Managing Insect-Borne Infections in People

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Many environments in which equine veterinarians work are prone to insects that can carry diseases.

Working out in the field as an equine practitioner has unique threats, many of which are not immediately discernible. One example is the potential for an insect bite to cause significant disease. Several infections are prevalent in both horse and human, but are not contagious from one to the other; specifically, West Nile virus from a mosquito bite and Lyme disease (Borrelia burgdorferi) from a tick bite.

While the equine industry has developed at least five different vaccines to immunize horses against West Nile virus (WNV), there is no licensed vaccine available for people. A dog vaccine against Lyme disease is sometimes used on horses, yet no licensed human counterpart is yet available. The animals have an opportunity for protection, but this is not the case for people caring for the animals.

These insect-borne infections often are not identified until a person has become sick with the disease. Recent studies have examined methods of protection and treatment for people bitten by one of these insect vectors.

Lyme Disease

Approximately 1-5% of people bitten by a tick will develop Borreliosis. In a preclinical study (2014, ncbi.nlm.nih.gov/pubmed/24165183), application of a topical 10% azithromycin gel at the time of tick extraction was 100% effective in eliminating B. burgorferi. Further examination of clinical trials (thelancet.com/journals/laninf/article/
PIIS14733099(16)305291/fulltext
) tested application of this gel in 505 patients as prevention for Lyme disease, compared to 490 patients receiving only a placebo. The gel was applied within 72 hours of being bitten by a tick and twice daily for three days.

The azithromycin gel was well tolerated in those patients receiving it as treatment. The findings were equivocal in that 2% of patients in each group developed Lyme disease, with the conclusion that there was no preventive effect. While systemic antibiotics still seems to be the most effective method of treatment for humans, research continues into both topical prevention and development of a vaccine.

West Nile Virus

Studies have been performed on treating West Nile virus infections in humans with administration of highly purified immune serum IgG and other antibody fragments derived from horses immunized against West Nile virus.

The results (mdpi.com/1999-4915/8/12/332/htm) were encouraging: Not only did the treatment efficiently neutralize WNV infection in tissue culture, but also passive transfer of equine antibodies significantly accelerated viral clearance in the spleens and brains of WNV-infected mice and protected against mortality. This procedure holds promise as a potentially effective treatment in patients infected with West Nile virus. 

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