José M. Venzal

Ticks (Ixodidae) on humans in South America

Twenty eight species of Ixodidae have been found on man in South America (21 Amblyomma, 1 Boophilus, 2 Dermacentor, 2 Haemaphysalis, 1 Ixodes and 1 Rhipicephalus species). Most of them are rarely found on man. However, three species frequently parasitize humans in restricted areas of Argentina (A. neumanni reported from 46 localities), Uruguay (A. triste from 21 sites) and Argentina–Brazil (A. parvum from 27 localities). The most widespread ticks are A. cajennense (134 localities in Argentina, Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Paraguay, Suriname and Venezuela), A. ovale (37 localities in Argentina, Brazil, Ecuador, French Guiana, Guyana, Paraguay, Suriname and Venezuela) and A. oblongoguttatum (28 sites in Brazil, Colombia, French Guiana, Guyana, Suriname and Venezuela). Amblyomma aureolatum (18 localities in Argentina, Brazil, French Guiana and Paraguay), A. cajennense, and A. triste are vectors of rickettsioses to man in South America. A better understanding of the respective roles of these and other tick species in transmitting pathogens to humans will require further local investigations. Amblyomma ticks should be the main subjects of these studies followed by species of Boophilus, Dermacentor, Haemaphysalis and Rhipicephalus species. In contrast with North America, Europe and Asia, ticks of the genus Ixodes do not appear to be major players in transmitting diseases to human. Indeed, there is only one record of an Ixodes collected while feeding on man for all South America.

The Amblyomma maculatum Koch, 1844 (Acari: Ixodidae: Amblyomminae) tick group: diagnostic characters, description of the larva of A. parvitarsum Neumann, 1901, 16S rDNA sequences, distribution and hosts.

A review of the largely confused Amblyomma maculatum Koch, 1844 tick group of the subgenus Anastosiella Santos Dias, 1963 (A. neumanni Ribaga, 1902, A. maculatum, A. parvitarsum Neumann, 1901, A. tigrinum Koch, 1844 and A. tristeKoch, 1844) is presented together with a discussion of the diagnostic characters used for the determination of adults, nymphs and, to a lesser extent, larvae. A key for this tick group is produced, including the description of the larva of A. parvitarsum, 1901. Sequences of 16S rDNA are obtained and compared with other Amblyomma spp., including two other species currently in Anastosiella but in the ovaletick group, A. ovale Koch, 1844 and A. aureolatum(Pallas, 1772). According to the morphology and the rDNA sequences, the maculatum group is reduced to A. maculatum (Neotropical-Nearctic), A. tigrinum (Neotropical) and A. triste (Neotropical) A. neumanni and A. parvitarsum are excluded from the subgenus. The distribution is sympatric in northern South America from where A. maculatumreaches the southern Nearctic and the range of A. tigrinum extends to the southern Neotropics. These species have been found on several domestic and wild vertebrates. A. triste and A. tigrinum have been also found on man. Their role as vectors of pathogens deserves further investigation.

Amblyomma aureolatum (Pallas, 1772) and Amblyomma ovale Koch, 1844 (Acari: Ixodidae): hosts, distribution and 16S rDNA sequences

DNA sequences of Amblyomma aureolatum (Pallas, 1772) and Amblyomma ovale Koch, 1844 were obtained to determine genetic differences between these tick species. Collections of these species are discussed in relation to distribution and hosts. Seven ticks collections (four from Brazil, one from Argentina, one from Uruguay and one from USA) house a total of 1272 A. aureolatum (224 males, 251 females, 223 nymphs and 574 larvae) and 1164 A. ovale (535 males, 556 females, 66 nymphs and 7 larvae). The length of the sequenced mitochondrial 16S rRNA gene fragment for A. aureolatum was 370bp and for A. ovale was 373bp. The DNA sequence analysis showed a 13.1% difference between the two species. Apart from one male A. ovale found on a toad, all adult ticks were found on mammals. The majority of adult specimens of both tick species were removed from Carnivora (96.1 and 84.3% of A. aureolatum and A. ovale, respectively), especially from dogs (53.1% of A. aureolatum, and 46.4% of A. ovale). Collections on wild Canidae were higher for A. aureolatum (23.3%) than for A. ovale (7.1%). On the other hand, collections of A. ovale adults on wild Felidae were higher (18.3%) than findings of A. aureolatum (9.2%). The contribution of other mammalian orders as hosts for adults of A. aureolatum and A. ovale was irrelevant, with the exception of Perissodactyla because Tapiridae contributed with 13.0% of the total number of A. ovale adults. Adults of both tick species have been found occasionally on domestic hosts (apart of the dog) and humans. Most immature stages of A. aureolatum were found on Passeriformes birds, while rodents and carnivores were the most common hosts for nymphs and larvae of A. ovale. A. aureolatum has been found restricted to the Neotropical region, covering the eastern area of South America from Uruguay to Surinam, including northeastern Argentina, eastern Paraguay, southeastern Brazil and French Guiana. A. ovale showed a distribution that covers the Neotropical region from central-northern Argentina throughout the Neotropics into the Nearctic region of Mexico with a few records from the USA, also with collection sites in Paraguay, Bolivia, most Brazilian states, Peru, Ecuador, French Guiana, Surinam, Guyana, Trinidad & Tobago, Venezuela, Colombia, Panama, Costa Rica, Nicaragua, Belize, Guatemala and several states of Mexico.

