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Dirofilaria immitis (the canine heartworm) is widespread in the tropics, with prevalence surpassing 30% in high-risk areas. In addition to the suitable climatic conditions that favour mosquito abundance and filarial larva development, there is low compliance with the recommended year-round use of preventives in these transmission hotspots. This represents a major concern, considering that melarsomine (first-line heartworm adulticide) is unavailable in several tropical countries, resulting in the so-called slow-kill protocol being the only available adulticide treatment option. In this article, the members of TroCCAP (Tropical Council for Companion Animal Parasites) review the current distribution of heartworm in the tropics and the availability of melarsomine, and discuss alternatives for the management of heartworm infections in dogs. Graphical Abstract

The present study aimed to determine the complete citrate synthase (gltA) and heat-shock protein (groEL) gene sequences of Anaplasma bovis and to infer phylogenetic relationships within the genus Anaplasma. Multiple alignments from single and concatenated sequences of the 16S rRNA, gltA and groEL genes of the genus Anaplasma were subjected to phylogenetic analyses. Percent identities of A. bovis nucleotide sequences were found highest with A. phagocytophilum in gltA (65.4%) and groEL (79.8%). Single gene phylogenetic tree results assumed similar phylogenetic positions within the genus Anaplasma, except for A. bovis. However, consensus and concatenated sequence phylogenetic trees showed similar results, revealing 2 subgroups within the genus.

Anaplasma marginale is an etiologic agent of bovine anaplasmosis. This study aimed to molecularly detect and characterize A. marginale that is prevalent in Mongolian cattle populations. A highly specific and sensitive nested PCR (nPCR) method based on the Msp5 gene was developed to detect A. marginale (Msp5 nPCR). The method detected A. marginale from the positive DNA samples obtained from different countries, while no amplicons were observed from DNA samples of several other bovine blood pathogens tested. The detection limit of Msp5 nPCR was determined to be 2 copies/μl. The method was tested against field blood DNA samples prepared from 300 Mongolian cattle in 2010. Results indicated a prevalence rate of 8.7% (26 of 300). On the other hand, partial DNA fragments of an Anaplasma sp. closely related to A. ovis (with 95.0% identity) were detected using a different nPCR method based on groEL gene. The phylogenetic analyses based on the Msp5, groEL and 16S rRNA genes demonstrated that A. marginale isolates in Mongolia were not divergent from the isolates distributed in other countries. The present study successfully established a new nPCR assay that can detect A. marginale, and reported the first molecular detection and characterization of A. marginale and an Anaplasma sp. closely related to A. ovis in Mongolian cattle populations.

Anaplasma marginale has been detected in the Philippines only by peripheral blood smear examination and serological methods. This study generally aimed to molecularly detect and characterize A. marginale in cattle and ticks in Cebu, Philippines. A total of 12 bovine blood samples and 60 Rhipicephalus (Boophilus) microplus ticks were collected on the Cebu Island in 2011. 16S rRNA-based screening-PCR and DNA sequencing revealed 8 cattle (66.7%) and 8 ticks (13.3%) to be positive for A. marginale, and 1 tick (1.7%) to be positive for A. centrale. Selected positive DNA samples were further characterized based on 16S rRNA (longer sequence), Msp5, Msp1α,gltA and groEL genes for phylogenetic analyses. Sequence identities of partial DNA fragments of A. marginale from the Philippines revealed 99.1-100% (16S rRNA, gltA, groEL and Msp5) and 94.3-97.6% (Msp1α) identities to the closest isolates from other countries. Moreover, sequence analysis of the Msp1α, gene showed 3 variants, including a case of co-infection with 2 variants. Phylogenetic analyses based on Msp1α and Msp5 genes revealed that Philippine A. marginale isolates formed a monophyletic lineage, and were phylogenetically related to Brazilian and Chinese isolates. On the other hand, a highly specific and sensitive nested PCR based on groEL, with a detection limit of 2 copies/PCR, was developed to detect A. marginale in the Philippines. This study reported the first molecular detection and characterization of A. marginale in cattle and R. microplus in Cebu, Philippines.

Anaplasma phagocytophilum causes human granulocytic anaplasmosis (HGA) and tick-borne fever in ruminants. A closely related and potentially novel Anaplasma sp. in Japan was recently characterized. The aims of the study were to provide molecular evidence for the presence of these 2 species in Japan, and to develop a reliable PCR method based on the nucleotide differences within the citrate synthase (gltA) gene. DNA samples from 182 ixodid ticks (134 Ixodes persulcatus, 35 Haemaphysalis douglasii and 13 I. ovatus) collected from 2 sites in Hokkaido, Japan, were screened for A. phagocytophilum and its closely related Anaplasma sp. (herein designated as Anaplasma sp. Japan) using 16S rRNA PCR, revealing a combined prevalence rate of 27.5% (50 samples). The positive samples were then used to evaluate a newly developed gltA-based nested PCR method. Selected positive samples were further characterized using the groEL gene for confirmation and phylogenetic analyses. Two groups of sequence results were obtained: those that had closer identities with (1) A. phagocytophilum (99.5-99.6% for 16S rRNA, 97.5% for gltA and 98.4% for groEL), and those that had closer identities with (2) Anaplasma sp. closely related to A. phagocytophilum in Japan (99.3% for 16S rRNA, 96.4-98.7% for gltA and 97.5-97.9% for groEL). The present study confirmed the distinct presence of A. phagocytophilum and its closely related Anaplasma sp. in Japan, and developed a new PCR detection method based on gltA that can distinguish the 2 organisms.