West Nile virus (WNV) infection has been identified in a horse in Colorado. It’s not really a surprise. West Nile virus is one of those pathogens that we know is coming back every year, we just don’t know exactly when. The date of return varies a bit from year to year, but tends to be fairly consistent within a region (e.g. if West Nile cases started to crop up in a certain state in mid-August last year, they are likely to start again at roughly the same time this year).
The timing of onset of WNV cases depends on a few things, including WNV circulation in birds, climate and mosquito populations. The latter is quite important since only certain mosquitoes like to bite both birds and mammals. These particular mosquitoes species (called bridging vectors) are the concern, since they are more likely to bite an infected bird, and then possibly transmit the virus to a horse (or human) if they bite them next. Mosquito populations aren’t the same all year and in all regions, which explains in part why WNV cases don’t start earlier in the year, and why there are some major regional variations in disease despite the widespread presence of mosquitoes.
In Ontario, I suspect we have a few more weeks before we get the first reports of cases for 2014, but the WNV season is approaching here as well.
Photo credit: Rennett Stowe (click image for source)
Ugonjwa wa West Nile virus (WNV) umegunduliwa kwa farasi mmoja huko Colorado. Si jambo la kushangaza. Virusi vya West Nile ni moja ya vimelea vinavyoweza kusababisha magonjwa ambavyo vinaonekana kila mwaka, lakini hatujui ni lini. Tarehe ya kurudi hutofautiana kidogo kutoka mwaka hadi mwaka, lakini huwa na uthabiti ndani ya mkoa (kwa mfano. Kwa mfano, ikiwa visa vya West Nile vilianza kutokea katika jimbo fulani katikati ya Agosti mwaka jana, inawezekana kuanza tena karibu wakati huo huo mwaka huu. Wakati wa kuibuka kwa ugonjwa wa WNV hutegemea mambo kadhaa, ikiwa ni pamoja na mzunguko wa WNV katika ndege, hali ya hewa na idadi ya mbu. Jambo hilo la mwisho ni muhimu sana kwa kuwa mbu fulani tu ndio hupenda kuumwa na ndege na mamalia. Aina hizi za mbu (zinaitwa vektor za daraja) ni wasiwasi, kwani zina uwezekano mkubwa wa kuumwa na ndege aliyeambukizwa, na kisha uwezekano wa kuambukiza virusi kwa farasi (au binadamu) ikiwa wataumwa baadaye. Idadi ya mbu haifanyi kazi kwa mwaka mzima na katika maeneo yote, na hii inaelezea kwa nini visa vya WNV havijaanza mapema mwaka, na kwa nini kuna tofauti kubwa za kikanda katika ugonjwa licha ya uwepo wa mbu. Ontario ina wiki chache kabla ya ripoti za kwanza za visa vya ugonjwa wa WNV Picha: Rennett Stowe (bonyeza picha kwa chanzo)