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Cases of paralysis by ixodid ticks have been reported in several animal species including snakes (Hanson et al., 2007), birds (Luttrell et al., 1996), cattle (Doube and Kemp, 1975), cats (Holland, 2008) and humans (Yeruham et al., 2000). Tick toxicosis has been associated with at least 60 species of ticks worldwide, including Dermacentor andersoni and Dermacentor variabilis in North America (Edlow and McGillicuddy, 2008), I. holocyclus in Australia (Atwell et al., 2001; Beveridge et al., 2004; Adamantos et al., 2005) and Ixodes redikorzevi in the Middle East (Yeruham et al., 2000). Ixodes cornuatus and I. holocyclus are recognized as the tick species most frequently causing paralysis in dogs in southeastern Australia (Jackson et al., 2007) and a prospective survey on 577 dogs affected by tick paralysis evaluated that about 5% of them had a fatal outcome (Atwell et al., 2001). The development of a vaccine (Masina and Broady, 1999) has been advocated for tick paralysis prevention, as a valid alternative to treatment with dog antiserum. Indeed, while polyclonal antiserum in dogs represents the optimal curative option for tick paralysis (Edlow and McGillicuddy, 2008), it exhibits major limitations linked to the high costs and to its effectiveness in the early stages of disease. In spite of the broad distribution of R. sanguineus, the role of this tick species as cause of paralysis in dogs remains anecdotic (Walker et al., 2000) and cases of tick paralysis in dogs were described only in a single report from Venezuela (Viloria, 1954). This paper presents the clinical history of 14 young dogs heavily infested by R. sanguineus in southern Italy,

which were presented with neurological signs of different degrees. Ten dogs died within a day due to their severe clinical conditions whereas four survived. Other causes of neurological disease in dogs were excluded and the diagnosis of tick paralysis by R. sanguineus was confirmed (ex juvantibus) by early and complete recovery of 4 dogs following acaricidal treatment and tick removal. 2. Materials and methods From May to June of 2011, 14 dogs were referred to the teaching hospital of the Faculty of Veterinary Medicine (University of Bari, Italy) with neurological disorders (Table 1). Dogs were of mixed-breed, different sex, aged 5–6 months, and used to live in a private animal shelter in Putignano (province of Bari, Apulia region, Italy). All dogs were previously dewormed using a combination of febantel/pyrantel/praziquantel (Drontal plus® ; Bayer AG, Germany) and vaccinated with two doses of a tetravalent vaccine (Duramune® DAPPI + LC; Fort Dodge Animal Health, Italy) at a 2 week interval. At admission, none of them had a history of treatment with any acaricide and high tick infestations were recorded (Fig. 1). Animals were evaluated for the presence of ticks by thumb counting of anatomical body regions (i.e., head, ears, breast-neck, thorax, abdomen, fore and hind limbs, interdigital areas, armpits, tail and inguinal area). The presence of ticks and their developmental stage were recorded by using previously described procedures (Otranto et al., 2005). The owner reported to have removed

Table 1 Sex, age (in months), date of onset of clinical signs, description of clinical signs, laboratory abnormalities and disease evolution in 14 dogs with suspected tick toxicosis. Dog

Sex

Dogs that died F 1a

Age

Onset of symptoms

Clinical signs

Laboratory abnormalities

5.5

27/05

weakness, hind limb incoordination, quadriplegia, respiratory distress weakness, hind limb incoordination, quadriplegia, respiratory distress weakness, hind limb incoordination, quadriplegia, dehydration, hypothermia weakness, hind limb incoordination, quadriplegia, dehydration, hypothermia weakness, hind limb incoordination, quadriplegia, dehydration, hypothermia weakness, hind limb incoordination, quadriplegia, dehydration, hypothermia cachexia, weakness, hind limb incoordination, quadriplegia, weakness, hind limb incoordination, quadriplegia, dehydration, hypothermia, respiratory distress weakness, hind limb incoordination, quadriplegia weakness, hind limb incoordination, quadriplegia

