Luísa N. Domingues

Coxiella symbiont in the tick Ornithodoros rostratus (Acari: Argasidae)

In the present study, the presence of tick-associated bacteria and protozoa in Ornithodoros rostratus ticks (adults, nymphs, and eggs) from the Pantanal region of Brazil were determined by molecular detection. In these ticks, DNA from protozoa in the genera Babesia and Hepatozoon, and bacteria from the genera Rickettsia, Borrelia, Anaplasma, and Ehrlichia were not detected. Conversely, all tested ticks (100%) yielded PCR products for 3 Coxiella genes (16S rRNA, pyrG, cap). PCR and phylogenetic analysis of 3 amplified genes (16S rRNA, pyrG, cap) demonstrated that the agent infecting O. rostratus ticks was a member of the genus Coxiella. This organism grouped with Coxiella symbionts of other soft tick species (Argasidae), having different isolates of C. burnetii as a sister group, and these 2 groups formed a clade that grouped with another clade containing Coxiella symbionts of hard tick species (Ixodidae). Analysis of tick mitochondrial 16S rRNA gene database composed mostly of tick species previously shown to harbor Coxiella symbionts suggests a phylogenetic congruence of ticks and their Coxiella symbionts. Furthermore, these results suggest a very long period of coevolution between ticks and Coxiella symbionts and indicates that the original infection may have occurred in an ancestor common to the 2 main tick families, Argasidae (soft ticks) and Ixodidae (hard ticks). However, this evolutionary relationship must be confirmed by more extensive testing of additional tick species and expanded populations.

Survey of pyrethroid and organophosphate resistance in Brazilian field populations of Rhipicephalus (Boophilus) microplus: Detection of C190A mutation in domain II of the para-type sodium channel gene

The cattle tick Rhipicephalus (Boophilus) microplus causes expressive damage to livestock in Brazil and other countries. Its control is becoming more difficult due to the development of resistance in populations. Early detection of resistance can help in developing effective control strategies. This study evaluated the susceptibility of R. microplus to cypermethrin and chlorpyriphos and was the first attempt to identify the mechanism of resistance (target site insensitivity) in cattle tick populations from Minas Gerais state (Southeastern Brazil). Engorged female ticks were collected from 10 ranches within the state of Minas Gerais, and susceptibility was evaluated with the larval packet test (LPT) using technical grade cypermethrin and chlorpyriphos. It was possible to analyze LPT results of seven populations. Target site insensitivity was investigated in all 10 isolates by using molecular approaches for detection of the T2134A substitution within the domain III S6 segment and the C190A in the domain II S4-5 linker from the para-type sodium channel gene. LPT showed that all seven populations were resistant to cypermethrin with resistance ratio (RR) ranging from 16.0 to 25.0 and 85.7% were resistant to chlorpyriphos (RR=2.2-15.6). Although the T2134A mutation was not detected, the C190A mutation was highly prevalent, being present in 82-100% of the alleles sampled in field populations. A significant correlation was found between the LC50 values for cypermethrin and the frequency of the C190A mutation suggesting that it might be responsible for the phenotypic resistance detected.

A novel Rickettsia infecting Amblyomma dubitatum ticks in Brazil

A total of 130 adult free-living ticks of Amblyomma cajennense and 9 free-living Amblyomma dubitatum were collected in the surroundings of the Pampulha Lake, within Belo Horizonte city, state of Minas Gerais, south-eastern Brazil. Each adult tick was tested for rickettsial infection by PCR protocols targeting the rickettsial genes gltA, htrA, and ompA. All the 130 A. cajennense ticks were negative by PCR. In contrast, all 9 A. dubitatum ticks were shown to contain rickettsial DNA. PCR products were sequenced, generating identical sequences for each gene among the 9 ticks, which were shown to contain a novel agent, here designated as Rickettsia sp. strain Pampulha. Phylogenetic analyses inferred from the 3 rickettsial genes (gltA, htrA, ompA) showed that Rickettsia sp. strain Pampulha segregated in the same cluster with R. tamurae, R. monacensis, and several other unclassified rickettsial strains; however, strain Pampulha is a unique Rickettsia strain for the New World, since its closest relatives, according to 3 genes (gltA, htrA, and ompA), are all from the Old World. Because A. dubitatum eventually bites humans, further studies are necessary to determine the potential pathogenicity of Rickettsia sp. strain Pampulha to humans.

