thesis -diro -final.doc

Used abbreviations

CNS – Central nervous system

CS – Caval syndrome

DEC- Diethylcarbamazine Citrate

D.immitis – Dirofilaria immitis

D. repens – Dirofilaria repens

D. tenuis – Dirofilaria tenuis

D. ursi – Dirofilaria ursi

D. conjuctivae – Dirofilaria conjuctivae

D. subdermata – Dirofilaria subdermata

D. striata – Dirofilaria striata

D. lutrae – Dirofilaria lutrae

GI – Gastro intestinal

HW – Heartworm

L– Larva

OD - Overdose

PDGF – Platelet Derived Growth Factor

TR – Tricuspid regurgitation

VD – Ventro dorsal

Annotation record

A.    David Elbeze, 5th year post BSc study student of UVM, Košice, Slovak Republic

B.     “Evaluation of the Prevalence of Dirofilaria in Slovakia and Europe”

C.     Department Parasitology and Infectious Diseases, UVM, Slovak Republic Tutor: Prof.MVDr. Valéria Letková, PhD, 2008, pages: 59, tables: 4, Figures: 16

The aim of our study was to evaluate the prevalence of Dirofilariosis in Slovakia and Europe in the past few years, as well as review the newest diagnostic and therapeutic methods available. Our conclusion was that the prevalence is rising progressively, especially in southern Europe, but the prevalence in Slovakia is still low despite of some positive cases.

Key words:  heartworm, dog, dirofilariosis.

1.    Introduction

1.1.   Background

Dirofilariasis is derived from the Latin words diro and filum, meaning "evil thread".  Of the two species occurring in domestic carnivores, dirofilaria immitis, the dog heartworm, is by far the more important. Dogs, cats, foxes, and other mammals are the natural hosts of Dirofilaria species, mosquitoes are the vector-intermediate hosts, and humans are the dead-end hosts(Laird, 2001). Transmission depends on ingestion of microfilariae by blood-sucking mosquitoes. The adult worms reside primarily in the pulmonary arteries and are frequently found in the right side of the heart responsible for a debilitating condition known as canine heartworm disease(Urquart and Armour, 1996).

Although primarily a problem of warm countries where the mosquito intermediate host abounds, the disease has become much more widespread in the past decade and has become a noticeable problem in North America and central Europe(Boreham and Atwell, 1988; Genchi, 2005). Other filariae parasites usually share an ecologic niche with D.immitis but with the exception of Burgia phangi, they do not cause clinically significant diseases. Infection and subsequent cardiopulmonary complications are preventable, and the disease is curable if diagnosis and treatment are timely(Knight, 1977).

1.2    Agents

The agents of dirofilariasis include members of the Dirofilaria genus within the Nematoda phyla. Animal and Human dirofilariasis are caused mainly by two Dirofilaria species: Dirofilaria immitis, which is associated with pulmonary dirofilariasis and some rare cases of extrapulmonary dirofilariasis and Dirofilaria repens, which is mainly associated with subcutaneous and conjunctival dirofilariasis.  Other members of the genus have been found to be occasionally the infectious agents of subcutaneous dirofilariasis(Laird, 2001)(table 1).

Adults (D.immitis) are long, white, thread-like worms (Fig 1). Males measure 12 to 16 cm long with the tail spirally coiled. It bears narrow alae and three pairs of large caudal papillae, one of which is postanal and three pairs of small ones near the tip of the tail. The left spicule is 324 to 375 um long and the right 90 to 229 um. Females are 25 to 30 cm long with the vulva opening just behind the posterior end of the esophagus(UCdavis, 2005). Approximately 75% of this growth is attained by the time the ovoviviparous females begin to release vermiform, embryos (microfilariae) into the circulation(Knight, 1987). Microfilariae are sheathless, 218 to 329 um long, and have a long pointed tail(UCdavis, 2005). Diagnostic methods to differ between species of dirofilaria will be discussed later.

Figure 1. Male and female adult heartworms recovered from the pulmonary arteries of a dog.

Table 1. Taxonomy of dirofilaria (UCdavis, 2005)

1.3   Life cycle

Adults are parasites mainly of the chambers of the right side of the heart and pulmonary artery. Individual eggs developing in the uterus are enclosed in a thin vitelline membrane. As the embryo elongates, the surrounding membrane stretches to conform as an enclosing sheath. At birth, the membrane is lost and the embryo appears in the blood as a sheathless microfilaria. Microfilariae are deposited in the blood of the chambers of the right side of the heart and pulmonary artery. They are carried through the lungs, into the left chambers of the heart, and into the systemic circulation. There is marked nocturnal periodicity in the peripheral blood. Mosquitoes serve as vectors.

