Life cycle of female ticks of Amblyomma cooperi Nuttal & Warburton, 1908 (Acari: Ixodidae) under laboratory conditions

Ciclo biológico de fêmeas do carrapato Amblyomma cooperi Nuttal & Warburton, 1908 (Acari:Ixodidae) sob condições de laboratório

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Life cycle of female ticks of Amblyomma cooperi Nuttal & Warburton, 1908 (Acari: Ixodidae) under laboratory conditions

[Ciclo biológico de fêmeas do carrapato Amblyomma cooperi Nuttal & Warburton, 1908 (Acari:Ixodidae) sob condições de laboratório]

A.T.S. Almeida¹, E. Daemon², J.L.H. Faccini²

¹Estudante de Pós-Graduação do CPGM-PV da UFRRJ

Docente - Universidade de Vila Velha

Rua Maranhão, 404/1001 - Praia da Costa

29101-340 - Vila Velha, ES

2Universidade Federal Rural do Rio de Janeiro

Recebido para publicação, após modificações, em 3 de outubro de 2000

E-mail [e-mail]

ABSTRACT

The biological cycle of female ticks of Amblyomma cooperi was studied under controlled conditions. The study has begun with two engorged females collected in a naturally infested wild capybara. The larvae originated from the oviposition of these two females were used for collecting young adults through artificial infestations in rabbits. The female parasitic and free living phases were evaluated using artificial infestation of ticks in a capybara. The average body weight of females was 958.2± 175.6mg, the average pre-egg laying period was 8.5± 1.4 days, the reproductive efficiency index was 59.5± 4.2 and the nutritional efficiency index was 77.3± 4.8. The incubation and eclosion periods were 41.9 and 5.9 days, respectively, and the rate of eclosion was 64%. These figures were obtained under high relative humidity conditions which were necessary for the success of the egg incubation process of this species. The preliminary data obtained with the artificial infestation in rabbits raises the possibility of this and other domestic species be used as an epidemiologic link between the domestic and the wild environment with the potential exposure of human populations to A. cooperi and to the maculosa fever agent.

Keywords: Tick, Amblyomma cooperi, life cicle, capybara

RESUMO

O ciclo biológico de Amblyomma cooperi foi estudado sob condições de laboratório. O estudo iniciou-se com duas fêmeas ingurgitadas coletadas de uma capivara selvagem naturalmente infestada. As larvas provenientes da postura foram utilizadas para obtenção de adultos, por meio de infestação artificial em coelhos. As fases parasitária e de vida livre das fêmeas foram avaliadas utilizando-se infestação artificial em capivara. A média de peso corporal foi de 958,2± 175,6mg, a média do período de pré-postura de 8,5± 1,4 dias e dos índices de eficiência reprodutiva e nutricional de 59,5± 4,2 e 77,3± 4,6, respectivamente. Os períodos de incubação e eclosão foram de 41,9 e 5,9 dias, respectivamente. A taxa de eclosão foi de 64%. Estes dados foram obtidos sob alta umidade relativa, necessária para o sucesso da incubação dos ovos dessa espécie. Os dados preliminares obtidos com a infestação artificial em coelhos levanta a possibilidade dessa e de outras espécies domésticas serem possíveis elos epidemiológicos entre o ambiente doméstico e o silvestre, com potencial risco de exposição humana a A. cooperi e ao agente etiológico da febre maculosa.

Palavras-chave: Carrapato, Amblyomma cooperi, ciclo biológico, capivara

INTRODUCTION

Ticks of wild animals in South America are not well studied with respect to their biological cycles in laboratories as well as under natural conditions. The few studies available are mainly concerned with the presence of new hosts. Amblyomma cooperi Nuttal & Warburton, 1908 (= A. lutzi Aragão, 1908) is an ixodidae species found specially in capybaras (Hydrochoerus hydrochaeris) in South America. Owing to these aspects and to its external characteristics, this parasitic species is commonly known as the "capybara whitish tick" (Aragão, 1936).

Monteiro & Tiriba (1976) considered A. cooperi as one of the main vectors of the Rock Mountain spotted fever (RMSF) in Brazil and Lemos et al. (1996) carried out the first isolation of rickettsias from the group which causes the RMSF.

The reports on the occurrence of this tick in bovines in the Bolivian Chaco region (Squire, 1972) and its 97.5% prevalence in capybaras under natural conditions in the Taim Ecological Reserve (RS, Brazil) (Sinkoc et al., 1997) suggest that A. cooperi may have been put in contact with human populations through the breeding of bovines and capybaras. It is noteworthy that the breeding of capybaras is widely spread in some regions of Brazil. Considering the above information and the lack of data about its biological cycle, some biological characteristics of the parasitic and non-parasitic phases of Amblyomma cooperi were analysed under controlled laboratory conditions.

MATERIALS AND METHODS

The experiments were carried out at the Laboratory of Ticks of the Parasitological Research Station W. O. Neitz, Animal Parasitology Department, Biology Institute of Universidade Federal Rural do Rio de Janeiro (UFRRJ), Seropedica County, Rio de Janeiro State and at the Center of Studies for the Reintroduction of Wild Animals (CEREAIS – partnership between IBAMA and Aracruz Celulose S/A), Aracruz County, Espírito Santo State.

