Dirofilaria infections in animals and

humans

Pathogenesis and clinical presentation: Dirofilaria

immitis versus Dirofilaria repens

Claudio Genchi, Med Vet, PhD, EVPC Dipl

Dept of Veterinary Science and Public Health, Università

degli Studi of Milano

Bucharest, June 14th, 2012

In spite of his denomination [heartworm

disease] is a respiratory [pulmonary] disease

In dogs, the heart is

usually involved in

the late stage of the

disease

Host response to HW infection

Cat: susceptible but

resisting host; usually not

microfilaraemic

unpredictable

Dog: usually microfilaraemic

reservoir

predictable disease

• Chronic disease

• Sometime acute

phases in the late

stage of the infection

• Clinical picture very

typical

• Acute symptoms

• Sometime chronic

disease

• No typical

symptoms

No lesions/symptoms for years

Inflammatory pulmonary

disease

Arterial pulmonary disease

(pulmonary hypertension,

“cor pulmonale”)

right heart congestive

failure

DOG Pathogenesis

Pulmonar disease

Vascular

disease

Parenchymal

disease

Cor polmonale

Vascular disease

• proliferative endarteritis

• thrombosis

1995

Wolbachia pipiens is a Gram-negative bacterium

belonging to rickettesiales

Tetracycline in drinking water (0.3%) prevents infection by B.

pahangi and L. sigmodontis, but not by A. vitae, in gerbils

1971: Wolbachia and the antifilarial properties of

tetracycline. An untold story

Prompted by a serious outbreak of staphylococcal dermatitis affecting

the filarial infected and non-infected Mongolian jirds, in 1971 J.W.

McCall observed that tetracycline used in treating the condition had a

prophylactic affect against Brugia pahangi and Litomosoides

sigmodontis but not against Acanthocheilonema viteae. The results

were presented at the 48th Annual Meeting of the American Society of

Parasitologists (25-29 June 1973), but none of this data was published

until 10 years later.

The following studies showed that B. pahangi and L. sigmondis arer

Wolbachia infected while A. vieae is an uninfected species.

What we learned in the ‘90s

4. Wolbachia is present in

most filarial nematodes,

with a few exceptions in

non pathogenic species

such as Acantocheilonema

vitae

Wolbachia pipientis an “old/new” story

Onchocerca volvulus

Onchocerca ochengi

Onchocerca gutturosa

Onchocerca gibsoni

Thelazia lacrimalis

Dirofilaria repens

Dirofilaria immitis

Wuchereria bancrofti

Brugia pahangi

Brugia malayi

Litomosoides sigmodontis

Acanthocheilonema viteae

93

100

95

65

100

61

100

58

68

100

100

100

100

73

64

100

100

There is a consistency of filaria/Wolbachia phylogenies

Filaria phylogeny Wolbachia phylogeny

Modified from Casiraghi et al. 2001, Parasitology

Electron micrograph of an

embryo of D. immitis

containing two wolbachiae

Immunohistochemical staining

of W. pipientis in D. immitis

using Ab against WSP

Wolbachia is a widespread intracellular symbiont

of filarial nematodes and arthropods

Wolbachia pipientis: what we know today

Wolbachia is necessary for the host nematode

100% prevalence in infected species (lateral chords male

and females/reproductive tract females/larvae)

whole branches of filarial trees consist of infected species

consistency of host/Wolbachia phylogenies

vertical transmission

Wolbachia pipientis: what we know today

Tetracycline treatment of filarial-infected hosts inhibits:

embryogenesis

development of L3-adult

microfilarial production

long term survival of adults

Antibiotic treatments are effective both on Wolbachia and

on filarial nematodes development and embryogenesis,

causing prophylactic effects and infertility of adult females

(Genchi et al., 1998; Casiraghi et al. 2002)

Effects of antibiotic treatment on D. immitis

embryogenesis

From Sacchi et al. 2003, Parassitologia

control treated treated

Inflammation

Cytokine pattern and polarization of the immune

response

Adverse reaction to chemotherapy

Desensitization of innate immunity

Defence against host response (e.g. through catalase

activity)

the release of bacteria has been shown to be

associated with the up-regulation of pro-inflammatory

cytokines, neutrophil recruitment and an increase in

aspecific immunoglobulins

There is an overall consistency of data indicating that

Wolbachia plays an important role in the pathogenesis

of filarial disease throughout

Adverse reactions to filaricidal therapy (ivermectin,

DEC) are associated with Wolbachia and/or its DNA

in the bloodstream and peak levels of Wolbachia

correlate with levels of pro-inflammatory cytokines.

