Geographic Spatial Distribution Patterns of Dirofilaria immitis and Brugia pahangi Infection in Community Dogs in Chiang Mai, Thailand

Abstract

Filariasis is emerging as a public health concern in tropical and subtropical areas. Filariasis is an endemic problem commonly found in southeast Asian countries. Using the PCR-restriction fragment length polymorphism (PCR-RFLP) of the ITS1 region with Vsp I, the overall prevalence rates of Dirofilaria immitis (12.2% (41/337); 95% confidence interval: 9.1–16.1%) and Brugia pahangi (8.3% (28/337); 95% confidence interval: 5.8–11.8%) were determined based on 337 free-roaming community dogs from 20 districts in Northern Thailand. Microfilaremia was found in only 6.2% of dogs (21/337). Co-infection with D. immitis and B. pahangi was observed in two dogs. Of the 215 blood samples examined using a Canine Heartworm Ag Kit, only 3.72% (eight dogs) were D. immitis antigen positive. Among these eight, six dogs had occult D. immitis infections. In terms of geographic distribution, we found the abundance of D. immitis and B. pahangi in the central areas at altitudes less than 400 m to be 12.1% and 10.3%, respectively. In contrast, at higher altitudes between 400 and 800 m, a significantly higher number of B. pahangi compared with D. immitis infected individuals were observed at 14.29% and 4.1%, respectively. In conclusion, D. immitis and B. pahangi were the most common filarial infections found in community dogs in Northern Thailand. Dogs might be an important reservoir of B. pahangi in that region. Increasing awareness and concern and including proper deworming programs for community dogs should be endorsed to reduce the transmission risk. Additionally, the population dynamics of the mosquito vector of B. pahangi across altitudinal gradients deserved further investigation.

Emergence of zoonotic Brugia pahangi parasite in Thailand

“…In epizootic cycle, epizootic B. pahangi parasite occurs in humans as an accidental host through vertical transmission (between human and vector hosts). In given foci, the numbers of enzootic B. pahangi infections present in animal reservoirs (domestic dogs and/or cats) and local vector populations infer the endemicity as the degree to which transmission of epizootic B. pahangi occurs in susceptible person(s) in an impoverished environment of urban, sub-urban, or rural areas [ 3 – 7 , 17 , 18 ].…”

“…As compared to other indoor-resting mosquitoes like Aedes aegypti and Culex quinquefasciatus , Ar. subalbatus is a peri-domestic species that rests outdoors but more likely it has the potential to transmit epizootic B. pahangi parasites in impoverished environment of semiurban and rural areas in Malaysia [ 6 , 7 , 19 ] and Thailand [ 8 , 9 , 17 , 18 ]. Adulthood infections are evident in Malaysia [ 6 , 7 , 19 ].…”

“…Parasitological approaches applied to or used in case surveillance for human B. pahangi filariasis rely upon standard microscopic diagnosis of B. pahangi microfilaremic infections in cats or dogs of clinical filariasis ( Figure-2 ). The preferred methods include thick blood films (using 20–60 mL blood of the ear vein, as well as cephalic, saphenous or jugular veins) [ 4 , 5 , 17 , 18 , 47 , 50 ] and other specific and sensitive methods such as Knott’s concentration technique (using 1 mL blood) and membrane filtration (using 1–2 mL blood). However, the most preferred method is the application of polymerase chain reaction (PCR) assays [ 6 – 9 , 17 , 18 , 46 , 47 , 50 – 52 ], which are highly specific and sensitive for B. pahangi distinguishable from other filarial parasites present in animal or human hosts or Ar.…”

“…The preferred methods include thick blood films (using 20–60 mL blood of the ear vein, as well as cephalic, saphenous or jugular veins) [ 4 , 5 , 17 , 18 , 47 , 50 ] and other specific and sensitive methods such as Knott’s concentration technique (using 1 mL blood) and membrane filtration (using 1–2 mL blood). However, the most preferred method is the application of polymerase chain reaction (PCR) assays [ 6 – 9 , 17 , 18 , 46 , 47 , 50 – 52 ], which are highly specific and sensitive for B. pahangi distinguishable from other filarial parasites present in animal or human hosts or Ar. subalbatus vector [ 6 - 8 ] but not many other mosquitoes [ 53 ] as described below.…”

“…As compared to other Aedes togoi and Cx. quinquefasciatu s [ 16 ], it is a relatively potent vector of B. pahangi and Dirofilaria immitis [ 8 , 17 , 18 ], as well as other viruses [ 64 – 66 ], in human settlement areas. Perhaps it has the potential to transmit these zoonotic parasites temporally and spatially in receptive environments [ 8 , 17 , 19 , 20 ].…”