Sonthaya Tiawsirisup

Ungulate malaria parasites

Haemosporida parasites of even-toed ungulates are diverse and globally distributed, but since their discovery in 1913 their characterization has relied exclusively on microscopy-based descriptions. In order to bring molecular approaches to bear on the identity and evolutionary relationships of ungulate malaria parasites, we conducted Plasmodium cytb-specific nested PCR surveys using blood from water buffalo in Vietnam and Thailand, and goats in Zambia. We found that Plasmodium is readily detectable from water buffalo in these countries, indicating that buffalo Plasmodium is distributed in a wider region than India, which is the only area in which buffalo Plasmodium has been reported. Two types (I and II) of Plasmodium sequences were identified from water buffalo and a third type (III) was isolated from goat. Morphology of the parasite was confirmed in Giemsa-reagent stained blood smears for the Type I sample. Complete mitochondrial DNA sequences were isolated and used to infer a phylogeny in which ungulate malaria parasites form a monophyletic clade within the Haemosporida, and branch prior to the clade containing bird, lizard and other mammalian Plasmodium. Thus it is likely that host switching of Plasmodium from birds to mammals occurred multiple times, with a switch to ungulates independently from other mammalian Plasmodium.

Distribution of mosquito (Diptera: Culicidae) species and Wolbachia (Rickettsiales: Rickettsiaceae) infections during the bird immigration season in Pathumthani province, central Thailand

Mosquito distribution in the immigration bird-nested area, Pathumthani province, was investigated from August to December in 2006. Mosquitoes were collected by using CO2-baited Centers for Disease Control light traps in which dry ice was used as a source of CO2 to attract mosquitoes. Six traps were operated from 4 p.m. until 7 a.m. on each study day. Four genera, which were Anopheles, Armigeres, Culex, and Mansonia with 14 species of mosquitoes were collected. Culex gelidus (13.94–59.41%) and Culex tritaeniorhynchus (32.87–70.30%) were most collected species in this area for every month. Other two species with moderate distribution in this area were Anopheles barbirostris (0.76–3.30%) and Mansonia uniformis (1.55–11.36%). Polymerase Chain Reactions were performed for testing Wolbachia infection in Cx. gelidus and Cx. tritaeniorhynchus only. Fifty-four percent (15/28 pools) of Cx. gelidus and none (0/20 pools) of Cx. tritaeniorhynchus were positive for Wolbachia infection. Wolbachia infection in other mosquito species collected in this and other areas need to be investigated to understand species and geographic variation of Wolbachia infection in mosquitoes in nature.

Genetic homogeneity of goat malaria parasites in Asia and Africa suggests their expansion with domestic goat host

Plasmodium was first identified in a goat in Angola in 1923, and only recently characterized by DNA isolation from a goat blood sample in Zambia. Goats were first domesticated in the Fertile Crescent approximately 10,000 years ago, and are now globally distributed. It is not known if the Plasmodium identified in African goats originated from parasites circulating in the local ungulates, or if it co-evolved in the goat before its domestication. To address this question, we performed PCR-based surveillance using a total of 1,299 goat blood samples collected from Sudan and Kenya in Africa, Iran in west Asia, and Myanmar and Thailand in southeast Asia. Plasmodium DNA was detected from all locations, suggesting that the parasite is not limited to Africa, but widely distributed. Whole mitochondrial DNA sequences revealed that there was only one nucleotide substitution between Zambian/Kenyan samples and others, supporting the existence of a goat-specific Plasmodium species, presumably Plasmodium caprae, rather than infection of goats by local ungulate malaria parasites. We also present the first photographic images of P. caprae, from one Kenyan goat sample.

Artesunate-tafenoquine combination therapy promotes clearance and abrogates transmission of the avian malaria parasite Plasmodium gallinaceum

