Relationship between microfilaria count and sensitivity of the direct smear for diagnosis of canine dirofilariosis

Courtney, Charles H.; Zeng, Qi-Yun

doi:10.1016/s0304-4017(00)00377-0

Cited by 23 publications

(13 citation statements)

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“…Because 8 of their samples showed no microfilariae on counting slides, they were considered to have less than 300 Mf/ml of blood. Another dog’s Mf count was below 300 Mf/ml as well, and therefore, the number of low microfilaremic dogs was assumed to be 9 [17]. A total of 11 dogs were in the higher microfilariae count group, with a total microfilariae count ranging from 438 to 44,538 Mf/ml of blood.…”

Section: Resultsmentioning

confidence: 99%

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Heat pretreatment of canine samples to evaluate efficacy of imidacloprid + moxidectin and doxycycline in heartworm treatment

Bendas

Mendes-de-Almeida

Simson³

et al. 2017

Parasites Vectors

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BackgroundConsidering the recent information on the increase of Dirofilaria immitis antigen detection by rapid assays in canine blood samples after heat treatment, the proposal that immune complexes block D. immitis antigen detection and that macrocyclic lactone + doxycycline (alternative protocol) might lead to increased production of those immune complexes, resulting in the erroneous diagnosis of adult worm elimination, and that there is no recommended adulticide marketed in Brazil, a study was performed to evaluate the interference of moxidectin + doxycycline (moxi-doxy) on diagnostic procedures when heartworm positive dogs are treated with this alternative protocol. Twenty-two naturally infected pet dogs were treated monthly with topical 10% imidacloprid + 2.5% moxidectin and with oral doxycycline (10 mg/kg BID/30 days) (moxi-doxy). All the dogs had their microfilaremia level determined prior to the first day of treatment, and were tested every 6 months for microfilariae (Mf) detection prior to heating, and for antigen detection prior to and after heating, the sample.ResultsThe results indicate that the treatment protocol can eliminate adult heartworms as early as 6 months after the first dose, especially in low microfilaremic dogs (< 300 Mf/ml). In this study, all dogs were free of heartworm antigen after 18–24 months of treatment. In a comparison of pre-heated samples and non-heated samples, sample pre-heating increased antigen detection sensitivity, and non-heated samples tended to be antigen-negative earlier than the pre-heated samples, especially when dogs had low microfilaremia levels. These discrepancies were not present in a subsequent sample of the same dog 6 months later.ConclusionsTwo negative antigen test results 6 months apart can be recommended as the criterion to consider when a dog has been cleared of infection. The initial microfilaremia level of a dog can be used to estimate the necessary time frame to end the treatment period.

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Section: Resultsmentioning

confidence: 99%

“…The final microfilariae number was the mean of the four counting results. When no microfilaria could be located on the counting slides, and yet the sample showed microfilariae positive on Knott’s test, the microfilaremia was assumed to be less than 300 Mf/ml [17]. …”

Section: Methodsmentioning

confidence: 99%

Heat pretreatment of canine samples to evaluate efficacy of imidacloprid + moxidectin and doxycycline in heartworm treatment

Bendas

Mendes-de-Almeida

Simson³

et al. 2017

Parasites Vectors

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“…It is easy to perform, rapid and inexpensive, it conserves mf morphology and size, and it enhances the sensitivity of mf detection in blood samples. Courtney and Zeng [20] showed that only in 80.9% of the samples in which D. immitis mf had been detected by the Knott’s test, the parasites could also be found in direct smears and that the sensitivity of the direct smear was especially low in samples with less than 10 mf per ml. This is of particular relevance for A. dracunculoides and A. reconditum mf, since the average number of mf/ml is usually low in these species [10,11,13].…”

Section: Resultsmentioning

confidence: 99%

Morphometric analyses of canine blood microfilariae isolated by the Knott’s test enables Dirofilaria immitis and D. repens species-specific and Acanthocheilonema (syn. Dipetalonema) genus-specific diagnosis

