''Philophthalmus gralli'', commonly known as the Oriental avian eye fluke, parasitises the
conjunctiva
The conjunctiva is a thin mucous membrane that lines the inside of the eyelids and covers the sclera (the white of the eye). It is composed of non-keratinized, stratified squamous epithelium with goblet cells, stratified columnar epithelium ...
l sac of the eyes of many species of birds, including birds of the orders
Galliformes
Galliformes is an order of heavy-bodied ground-feeding birds that includes turkeys, chickens, quail, and other landfowl. Gallinaceous birds, as they are called, are important in their ecosystems as seed dispersers and predators, and are often ...
and
Anseriformes
Anseriformes is an order of birds also known as waterfowl that comprises about 180 living species of birds in three families: Anhimidae (three species of screamers), Anseranatidae (the magpie goose), and Anatidae, the largest family, which in ...
. In
Brazil
Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
this parasite was reported in native Anseriformes species. It was first discovered by Mathis and Leger in 1910 in domestic chickens from
Hanoi, Vietnam
Hanoi or Ha Noi ( or ; vi, Hà Nội ) is the capital and second-largest city of Vietnam. It covers an area of . It consists of 12 urban districts, one district-leveled town and 17 rural districts. Located within the Red River Delta, Hanoi is ...
.
[ Birds are definitive hosts and freshwater snail species are intermediate hosts (e.g. ''Tarebia granifera'' and ''Melanoides tuberculata'').]
Life cycle
''Philophthalmus gralli'' reaches sexual maturity in a bird and produces eggs. Fully embryonated eggs are shed into the water from the definitive host's eyes. Miracidium
The Miracidium is the second stage in the life cycle of trematodes. When trematode eggs are laid and come into contact with fresh water, they hatch and release miracidium. In this phase, miracidia are ciliated and free-swimming. This stage is comp ...
is induced to hatch when ripe eggs are released from the worm into water. Upon contact with a snail, the miracidium perforates the host epidermis
The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water rele ...
with the aid of secretions and the anterior cilia. It penetrates the snail far enough to release a single rediae. The mother redia localizes in the heart and produces daughter rediae, which migrate to digestive glands to continue its development and produce megalurous cercariae. Cercariae are released from the snail and encyst on aquatic vegetation or other solid objects in the water. The definitive host, which is usually an aquatic bird, becomes infected upon ingestion of metacercariae. Excystment of the metacercariae occurs immediately upon reaching the mouth or crop of the bird and not in the stomach or intestine as in many other digenetic
Digenea (Gr. ''Dis'' – double, ''Genos'' – race) is a class of trematodes in the Platyhelminthes phylum, consisting of parasitic flatworms (known as ''flukes'') with a syncytial tegument and, usually, two suckers, one ventral and one oral ...
trematodes. Within three to five hours after ingestion, immature worms may be found in the esophagus, nasal passages, the orbit and the lobes of the lacrimal gland
The lacrimal glands are paired exocrine glands, one for each eye, found in most terrestrial vertebrates and some marine mammals, that secrete the aqueous layer of the tear film. In humans, they are situated in the upper lateral region of each or ...
. Humans rarely serve as incidental hosts, but may do so when they ingest metacercariae on aquatic vegetation.
Morphology
The ''P. gralli'' egg is nonoperculate and oval. The shell is thin and elastic and has an internal thickening at the small end.
The miracidia is composed of twenty epidermal plates arranged in four tiers, which have six, eight, four, and two cells, respectively. It consists of two excretory pores and two pairs of lateral sensory papillae.
The morphology of a redia is elongated and cylindrical. It has a well-developed anterior pharynx and a long intestinal tract. Birth pore is found between first and second quarter of body. Lateral processes are near posterior tip of body.
The cercaria has two suckers: a ventral sucker and rounded subterminal sucker. Intestinal ceca bifurcate posterior to pharynx. Excretory bladders are located at posterior end of the cercarial body.
The metacercarial cyst is elongated and oval-shaped with sensory papillae. The excysted metacercarial is oval-shaped with a subterminal sucker and a ventral sucker.
The adult form of ''P. gralli'' is fusiform shaped. Body surface is covered by small spines at acetabular region. The two suckers are orally and subterminally located. Pharynx is located immediately posterior to oral sucker. Acetabulum is located at anterior third level of body. Both female and male organs are found within the body.
Therapy
The most common way to rid of ''Philophthalmus gralli'' is removal with forceps or flushing the worms out. Doramectin may also be used.
Clinical symptoms
Clinical symptoms are a result of flukes attaching to the conjunctiva. It has different effects, depending on the host. Infection may cause congestion and erosion of the conjunctivae, conjunctivitis with persistent lacrimation,
Infections in ostriches
The first case of philophthalmiasis in captive-reared ostriches was described in the United States in 1980.
References
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External links
{{DEFAULTSORT:Philophthalmus Gralli
Plagiorchiida
Parasites of birds
Animals described in 1910