Furthermore, a major surface protein of Wolbachia

(WSP) from D. immitis has been shown to provoke

chemiokinesis and IL-8 production in canine

neutrophils in vitro.

There is an overall consistency of data indicating that

Wolbachia plays an important role in the pathogenesis

of filarial disease throughout

The last two points (desensitization of innate

immunity and defence against host response)

open the question of the biological role of

Wolbachia in filarial nematodes:

Wolbachia “manipulates” the immune response,

thus allowing the long-term survival of the filariae

in immuno-competent hosts.

then …

Dirofilaria/Wolbachia symbiosis is friendly for

the parasite but is quite a foe for the host

Proliferative endarteritis: lesions are progressively

worsening during the infection and when worms are

dying

D. immitis in an asymptomatic dog:

the endothelium has no evident

damages

Proliferative endarteritis in a

dog death for

thromboembolism

Thrombosis

The thrombosis is a

consequence of the

platelet activation on the

sub-epithelial tissues

caused by pro- and

inflammatory products

released by the worms

(Wolbachia

endosymbionts) after

spontaneous or

pharmacological death

Spontaneous thromboembolism

Parenchymal disease

• Alveolar damage

• Eosinophilic pneumonia [very

severe in cats]

… as a consequence the heart disease

• increase of pulmonal

resistance

• cor polmonale

• right heart congestive

failure

LV

RV

To note, the right ventricle, as a

consequence of its anatomical

structure (pocket cling to left

ventricle), is adaptable to volume

overloading but not to pressure

overloading

Reduction of vascular stream (obstruction of

small arteries and capillaries)

+

loss of wall elasticity (severe arteritis)

Pulmonar hypertension

Increase of the post-charge

Post-charge overloading

Cor pulmonale (recruitment of collateral vessels)

right heart congestive failure

Microfilarial pathology

Mfs can embolise in

several organs, as the

kidney causing

glomerulonephritis

complicate by the

deposition of Ag/Ab

complexes.

Acute on chronic

Chronic respiratory disease

caval syndrome thromboembolism pneumothorax

Clinical Presentation

Clinical Presentation

no symptoms for years

unless exaggerated worm burden

and/or strenuous exercise

coughing

lipothymias

abdominal effusion

Apparently good health

[fat], but ascites

[abdominal effusion]

Clinical Presentation

right heart congestive failure

ascites

weight loss

disorexia

atrial fibrillation (> 15 kg bw)

Pneumothorax

Caval Syndrome

• Due to sudden rising of pulmonary

pressure (thromboembolism) and/or

cardiac output failure

• Heartworm displacement from pulmonary

arteries to the right cardiac chambers.

Caval Syndrome

Caval Syndrome

• Most frequently in small size dogs (< 11 kg)

3 main symptoms :

• Dyspnoea

• Cardiac murmur (thrill)

• Haemoglobinuria (haematuria)

Caval syndromeMechanical damage of RBC

for blood high pressure and

vortex

Caval syndrome

Cat

Where canine HW infection exists, feline HW infection exists

too!

HW prevalence in cats is 8-10% of prevalence in dogs.

In cats, HW infection is basically pulmonary. Clinically, the

infection can be asymptomatic, chronic or acute. The most

frequent signs are respiratory or digestive. Frequent

respiratory signs are dyspnoea, and tachypnoea and less

frequently, sneezing. Vomiting not associated with eating is

frequent but other symptoms such as diarrhoea are

occasionally described. Some affected cats also present

prostrated, anorectic, showing weight loss.

Dyspnoea Coughing

Vomiting

Hemoptysis Lipothymias

Coughing Vomiting

Weight loss

Diarrhoea

In those very rare cases where worms are located in the

right heart, a systolic cardiac murmur due to tricuspid valve

insufficiency and galloping cardiac rhythm are common

findings at auscultation.

Neurological signs such as ataxia, syncope, blindness, or

vestibular alterations, can be seen depending on the ectopic

localization of the migrating worms.

