Page 42 - VetCPD Jnl Volume 7, Issue 4

VETcpd - Parasitology
The most common clinical presentation in dogs is mild to moderate pulmonary signs. The most significant of these are coughs (either productive or unproductive), and dyspnoea, with or without tachypnoea. A less common but more severe consequence of infection is a varying degree of coagulopathy (Morgan et al. 2005).The mechanism of this aspect of infection is still poorly understood but can lead to potentially life threatening signs including anaemia, haematomas, neuropathies, increased and prolonged post-operative bleeding and post traumatic haemorrhage. Although less common, these more severe signs can occur even if the parasite is present in low numbers.
Figure 1: Life-cycle of Angiostrongylus vasorum (diagram courtesy Bayer)
7. After ingestion, L3 larvae penetrate the wall of the intestines and migrate through the liver, venous circulation and right heart into the lung where they mature into adults.
6. Dogs become infected by ingesting L3 larvae contained in small snails and slugs that act as intermediate hosts
As well as dogs, foxes are natural hosts for lungworm
2. The adult worms lay eggs which hatch into L1 larvae
3. The L1 penetrate
the bronchial walls, are coughed and swallowed and pass out in the dog’s faeces, contaminating the environment
4. Slugs and snails feed on decaying dog faeces and are infected by L1 larvae.
5. L1 larvae develop into infectious L3 larvae in the snail. Infected snails or slugs are ingested by the dog or fox
1. Adult worms are found in the heart and pulmonary arteries
Frogs can also be intermediate hosts
A.vasorum has spread rapidly over the
past 10 years from endemic foci in
Wales, the South West and South East of
England to across the whole of the UK.
Increased reporting of cases has been seen
in domestic dogs, with 20% of practices
across the country having seen at least
one case over a 12 month period (Kirk Features: Tail of L1 larvae has a et al. 2014).This increase in range and dorsal notch and is often coiled number of cases had occurred in the face
of increased awareness and publicity so
Length: 334-380μm.
(Images courtesy: Pedro Serra, NWL labs)
it was initially unclear whether increased
reporting may be distorting true infection
and disease incidence figures.To establish Crenosoma vulpis
if this perceived spread and increasing Only
Angiostrongylus vasorum
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number of cases was genuine, post mortem surveys were carried out on foxes in 2005 (Morgan et al. 2008) and in 2014 (Taylor et al. 2015) which act as wildlife reservoirs.The overall prevalence rose from 7 to 18% in foxes during this period and extended to regions previously clear of infection such as Northern England and Scotland. The spread of A.vasorum is therefore genuine but not uniform, with focal areas of very high prevalence and other areas remaining free of infection. Case reporting sites by IDEXX and
Bayer have been useful in mapping areas of high prevalence and the introduction
of A.vasorum into new areas. Reporting
of cases is only voluntary however, and distribution of infection very fluid with new foci forming. It is likely that a
variety of factors are driving the spread of A.vasorum including increased movement of dogs around the country and possibly the movement of horticultural products containing slugs and snails.A milder climate leading to increased periods of slug and snail activity may also be playing a role. Smaller slug species are also infected and while they carry a smaller number of the total parasite population, their small size increase the likelihood of accidental ingestion by dogs (Aziz 2016).
Page 38 - VETcpd - Vol 7 - Issue 4
Length: 243-281μm.
Features: Tail is straight and pointed and larvae
Table 1: Morphological characteristics allowing differentiation between L1 lungworm larval stages in the faeces
straighter in faecal samples, rarely coiled
Free living soil nematode
Length: variable. Features: variable
Diagnosis has traditionally relied upon
the Baermann faecal analysis for the detection of L1 larvae. In experienced hands this can be highly specific but is relatively insensitive as larvae are only shed intermittently and requires examination
of fresh faecal samples over three consecutive days to improve sensitivity. Misidentification of A.vasorum larvae with Crenosoma vulpis or free living nematodes contaminating samples can lower specificity (Table 1). It can be carried
out in-house but is time consuming where rapid diagnosis is required. Other methods such as faecal smear (Humm
and Adamantos 2010) are also possible to conduct in house with more rapid results, but also suffer from limited sensitivity.
A new, point-of-care test, AngioDetectTM (Idexx Laboratories, USA) has been developed for detecting circulating antigen in the blood. Reported sensitivity has been approximately 85% in detecting patent A. vasorum infection and specificity close to 100%.This test allows for more rapid diagnosis in a clinical setting and
also allows many dogs with clinical signs compatible with A.vasorum infection to
be tested relatively economically and rapidly.This in turn allows a picture within