RELAPSING FEVER SPIROCHAETE- Associated disease in birds and MAMMALS
avian Spirochaetosis
Avian (fowl) spirochaetosis (avian borreliosis) caused by B. anserina is an acute septicaemic disease that occurs among domestic poultry worldwide in areas where fowl ticks in the genus Argas reside.
The disease is most commonly seen in tropical and subtropical regions(32). Borrelia anserina is considered an unusual member of the RF spirochaete group, as it has more than one vector and causes a disease that is not characterized by relapsing fever. The latter seem to be due to the fact that B. anserina does not appear to undergo antigenic variation1-62). Various Argas ticks both serve as the primary vector and reservoir of the spirochaete, which is transmitted trans-stadially and also transovarially in some tick species. Adult ticks can survive for up to 3—4 years without feeding and carry B. anserina longer than a year. The A rgas ticks live in poultry houses or under tree bark. Mosquitoes and mites can also transmit the infection, and other routes of transmission that do not involve vectors are possible.Gallinaceous birds (turkeys, chickens, pheasants) are the primary hosts of B. anserina, but natural infections also occur in domestic geese and ducks. Free- ranging flocks that are extensively reared are most likely to be infected. Additionally, the disease has been reported in canaries and the African grey parrot (Psittacus erithacus)(32’63). The disease has not, to date, been diagnosed in free-living wild bird species. Strains of variable virulence exist and the disease may vary in severity. In birds infected with virulent strains, the disease is clinically characterized by elevated body temperature, depression, anorexia and green diarrhoea. Later in the course, birds show paresis or paralysis and become anaemic(63). The predominant gross lesion is an enlarged and mottled spleen, often in combination with hepatomegaly and swollen kidneys.
Usually the intestinal contents are green and mucoid. Small haemorrhages may be seen, especially in the liver and at the junction between the proventriculus and ventriculus. Infrequently a fibrinous pericarditis is present. The most characteristic histopathological findings are erythrophagocytosis and hemosiderosis in the spleen and liver(63). Spirochaetes can be demonstrated in tissue sections, which are stained by silver impregnation methods. Borrelia anserina is not known to cause relapsing fever in humans.Disease in Wildlife Caused by other RF Spirochaetes
The role of wild animals as reservoirs for B orrelia spp. is well established, but little is known regarding how these infections might affect them. Disease in wildlife infected with RF spirochaetes appears rare, and there are only a few reports of fatal spirochaetosis in free-ranging wild animals.
The first (and so far only) report of a RF-related spiro- chaetosis in a wild bird is from the USA. An acute septicemic spirochaetosis was diagnosed in an adult northern spotted owl ( Strix occidentalis caurina) that was found dead in Washington in 1994(64). Gross findings included normal body condition, enlarged liver and spleen, and serofibrinous polyserositis. Microscopic pathology revealed infiltration of inflammatory cells and mild multifocal necrosis in liver and spleen, and acute inflammation in the choroid plexus of the brain. Long, spiral-shaped bacteria were found in silver-stained microscopic sections of several organs, and by PCR these were identified as a Borrelia species, most closely related to B. hermsii. This agent causes RF in humans in the western USA and Canada (Table 27.1) and was endemic in the area where the owl was found. The authors suggested that the most likely source of infection for the owl was directly transmission by predation or contact with secretions or excreta from an infected animal/reservoir species. In 2008, a spirochaete identical to the owl isolate was detected in the blood of a pine squirrel (Tamiasciurus hudsonicus) that was captured in an area in Montana, USA, where humans had contracted RF(65).
This finding of the same B. hermsii strain in a mammal and a bird separated by more than 500 km showed a broader geographic distribution and host range for the bacteria than previously envisaged.In Europe, the only report of fatal RF spirochaetosis is in a bat in the UK(66). In 2008, a juvenile Pipistrellui species was found alive but died after a few days of rehabilitation. The major post mortem findings were anaemia, excess amount of fluid in the thoracic cavity, and enlarged liver, spleen and adrenal glands. Histopathological examinations showed multifocal necrosis and infiltration by macrophages in the liver, inflammation of the lungs, and extramedullary hematopoiesis in the spleen. Long, undulating bacteria were found in Warthin-Starry-Stained microscopic sections of the liver, lung and spleen and in blood vessels. By PCR these were identified as a novel spirochaete, most closely related to B. recurrentis, B. duttonii and B. crocidu- rae, which are associated with HRF in Africa and Asia (Table 27.1). The novel spirochaete was not related to a Borrelia isolate that has been identified in the bat tick O. (Carios) kelleyi in the USA(67). An Argas Vespertilionis larval tick was found on the dead bat, and this might have been the source of the infection, but PCR was not performed on the tick. This tick species is widely distributed in various bat species in Europe, southern Asia and North Africa.
The reports referred to above, identify RF spirochaetes as pathogens for wildlife, both among birds and mammals. Such infections might be under-diagnosed in wild animals.
The most rapid diagnostic test is the identification of the spirochaetes in Giemsa-stained blood smears obtained during a febrile period. Thick blood smears can improve the sensitivity, but the morphology of the spirochaete is better conserved in thin smears. Spirochaetes may also be seen by examining wet preparations of 10- fold diluted blood by phase contrast or dark field microscopy. An enrichment method based on centrifugation raises the sensitivity of microscopy detection1-4). Molecular methods (PCR) are the most sensitive diagnostic tool and are used with increasing frequency1-61).