In acute cases, cats can die so quickly that owners are

usually not able to report any clinical signs before sudden

death.

Cat

Four year-old, female cat.

Sudden death, the owner told that

the cat was normal until the previous

evening and he found the cat dead

early in the morning without any

previous clinical sign.

At necropsy, one female adult worm

and signs of thrombembolism

Sudden death and hemoptysis

Clinical signs are usually more evident when young

parasites arrive in the pulmonary arteries (4 to 6 months

after infection) and later when adult worms die. Congestive

heart failure, common in dogs, is not frequently in cats.

Some infected cats recover spontaneously. However, even

in cases of chronic infection, there is always the risk of

reversion to the acute phase when adult parasites die. It is

associated with an intense pulmonary inflammatory reaction

in response to thromboembolism that is responsible for

pulmonary infarction and hemorrhage.

Circulatory collapse and respiratory failure usually follow.

Clinical signs at this stage can include dyspnea, cyanosis,

hypothermia, ataxia, hemoptysis and syncope.

Cat

34 9

79% 21%

self cured

death

3 6 11 23

7% 14% 26% 53%

sudden death

died after 8-4 months asymptomatic, self cured after 21-48 months

symptomatic, self cured 18-49 months

43 cats HW Ag and

ECHO positive

Cat

Feline HW disease is now recognized as a significant

pulmonary syndrome defined as Heartworm Associated

Respiratory Disease (HARD). The syndrome has been

observed in aborted infections too.

Clinical signs associated with HARD are anorexia,

lethargy, weight loss, coughing, rapid heart rate, vomiting,

diarrhoea, blindness, convulsions, collapse and sudden

death.

Cat: HARD

Both experimental and in filed studies have shown that the

HARD occurs even in cats with no adult parasites. Thus,

unlike in dogs, HW disease in cats should not be linked only

with adult worms and parenchymal disease but should be

associated with the arrival and the early death of immature

worms soon after they reach the pulmonary arteries.

HW-Ab positive cats, but free of adult HWs, have the same

type of pulmonary lesions, suggesting that even transient

infection with HW leaves cats with long-lasting pulmonary

pathology.

Prophilaxys Chemically abbreviated HW infection

infection

Pu

lmo

na

lya

rte

rio

les

Alv

eo

li

When the worms reach the pulmonary arteries, acute

inflammatory responses at the vascular and parenchymal

level follow characterized by the activation of pulmonary

intravascular macrophages (PIM, abundant in cats but not in

dogs). The activation of PIMs is a unique and likely the most

important feature of HW infection in cats and is responsible

for the exacerbated pulmonary reaction.

At this stage, pulmonary radiographic findings include an

interstitial inflammatory pattern related to the increased

production of cytokines by macrophages.

Cat: HARD

Studying the pathogenesis of acute death syndrome in HW

infected cats, it has been shown that the most severe lung

reactions occurred in hypersensithyzed cats [IgE response]

exposed to dead worms or antigens from adult parasites.

The acute death syndrome is a consequence of an acute,

IgE mediated systemic anaphylactic reaction.

Cat

Although Dirofilaria immitis causes a very severe

disease in dogs and cats, there is increasing concern

about D. repens infection

Owners require healthy pets

D. repens can causes distress in infected animals

In sensitized hosts the disease can be severe/ very

severe

Dirofilaria repens

Most infections asymptomatic or accidentally diagnosed during

surgery

Subcutaneous, cold, not painful and nodules movable on the

underlying tissues containing the adult parasite or mf

Courteously Z. Svobodova, Fac.

Med Vet, Brno, Czeck Republic

Dirofilaria repens infection: subcutaneous dirofilariosis

Worms are visulized by ECO as double linear parallel

hyperechoic structures similar but thinner than D. immitis

adult’s echoes

Dirofilaria repens worms can be visualized by

echography in cutaneous nodules and removed by a

mini-invasive procedure

Venco et al Int J Appl Vet Med 9:217-223 2011

D. repens scrotal nodule

Seldom, in severe infection, the clinical findings

[localized alopecia due to scratching and rubbing] and

generalized dermatitis seems to be mediated by

Wolbachia endosymbionts

Courtesy T Živičnjak et al, 2006