anemia-neutrophilia-low PLT

2

M

6.5

26/05

3a,b

F

5.5

14/06

4b

F

7.5

14/06

b

F

7

11/07

5 6a,b

M

4.5

17/06

7

F

6.5

26/05

8b

M

6.5

27/05

9 M 4.5 F 6.5 10 Dogs that survived M 5 11

11/07 24/06 12/05

12

F

7

3/06

13

F

6.5

24/06

14

M

5

24/06

a b

hind leg swollen and painful, weakness, hind limb, incoordination (paraparesis) hind leg swollen and painful, weakness, hind limb incoordination (paraparesis) cachexia, weakness, hind limb,incoordination (paraparesis) cachexia, weakness, hind limb incoordination (paraparesis)

The owner reported to have removed many ticks the day before the presentation. Dogs from which serum chemistry analysis and a coagulation profile was performed.

anemia-low PLT anemia-neutrophilia-low PLT-hypoAlb anemia-neutrophilia-low PLT-hypoAlb-gammopathy pancytopenia pancytopenia-HypoAlb anemia-neutrophilia anemia-low PLT anemia anemia anemia-neutrophilia-eosinophiliahypoAlb neutrophilia-low PLT

anemia-neutrophilia

D. Otranto et al. / Veterinary Parasitology 188 (2012) 325–329

Fig. 1. Dog no. 3 massively infested by Rhicephalus sanguineus.

“many ticks” (not quantifiable) from three dogs (nos. 1, 3 and 6) one day before the presentation of clinical signs (Table 1). At the clinical examination, additional ticks were removed from the dogs, which were treated with a spot-on formulation of Fipronil 10%/(S)- Methoprene 9% (Frontline Combo® , Merial S.A.S., France). Collected ticks were stored in individual vials and later identified at the species level using morphological keys (Walker et al., 2000). At presentation, one or more neurological signs of paralysis (e.g., hind limb weakness, inability to stand and walk, quadriplegia, hypothermia, slow and labored respiration with expiratory effort) were recorded. Reduced or absent spinal reflexes in all four limbs with normal pain sensation were found upon neurological examination. A complete blood count (CBC) was obtained using an automated cell counter (Abbott Cell-Dyn 3700) and serum proteins were determined by agarose gel electrophoreses. The following hematological and serum biochemistry parameters were recorded: hemoglobin concentration (Hb), hematocrit (Hct), nucleated red blood cells (nRBC), white blood cells (WBC), platelet count (PLT), total serum protein (TP), albumin and -globulin. Hematological reference ranges were previously determined (Feldman et al., 2000; de Caprariis et al., 2011). Blood and buffy coat smears were prepared and stained using the MGG Quick Stain (Bio Optica Spa, Italy) and stained-smears were examined under light microscopy for the presence of intracellular inclusions (or free forms) of common tick-borne pathogens (Otranto et al., 2010). Specifically, blood and buffy coat smears were examined for Anaplasma platys, E. canis, Babesia spp. and H. canis inclusions. Each smear was examined for 10 min under a 100x oil immersion objective. Supportive therapy prescribed to dehydrated and/or hypothermic dogs (nos. 3–8) included rehydration with lactated Ringer’s solution with addition of dextrose (2.5%). A prophylactic antibiotic treatment with amoxicillin (at 20 mg/kg q 12 h) was administered intravenously for 24 h, to prevent aspiration pneumonia in dogs with respiratory distress (nos. 1, 7 and 8).

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Fig. 2. Blood buffy coat Giemsa-stained smear with a high parasitemia of ellipsoidal-shaped gamonts of Hepatozoon canis in leukocytes cytoplasm. Scale bar = 10 ␮m.

