Seasonal occurrence of Rhipicephalus sanguineus in Okayama Prefecture, Japan and effect of temperature on development of the tick

The evaluation of cystatin protein vaccines based on the stress response of ticks triggered by low-temperature and toxin stress in Haemaphysalis doenitzi

BACKGROUND

Ticks, which are obligate blood-feeding parasites, transmit a wide range of pathogens during their hematophagic process. Certain enzymes and macromolecules play a crucial role in inhibition of several tick physiological processes, including digestion and reproduction. In the present study, genes encoding type 2 cystatin were cloned and characterized from Haemaphysalis doenitzi, and the potential role of cystatin in tick control was further assessed.

RESULTS

Two cystatin genes, HDcyst-1 and HDcyst-2, were successfully cloned from the tick H. doenitzi. Their open reading frames are 390 and 426 base pairs, and the number of coding amino acids are 129 and 141, respectively. In the midgut, salivary glands, Malpighian tubules and ovaries of ticks, the relative expression of HDcyst-1 was higher in the midgut and Malpighian tubules, and HDcyst-2 was higher in the salivary glands of H. doenitzi, respectively. Lipopolysaccharide (LPS) injection and low-temperature stress elevated cystatin expression in ticks. Enzyme-linked immunosorbent assay showed that both rHDcyst-1 and rHDcyst-2 protein vaccines increased antibody levels in immunized rabbits. A vaccination trial in rabbits infected with H. doenitzi showed that both recombinant cystatin proteins significantly reduced tick engorgement weights and egg mass weight, in particular, rHDcyst-1 significantly prolonged tick engorgement time by 1 day and reduced egg hatching rates by 16.9%. In total, rHDcyst-1 and rHDcyst-2 protein vaccinations provided 64.1% and 51.8% protection to adult female ticks, respectively.

CONCLUSION

This is the first report on the immunological characterization of the cystatin protein and sequencing of the cystatin gene in H. doenitzi. Cystatin proteins are promising antigens that have the potential to be used as vaccines for infestation of H. doenitzi control. © 2024 Society of Chemical Industry.

Observations on Some Biological Characteristics of Rhipicephalus sanguineus Sensu Lato (Acari: Ixodidae) Under Natural and Laboratory Conditions in Nigeria

The brown dog tick, Rhipicephalus sanguineus sensu lato (s. l.) is a globally distributed tick of medical and veterinary significance. This study reports some observations on the biological characteristic of the brown dog ticks kept under natural and laboratory conditions in Nigeria. Variation in biological parameters was observed within the Nigerian R. sanguineus s. l. population kept under various conditions. A higher number of R. sanguineus exhibited the type 1 oviposition pattern than the type 2 pattern. The type 1 pattern was observed in 84.2 % and 80 % of R. sanguineus s. l. reared under laboratory and natural conditions, respectively. The pre-oviposition period was significantly shorter in ticks maintained under laboratory conditions than under natural conditions. Similarly, ticks kept under laboratory conditions laid significantly more eggs with higher egg mass weight than ticks kept under natural conditions. Furthermore, the incubation period and the total weight loss by female ticks throughout the oviposition period differed significantly between the two groups (P < 0.05). The engorged R. sanguineus s. l. females kept at 4 °C survived for up to 21 days and remained viable producing fertile eggs. Egg of R. sanguineus s. l. kept at 4 °C for up to 63 days retain viability and were able to hatch to larvae after variable incubation periods when returned to ambient temperatures depending on the duration of storage at 4 °C. The results showed that the tropical lineage of the brown dog tick can survive and remain fecund at low temperatures, suggesting that it can be translocated and established in temperate regions.

Molecular identification and genetic analysis of Rhipicephalus sanguineus sensu lato of dogs in Nigeria, West Africa

The brown dog tick, Rhipicephalus sanguineus sensu lato, is a ubiquitous and taxonomically controversial pest of dogs with immense veterinary and public health significance. Genetic analyses of specimens from various geographical origins reveal intraspecific diversity within the taxon. Little information is available on the genetic characteristics of R. sanguineus s.l. in Nigeria, West Africa. In this study, 460 bp of the mitochondrial 16S rDNA gene of R. sanguineus s.l. collected from dogs in different ecological zones of Nigeria was amplified, sequenced and characterized. Phylogenetic and pairwise analyses were used to compare the sequences generated in this study to each other and to sequences in GenBank. The sequences in this study were highly similar (>98%) to each other and clustered with sequences of the R. sanguineus s.l. tropical lineage in GenBank. None of the sequences in this study clustered with the 'southeastern Europe' or temperate lineage. The mean intraspecific divergence among R. sanguineus s.l. in this study was 1.7% (range: 0-8.0%). Furthermore, the sequences in this study showed mean divergence of 1.5% (0-10%), 5.0% (3.8-13.9%) and 9.7% (6.9-19.8%) from sequences of the tropical, southeastern Europe and temperate lineages, respectively. Interestingly, sequences in this study showed a mean divergence of 9.3% (1.0-17.8%) from the Rhipicephalus sp. morphotype 4 (GenBank acc. nr. KC243850) earlier identified from cattle in Nigeria, suggesting diversity in this taxon in Nigeria. Further studies are needed to elucidate the veterinary and public health significance of R. sanguineus s.l. in Nigeria taking into cognizance the existence of intraspecific variation in vector competence.