Figure 2.  Microfilarial anatomy

After microfilariae are ingested during bloodfeeding, they migrate from the intestine within 24 to 36 hours into the Malpighian tubules, where further development and a molt from the first to the second stage juvenile occurs. After 9 days they enter the abdominal hemocoel, where the second molt occurs. Third stage larvae are about 900 um long and appear 10 to 20 days after entering the mosquito. The third stage juveniles migrate to the mouthparts of the moquito. Infection of dogs occurs while mosquitoes are feeding. Third stage juveniles escape onto the skin and enter it through the feeding site. For about 80 days, juveniles are in the subcutaneous tissues and muscles where the third molt takes place 9 to 12 days after entry. In the tissues, the fourth stage juveniles attain lengths up to 25 mm. They begin entering the right side of the heart shortly after the fourth molt 60 to 70 days after entering the dog. Development to maturity with males 14 to 19 cm long and females 23 to 31 cm takes 174 to 223 days, at which time microfilariae appear in the blood. The reproductive period exceeds 2 years and may extend to 5(Knight, 1987; Schrey and Trautvetter, 1998; Theis, 2005; UCdavis, 2005; Urquart and Armour, 1996).
 

            Figure 3.  heartworm life cycle in dog and cat

1.4   Vectors and Hosts

The successful completion of the life cycle of this parasite is dependent on several factors mainly including the vector, a suitable definition host and the parasite itself. Considering the number of factors may adversely affect the process, the remarkable success of this parasite reflects the abundance of adequate vectors and a ubiquitous reservoir of infection among canines especially(Ludlam et al., 1970).

Both D. immitis and D. repens are transmitted via the common mosquito vectors, Anopheles, Culex, and Aedes.  However, more than 60 species of mosquitoes from six different genera are capable of acting as the vector-intermediate host.  Also, it is believed that some species of fleas, lice, and ticks also act as vectors of D. immitis.  D. ursi is transmitted by blackflies, and D. tenuis is transmitted by the black salt marsh mosquitoes, Aedes taeniorhynchus and Anopheles quadrimaculatus(Laird, 2001).

There are approximately three thousands species of mosquitoes, but less than seventy have been identified as potential vectors of D.immitis. not all of them are adequate vectors under natural conditions. Of 28 susceptible species in the US, infective larvae have been found in the mouthpart of only 14 species, not all of them with the ability to transmit infection by bite. It seem that in each geographic region different vector species play variable roles, depending on the environmental conditions and the reservoir of the parasite(Knight, 1987). Infected mosquitoes usually carry one to three infective larvae, paradoxally the chances of a mosquito to produce infective larvae after ingesting a blood meal containing many microfilariae is relatively low. The transmission rate is proportional to the density of mosquitoes and the number of bites they inflict. Risk of infection and severity of heartworm disease are directly proportional to the prevalence of infected mosquitoes, wich is also related to the parasite reservoir in the canine community, which may be very elevated in endemic areas all over the world(Rodhain, 1995; Trotz-Williams and Trees, 2003; University of Guelph. Dept. of Pathology et al., 1982).

The dog is the main reservoir of infection, and most other mammals are probably infected by mosquitoes that have fed on dogs. However, most wild canides seem to be equally susceptible and D.immitis infection is well established in coyotes and red foxes(Knight, 1977; Laird, 2001). Cats, on the other hand, have very limited reservoir potential and are not considered as ideal host for D.immitis(Dillon, 1984). other hosts capable of supporting patent infections, such as ferrets and sea lions, are too environmentally isolated to play an important role in the parasite’s life cycle(Knight, 1987). Since some mosquito species feed on both animals and humans, Dirofilaria infection in humans occur occasionally, however, humans are considered accidental hosts and are a dead end for the parasite’s life cycle as the adult worm never reach full maturity and is usually found dead. D. repens and D. conjuctivae play a bigger role as zoonoses affecting the eye and subcutaneal tissues in several reported cases all over the world(Muro et al., 1999; Walther and Muller, 2003).

 

  Figure 4.  a female mosquito, vector of D.immitis
 

1.5   Geographic distribution

D.immitis is spreading progressively from regions of subtropical climate to temperate areas. In the last 25 years D.immitis has established itself in northeastern USA, parts of Canada, northern Italy and northeastern France(Schrey and Trautvetter, 1998). Climatic conditions can disrupt the mosquito’s reproductive cycle by adversely affecting its habitat and shortening the longevity of the adults. To be an effective vector, a mosquito must take at least two blood meals separated by sufficient time to permit the maturation of the larvae to the infective stage. A climate that provides adequate temperature and humidity to support a viable mosquito population, and also sustain sufficient heat to allow maturation of ingest...