Two A. cooperi engorged females, identified according to Aragão & Fonseca (1961), were collected in a naturally infested wild capybara (Hydrochoerus hydrochaeris) at CEREAIS. After the collection, the specimens were kept in the dark in a chamber regulated at 27± 1ºC, 80± 10% relative humidity before and during the egg-laying period.

Eggs layed by each female were weighed in an analytic scale every two days and placed in 5ml plastic syringes, which had their end cut and covered with a hydrophilic cotton wad. Half of the syringes had the cotton wad humidified with one millilitre of distilled water every two days whereas the other half had the wad kept dry. By the end of the incubation period, all wads were kept dry. By the end of the incubation, artificial infestations on rabbits were carried out according to the technique developed by Neitz et al. (1971) for the collection of unfed adults used in the experiments.

The capybaras were submitted to a previous physical restraint followed by administration of ketamine (30.0 mg/kgLW/IM) (Clark & Olfert, 1986). Infestation occurred freely on the animals using 32 couples of ticks of approximately 20 day-old post ecdysis. The eggs from the engorged females were processed as described above with the exception that the cotton wads were kept dry for the eggs of the first half of the oviposition and humidified for the rest of them.

The biological characteristics studied in the non-parasitic phase were: average body weight of the engorged females, number of eggs layed and the female reproductive (REI) and nutritional (NEI) efficiency indices after oviposition (Bennett, 1974), pre-oviposition, oviposition, egg incubation and larval eclosion average periods and eclosion percentage. For the parasitic phase, the biological traits studied were: parasitic period and percentage of engorged females recovery.

RESULTS AND DISCUSSION

The data related to the oviposition of females which started the colony and the biological characteristics of the eggs incubation and larvae eclosion are shown in Tables 1 and 2. It is noteworthy the fact that no eclosion took place in syringes where oviposition was kept with a dry cotton.

In the adult ticks obtained from artificial infestation, a parasitic period of 9.5± 2.0 days was observed in an interval of 7-13 days, being the 8^th day the day of the highest engorged females detachment. The engorged females recovery was 40.6%. This value should not be considered typical for A. cooperi as the place where the animal was kept allowed eventual escapes of engorged females.

Comparing the data shown in Table 1 with those obtained from females originated from the artificial infestation in capybaras (Table 3), it can be observed that for artificial infestation there is a slight increase in the pre-oviposition period and NEI, a large increase in the oviposition period, in the oviposition weight and in the REI, and there is a weight loss of the female after oviposition and an average weight loss of the females (with a greater sampling uniformity). Considering the conditions in which this study was carried out, it is believed that the data presented in Table 3 may be regarded as closer values to reality for the biological traits of A. cooperi as the amount of females was greater and their weights more homogeneous.

In Figure 1, the oviposition rhythm of A. cooperi females originated from artificial infestation can be observed. It is also noted that more than 50% of the egg laying occurred until 7^th day of oviposition and that more than 90% occurred until 17^th day. These data differed from those observed for A. cajennense as, for example, in this species approximately 90% of the egg laying occurred until 10^th day (Prata & Daemon, 1997). This discrepancy can be partially explained by the greater average body weight of A. cooperi females which causes a lengthening of the oviposition period.

It can be observed that under similar conditions of temperature and relative humidity, the REI of Amblyomma cooperi (59.5 ± 4.2) is similar to that of Boophilus microplus (Gloria et al., 1993) and Anocentor nitens (Daemon & Serra Freire, 1984) but superior to that of Amblyomma cajennense (Sanavria et al., 1996; Prata & Daemon, 1997) and inferior to that of Rhipicephalus sanguineus (Bellato & Daemon, 1997), whereas the NEI (77.3± 4.6) is greater than that found in A. cajennense (Sanavria et al., 1996; Prata & Daemon, 1997) and Anocentor nitens (Daemon & Serra Freire, 1984), and similar to that of B. microplus (Gloria et al., 1993) and Rhipicephalus sanguineus (Bellato & Daemon, 1997). Thus, it can be pointed out that the levels of A. cooperi REI and NEI are compatible with those found in the literature for other species. This means that the method used to obtain and keep the females was adequate.

Table 4 shows the results related to the egg incubation and larval eclosion periods and the percentage of eclosion of eggs obtained from female ticks which originated from the artificial infestation on capybaras and that were kept in humid cotton wad. From the 54 syringes kept without a humidified cotton, the incubation process has been observed in only 14 of them, showing the following average values: incubation period 41.5± 7.6 days (32 – 54 days), eclosion period 2.6± 2.0 days (1 – 7 days), eclosion percentage 36.2± 48.6% (1 – 99%). Comparing these values with those presented in Table 4, the necessity of humidifying the cotton wad becomes evident providing the relative humidity inside the syringes and increasing the chances of successful incubation of A. cooperi eggs.

Although the preliminary results obtained with artificial infections in rabbits have not been presented in this paper, evidence was gathered that this species can be used as a host for immature phases of A. cooperi. This observation leads to the necessity of developing similar works with other domestic and wild species as possible A. cooperi hosts. This would be useful not only for keeping the colonies but also on evaluating the capacity of the domestic species to become an epidemiological link between the wild and domestic environments, exposing human populations in contact with A. cooperi eventually infected with the etiological agent of the Rocky Mountain spotted fever.

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Publication Dates

• Publication in this collection
  12 June 2002
• Date of issue
  June 2001

History

• Received
  03 Oct 2000