Clinical aspects and dynamics of auricular parasitosis in Gir cattle

We evaluated the dynamics of ear infestations caused by Rhabditis spp. and Raillietia spp., which were correlated with animal age, intensity of clinical signs and climate factors. Sixty-four Gir cattle were distributed into three groups: GA - 23 calves with 4 to 6 months of age; GB - 18 calves with 7 to 12 months of age; and GC - 23 heifers with 13 to 33 months of age. Five samplings, defined as S1, S2, S3, S4 and S5 were performed every three months from August 2008 to August 2009. The ear secretion was collected using the auricular washing method for the right ear and a swab for the left ear. A clinical assessment of the animals was performed, and they were classified according to the presence and severity of otitis. The highest relative frequency of rhabditosis was 52.2% in GC at the last sampling. In the first sampling, 42.2% of the animals were infested by Raillietia spp. The older cattle were more susceptible to infestations by both parasites. No correlation of Rhabditis spp. and Raillietia spp. parasitism with climate factors was found. The results showed that both parasites could infest Gir cattle, and in most cases, there was no co-infestation. Only older animals parasitized by the nematode showed clinical signs of the disease.

Effects of urea on the cattle tick Rhipicephalus (Boophilus) microplus (Acari: Ixodidae)

This study aimed at evaluating the effects of urea on Rhipicephalus (Boophilus) microplus. The experiment was divided into two stages. In Stage I, Brachiaria brizantha was placed into 30 pots, each with an area of 18 cm(2).These were divided into three groups of ten pots each: G1 non-treated control group, G2 treated with 15 g of urea per pot and G3 treated with 15 g of urea+10% of ammonium sulphate. Three engorged female ticks were placed in each pot and then 1.8l of water were added. In the second stage, a control group was maintained without the addition of urea and another group was treated with urea, each group comprising ten Mombaça grass (Panicum maximum cv. Mombaça) beds. On day zero, 12 engorged females were placed in each grass bed where were then fertilized with 60 g of urea per bed, only in the grass beds of the treated group. On the 27th day, the grass was cut in beds 1-5 in both groups and beds 1-5 in the treated group were fertilized a second time. On the 40th day, pieces of white flannel measuring 1.60 m × 1.00 m were spread over the grass to check for larvae presence. In stage I, observations conducted 24h after contact with urea showed a 100% death rate among the engorged females in G2; in group 3, only one engorged female still remained alive. In stage II, the counting of larvae reported 85.97% (P<0.0001) fewer parasites in the treated group compared to the control group.

Caracterização do controle de Haematobia irritans e Rhipicephalus (Boophilus) microplus no Triângulo Mineiro e Alto Paranaíba, Minas Gerais

The effective control of Haematobia irritans (horn fly) and Rhipicephalus (Boophilus) microplus (cattle tick) is crucial for increasing the productivity of livestock industry in Brazil, but still remains a challenge. A greater knowledge about parasite control in the field is necessary to establish control strategies closer to farmers reality and easier to be performed. This study characterized the practices adopted for controlling such ectoparasites on 23 cattle ranches from the Triângulo Mineiro and Alto Paranaiba region in the state of Minas Gerais, through interviews. Most interviewees recognized the importance of these parasites to livestock, however, many problems related to parasite control were observed. Control of horn flies and cattle tick was a routine in 17.4% and 95.7% of the ranches, respectively, triggered by high infestations on animals. More than six insecticide/acaricide treatments were applied yearly in all cattle ranches controlling horn flies and in 76.5% of the ranches controlling the cattle tick. Pesticide products were applied mostly by manual backpack sprayers (63.6%) without restraining the animals in 45.5% of ranches. Product dilution following manufacturers recommendations was performed by 45.5% of interviewees, but 63.6% of them used lower doses per animal than technically recommended. Associations of organophosphates and pyrethroids were the main products used to control both parasites. Although pesticide use was a routine practice, the use of personal protective equipment (PPE) was not common among surveyed people. Most interviewees were able to recognize epidemiological characteristics of the parasites; however, parasite control measures adopted at most cattle ranches tend to jeopardize the efficacy of products, susceptibility of parasites and sustainability of control programs.