To the Editor: Dugdale recently suggested that people who develop skin reactions to mosquito bites may be protected against Ross River virus (RRV) disease.1 He noted that seven patients with a history of RRV disease all reported no skin reaction to mosquito bites, and 18 patients with no past history of RRV disease reported reacting to such bites. We argue that this correlation is entirely to be expected, as the lack of reaction to mosquito bites illustrates that the individuals have been previously exposed to many bites. At least two studies have shown a clear inverse correlation between mosquito exposure and bite reactions.2,3 Clearly, exposure to a large number of mosquito bites increases the risk of infection.4 Thus, a reaction to mosquito bites probably does not protect against RRV disease, but is simply a marker for low exposure to mosquito bites and therefore low risk of RRV infection.

The rationale behind the association of itching bites and protection against RRV infection is also tenuous. Virus is likely to reach the circulation within seconds of introduction by the mosquito, whereas allergic reactions take minutes to develop. It is unlikely that a local reaction will affect viral replication at distant sites.

In Dugdale's study, only people with a history of symptomatic RRV disease had undergone RRV serological testing. As about 30% of Queenslanders are seropositive,5 and 60%–75% of RRV infections are thought to be asymptomatic,6 some of the 18 people with no past history of RRV disease might be expected to have had asymptomatic RRV infection. This raises the question, does reaction to mosquito bites correlate with asymptomatic RRV infection?