Clinical manifestations of malaria infection in vertebrate hosts arise from the multiplication of the asexual stage parasites in the blood, while the gametocytes are responsible for the transmission of the disease. Antimalarial drugs that target the blood stage parasites and transmissible gametocytes are rare, but are essentially needed for the effective control of malaria and for limiting the spread of resistance. Artemisinin and its derivatives are the current first-line antimalarials that are effective against the blood stage parasites and gametocytes, but resistance to artemisinin has now emerged and spread in various malaria endemic areas. Therefore, a novel antimalarial drug, or a new drug combination, is critically needed to overcome this problem. The objectives of this study were to evaluate the efficacy of a relatively new antimalarial compound, tafenoquine (TQ), and a combination of TQ and a low dose of artesunate (ATN) on the in vivo blood stage multiplication, gametocyte development and transmission of the avian malaria parasite Plasmodium gallinaceum to the vector Aedes aegypti. The results showed that a 5-d treatment with TQ alone was unable to clear the blood stage parasites, but was capable of reducing the mortality rate, while TQ monotherapy at a high dose of 30mg/kg was highly effective against the gametocytes and completely blocked the transmission of P. gallinaceum. In addition, the combination therapy of TQ+ATN completely cleared P. gallinaceum blood stages and sped up the gametocyte clearance from chickens, suggesting the synergistic effect of the two drugs. In conclusion, TQ is demonstrated to be effective for limiting avian malaria transmission and may be used in combination with a low dose of ATN for safe and effective treatment.

Natural infection of questing ixodid ticks with protozoa and bacteria in Chonburi Province, Thailand

Ixodid ticks are important vectors of tick-borne disease agents affecting humans and animals, with wildlife often serving as important reservoirs. This study examined protozoal and bacterial infection in questing ticks in forest habitats in Chonburi Province, Thailand in 2015, using PCR and DNA sequencing techniques. A total of 12,184 ticks were morphologically identified to species and a subset of ticks were confirmed by PCR, targeting the tick mitochondrial 16S rRNA gene. Tick species collected included Haemaphysalis lagrangei (92.8%), H. wellingtoni (0.1%), and Rhipicephalus microplus (7.0%). In total, 419 tick pools [ELM(1] [ST2] were examined by PCR amplification of a fragment of the 18S rRNA gene of Babesia and Theileria species, and the 16S rRNA gene of bacteria in the family Anaplasmataceae. Results revealed a tick infection rate for the tick pools of 57.0% (239/419) including four pathogens and one bacterial symbiont. The highest infection rate in H. lagrangei, H. wellingtoni, and R. microplus pools was recorded for Anaplasma spp. at 55.6% (233/419) including three Anaplasma species genotype groups Anaplasma spp. closely related to A. bovis, A. platys, and unidentified Anaplasma spp. Theileria spp. showed a lower infection rate in H. lagrangei at 4.3% (18/419) with three Theileria species genotypes closely related to T. cervi, T. capreoli, and unidentified Theileria spp. Only 0.2% (1/419) of H. lagrangei pools contained Babesia spp., Ehrlichia spp., or Wolbachia spp. [ELM(3] [ST4] These findings provided information on tick species in wildlife habitats and detected protozoa and bacteria in the ticks. The results suggest that these tick species are possible vectors for transmitting tick-borne disease agents in Thailand wildlife habitats.

Vector competence of Aedes albopictus (Skuse) and Aedes aegypti (Linnaeus) for Plasmodium gallinaceum infection and transmission

Avian malaria caused by Plasmodium gallinaceum is an important mosquito-borne disease. Eradication of this disease remains problematic since its competent vectors are diverse and widely distributed across the globe. Several mosquito species were implicated as competent vectors for this parasite. However, studies on vector competence for P. gallinaceum remain limited. In this study, vector competence in the two most predominant mosquito vectors in tropical countries, Aedes albopictus and Ae. aegypti, was compared. In order to determine their infection rates, Ae. albopictus (>F10), Ae. aegypti (>F10), and Ae. aegypti (<F10) mosquitoes were equally divided and allowed to feed on infected chickens with 15 different gametocyte levels (0.1-5.2%). On day five post blood feeding (PBF), 60 mosquitoes from each group were dissected, and the number of oocysts in midgut was examined. Infections with P. gallinaceum were observed in all groups, but the number of oocysts produced was significantly different. To evaluate the transmission ability of these mosquitoes after having been fed on different levels of gametocytes, the infected mosquitoes were allowed to feed on naïve chickens on day 10 PBF, and the chicken bloods were monitored for 21days PBF. All groups of mosquitoes demonstrated a high degree of infection rates. The infection rates in chickens were 80-100% after having been bitten by infected Ae. albopictus (> F10) and Ae. aegypti (> F10) and 40-60% by infected Ae. aegypti (<F10). These findings demonstrated that Ae. albopictus (>F10) and Ae. aegypti (>F10) were highly competent vectors for P. gallinaceum infections. These mosquitoes play a crucial role in the transmission cycle of this parasite in nature.