Avian spirochetosis (AS) is an enteric disease of birds caused by colonization of anaerobic spirochetal bacteria of the genus Brachyspira
in the bird's intestines (specifically the cecum and rectum). There are seven types of Brachyspira
that infect birds, however the four main pathogenic (disease-causing) species that affect chickens are B. intermedia, B. pilosicoli, B. alvinipulli
and B. hyodysenteriae
. AS is known to cause mild to moderate, subacute to chronic disease historically in flocks of laying hens and broiler breeders. The severity of the infection depends on the particular strain of Brachyspira
, extent of colonization, the chicken's age and overall health and immune status. Infection is particularly common in chickens under free-range conditions.
Clinical Signs of Avian Spirochetosis
Infections can vary from being asymptomatic to severe, with increased mortality rates. Most commonly, infections are mild or moderate and generally are characterized by diarrhea with caramel colored, frothy feces resulting from increased gas production in the intestines. Other signs include:
- Egg-related: In pullets, infection may cause a delay in the onset of egg laying, and a decrease in numbers and quality of eggs. In adult hens, infection often causes a decrease in egg production. The eggs also may be smaller, be lighter, have paler yolks, and have poorer shell quality than those from uninfected chickens. The shells of eggs may be contaminated with feces.
- Fecal-related: Infected chickens often will have wet droppings, feces smeared on the feathers around the cloaca (“pasty vents”), and caramel colored, frothy feces resulting from increased gas production in the intestines.
The progeny of chickens with AIS may be weak and show depressed weight gain, despite not being colonized.
Transmission of Avian Spirochetosis
can be initially introduced into flocks through wild birds, rodents, insects (such as flies), domestic and feral dogs or cats, other livestock (pigs or horses), other poultry species (ducks, geese, turkeys, pheasants, etc.), and even humans. Ducks in particular, are known to be subclinical carriers of Brachyspira
spp., meaning that they are often easily infected but never develop clinical signs of disease, however they will shed the bacteria in their feces. Brachyspira
are most commonly spread between flock members through environmental contamination with feces from infected birds. When chickens are exposed to the same environments as infected hosts, they are at risk of becoming infected.