Dog overpopulation and burden of exposure to canine distemper virus and other pathogens on Santa Cruz Island, Galapagos

Dog overpopulation and diseases are hazards to native island species and humans on the Galapagos. Vaccination and importation of dogs are prohibited on the Galapagos. Risk management of these hazards requires the use of science-based risk assessment and risk communication. The objectives of the study reported here were (i) to estimate the human:dog ratio and (ii) the prevalence of and identify exposure factors associated with positive antibody titers to canine distemper virus (CDV) and other pathogens, as well as infection with intestinal parasites in owned dogs on Santa Cruz Island, Galapagos in September 2014. The observed human:dog ratio was 6.148:1 which extrapolates to 2503 dogs (two times more than a recent dog count conducted by Galapagos Biosecurity Agency in March 2014). The proportion of spayed female dogs (50%) was higher, compared to neutered male dogs (30%) (p=0.04). Prevalence of dogs with positive antibody titers to CDV was 36% (95% CI=26, 46%), to canine parvovirus was 89% (95% CI=82, 95%), and to canine adenovirus was 40% (95% CI=30, 51%). The frequency of seropositive dogs to CDV was lower in urban dogs (26%), compared to rural dogs (53%) (p<0.05). A positive interaction effect between rural residence and spay/neuter status on seropositivity to CDV was observed, which we discuss in this report. Because vaccination is prohibited, the dog population on Santa Cruz is susceptible to an outbreak of CDV (particularly among urban dogs) with potential spill over to marine mammals. Dog's age (1-2 or 3-14 years old, compared to younger dogs), and residence (rural, urban) were associated with positive antibody titers to parvovirus, adenovirus, Ehrlichia spp., or Anaplasma spp., as well as infection with Ancylostoma spp., an intestinal parasite in dogs that can be transmitted to humans, particularly children. These results provide the most comprehensive assessment of dog overpopulation and exposure to CDV and other pathogens on the Galapagos to date.

Cold-stress response of engorged females of Rhipicephalus sanguineus

We investigated the effect of prolonged exposure to low temperature on engorged females of Rhipicephalus sanguineus. Five groups of two females (F1-F5) were maintained at 8 ± 2°C, 70 ± 10% RH, and 24 h scotophase, for 15, 30, 45, 60 and 75 days. One group was maintained in the incubator (26 ± 1°C, 70 ± 10% RH, and 24 h scotophase) as control. The results show that egg hatch rate, longevity and reproductive fitness of engorged females of R. sanguineus are negatively correlated with the duration of exposure to low temperature, whereas preoviposition period was positively correlated with exposure to the cold. This shows that the engorged female ticks are sensitive to prolonged exposure to low temperature, and it may explain why females of this tick species are not reproductively active during winter. Our results confirm that temperature is a major limiting factor for the establishment of stable R. sanguineus populations in cold temperate regions of Europe.

Biology and ecology of the brown dog tick, Rhipicephalus sanguineus

The brown dog tick (Rhipicephalus sanguineus) is the most widespread tick in the world and a well-recognized vector of many pathogens affecting dogs and occasionally humans. This tick can be found on dogs living in both urban and rural areas, being highly adapted to live within human dwellings and being active throughout the year not only in tropical and subtropical regions, but also in some temperate areas. Depending on factors such as climate and host availability, Rh. sanguineus can complete up to four generations per year. Recent studies have demonstrated that ticks exposed to high temperatures attach and feed on humans and rabbits more rapidly. This observation suggests that the risk of human parasitism by Rh. sanguineus could increase in areas experiencing warmer and/or longer summers, consequently increasing the risk of transmission of zoonotic agents (e.g., Rickettsia conorii and Rickettsia rickettsii). In the present article, some aspects of the biology and ecology of Rh. sanguineus ticks are discussed including the possible impact of current climate changes on populations of this tick around the world.

Epidemiological survey of Anaplasma platys and Ehrlichia canis using ticks collected from dogs in Japan

Detection of Anaplasma platys and Ehrlichia canis in ticks recovered from dogs in Japan was attempted using a species-specific nested PCR based on the 16S rRNA gene. A total of 1211 ticks recovered from 1211 dogs from all over Japan were examined for A. platys and E. canis. Four tick samples from Fukushima, Miyazaki and Kagoshima Prefectures recovered from four different dogs showed a positive reaction for A. platys. Although the four dogs did not show any clinical signs and no blood examination data were available, it is possible that A. platys has already been spread widely in Japan. No positive reactions were observed in any ticks examined for E. canis.