The taxonomic status of Rhipicephalus sanguineus (Latreille, 1806)

The brown dog tick, Rhipicephalus sanguineus sensu stricto, is a species with considerable public health and economic importance. However, the taxonomic status of this species is far from resolved. After more than 110 years of scientific work on R. sanguineus s.s., the situation is that there is no type, no solid description, nor is there a consensus about the range of morphological variability within the species. Recent findings based on laboratory crosses and molecular genetics strongly suggest that there are several entities grouped under the same name. Here we review the history of the taxon, and we point out the caveats behind any further work on this tick. The current taxonomic status of R. sanguineus s.s. thus lacks an informative original description, and is based on the existence of several morphological descriptions based on ticks originating from different populations, which show, in some cases, biological incompatibility and significant genetic divergence. We suggests that as a result it is not possible to assign the specific name R. sanguineus s.s. to any population. Further work is required based on the rules issued by the International Code of Zoological Nomenclature to clearly define the morphological range of the different populations.

Mitochondrial DNA analysis of Rhipicephalus sanguineus sensu lato (Acari: Ixodidae) in the Southern Cone of South America

A genetic analysis of partial sequences of the mitochondrial 16S and 12S rDNA genes of Rhipicephalus sanguineus sensu lato collected in the Southern Cone of South America was carried out. Also, sequences of ticks belonging to this taxon from Europe, Africa and other South American localities were included. TCS networks constructed with 16S rDNA sequences showed two clusters of haplotypes, namely, Southern lineage (ST) and Northern lineage (NT). Haplotypes representing the specimens coming from localities of Argentina, Uruguay and Chile were included in the ST lineage, while haplotypes from Brazil, Paraguay, Colombia, South Africa, Mozambique and from two localities of Northern Argentina were grouped in the NT lineage. The phylogenetic trees obtained with both 16S and 12S sequences showed two distinct clades, one containing R. sanguineus s.l from Argentina, Uruguay, Chile (ST lineage) and Western Europe (Italy and France), and a second clade including R. sanguineus s.l from Argentina, Paraguay, Brazil, Colombia (NT lineage), South Africa and Mozambique. The results herein reported revealed that the taxon R. sanguineus s.l is represented by two lineages in the Southern Cone of South America. According with the genetic comparative analysis, NT lineage and the ticks from Mozambique and South Africa represent a species that is not R. sanguineus s.s, while R. sanguineus s.l ticks from Western Europe and Southern South America (ST lineage) probably represent true R. sanguineus, because the type locality of R. sanguineus s.s is located in France. The taxonomic issue described for R. sanguineus s.l in the South America has epidemiological implications. Difference in the vectorial competence for Ehrlichia canis between the two lineages of R. sanguineus s.l was found in previous works. Further investigations are needed in order to verify a possible different vectorial competence for the other pathogens transmitted by these ticks.

Reinstatement of Rhipicephalus (Boophilus) australis (Acari: Ixodidae) With Redescription of the Adult and Larval Stages

ABSTRACT Rhipicephalus australis Fuller, the Australian cattle tick, is reinstated and the adults and larvae redescribed from material collected in Australia. This long ignored boophilid was previously known as R. microplus Canestrini for specimens reported in Australia and New Caledonia. The adults of R. australis are easily recognized by a combination of characters, such as the ventro-medial spurs in the palpal segments of the male, and the abundant, plumose, pale white setae on the dorsum of the female. Other details, such as coxal and adanal shields are more variable among different populations and may lead to incorrect determinations. Larvae of R. australis are clearly smaller than those of R. microplus. The use of principal components analysis on body measurements leads to a clear separation of larvae of both taxa. A phylogenetic analysis based on 12S- and 16S-rDNA gene sequences supports the conspecificity of the neotype material on which the reinstatement of the species is proposed, and of the specimens used for previous interspecific crosses. R. australis is now known to be present in Australia, New Caledonia, the island of Borneo, Philippines, Sumatra, Java, New Guinea, Cambodia, and Tahiti. Both R. microplus and R. australis coexist in some countries in southeastern Asia. Given the extreme importance of these ticks for the cattle industry, field data on their distribution in the region are required to know the actual range of these species and to understand the evolution of the group.

