Mites and the Modes of Transmission
Back in the 60′s, researchers at Cornell surveyed the presence of this mite in 19 species of wild birds in Upstate New York. Their results showed almost half of the birds/nests were infected. Mites have strong legs and can move rather quickly. They even found mites 15 yards from the tree with the infested bird nest (Foulk and Matthysse 1965). Secondly, they are transported by their hosts (phoresy is the technical term). Maybe that is how they got to Hawaii (Van Ripper III 1991). Birds are not the only carriers; rats, mice, and gerbils can carry them as well (Miller and Price 1977, Lucky et al. 2001). In poultry, however, the most direct method of transmission is when the mites remain in the barn, on the cages and equipment between production cycles. If an effective pest treatment is not done, there is a high likelihood of infestation in the next flock. They can also affect pullet (female baby chicks) facilities so sometimes the chicks are sprayed before being moved to egg production facilities (Kells and Surgeoner 1997). They likewise travel on eggs.
The most common form of transmission in households is via a nest in the immediate vicinity of the eaves. After the birds leave the nest, the mites go in search of a new host. Heat, CO2, and movement attract the mites towards their alternate hosts.
Negative Host Impact
In wild birds, the irritation caused by the mites curtails the fledgling phase. This in turn causes significant mortality since the survival rate of the young birds is lower than if they would have stayed in the nest until full development (Chapman and George 1991). Masan (1997) discovered that nestlings caused dramatic increases in mite reproduction. As many as 500 thousand mites have been found in one nest (Clark 1991). Usually the eggs are laid upon the chicks, unless the colony is too large in number. They prefer to feed on the head and vent areas (Sikes and Chamberlain 1954). Another word for vent is cloaca, which means “sewer” in Latin. It is the multi-tasking posterior opening for the intestinal, urinary, and genital tracts in birds.
They have been implicated in the potential spread of various diseases (Miller and Price 1977). Mites can transmit viral strains of encephalitis to birds (Chamberlain and Sikes 1955, Mullen and O’Connor 2002). Professor Proctor (2004) thinks that they can potentially transmit West Nile Virus. Thirdly, Salmonella has been transmitted by the red chicken mite, so transmission of that bacterium by the NFM seems possible too (Valiente Moro et al. 2007).
Although O. sylviarum’s natural hosts are small wild birds, they do infect domesticated birds, proving how versatile these creatures can be (Proctor and Owens 2000). Most chickens don’t die from mites. One reason could be that the physiological stress creates corticosteroids in their blood, which stops the mites from feeding (Hall and Gross 1975). Nonetheless, the poultry industry says that the economic costs have been high. Irritation from the mites can disrupt incubation and result is less eggs hatching (Clark 1991). Blood loss can cause anemia in hens and lead to fewer eggs laid, and even death (Bruneau et al. 2002). Roosters lose weight and become less potent (Clark 1991). Birds were found to develop an immune response (Minnifield et al. 1993). Economic costs to the poultry industry for both the NFM and the red chicken mite in the UK and European Union were $7.5 to $265 million per year respectively (Anonymous B 2006). Damage estimates in US appear not to be fully known.
I found many case studies in dermatology journals of avian mite dermatitis since it is frequently misdiagnosed (Orton et al. 2000). The mites inject saliva that causes intense itching (Apperson and Waldvogel 2002). This saliva may also contain anti-coagulants and an anesthetic (Barrett et al. 2007). The mite bites result in “pruritic papules” (Lucky et al. 2001). Our exterminator told us that some doctors had incorrectly prescribed strong antibiotics since they suspected scabies. In some, they can even cause asthma (Lucky et al. 2001). The best way to remove them is with a sticky link roller (pers. experience) since soaps or shampoos are ineffective (Williams 2007 pers. com). Notwithstanding, mites definitely prefer birds. This may be due to cheliceral chemosensilla that allow them to recognize substances in the blood (Sonenshine et al. 1986). Researchers have tested many other hosts for suitability including mice, rabbits, swine, cattle, and humans, and have tried to devise in vitro systems. These “accidental hosts” (or temporary snacks!) were not as good as the real thing (Sikes and Chamberlain 1954, Carroll and Young 1994). I found no research indicating that these mites could live on humans on a sustained basis, but as Prof. Proctor puts it “that doesn’t stop them from biting!” (VanDyk 2007).