3. Results Out of 14 animals, 10 (nos. 1–10) died within 24 h from the presentation whereas four (nos. 11–14) recovered, within three days, following treatment with a spot-on formulation of Fipronil 10%/(S)-Methoprene 9% and no clinical neurological signs were recorded during six months follow-up. At the very beginning of their presentation, all animals showed hind limb incoordination, generalized weakness, and difficulty in movements. These clinical signs evolved rapidly (within 12–24 h) to inability to stand and walk, quadriplegia, hypothermia, and slow, labored respiration with fatal exitus in ten animals (nos. 1–10). The dogs’ owner declined necropsy. All dogs were massively infested by ticks (intensity of infestation, 63–328), which were all morphologically identified as R. sanguineus. Ten animals were positive by blood smear examination for H. canis with a high parasitemia (i.e., nos. 1–8 and 11–12; Fig. 2) and two of them (nos. 1 and 2) also for B. vogeli. Out of the four remaining dogs, two were negative for these hemoparasites (nos. 12 and 13), and for two dogs (nos. 9 and 10) hematological samples were not processed. A commercial assay (SNAP® 4DX test kit- Idexx Laboratories) failed to detected antibodies against E. canis, Anaplasma phagocytophilum/A. platys, Borrelia burgdorferi and Dirofilaria immitis, in all tested animals. Non-regenerative anemia and neutrophilia were the main hematological alterations detected in all dogs. Lowgrade thrombocytopenia was detected in six dogs (nos. 1–6 and 8) and hypoalbuminemia (nos. 3, 4, 6 and 11) in four dogs; two dogs were pancytopenic (nos. 5 and 6) and only one dog showed a polyclonal gammopathy (no. 4). In addition, serum biochemistry analysis including a coagulation profile was performed in four dogs (Table 1) and parameters were within the normal reference ranges (cholinesterase levels were not reduced) with the exclusion of an increase in creatine phosphokinase activities likely due to prolonged recumbence.

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4. Discussion The neurological alterations of dogs examined herein were associated with the heavy R. sanguineus infestation, probably as an effect of neurotoxins inoculated by ticks while feeding upon them. All dogs examined were presented in a limited period of time (May–June 2011) when the number of on-host ticks typically rises steadily in the geographical area from which the animals came (Lorusso et al., 2010). Indeed, May and June are the months in which R. sanguineus ticks are highly active with many engorged females feeding on animals (Dantas-Torres and Otranto, 2011). The recovery of 4 of the 14 dogs following tick removal and acaricidal treatment without any other specific symptomatic therapy (e.g., polyclonal antiserum), further supports the diagnosis (ex juvantibus) of tick toxicosis and also indicates that ten animals probably died because they were presented too late for medical care, at an advanced stage of neuromuscular dysfunction. The neurological signs observed (i.e., limb incoordination, generalized weakness, difficulty in movements rapidly evolving to inability to stand and walk, quadriplegia, slow and labored respiration with expiratory effort) were similar to those recorded in cases of tick paralysis caused by I. cornuatus and I. holocyclus. The main differential diagnosis for the clinical presentation found in the affected dogs include other potential causes of diffuse lower motor neuron diseases in dogs such as botulism, acute idiopathic polyneuropathy and snake envenomation (Malik and Farrow, 1991). Briefly, botulism may occur simultaneously in dogs after ingestion of rotting food or carrion (which is not the case for dogs described here, which were fed exclusively with commercial food) and it is clinically characterized by difficulties in prehension of food and swallowing with drooling of saliva and regurgitation (Shelton, 2002). Acute idiopathic polyneuropathy has been described in dogs exposed to raccoon saliva or in animals with a history of previous systemic disease with hyperesthesia and neurogenic muscular atrophy lasting for more than five to seven days (Malik and Farrow, 1991). In the neuromuscular paralysis conditions above, respiratory pattern is rapid and shallow whereas in our cases it was slow and characterized by an expiratory effort, similar to that recorded in tick paralysis (Holland, 2008). Thus, neurological signs herein described differ from other common potential causes of lower motor neuron diseases, resembling those of tick paralysis. Undoubtedly, the positivity to H. canis recorded in 10 out of the 12 dogs for which the hematological examination was performed, agrees with the high level of tick infestation recorded and the endemicity of H. canis in the region from which the dogs originated (Otranto et al., 2011; Dantas-Torres et al., 2012). Most importantly, all animals positive for H. canis presented several H. canis gamonts in each microscopical field at blood smear cytology (Fig. 2). This indicates a high level of tick pressure on dogs and in the environment they lived. Interestingly, paralysis-like signs have been induced in a dog inoculated with egg extracts from R. sanguineus (Mans et al., 2004). This might suggest that tick ingestion, the primary mode of transmission for H. canis, should also be considered as a possible way of