Hosts, distribution and genetic divergence (16S rDNA) of Amblyomma dubitatum (Acari: Ixodidae).

We supply information about hosts and distribution of Amblyomma dubitatum. In addition, we carry out an analysis of genetic divergence among specimens of A. dubitatum from different localities and with respect to other Neotropical Amblyomma species, using sequences of 16S rDNA gene. Although specimens of A. dubitatum were collected on several mammal species as cattle horse, Tapirus terrestris, Mazama gouazoubira, Tayassu pecari, Sus scrofa, Cerdocyon thous, Myocastor coypus, Allouata caraya, Glossophaga soricina and man, most records of immature and adult stages of A. dubitatum were made on Hydrochoerus hydrochaeris, making this rodent the principal host for all parasitic stages of this ticks. Cricetidae rodents (Lundomys molitor, Scapteromys tumidus), opossums (Didelphis albiventris) and vizcacha (Lagostomus maximus) also were recorded as hosts for immature stages. All findings of A. dubitatum correspond to localities of Argentina, Brazil, Paraguay and Uruguay, and they were concentrated in the Biogeographical provinces of Pampa, Chaco, Cerrado, Brazilian Atlantic Forest, Parana Forest and Araucaria angustifolia Forest. The distribution of A. dubitatum is narrower than that of its principal host, therefore environmental variables rather than hosts determine the distributional ranges of this tick. The intraspecific genetic divergence among 16S rDNA sequences of A. dubitatum ticks collected in different localities from Argentina, Brazil and Uruguay was in all cases lower than 0.8%, whereas the differences with the remaining Amblyomma species included in the analysis were always bigger than 6.8%. Thus, the taxonomic status of A. dubitatum along its distribution appears to be certain at the specific level.

Amblyomma triste Koch, 1844 (Acari: Ixodidae): Hosts and seasonality of the vector of Rickettsia parkeri in Uruguay

Amblyomma triste Koch, 1844, the tick species most frequently involved in human bites in Uruguay, has been implicated as a vector of human rickettsiosis. Seasonal abundance of adult A. triste was examined by standard flagging at three sites where human tick bites and cases of the disease have been reported. Adult tick activity occurred from August to February (end of winter to mid summer in the southern hemisphere) with a peak in spring. Activity declined in step with decreasing temperatures and photoperiod during winter. This period of activity coincides with seasonal outbreaks of human rickettsiosis in the region. In a small mammal survey, the Sigmodontinae rodents Scapteromys tumidus (Waterhouse, 1837) and Oxymycterus nasutus (Waterhouse, 1837) and the small marsupial Monodelphis dimidiata (Wagner, 1847) were the main hosts for immature A. triste. Immature ticks were observed on hosts in November, well within the period of peak adult abundance. In stored collections, immature ticks were most often collected from January to March. These data suggest that one generation might be completed in 1 year. The main animal host for adult A. triste at our study sites was the domestic dog. Humans were afflicted by the tick in rural and suburban settlements where other host animals are scarce or extinct and where dogs are common.

Ticks (Ixodida: Ixodidae) parasitising humans in Uruguay

Abstract During routine collections between November 1999 and November 2002, three species of tick (Amblyomma tigrinum, Amblyomma triste and Rhipicephalus sanguineus) were found on humans in southern Uruguay. The finding of R. sanguineus and A. triste on humans is of particular concern because these tick species may be involved in the transmission of the pathogens causing human rickettsioses, a type of disease already known to occur in Uruguay.

Description of a New Species of Bat-Associated Argasid Tick (Acari: Argasidae) from Brazil

abstract:  A new species of argasid tick (Acari: Argasidae) is described from immature and adult specimens collected from several localities in Brazil. A complete morphological account is provided for all postembryonic life stages, i.e., larva, nymph, female, and male. Ornithodoros cavernicolous n. sp. is the 113th in the genus. Morphologically, the new species shares common features, e.g., presence of well-developed cheeks and legs with micromammillate cuticle, with other bat-associated argasid ticks included in the subgenus Alectorobius. In particular, the new species is morphologically related to Ornithodoros azteci Matheson, with which it forms a species group. Phylogenetic analysis based on the 16S rRNA gene sequences supports the placement of the new species within a large clade that includes other New World bat-associated argasids. However, the new species seems to represent an independent lineage within the genus Ornithodoros.