Epidemiological survey of Babesia species in Japan performed with specimens from ticks collected from dogs and detection of new Babesia DNA closely related to Babesia odocoilei and Babesia divergens DNA

Detection and analysis of Babesia species from ticks recovered from dogs in Japan were attempted by PCR and nucleotide sequence analysis based on the 18S rRNA gene, respectively. A total of 1136 ticks were examined for Babesia DNA by 18S rRNA-based PCR and nucleotide sequencing. Partial sequences of Babesia canis vogeli DNA were detected from six ticks in Aomori, Nara, Hiroshima, Oita, and Okinawa Prefectures; and Babesia gibsoni Asia-1 DNA was also detected in four ticks in Osaka, Hiroshima, Miyazaki, and Okinawa Prefectures. Unique sequences of 1678 bp were also obtained from Ixodes ovatus ticks in Akita and Fukui Prefectures. The sequences were similar to those of Babesia odocoilei (97.7%) and Babesia divergens (97.6%). This is the first report of the detection of DNA belonging to this group in Japan.

Ixodid tick species recovered from domestic dogs in Japan

The species of ixodid ticks (Acari: Ixodidae) recovered from domestic dogs in Japan between September to November 2000 and April to June 2001 were identified. A total of 4122 ticks, including 1624 larvae, 1200 nymphs, 1016 females and 282 males were removed from 1221 dogs during these periods. Haemaphysalis longicornis (Neumann) was the most frequently found (40.3% of dogs), followed by H. flava (Neumann) (16.1% of dogs), Rhipicephalus sanguineus (Latreille) (4.8% of dogs) and Ixodes ovatus (Neumann) (4.1% of dogs). Small numbers of H. hystricis (Supino), H. campanulata (Warburton), H. japonica (Warburton), H. ias (Nakamura and Yajima), I. persulcatus (Schulze), I. nipponensis (Kitaoka and Saito) and Amblyomma testudinarium (Koch) were also recovered. In the spring sample, a total of 1408 ticks (78 larvae, 411 nymphs, 792 adult females and 127 adult males) were recovered from 570 dogs. The autumn sample included a larger proportion of larval stage and fewer adult ticks (1546 larvae, 789 nymphs, 224 adult females and 155 adult males). Haemaphysalis longicornis, H. flava and I. ovatus showed a wide geographical distribution from northern to southern Japan, whereas R. sanguineus were mainly distributed in the subtropical Okinawa prefecture with a few exceptions. Dogs in rural areas more frequently carried H. longicornis, H. flava and I. ovatus than dogs in urban or suburban areas, whereas R. sanguineus was more associated with the dogs in urban/suburban areas. Exposure to a garden was significantly associated with R. sanguineus and exposure to woodland was significantly associated with H. flava and I. ovatus. This is the first systematic survey of canine ticks in Japan.

Effects of infestation by Rhipicephalus sanguineus on lymphocyte blastogenic responses to mitogens in dogs

Mitogen blastogenic responses of lymphocytes from dogs infested with adult Rhipicephalus sanguineus and the effects of salivary gland extracts (SGE) of the tick on the blastogenic responses of lymphocytes from normal dogs were studied. Infestation by R. sanguineus significantly suppressed concanavalin A, phyto-hemagglutinin and pokeweed mitogen responses of lymphocytes from dogs. The inhibition of lymphocyte responses of dogs in the first infestation was greater than that in the second infestation. SGE from R. sanguineus also suppressed all mitogen blastogenic responses of lymphocytes from healthy dogs in vitro. These suppressive effects of SGE on the blastogenic responses of PBL to mitogens were significantly inhibited by trypsin digestion. It is suggested that some proteins in SGE contribute to the suppressive effects of SGE on the blastogenic responses of peripheral blood lymphocytes from dogs.

Survey of tick-borne diseases in dogs infested with Rhipicephalus sanguineus at a kennel in Okayama Prefecture, Japan

Serological tests were performed to investigate extent of tick-borne diseases in dogs infested with Rhipicephalus sanguineus at a kennel in Okayama Prefecture. Three of 22 dogs (13.6%) were positive for Ehrlichia canis. Two of 19 dogs (10.5%) were positive for Rickettsia japonica. Three of 22 dogs (13.6%) were positive for Babesia gibsoni. None of these animals were positive for Coxiella burnetii or Hepatozoon canis. A microfilaria was detected in a drop smear of hemolymph from an engorged female tick, however, species was not determined. It is possible that these ticks can transmit pathogens to domestic dogs which are rare in Japan.

Dogs develop resistance to Rhipicephalus sanguineus

The capacity of Beagle dogs to develop resistance against infestation by adult females of Rhipicephalus sanguineus was investigated. The number of successive engorged females recovered from dogs at the second infestation of the tick was significantly less than at the first infestation. However, there were no significant differences in body weight, body length, body width of engorged females, feeding behavior, preoviposition periods or egg weight.