Lorentz²,

et al. 2013

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BackgroundConsidering the increasing importance of small animals travel medicine and the spread of filariae with zoonotic potential to non-endemic European areas, routine filarial diagnosis in dogs is becoming important. Dirofilaria immitis, D. repens, Acanthocheilonema dracunculoides and A. reconditum are the most common canine filarial nematodes presenting blood circulating microfilariae (mf) which can be differentiated to species level by the acid phosphatase activity patterns or by PCR. Available data on the size of the mf vary considerably in the literature. The aim of this study was to validate morphometric criteria for filarial identification in blood samples of dogs after concentration of mf with the modified Knott’s technique.MethodsMorphometric analysis of 10 mf from samples identified to species level by acid phosphatase activity and partially confirmed by PCR were performed with specimens from 377 dogs.ResultsThe mean length and width of D. immitis mf from 60 dogs were 301.77±6.29 μm and 6.30±0.26 μm, of D. repens mf from 171 dogs 369.44±10.76 μm 8.87±0.58 μm, of A. dracunculoides mf from 133 dogs 259.43±6.69 μm and 5.09±0.47 μm and of A. reconditum mf from 13 dogs 264.83±5.47 μm and 4.63±0.52 μm.For a subset of 30 samples, morphometric analysis was repeated with identical results in two laboratories. Furthermore, the size of mf concentrated and fixed by the Knott’s technique was shown to be stable over 105 days.ConclusionsThe Knott’s test enables to clearly distinguish between D. immitis, D. repens and Acanthocheilonema spp. However, due to the overlapping size ranges of A. dracunculoides and A. reconditum, biochemical or molecular methods are required to distinguish these two species.

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“…Only limited information has been available on the blood volume required in DBS, and most importantly, the lowest mff concentration permitting a quick detection with the DBS and QBC tube methods. The sensitivity of DBS has been reported at a high level only when mff counts exceeded 1000 ml 21 (Rawlings, 1986), but in a recent study a 100% sensitivity was documented for mff counts higher than 50 ml 21 (Courtney & Zeng, 2001). In DBS the differentiation between D. immitis and Dipetalonema reconditum mff can be assessed by their number and motility pattern, though this method is considered of low diagnostic yield, especially for those areas where D. immitis frequently coexists with other non-pathogenic filarial species (Papazahariadou et al, 1994;Dillon, 2000).…”

Section: Introductionmentioning

confidence: 99%

Comparative methodology for the detection and differentiation of circulating microfilariae of Dirofilaria immitis in the dog

et al. 2004

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The sensitivities of the Knott's test (four 20-microl sediment aliquots), quantitative buffy coat capillary tube method (QBC tube, 111 microl of whole blood) and direct blood smear (DBS, 20 microl of whole blood) were evaluated for the detection of microfilaraemia in dogs. Undiluted whole blood samples taken from 70 Dirofilaria immitis antigen-positive dogs and 10 serially diluted microfilaraemic blood samples at concentrations of 400, 200, 100, 50, 25 and 12 microfilariae (mff) ml(-1) were examined. For filarial speciation, the buffy coat of QBC tubes was mixed with one drop of methylene blue-formalin solution and examined as a direct smear. In 52/70 microfilaraemic blood samples, the number of mff ranged from 12 to 321987 ml(-1) (median: 3199 ml(-1)). The diagnostic sensitivity of the Knott's test, QBC tube method and DBS in undiluted blood samples attained the 100%, 98% and 92.3% levels, respectively. Eighteen dogs tested amicrofilaraemic by all three methods. At concentrations of 400 mff ml(-1), a 100% sensitivity was found by all three methods, while at 200 mff ml(-1) the Knott's test, QBC tube and DBS were 100%, 100% and 90% sensitive, respectively. The relevant figures at 100 mff ml(-1) were 100%, 100% and 80%, at 50 mff ml(-1) 100%, 100% and 50%, at 25 mff ml(-1) 100%, 100% and 10% and at 12 mff ml(-1) 80%, 50% and 10%. At 50 and 25 mff ml(-1), the DBS was less sensitive compared to the other two methods, while at 12 mff ml(-1), only to the Knott's test. A significant correlation was found between the QBC tube method and Knott's test regarding mff speciation. Therefore, the QBC method may be considered a reliable alternative to the Knott's test for both the detection and speciation of mff in the dog.

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Relationship between microfilaria count and sensitivity of the direct smear for diagnosis of canine dirofilariosis

Cited by 23 publications

References 1 publication

Heat pretreatment of canine samples to evaluate efficacy of imidacloprid + moxidectin and doxycycline in heartworm treatment

Heat pretreatment of canine samples to evaluate efficacy of imidacloprid + moxidectin and doxycycline in heartworm treatment

Morphometric analyses of canine blood microfilariae isolated by the Knott’s test enables Dirofilaria immitis and D. repens species-specific and Acanthocheilonema (syn. Dipetalonema) genus-specific diagnosis

Comparative methodology for the detection and differentiation of circulating microfilariae of Dirofilaria immitis in the dog

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