September 11 - Crocodylocapillaria longiovata

A few months ago, you met Capillaria hepatica, a nematode worm that sometimes infects humans, but mostly uses rodents as its host. Today's parasite is Crocodylocapillaria longiovata, which is another Capillariid. This one, however, uses crocodiles, namely Johnston's Crocodile (Crocodylus johnstoni) and the biggest, nastiest crocodile of them all, the Saltwater Croc (Crocodylus porosus), as its hosts. These nematodes live in the stomach of the crocodiles and lay unusually long eggs (hence their specific name), which will eventually become embryonated, as seen in the drawing.

September 10 - Agema silvaepalustris

Pentastomids are a group of parasites that primarily infect the respiratory tracts of reptiles and amphibians, with a few species that infect birds and mammals (see Armillifer agkistrodontis). While they might look like worms, pentastomids are more closely related to arthropods, and they are ubiquitously found in the lungs of crocodiles. In fact, it's quite likely that every single species of living crocodilians is infected with pentastomids, indicating that these two groups have had a long co-evolutionary history which stretches back millions or possibly even hundreds of millions of years.

Today's parasite is Agema silvaepalustris and it is found in the lungs of the dwarf crocodile Osteolaemus tetraspis, which lives in the equatorial rain forest zone of West and Central Africa. The crocodiles become infected when they eat fish that possess the larval instars of A. silvaepalustris. The lungs of an individual crocodile can be infected with a few dozen to over a hundred of these parasites, and it is amazing to think that these weird little banana-shaped critters are more closely related to shrimps and crabs than any actual "worm"!

For further details, see:
Riley, J., Hill G. F., Huchzermeyer, F. W. (1997) A description of Agema, a new monotypic pentastomid genus from the lungs of the African dwarf and slender-snouted crocodiles. Systematic Parasitology 37: 207-217.

Contributed by Tommy Leung.

September 9 - Trichinella zimbabwensis

Parasitic nematodes in the genus Trichinella are commonly found in endothermic (warm-blooded) animals. The most common species, Trichinella spiralis, is found in many species of mammals. The infective larvae live in specialised capsules call "nurse cells" (which are muscle cells which have been heavily modified by the parasite), and they are transmitted into different mammalian host via carnivory or scavenging on carcasses. Trichinella zimbabwensis deviates somewhat from this pattern. While it is still transmitted to a new host via the ingestion of infected muscle tissue, unlike T. spiralis, it does not encapsulate and it is also found in reptilian hosts, specifically crocodiles. However, it does not occur exlusively in reptiles and can also infect mammals. Given that it is able to survive in both ectothermic and endothermic hosts, while other species of Trichinella can only survive in endothermic hosts in the wild, this raises intriguing questions about the evolutionary origin of the genus Trichinella.

For more details, see:
Pozio, E. et al. (2002) Trichinella zimbabwensis n.sp. (Nematoda), a new non-encapsulated species from crocodiles (Crocodylus niloticus) in Zimbabwe also infecting mammals. International Journal for Parasitology 32:1787-1799.

Contributed by Tommy Leung.

September 7 - Acanthostomum americanum

Acanthostomum americanum is a digenean trematode found in the intestine of Morelet's crocodile (Crocodylus moreletii) from Yucatan, Mexico. The crocodiles acquire this parasite when they eat fish that are infected with the parasite's encysted larval stages.The early juveniles of these worm are characterized by the lack of spines on the oral sucker, which is likely to be an adaptation which allows it to make a smooth seal with the intestinal wall before suction, which maintains the developing parasite in position between the intestinal villi. As the parasite grows, so do the spines around its oral sucker, which then take over the role of anchoring it firmly in the intestinal mucosa.


Image adapted from:
Moravec, F. 2001. Some helminth parasites from Morelet's crocodile, Crocodylus moreletii, from Yucatan, Mexico. Folia Parasitologica 48: 47-62.

Contributed by Tommy Leung.

September 6 -Haemogregarina crocodilinorum

There are five species of hemogregarine apicomplexan blood parasites (distant relatives of malaria parasites) that have been described from alligators and crocodiles. Haemogregarina crocodilinorum is the one that infects the American alligator, Alligator mississippiensis. This parasite is most likely transmitted by the leech, Placobdella multilineata, which is commonly found on alligators throughout the Southeast.

September 5 - Griphobilharzia amoena

Today's parasite is a schistosome blood fluke which has been described from the Australian freshwater crocodile (Crocodylus johnstoni). While most schistosomes are known from mammalian and avian hosts, Griphobilharzia amoena is found in a reptilian host. Like other schistosome (as opposed to most digenean flukes), G. amoena is dioecous (they have males [left] and females [right]). This fluke occupies an important position in terms of research into the evolution history of schistosomes; it has been hypothesised that the evolution of dioecy in these blood flukes was accompanied by the evolution of endothermy ("warm-bloodedness") in their hosts. With G. amoena being found infecting a crocodilian, it seems to suggest that the origin of dioecy dates back before the evolution of endothermy. However, in another twist, it has also been suggested that the ancestors of modern crocodiles were originally endotherms which had reevolved ectothermy ("cold-bloodness"). Appropriately, "Gripho" - which forms a part of this parasite's name, actually means "a riddle".

Description for Griphobilharzia amoena:
Platt, T. R., Blair, D., Purdie, J. and Melville, L. (1991) Journal of Parasitology 77:65-68.

The paper which suggest crocodiles reevolved ectothermy:
Seymour, R. S., Bennett-Stamper, C. L., Johnston, S. D., Carrier, D. R. and Grigg, G. C. (2004) Physiological and Biochemical Zoology 77:1051-1067.

Contributed by Tommy Leung.