acquiring tick toxins. Nonetheless, the relationship between egg toxins (ixovotoxins) and paralysis toxins needs further research, as ticks that possess egg toxins do not necessarily induce paralysis during blood feeding (Mans et al., 2004). Differently from H. americanum infection, which might cause muscular pain, muscle atrophy, generalized stiff gait and hind limb paresis (Macintire et al., 1997), no neuromuscular alterations are usually reported in H. canis infected dogs. Indeed, H. canis often causes chronic infections with mild or no apparent clinical alterations to its host (Baneth et al., 2003). A high H. canis load may induce clinical signs such as lethargy, fever, anorexia, weight loss, lymphadenomegaly, and anemia (Baneth et al., 1995; Baneth and Weigler, 1997). Consequently, the hematological abnormalities recorded here, which may have been caused by H. canis infection, include leukocytosis, lymphocytosis, neutrophilia, eosinophilia, monocytosis and thrombocytopenia. These abnormalities are commonly found in young dogs infected with H. canis (de Caprariis et al., 2011; Otranto et al., 2011). Although R. sanguineus has only been implicated in one case of tick paralysis in a dog (Viloria, 1954), our findings may suggest a potentially higher toxicosis virulence of tick populations circulating in southern Italy. There is evidence indicating that the production of paralysis toxins is associated to the occurrence of Wolbachia spp. symbionts in tick species originating from several regions (Harwood and James, 1979). This finding fits with the evidence of geographical variants of R. sanguineus in tick populations as demonstrated by biological and molecular data (Szabó et al., 2005). Further studies should address the genetic make-up of this tick species in order to better understand the relationship between R. sanguineus populations and variations in their capability to produce neurotoxins and their susceptibility as vectors of pathogens. 5. Conflict of interest statement The authors declare there are no conflicts of interest. References Adamantos, S., Boag, A., Church, D., 2005. Australian tick paralysis in a dog imported into the UK. Aust. Vet. J. 83, 352. Atwell, R.B., Campbell, F.E., Evans, E.A., 2001. Prospective survey of tick paralysis in dogs. Aust. Vet. J. 79, 412–418. Baneth, G., Harmelin, A., Presentez, B.Z., 1995. Hepatozoon canis in two dogs. J. Am. Vet. Med. Assoc. 206, 1891–1894. Baneth, G., Weigler, B., 1997. Retrospective case-control study of hepatozoonosis in dogs in Israel. J. Vet. Intern. Med. 11, 365–376. Baneth, G., Mathew, J.S., Shkap, V., Macintire, D.K., Barta, J.R., Ewing, S.A., 2003. Canine hepatozoonosis: two disease syndromes caused by separate Hepatozoon spp. Trends Parasitol. 19, 27–31. Beveridge, I., Coleman, G., Gartrell, W., Hitchman, A., Whitnall, V., 2004. Tick paralysis of dogs in Victoria due to Ixodes cornuatus. Aust. Vet. J. 82, 642–643. Dantas-Torres, F., 2008. The brown dog tick, Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae): from taxonomy to control. Vet. Parasitol. 152, 173–185. Dantas-Torres, F., Otranto, D., 2011. Rhipicephalus sanguineus on dogs: relationships between attachment sites and tick developmental stages. Exp. Appl. Acarol. 53, 389–397. Dantas-Torres, F., Latrofa, M.S., Weigl, S., Tarallo, V.D., Lia, R.P., Otranto, D., 2012. Hepatozoon canis infection in ticks during spring and summer in Italy. Parasitol. Res. 110, 695–698.

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