Experimental and natural infections of Simulium sanchezi by Mansonella ozzardi were studied in the area of Síquita, Territorio Federal Amazonas, Venezuela. The microfilariae developed synchronously in the blackflies, reaching stage L3 in seven to eight days at temperatures between 23 degrees and 27 degrees C. Larvae in different stages of development, including infective forms, were found in 0.6% of 662 unfed wild-caught females. These results confirm that simuliids are the main vectors of M. ozzardi in the American continent.

Some cases of sudden deaths in cattle, sheep and goats reported to the National Veterinary Laboratory, Gaborone were investigated. The clinical signs included: stupor, weakness, staggering, trembling, dyspnoea (difficulty in breathing), salivation, diarrhoea, and convulsions for those in extremis. The most consistent sign was the muddy coloured mucous membranes. Necropsy findings included: marked gastroenteritis and generalized congestion and petichiation in all internal body organs and chocolate brown coloured blood that clotted poorly. The presence of nitrate/nitrite in the blood of live animals, amniotic fluid, urine, ocular fluid, urine, drinking water and consumed forage were demonstrated by the diphenylamine test and subsequently confirmed by Gries test. Further confirmation of nitrate/ nitrite poisoning was by response to therapeutic intervention with methylene blue using the intravenous route of inoculation.Environmental factors that may have contributed to the poisoning episodes included, drought, high ambient temperatures, low cloud cover, soil leaching after flooding, soil moisture content and forage nitrogen content and natural geoformations associated with high nitrate content in the water. This is the first account of confirmed cases of nitrate/ nitrite poisoning in livestock in Botswana.

Acute deaths involving 141 Tswana breed of cattle and 15 Black Head breed of sheep were reported within 2 to 48 hours of drinking water at Mahibitswana crush, Shoshong village in Mahalapye district, Botswana. The water was from an open well at the crush, the latter being a designated communal livestock collection area used for watering, inspection, treatment and vaccination of livestock by Veterinary services personnel. At the time of the ambulatory visit, 7 sheep and 41 cattle belonging to this crush were reported dead. Donkeys and goats watered from the same source were not affected. The signs were acute and included hind limb weakness with subsequent recumbency, severe dyspnoea, tachycardia, a thready pulse and mud colored mucus membranes. The latter were injected in some animals. Slight frothing at the mouth was evident. The menace reflex to check for visual acuity was blunted. Parenteral administration of Vitamin B complex (Virbac) using the intramuscular route of inoculation in addition to dexa-tomanol and long acting terramycin, resulted in amelioration of the clinical signs. Recovery was uneventful and relapses were not reported. This is the first published report of suspected elemental sulphur poisoning among ruminants in Botswana.